Quantum Graffiti [Archive]

marcus

Jun1-05, 06:26 PM

exerpts from Dirk van Delft article in NRC Handelsblad 22 January, the Science and Education section

<<Renate Loll investigates the microstructure of space and time

Probing the Quantum Foam

[On the smallest scale, spacetime is not smooth-flowing, but choppy. The Utrecht phsicist Renate Loll has for the first time glued together out of microbricks a world with the right number of dimensions---Dirk van Delft]

For Renate Loll the year 2005 couldnt go neater. Before Christmas, the theoretical physicist (born in Aachen and fellow at the University of Utrecht's Spinoza Institute) received from the Netherlands Scientific Reseach Organization (NWO) 1.25 million Euro to build up, over the next 5 years, her own Group, which investigates the quantum structure of spacetime.

Shortly before that she had already brought in 2.93 million, to build a network of 13 European institutes which will work together in the area of Random Geometries

This involves a technique which can be used to explain spacetime at extremely small scale, but which, as a mathematical method, can also be applied elsewhere.

"I enjoy thinking," says Renate Loll in her workroom in the Minnaert building, on the border of Utrecht Campus Uithof.

"It keeps my wits in shape. With the structure of spacetime you really find yourself at the edge of the imaginable. there are still a lot of riddles to solve. And it is exciting to open up paths that no one has traveled yet."

"In physics it's clear what direction one is working towards. I was also at the London School of Economics for a year. there it was all about human relations, which is frustrating and difficult. My partner is also a physicist, which I consider an advantage, since you have someone to talk about your work with. And after being a while in this field, competition plays less of a role. Also I like it that I never have to explain when I'm staring at a piece of paper for hours in the middle of the night.">>

==================================

http://www.phys.uu.nl/~loll/Web/press/NRCdeutsch.htm

here is the German text of the part I translated:

<<Renate Loll untersucht die Mikrostruktur von Raum und Zeit

Basteln mit Quantenschaum

[Auf der allerkleinsten Skala ist die Raumzeit nicht fließend, sondern zerstückelt. Die Utrechter Physikerin Renate Loll klebte als erste aus Mikrobausteinen eine Welt mit der richtigen Anzahl Dimensionen zusammen. Dirk von Delft]

Für Renate Loll kann im Jahr 2005 schon nichts mehr schief gehen. Die in Aachen geborene theoretische Physikerin, Mitarbeiterin des Spinoza-Instituts der Universität Utrecht, bekam vor Weihnachten von der Niederländischen Organisation für wissenschaftliche Forschung (NWO) 1,25 Millionen Euro, um innerhalb von 5 Jahren eine eigene Gruppe aufbauen, die die Quantenstruktur der Raumzeit untersucht. Kurz zuvor hatte sie schon von der EU 2,93 Millionen eingeheimst, um ein Netzwerk von 13 europäischen Instituten aufzubauen, die auf dem Gebiet der sogenannten Zufallsgeometrien zusammen arbeiten. Dabei geht es um eine Technik, die Raumzeit auf extrem kleiner Skala zu erfassen, die aber als mathematische Methode auch anderswo einsetzbar ist.
„Ich denke gerne“, sagt Renate Loll in ihrem Arbeitszimmer im Minnaertbau, am Rand des Utrechter Campus’ Uithof. „Das hält mich geistig fit. Bei der Struktur von Raumzeit befindet man sich wirklich am Rand des Vorstellbaren. Es gibt noch viele Rätsel zu lösen, und es ist spannend Wege einzuschlagen, die noch niemand gegangen ist. In der Physik ist es klar, in welche Richtung man arbeitet. Ich war auch ein Jahr lang auf der London School of Economics. Da geht es um das Verhalten von Menschen, was frustrierend schwierig ist. Mein Partner ist auch Physiker, was ich als Vorteil ansehe, da man mit jemandem über seine Arbeit sprechen kann. Und sobald man länger in diesem Fach dabei ist, spielt das konkurrierende Element eine geringere Rolle. Auch finde ich es angenehm, dass ich nichts erklären muss, wenn ich mitten in der Nacht stundenlang auf ein Blatt Papier starre.“>>

marcus

Jun1-05, 07:09 PM

more exerpts from Dirk van Delft article in NRC Handelsblad 22 January, the Science and Education section
http://www.phys.uu.nl/~loll/Web/press/NRCdeutsch.htm

<<Loll's field is Quantum Gravity. Of which the fundamental problem is that Einstein's description of gravity (the 1915 General Theory of Relativity) is in conflict with the quantum theory developed in the 1920s by Heisenberg, Schroedinger, Dirac, and others.

According to Einstein, four-dimensional spacetime (three for space and one for time) is curved by mass, or energy. As a consequence, a lightray passing the sun will be diverted. When, during a 1919 solar eclipse, Eddington observed this effect, Einstein became instantly world-famous.

According to Einstein, spacetime is flexible (malleable, ductile), but also at the same time continuous and smooth-----for example it does not have breaks (fractures, gaps, rips....)

Planck scale
In quantum theory, which describes the microscopic structure of the world, this view can no longer be considered correct. Among the pillars of this theory are the famous Heisenberg Uncertainty Relations ("Un-sharp relations"):

the smaller the length-scale considered, the greater must be the accompanying energy fluctuations

these fluctuations must express themselves, according to Einstein, in a bending of spacetime

Loll: "At the Planck scale---the smallest length unit which one can meaningfully talk about in quantum theory, where it has to do with numbers with 35 zeros after the decimal point---the energy fluctuations are extremely big. In my theory spacetime becomes infinitely bent by them, with infinitely many wrinkles.

but there are physicists who work with rips and gaps. Instead of a continuum, the spacetime splits up into isolated fragments, and many speak of Quantum Foam.

The job of quantum gravity is to describe this turbulent distortion of spacetime, and the mathematics of Einstein's continuous spacetime with wavelike disturbances is no longer adequate....>>

=================================
here is the German source for that section:

<<Lolls Arbeitsgebiet ist die Quantengravitation. Deren grundlegendes Problem ist, dass Einsteins Beschreibung der Schwerkraft, die allgemeine Relativitätstheorie von 1915, mit der Quantentheorie auf Kriegsfuß steht, die in den zwanziger Jahren von Heisenberg, Schrödinger, Dirac und anderen entwickelt wurde. Bei Einstein wird die vierdimensionale Raumzeit (drei für den Raum, eine für die Zeit) unter dem Einfluss von Masse (oder Energie) gekrümmt. Die Folge ist, dass ein an der Sonne vorbei laufender Lichtstrahl abgelenkt wird. Als Eddington 1919 während einer Sonnenfinsternis diesen Effekt beobachtete, war Einstein mit einem Schlag weltberühmt. Bei Einstein ist die Raumzeit dehnbar, aber zugleich auch kontinuierlich und glatt, sie enthält beispielsweise keine Risse.

Planckskala. In der Quantentheorie, die die mikroskopische Struktur der Welt beschreibt, lässt sich diese Sichtweise nicht mehr aufrecht erhalten. Zu den Säulen dieser Theorie gehören die berühmten Unschärferelationen von Heisenberg: je kleiner die betrachtete Längenskala, desto größer die damit einhergehenden Energiefluktuationen. Diese Fluktuationen äussern sich jedoch Einstein zufolge in einer Krümmung der Raumzeit. Loll: „Auf der Planckskala – der kleinsten Längeneinheit, über die man in der Quantentheorie noch sinnvoll sprechen kann und wo man es mit Zahlen mit 35 Nullen hinter dem Komma zu tun hat – sind die Energiefluktuationen extrem groß. In meiner Theorie wird dadurch die Raumzeit unendlich gekrümmt, mit unendlich vielen Falten. Aber es gibt auch Physiker, die mit Rissen oder Löchern arbeiten. Anstelle eines Kontinuums zerfällt die Raumzeit in einzelne Bröckchen, manche sprechen von Quantenschaum. Die Aufgabe der Quantengravitation ist die Beschreibung dieser turbulenten Verformung der Raumzeit, und dazu reicht die Mathematik von Einsteins kontinuierlicher Raumzeit plus wellenartigen Störungen nicht mehr aus.“>>

marcus

Jun2-05, 01:29 AM

more exerpts from Dirk van Delft article
http://www.phys.uu.nl/~loll/Web/press/NRCdeutsch.htm

<<How to reconstruct our known Universe, with its four-dimensional spacetime, from wildly fluctuating quantum foam? In the fall of 2004 Renate Loll scored a breakthrough regarding this long-outstanding open question. Her point of departure was not a new one: take microscopic pieces of flat spacetime and join them to each other in every conceivable way. By combining all possibilities in a sum---a standard proceedure in quantum theory---one could build a macroscopic Universe.

Loll: "I was working not with two-dimensional, but instead four-dimensional, triangles. this kind of geometrical modeling appeals to me. The problem of the summation method, up till now, was always that the resulting universe had either two, or infinitely many, dimensions. Something in the approach was fundamentally wrong."

Rolled up A structure made out of four-dimensional "triangles" does not itself have to be four-dimensional. In the case of flat two-dimensional triangles, the result can, for example, be a kind of "rolled up" structure just like a familiar water-pipe that looks one-dimensional from a distance.

Furthermore, the choice of triangular building blocks is not essential: rectangular blocks would lead to the same macroscopic end result. the geometric peculiarities occur because of the enormous number of microscopic pieces. However using triangles is mathematically convenient.

Loll's decisive idea was to place an additional causal requirement on the triangles: cause must preceed effect. "That's how it goes in research: a fantastic idea develops in your head, and you determine that---ahhhh!---that just might work! The years of struggling, that it took to make you receptive to the insight, no longer matter. So then you talk it over with colleagues with reliable expertise in triangulation methods, and they say: 'Forget it. No way will that work!'

But in this business one shouldn't let oneself be discouraged easily! Next I pursued the question of whether the same idea would lead to something interesting in the simple case of two dimensions, which in fact it did.

From that point on, with the help of computer models, I made the step to three and four dimensions. With the result that we actually obtained a four-dimensional universe." this work appeared on 24 September in the renowned Journal Physical Review Letters>>

================================

here is the German source for the above:

<<Wie rekonstruiert man unser bekanntes Universum mit seiner vierdimensionalen Raumzeit aus wild fluktuierendem Quantenschaum? In dieser seit Jahrzehnten offenen Frage gelang Renate Loll im Herbst 2004 ein Durchbruch. Ihr Ausgangspunkt war dabei nicht neu: man nehme mikroskopische Stücke flacher Raumzeit und klebe sie auf jede nur erdenkliche Weise aneinander. Indem man alle diese Möglichkeiten überlagert – ein Standardansatz in der Quantentheorie – baut man sich ein makroskopisches Universum. Loll: „Ich arbeite nicht mit zwei-, sondern vierdimensionalen Dreiecken. Diese Art geometrischer Formulierung spricht mich an. Das Problem der überlagerungstechnik war bisher immer, dass das sich ergebende Universum entweder zwei oder unendlich viele Dimensionen besaß. Man hatte also irgendetwas grundlegend falsch gemacht.“

Aufgerollt. Eine Struktur, die aus vierdimensionalen „Dreiecken“ aufgebaut ist, ist selbst nicht wieder unbedingt vierdimensional. Im Fall von flachen zweidimensionalen Dreiecken kann das Ergebnis zum Beispiel eine Art „aufgerollter“ Struktur sein, die, genau wie ein von weitem betrachtetes Regenabflussrohr, auf großen Skalen eindimensional erscheint. Im übrigen ist die Wahl dreieckiger Bausteine nicht wesentlich: viereckige Bausteine würden dasselbe makroskopische Endergebnis liefern. Bei der enormen Zahl mikroskopischer Bausteine fallen deren geometrische Einzelheiten im Endresultat heraus. Die Wahl von Dreiecken ist lediglich mathematisch bequem.
Lolls entscheidende Idee war, an die Dreiecke zusätzliche kausale Anforderungen zu stellen: Ursachen müssen Folgen vorausgehen. „So geht das in der Forschung: in deinem Kopf entwickelt sich eine fantastische Idee und du stellst fest – ahhhh! – das geht ja! Die Jahre der Anstrengungen, die dich für diese fantastische Eingebung empfänglich gemacht haben, spielen auf einmal keine Rolle mehr. Dann besprichst du dich mit Kollegen, die mit der Dreieckstechnik vertraut sind, und die sagen: ,Vergiß es. Das klappt sowieso nicht.’ Aber in diesem Fach darf man sich nicht zu schnell entmutigen lassen! Ich bin dann zunächst der Frage nachgegangen, ob dieselbe Idee im einfachen Fall von zwei Dimensionen etwas Interessantes ergab, was sie auch tat. Daraufhin machte ich mit Hilfe von Computermodellen den Schritt zu drei und vier Dimensionen. Mit dem Ergebnis, dass wir tatsächlich ein vierdimensionales Universum erhielten.“ Diese Arbeit erschien am 24. September in der renommierten Fachzeitschrift Physical Review Letters.>>

It seems to me that Dirk van Delft may have taken liberties with some pronouns and substituted the First Person Singular where Loll might have said, or meant to say, the Plural. Anything can happen in popular journalism for mass media, especially if it makes the story more gripping. In the scholarly writings that I've seen, in contrast to this journalistic account, Loll says "we" and includes her co-workers Ambjorn and Jurkiewicz without exception.

marcus

Jun2-05, 10:01 AM

In case anyone missed them, I'll repeat the links to some other "Triangulations" Quantum Gravity PF threads:

http://www.physicsforums.com/showthread.php?t=76674
(Why CDT changes the map of quantum gravity)

http://www.physicsforums.com/showthread.php?t=57311
(Two world-theories)

http://www.physicsforums.com/showthread.php?t=75472
(The running of the spacetime dimension)

marcus

Jun3-05, 01:14 AM

<<Die große Herausforderung, die noch vor Renate Loll und ihrer im Aufbau befindlichen Forschungsgruppe liegt, ist nachzuprüfen, ob die so erzeugte vierdimensionale Raumzeit makroskopisch wieder schöne glatte „Einsteinsche“ Eigenschaften annimmt. Loll: „Sobald dies bestätigt ist, können wir daran gehen, die Quantengravitation im Bereich zwischen Planck- und Makroskala zu untersuchen. Fragen gibt es da zur Genüge. Verursacht die zusätzliche Raumzeitstruktur einen kumulativen Effekt, der seine Spuren in einem Lichtstrahl hinterlässt, der uns aus der Tiefe des Weltalls erreicht? Ein anderer Knackpunkt: wie sieht es mit der Quantengravitation schwarzer Löcher aus, Objekten, die so kompakt sind, dass absolut nichts, auch kein Licht, aus ihnen herausdringen kann, die aber dennoch aufgrund der Heisenbergschen Unschärfe strahlen? Da gibt es noch viele ungelöste Rätsel.“>>

<<The big challenge, that still faces Renate Loll and the research group she is building up, is to verify that the spacetime now shown to be four-dimensional does in fact aquire smooth Einsteinian properties at large scale.

Loll: "As soon as that is confirmed, we will be able to move on to explore the region between Planck-scale and macro-scale. There are enough research problems to satisfy anybody here. Does the spacetime structure we are assuming have a cumulative effect, that would leave measureable traces in the light reaching us from the depths of the universe?

Another critical point: how does quantum gravity describe black holes---objects so compact that no light can escape them, yet which nevertheless radiate by reason of the Heisenberg Uncertainty Relations. there are a whole bunch of unsolved riddles.">>

http://www.phys.uu.nl/~loll/Web/press/NRCdeutsch.htm

marcus

Jun3-05, 08:02 PM

as part of keeping track of gossip and real-life details of causal triangulations gravity, we could keep track of who potentially are the researchers who might be bringing out papers, and what the rate of posting is.

I will use these links, and try to edit out anything they bring up by mistake. Like Lee Smolin's 2003 survey mentions dynamical triagulations but is not really ABOUT that, so I dont count it.

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2003/0/1

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2004/0/1

Last 12 months:
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

2003 3
2004 4
LTM 6

here are the authors who have recent CDT articles, or those like Bianca Dittrich who have one in the works already being cited but not on arxiv yet:

Jan Ambjorn
Mohammad Ansari
Bianca Dittrich
Jerzy Jurkiewicz
Tomasz Konopka
Renate Loll
Fotini Markopoulou
Johan Noldus (postdoc with Loll at Utrecht)
Lee Smolin

this is probably not a complete list. it does not include Loll's graduate students at Utrecht,
http://www.phys.uu.nl/~loll/Web/students/students.html
and people like Arundhati Dasgupta who have written CDT papers but they were before 2003. but this is some of the people.

marcus

Jun3-05, 10:15 PM

The Dynamical Triangulations Sex Manual is mainly to explain the pleasureful maneuvers called

1. the Einstein-Hilbert action
and
2. the Wick rotation

(relevant passages of the manual will be covered in the thread here called
Introduction to Loop[-and-allied] Quantum Gravity
http://www.physicsforums.com/showthread.php?p=589732#post589732
which is not only about core LQG but lately has also a Causal Triangulations section.)

marcus

Jun5-05, 11:34 AM

topology change is included in the state sum in these two papers
by Loll and her graduate student Willem Westra

http://arxiv.org/find/hep-th/1/au:+Westra_W/0/1/0/all/0/1

a paper in preparation by Loll and Dittrich giving a CDT black hole model
must I suppose also deal with topology change

here is the citation for that paper given in "Reconstructing the Universe"

[20] B. Dittrich and R. Loll: Counting a black hole in Lorentzian product triangulations, preprint Utrecht, to appear.

marcus

Jun6-05, 10:29 AM

the common turf is "non-perturbative quantum gravity"---what does that mean?

the goal of n.-p. QG was recently described as "consistent quantum dynamics on the set of all Lorentzian spacetime geometries"

As I read it, "Lorentzian" in this context means "causal" or layered.

In the usual version LQG, the set of spatial geometries appears as a set of connections on a differentiable manifold. At least IMHO, this could be an obstacle. It looks like usual LQG is pre-committed to space being 3D at all scales. At this moment I cannot imagine how the standard-version LQG set of geometries could be generalized to include ones with dynamic, or varying, dimension.

On the other hand Loop-and-allied approaches includes a bunch of different things and is not permanently anchored to one standard formalism---it tends to be pragmatically definable only by what Loop people do: by what the people who will show up at the Loops 05 conference are interested in and working on at the time.

In the past twelvemonths we have seen some papers by Laurent Freidel and Etera Livine and others in which spinfoams are modified to be "Lorentzian". It would seem natural for people in the Causal Sets line of investigation to accomodate with causal triangulations (which may even have been inspired by causal sets, to what extent I can't be sure)

BTW as of 6June recent annual CDT posting
(see earlier post http://www.physicsforums.com/showpost.php?p=591375&postcount=11 ) has been

2003 3
2004 4
LTM 7

marcus

Jun6-05, 11:40 PM

Hermann Nicolai's own research field is string, but he also has a broad balanced vision of quantum gravity and the section of AEI Golm that he directs is one of the most effective QG research institutions in the world.
Past/present AEI members that you could consider to be AEI "products" include Thomas Thiemann, Martin Bojowald,
Hanno Sahlmann, Renate Loll, Bianca Dittrich (many other wellknown QG people have passed through there as well). AEI is one place they do string and LQG in a balanced way, along with solid work in numerical relativity etc.

in QG if somebody is doing something interesting and new there is a substantial chance that if you look at their CV you will find that the person has spent a year or a few years in Nicolai's department of AEI

in some sense it is Nicolai perspective behind the October Loops 05 conference because he is one of the local organizers but also the other local organizing committee members are his AEI people.

So even though the guy is a mere string theorist, :wink: I want to pay careful attention to his perspective on QG. Well he just posted an article today on arxiv that gives some in the introduction. It is Nicolai's contribution to Abhay Ashtekar's book "A hundred years of relativity":

----quote from Nicolai http://arxiv.org/abs/gr-qc/0506031 -----

1. Introduction

As we look back 90 years to take stock of what has been achieved since Einstein explained gravity in terms of spacetime geometry and its curvature, the progress is impressive. Even more impressive is the wealth of structure contained in Einstein’s equations which has been revealed by these developments.

Major progress has been made concerning

•Exact solutions (Schwarzschild, Reissner-Nordstrom, Kerr, axisymmetric stationary solutions,...)

•Cosmological applications (standard FRW model of cosmology, inflationary universe,...)

•Mathematical developments (singularity theorems, black hole uniqueness theorems, studies of the initial value problem, global stability results,...)

•Conceptual developments (global structure and properties of spacetimes, horizons, black hole entropy, quantum theory in the context of cosmology, holography,...)

• Canonical formulations (Dirac’s theory of constrained systems, ADM formalism, Ashtekar’s variables,...)

• Higher dimensions (Kaluza Klein theories, brane worlds,...)

• Unified theories ‘beyond’ Einstein (supergravity, superstrings, supermembranes and M(atrix) theory,...)

• Quantizing gravity (perturbative and canonical quantization, path integral approaches, dynamical triangulations, spin networks and spin foams,...)

All these subjects continue to flourish and are full of promise for further and exciting developments (hinted at by the dots in the above list)....

----end quote---

From this one would say that Nicolai sees quantizing gravity as just one of the main research directions stemming from Gen Rel, and that when it comes to specific approaches to quantum gravity he mentions DT, the spin networks of LQG, and spin foams more or less on the same footing, and then says dotdotdot...

Gerard 't Hooft is another person whose perspective on QG and Triangulations gravity in particular is worth noting. Coincidentally Renate Loll is at 't Hooft's institute: the ITP at Utrecht is home to both.
If you have a fast connection and want a 't Hooft perspective here is
a video (but it is 202 MB)
http://pitp.physics.ubc.ca/archives/CWSS/showcase/panels.html
click on the first panel discussion, or download the video directly:
http://pitp.physics.ubc.ca/archives/CWSS/showcase/panel1.wmv
Peter Woit reported on what 't Hooft said at this May 2005 conference here
http://www.math.columbia.edu/~woit/blog/archives/000201.html

marcus

Jun7-05, 02:27 PM

To update the earlier list, here are authors who have recent CDT articles, or one in the works, like Dario Benedetti and Francesco Zamponi who have a paper with Loll that is being cited but not on arxiv yet:

Jan Ambjorn
Mohammad Ansari
Dario Benedetti (grad student at Utrecht)
Bianca Dittrich
Jerzy Jurkiewicz
Tomasz Konopka
Renate Loll
Fotini Markopoulou
Johan Noldus (postdoc at Utrecht)
Lee Smolin
Willem Westra (grad student Utrecht)
Francesco Zamponi

some of the authors are on this list of u.U. students
http://www.phys.uu.nl/~loll/Web/students/students.html
only recent authors are listed so we miss those like Arundhati Dasgupta who have written CDT papers but before 2003.

these arxiv links the relevant articles

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2003/0/1

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2004/0/1

Last 12 months:
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

I'm unable to identify the graduate student with Loll and Julian Barbour in this picture. Anybody know?

http://perimeterinstitute.ca/images/marseille/marseille103.JPG

marcus

Jun8-05, 05:47 PM

topology change is included in the state sum in these two papers
by Loll and her graduate student Willem Westra

http://arxiv.org/find/hep-th/1/au:+Westra_W/0/1/0/all/0/1
...
...
here is the citation for that paper given in "Reconstructing the Universe"

[20] B. Dittrich and R. Loll: Counting a black hole in Lorentzian product triangulations, preprint Utrecht, to appear.

That was post #13 of this thread, of 5June.

By coincidence the day after i posted that, the paper of Dittrich Loll appeared and now I have been reading it and have some impressions. I hope maybe some other PF posters have too.

http://arxiv.org/gr-qc/0506035

I would emphasize the word PRODUCT triangulations. Loll and Dittrich are defining a simplicial manifolds concept analogous to FIBER which they spell "fibre". Also they use the terms base and "tower"
in a product triangulation there is a base triangulations B and on that base there are tower triangluations, like a vertex tower, an edge tower etc.

Look at pages 6 and 7. So after the definitions are taken care of they have a product triangulation B x F, where F consists of towers over simplexes in B.

And it turns out that a CAUSAL or Lorentzian triangulations is simply one simple kind of PRODUCT. In other words with the basic multipurpose concept of product triangulation, once you have defined it then it is just a throwaway one-liner to say what causal spacetime triangulations are.

so that is good, one expects that in good mathematics.

and this concept of product triangulation is also helping Dittrich and Loll get a handle on black holes-----here the base space B is 2D, one for time and one for radial distance. so they can triangulate their black hole and have a convenient handle on distance from center

marcus

Jun8-05, 06:43 PM

Gerard 't Hooft is another person whose perspective on QG and Triangulations gravity in particular is worth noting... Renate Loll is at 't Hooft's institute: the ITP at Utrecht is home to both.

http://www.physicsforums.com/showthread.php?t=46806

this thread is about 't Hooft talk at the KITP 25th birthday conference. it has links to audio and slides, also some slides are transcribed to save the reader having to download graphics

A couple of posts back there was a hint of a Hermann Nicolai perspective on CDT Triangulations approach to quantum gravity. I would guess if you are a grad student and want to do QG then if you go to Uni Potsdam you are very welcome to do that----you dont have to only do string theory or loop gravity. path integral/CDT was the first specific line of QG research that Nicolai listed.

so we have a glimmer of where AEI-Potsdam is, but I have also been looking for some perspective on Loll's work by 't Hooft. and I have not found anything. Only that in some sense his institute at Utrecht has placed a "BET" on Triangulations by getting Loll there.

I'll keep an eye out for 't Hooft views of the QG roadmap.

marcus

Jun9-05, 06:16 PM

this is from Smolin's opinion piece in June2005 "Physics Today". the piece is called "Why no 'new Einsteins'?".

----------quote from Smolin June 2005 article------

...Alternatives to strings

More worrisome, young theorists who pursue alternatives to string theory have had great difficulty finding any academic positions in the US. This is true of those who pursue alternative programs in particle physics...and...of those who pursue alternative approaches to quantum gravity such as dynamical triangulations, causal sets, and loop quantum gravity. These subjects are all pursued much more vigorously outside the US, because leading researchers in these areas are drawn to leave US universities...

---end quote----

what I want to call attention to is a sudden shift in priorities among the alternatives and the increased prominence of CDT "triangulations". Remember that in terms of numbers of researchers and annual postings on arxiv, CDT is a much smaller, newer, and until recently less prominent effort than LQG. for whatever reason, when Smolin lists a few QG alternatives he mentions triangulations FIRST.

This is a small matter, but it reminded me of what I just heard in Hermann Nicolai's perspective on QG. From post #15 of this thread:

Hermann Nicolai's own research field is string, but he also has a broad balanced vision of quantum gravity and the section of AEI Golm that he directs is one of the most effective QG research institutions ...

----quote from Nicolai http://arxiv.org/abs/gr-qc/0506031 -----

1. Introduction

As we look back 90 years to take stock of what has been achieved since Einstein explained gravity in terms of spacetime geometry and its curvature,...

• Unified theories ‘beyond’ Einstein (supergravity, superstrings, supermembranes and M(atrix) theory,...)

• Quantizing gravity (perturbative and canonical quantization, path integral approaches, dynamical triangulations, spin networks and spin foams,...)

----end quote---

... when it comes to specific approaches to quantum gravity he mentions DT, the spin networks of LQG, and spin foams more or less on the same footing,...

Not only on the same footing (in spite of the fact that CDT is a newer and smaller effort) but he mentions the triangulations approach before the other two.

BTW the whole Smolin article is well worth reading. He explores why Europe is currently doing better than US at promoting progress in theoretical physics. (overcommitment to string dead end has cost the US lead), and Smolin looks at some policy measures aimed not only at breaking the institutionalized string stranglehold but preventing any one speculative program from monopolizing theory funding and career opportunities in the future.

Hopefully the Smolin article will be made generally available online.

Woit's blog discusses the Smolin article "Why no 'new Einstein'?"
and gives some more and lengthier quotes.
http://www.math.columbia.edu/~woit/blog/archives/000204.html

marcus

Jun9-05, 09:00 PM

Smolin's June 2005 "Physics Today" article is worth quoting some. It is 4 pages and towards the end, on page 4, he makes some proposals---here's a sample:

------quote Smolin-----
To prevent overinvestment in speculatative directions that may end up as dead ends, departments should ensure that different points of view about unsolved problems, and rival research programs, are represented on their faculties.

Research groups should seek out people who pursue rival approaches, and include them as postdocs, students, and visitors. Conferences in one research program should be encouraged, by those funding them, to invite speakers from rival programs. Instructors should encourage students to learn about competing approaches to unsolved problems, so that the students are equipped to choose for themselves the most promising directions as their careers advance.

Funding agencies and foundations should take steps to see that at every level scientists are encouraged to freely explore and develop all viable proposals to solve deep and difficult problems. Funding should go to individual scientists for individual thought and not to research programs. A research program should not be allowed to become institutionally dominant until supported by convincing scientific proof of the usual kind. Before such proof is demonstrated, alternative and rival approaches should receive encouragement to ensure that the progress of science is not stalled by overinvestment in a direction that turns out to be wrong.

----end quote---

marcus

Jun9-05, 09:42 PM

Here is a sample from page 3 of the four-page printout. this is where Smolin is introducing his proposals, before he starts listing them

-------quote Smolin June 2005 Physics Today article-----

...my purpose here is not to argue for or against any existing research program. It is to propose that, under the pressure to support programs advanced decades ago by now influential senior scientists, we have forgotten that theoretical physics is most often advanced by people who ingnore established research programs and invent their own ideas and forge their own directions. Such people are often, but not always, young people, whose careers are the most vulnerable. If we do not explicitly make room for these kinds of people, they will leave physics or they will continue, as now, to leave the US to do the physics they want to do.

-------end quote----

a point there! For instance if you wanted to do interesting quantum gravity research you might well find you had to go to Utrecht, or Potsdam, or Waterloo (Holland, Germany, Canada.) AFAIK there is nobody in the whole US doing Causal Dynamical Triangulations.

In the next paragraph, which I won't type in, he talks about research funding policies followed in several other countries. Here is a sample of what follows:

----quote Smolin----

...When a group of researchers aggressively pursues a research program that has little interaction with either experiment or outsiders, the group tends to overinterpret results, undervalue risks, and complacently postpone facing up to hard questions and negative results. This is groupthink---a well-documented phenomenon in government, intelligence agencies, and business...

---endquote---

he is talking here about the need for departments to be diversified, in the theory section, so that one group doesnt get the mistaken notion of being the primadonnas or the only game in town or some such idea, but different approaches can bump against each other now and then and keep each others complacency and arrogance under control. They can ask each other embarrassing questions at colloquia and other useful functions. Actually helps them think better. It used to be pretty common academic practice to diversify your department. Diversity may have declined.

marcus

Jun10-05, 12:56 PM

Lubos Motl has posted this link which he says has a copy of the text of Smolin article "Why no 'new Einstein'?"

http://waltf007.mindsay.com/

what I have is a paper hardcopy that I was typing in some quotes from. If the Lubos link works then anyone who wants can see the whole article.

Here is the link to Lubos blog, for his generally unfavorable comments
http://motls.blogspot.com/2005/06/why-no-new-einstein.html

arivero

Jun11-05, 04:16 AM

Here is the link to Lubos blog, for his generally unfavorable comments
http://motls.blogspot.com/2005/06/why-no-new-einstein.html

I would recomment everyone to go to Woit's and Lubos's threads in the respective blog and to try to collaborate on interpreting the article.

As for the answer of Lubos, he seems to interpret that the important point of the article were the constructive proposals and then he attacks them; but note that Smolin himself disminishes the literal importance of such proposals by using the reference to Jonathan Swift's 1729 essay.

marcus

Jun11-05, 08:12 AM

... he seems to interpret that the important point of the article were the constructive proposals ...but note that Smolin himself disminishes the literal importance of such proposals by using the reference to Jonathan Swift's 1729 essay.

Like you, I also heard the faint echo of Swift's despairingly bitter satire "A Modest Proposal".

Anyone who has not already read the Swift essay might want to have a look

http://darkwing.uoregon.edu/~rbear/modest.html

an alternative (of the many versions on the web)
http://www.english.upenn.edu/~jlynch/Courses/95c/Texts/modest.html

Despite the echo of Swift's title, I think Smolin made all his proposals seriously. I do not think any of them were intended ironically.

Indeed, if there is any irony (and perhaps you are right that there is some, which I just did not hear at first) then it is that the three of them I quoted shouldn't even have to be proposed.

Correct me if I am wrong, but isn't diversity in academic departments---representing rival theories---a time-honored practice? Didn't used to be quite normal for an active department head, wanting to build up a department and improve its standing, to bring in strong representatives of alternative theoretical lines? This was my impression from casually observing of a few departments in US universities (can't say I ever paid really close attention). Please let me know if you have a different impression of academic norms.

If the aim was a department with a strong national reputation then rather than consisting of all one dominant breed of theorist it needed more to resemble the PRIVATE ZOO of rare beasts assembled by some wealthy Victorian gentleman.

I do think that there are successful contemporary examples of this (but you Alejandro would know better which they are, London Imperial, Marseille, Cambridge, Lyon, Potsdam, Utrecht, British Columbia, Rome, Penn State...?) but balanced theoretically diverse departments are currently rare in the US, to our considerable misfortune.

marcus

Jun11-05, 08:26 AM

... he seems to interpret that the important point of the article were the constructive proposals ...but note that Smolin himself disminishes the literal importance of such proposals by using the reference to Jonathan Swift's 1729 essay.

Possibly differing with Alejandro on this, I would reckon these proposals of Smolin, that I quoted earlier, to be completely serious.

------quote Smolin-----
To prevent overinvestment in speculatative directions that may end up as dead ends, departments should ensure that different points of view about unsolved problems, and rival research programs, are represented on their faculties.

Research groups should seek out people who pursue rival approaches, and include them as postdocs, students, and visitors. Conferences in one research program should be encouraged, by those funding them, to invite speakers from rival programs. Instructors should encourage students to learn about competing approaches to unsolved problems, so that the students are equipped to choose for themselves the most promising directions as their careers advance.

Funding agencies and foundations should take steps to see that at every level scientists are encouraged to freely explore and develop all viable proposals to solve deep and difficult problems. Funding should go to individual scientists for individual thought and not to research programs. A research program should not be allowed to become institutionally dominant until supported by convincing scientific proof of the usual kind. Before such proof is demonstrated, alternative and rival approaches should receive encouragement to ensure that the progress of science is not stalled by overinvestment in a direction that turns out to be wrong.

----end quote---
(to see these in context of the whole essay you can try
http://waltf007.mindsay.com/
this provided by Lubos Motl
Smolin's proposals are a bulleted list right at the end of the essay)

To me, the irony is that no one should have to make such proposals: theoretical diversity should be an obvious growth strategy to avoid dead ends (like the string fiasco we are now witnessing) and to promote stimulating exchanges, challenges that keep people inventive and resourceful, crossfertilization of ideas, and to avoid the boredom of so many identical ideological cookies.
No one should have to tell this to the deans, chairmen, hiring committees, funding agencies, foundations, conference organizers. Their forerunners in earlier generations knew this. why (especially in the US) have they lapsed?

arivero

Jun12-05, 05:34 AM

Hmm Marcus, you have a point. It seems that Smolin's explicit mention of such obvious rules is done to show that there are not been applied or that in the cases where there are being applied some other mechanism blocks them (not necessarily a bureaucratic mechanism). Still, I think that the goal of the author of such enumeration could be not to impose (by bureaucratic mechanims) such rules, but to underline the existence of a blockage. Mostly a way to tell "guys, this is not working".

nightcleaner

Jun12-05, 10:18 AM

hi marcus and arivero.

I am over my time limit today and will get bumped momentarily. However, I did notice that last month Smolin was at Columbia University, speaking in a small venue before an audience that included Brian Greene. My own very limited experience of administrators has been that they like to be in control and hate to let outside agitators in to spoil their nice plans.

Thanks,

Richard

marcus

Jun12-05, 12:50 PM

hi Alejandro, hi Richard

I just noticed that this thread has no link to the Loops 05 conference.
they have updated the conference site recently, and have posted a list of participants (besides the invited speakers and topics they already had)

http://loops05.aei.mpg.de/

with Smolin's essay, there are some puzzling things about it (for me and I guess for others as well)

the concrete proposals to diversify programs at instute and departmental level, have more diverse conferences (BTW Loops 05 includes string with Dijkgraaf an invited speaker), diversify student and postdoc support by making it more to individual on merit and less on program-allegiance----all that concrete practical stuff seems sensible and do-able

but it doesnt really have much to do with the historical example of A. Einstein. or? So is this basically two different essays? Or is the Einstein part of it more rhetorical than substantive? Should it have been edited to make the two-fold thrust of it explicit.

what I see as sensible proposals to diversify are just a ways of making US research better and even just restoring some practices that may have lapsed in the last 10 or 20 years.

arivero

Jun12-05, 01:21 PM

A bit of gossip. One of the motivation for the title of Smolin's article (I am one preferring a new Sommerfeld, for instance) is that time ago the "Discover" magazin touted him as "The New Einstein".

Of course, he has used Einstein as an example in other talks, I found this abstract (http://www.quantum.univie.ac.at/QUPON/Smolin.pdf). Ah, the bibliography there mentions a forthcoming work of Smolin, and the pun in the title is also evident: " All strung-out "

marcus

Jun12-05, 01:39 PM

A new Sommerfeld would be soooooo nice!

A new alpha! something as basic as the fine structure constant (approx. 1/137). a Sommerfeld who would see a new pattern in the Standard matter model.

Yes we could do with a new Sommerfeld. I actually do not know much about him. Know anything more of interest?

Smolin? I thought everybody realized that it was not Smolin who is our new Einstein but instead it is Renate Loll! :biggrin:

I am glad to hear about the new book coming out from Basic Books publishing house in July 2005. That is next month!

what a thoughtful and timely title

4. Lee Smolin: “All Strung Out”, Basic Books (to appear in july 2005)

http://www.quantum.univie.ac.at/QUPON/Smolin.pdf

I found this at AMAZON.COM about Smolin's new book ALL STRUNG OUT to be released (it says) on 3 July 2005.

http://www.amazon.co.uk/exec/obidos/ASIN/0465078389/qid=1118607919/sr=1-8/ref=sr_1_2_8/026-9746814-8064469

marcus

Jun14-05, 01:37 PM

http://www.math.columbia.edu/~woit/blog/archives/000204.html

there has been a 75+ post discussion here of Lee Smolin's essay Why no 'new Einstein'?

post #76 is a four page (printed out) comment by Smolin, about his essay and about what people had to say about it and other side points that came up.

I think it is real interesting, and well-written

Naturally CDT (Loll-type simplex gravity, computer simulations) came up, I guess because CDT is a fundamentally new development in quantum gravity and a hot issue now, so we have some additional comment or viewpoint from Smolin on that.

post #26 of this thread gave a link supplied by Motl to text of Smolin essay

... you can try
http://waltf007.mindsay.com/
this provided by Lubos Motl
Smolin's proposals are a bulleted list right at the end...)

selfAdjoint

Jun14-05, 08:42 PM

Smolin's comments are a must-read for anyone interested in several things that have been posted here in the past. Such items as Thiemann's LQG quantization of the closed string and the assertion that LQG quantization must be wrong because it doesn't produce an anomaly as "it is known" to be required. Smolin tracks this down to the difference between quantizing with a fixed background and in a background free environment. And Smolin says, in response to a request for a blanket term to cover everything from Thiemann to Loll by way of Rovelli and Smolin himself with all their coworkers, that he uses background-free approach to quantum gravity. I propose that WE declare Background Independent Quantum Gravity (BIQG) to be the term we use here on PF and that you, Marcus get behind it as you have 8\pi G so we can really sell it.

Would it be possible to get a copy of Smolin's comment posted here?

marcus

Jun14-05, 09:30 PM

... I propose that WE declare Background Independent Quantum Gravity (BIQG) to be the term we use here on PF and that you, Marcus get behind it as you have 8\pi G so we can really sell it.

Would it be possible to get a copy of Smolin's comment posted here?

Hi selfAdjoint, you are kind to think that I am persuasive enough to sell notation or improvements to widely current terminology!

I approve of your idea. But I personally did not even succeed in "selling" 8\pi G . Which was Baez suggestion or someone before him. I am not ashamed of having tried though. We had fun trying to make Baez 8\pi G version of the Planck units usable.

I think your idea of reforming common parlance to say BIQG is basically a good one. Let me go look at the Loops 05 website and see what they say at the top of their conference homepage. If it says BIQG, or words to that effect, that would be a good sign.

I am going to
http://loops05.aei.mpg.de/
to check out the wording

be right back

Yes, you are in luck. at the top of the page it says LOOPS '05

and then under that it says<<In the Einstein year 2005, the annual international meeting on non-perturbative/background independent quantum gravity takes place from 10-14 October 2005 at the Albert-Einstein-Institute in Potsdam, Germany. The aim of this conference is to summarise the status and open problems of the various approaches and to present new ideas and research directions.>>

that language would have passed Hermann Nicolai and it is what you are suggesting BIQG
except that it leaves open the possibility of also saying Non-perturbative QG. Strictly speaking the AEI website says "non-perturbative/background independent quantum gravity"

I think we can ignore that other option

I will think about this. As a general rule a journalist or librarian should not ever try to innovate. only use off-the-shelf language. if you innovate terms do it only for fun and then go back to already established language.

but if the professionals are going to change terminology (like Smolin and Nicolai) then we should be alert and ready.

Chronos

Jun15-05, 12:03 AM

Chiming in, I entirely agree with SA. Without background independence I see no hope for a workable quantum theory of gravity. Any first cause proposal must be background independent in my mind. I realize I'm borrowing heavily from information theory, but I believe that is the only approach that has a fighting chance of being correct. Treating the universe as a quantum computer has attractive features.

marcus

Jun15-05, 10:23 AM

Smolin's comments are a must-read for anyone interested in several things that have been posted here in the past....

Would it be possible to get a copy of Smolin's comment posted here?

I took your suggestion and posted it!

http://www.physicsforums.com/showthread.php?p=604594#post604594

selfAdjoint

Jun15-05, 11:39 AM

Thank you Marcus!

marcus

Jun15-05, 12:05 PM

Thank you Marcus!

You are most welcome, selfAdjoint!
I was just at Not-Even-Wrong and noticed that Peter has reposted Smolin's response with its own heading

http://www.math.columbia.edu/~woit/blog/archives/000206.html

so now it is easier to link to it directly than before when it was imbedded in the original thread

marcus

Jun16-05, 01:52 PM

I want to keep the link handy to the Loops 05 program
http://loops05.aei.mpg.de/index_files/Programme.html

elsewhere in this thread there is this main link
http://loops05.aei.mpg.de
but it does not reveal the file address for the programme.

Alejandro also provided the link for the Strings 05 conference which starts 11July in Toronto. I will fetch that---it will be interesting to see the titles of the talks whenever the schedule is filled in

the Loops 05 Program page so far just has the list of invited speakers and says that more will be posted in July, which would be nice (plenty of time for participants to do their homework before the October conference date)

yes, here is the link Alejandro found for Strings 05 (July 11-14)
http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/program.html

selfAdjoint started me thinking how one can describe the Quantum Gravity programs that are the main rivals to string. One could say simply "non-string QG" or "QG alternatives to string". the map of this research territory is gets complex and interesting the more I look at it.
I do not think the main contenders are typified by a conventional narrowly defined LQG.

It occurred to me to try defining the non-string QG people by something like "Erdos numbers". Let's say the people who have low Freidel number or Loll number. this is not to presume to judge that those two researchers have special merit, but simply to use the fact that they are WELL-CONNECTED by co-authorship with the group of people I'm trying to characterize.

these are the people whose work currently rivals or challenges string in the sense that if support in US physics departments were diversified (a "mixed strategy" instead of all the eggs in one basket) then it would be people like this who would get more job-offers and postdoc fellowships.

It would not be some string theorist's stereotype of a stock-LQG researcher because there are not very many of those---I cant think of any young ones.

Anyway, who are Freidel and Loll? Freidel got his PhD in 1994 (quantum groups and theory of knots) advisor was Jean-Michel Maillet. They have a paper or papers on arXiv from around 1992-1994 which can give an idea.
http://www.ens-lyon.fr/PHYSIQUE/Theorie/rapport-activite-94-96/node14.html
Here are photos of theory people at the Ecole Normale, Lyon, including Freidel and Maillet
http://www.ens-lyon.fr/PHYSIQUE/Theorie/trombinoscope2.html

Loll got her PhD in 1989 at London Imperial College. Chris Isham is there. At the moment I don't know what her thesis was about or who her advisor was.

If you wanted to include LQC-cosmology then you could add Martin Bojowald and then almost anybody you can think of would have co-authored with one of those three.-----would have Freidel number or Loll number equal to one (or two at the most) or else Bojowald number equal to one.

Maybe some has a different idea? Or would use different nodes to define the network?

It was interesting to see that the topic of Freidel's thesis (1994) was "Integrable models, quantum groups, and knot theory"-----so it was in the general area of quantum algebra.

marcus

Jun16-05, 07:12 PM

I think there is a generational shift in non-string Quantum Gravity. Only a few years ago (I think as recently as two years back) the symbolic figures were unquestionably the LQG founding fathers like Rovelli and Smolin and Ashtekar. At a representative conference one or more would head the line-up and speak for the field.

now it seems slightly different, I think there could be a conference in non-string Quantum Gravity approaches where the question i would be asking is "Is Laurent Freidel going to be speaking?" and is Renate Loll going to be there? and what are THEY going to talk about?

Not too long ago with in a similar situation i would be asking about the work of people who today are more like generals---not on the front lines. the field is moving right along and this is a normal and good progression, it does not diminish my respect for Sm. Rov. Ash. and thankfulness for what they have accomplished, but it does mean that I want to know a little bit more about the generation that is coming up, and central figures in it, like Loll.

Maybe you, with your different perspective, do not care. But I am interested in where she came from, training and early work. As one of her earliest, Renate published this paper in Physical Review D vol 41, in 1990, "Noncommutativity of constraining and quantizing: a U(1) gauge model"
and she got her PhD in 1989 from London Imperial College. I will try to pick up more details as we proceed.

Loll's Utrecht website has a list of her students and postdocs in her program. I gave a link earlier. but beyond that she is picking up new CDT people, which i want to keep aware of. She has a paper in the works with these two:
Francesco Zamponi
http://glass.phys.uniroma1.it/zamponi/pagine/fisica.html
Dario Benedetti (was at Rome, student of Amelino-Camelia, now at Utrecht)
http://www.phys.uu.nl/~benedett/home/

marcus

Jun20-05, 09:38 AM

since this thread is for news and gossip bearing on CDT (Loll-type triangulations approach to quantum spacetime dynamics), here a relevant research computing development:

http://biz.yahoo.com/fool/050617/111903931827.html?.v=2

In CDT some of the simulations take weeks on an older work station. The new IBM computer "Watson Bluejean", or whatever they call it, does 91 teraflops or 91 E12 floating point arithmetic operations per second. Should speed a gravity researcher's simulations up considerably.

<<... strengthen IBM's already strong position in the burgeoning field of nanotechnology. By reducing the time it takes to run simulations from months or weeks down to mere days or hours, Watson Blue Gene holds the potential to exponentially increase our understanding of the complex fields of materials sciences, quantum chemistry, and molecular and fluid dynamics.

...

IBM officials are confident that they'll be able to develop a successor capable of a 1 petaflop performance level by the end of the decade. That's 1 quadrillion calculations per second -- 10 times as powerful as Watson Blue Gene.>>

it strikes me there is an analogy between quantum gravity simulation, with all these microscopic geometric "moves" where you swap simplexes around, and PROTEIN FOLDING

<<..The first area where the new computer will prove useful is in modeling how proteins fold...>>

Hope Loll et al can get some time on a Blujean

In case it works better, here is another link to the same article
http://news.yahoo.com/s/fool/20050617/bs_fool_fool/111903931827;_ylt=AtgSlcORRLSVEnePChhelZojtBAF;_yl u=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl

marcus

Jun20-05, 10:27 AM

I want to keep the link handy to the Loops 05 program
http://loops05.aei.mpg.de/index_files/Programme.html
...
http://loops05.aei.mpg.de
...

Alejandro also provided the link for the Strings 05 conference...---it will be interesting to see the titles of the talks whenever the schedule is filled in.
[The conference is 3 weeks away.]

yes, here is the link Alejandro found for Strings 05 (July 11-14)
http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/program.html
...

I just checked the Strings 05 schedule. It now lists three events of broad public appeal (but unfortunately so far none of the regular talks)

Public Talks: Saturday July 16, 2-5p.m.

Robbert Dijkgraaf U. Amsterdam
"Strings, Black Holes, and the End of Space and Time"

Leonard Susskind Stanford U.
"Cosmic Landscape: String Theory and the Illusion of Intelligent Design"

Panel discussion: Tuesday, July 12, 19:00-21:00
"The Next Superstring Revolution"

ohwilleke

Jun20-05, 11:05 AM

It occurred to me to try defining the non-string QG people by something like "Erdos numbers". Let's say the people who have low Freidel number or Loll number. this is not to presume to judge that those two researchers have special merit, but simply to use the fact that they are WELL-CONNECTED by co-authorship with the group of people I'm trying to characterize.

[snip]

Maybe some has a different idea? Or would use different nodes to define the network?

My guess is that if you really looked at the numbers you'd find maybe a dozen co-authorship clusters. But, at the point, you'd really need to take a further step. If you wanted to be content neutral about it, the next step would be to which which co-authorship clusters frequently cite each other. This would likely collapse the number of QG programs to less than half a dozen.

For example, to take the example of the MOND literature (which is not really a QG program, but just used to show the method), with which I am quite familiar and which would normally be viewed as one research program, there are probably three or four major co-authorship clusters, but all would cite each other frequently, and then there would be maybe two co-authorship groups (Mannheim, for example) who have similar research programs, but are pursuing separate theories.

But, if you looked strictly at co-authorship, you'd miss the fact that there are entire co-authorship groups writing about the exact same thing who have never authored a paper with the core investigator (Milgrom) or anyone who has co-authored a paper with him.

Another way to approach it would be to use the less rigorous measure of people who speak at the same conferences, rather than people who co-author papers.

marcus

Jun22-05, 12:21 PM

My guess is that if you really looked at the numbers you'd find maybe a dozen co-authorship clusters...

sounds like a reasonable guess
the main obstacle to actually doing co-authorship analysis is my own laziness
:smile:

at the moment nearly everybody I can think of in non-string quantum gravity has co-authored with either Freidel, or Loll, or Bojowald
so if I just want a rough and ready ad hoc way to say who the people are that I think of as "LQG people" then I can just use "erdos numbers" for those three.

some other three would also work about as well, and my "seive" would have failures that i havent thought of, and it is completely unscientific

but you are proposing something much more objective---that would include for example Martin Reuter. I would miss him. but he's on the Loops 05 invited speaker list. I would make a lot of mistakes like that, with my quick and dirty subjective test.

BTW ohwilleke, I just posted a new Moffat in astronomy forum
Galaxy Rotation Curves Without Non-Baryonic Dark Matter
J. R. Brownstein, J. W. Moffat
43 pages, 7 figures, 4 tables, 101 galaxies
Abstract: "We apply the modified acceleration law obtained from Einstein gravity ...The fits are compared to those obtained using Milgrom's phenomenological MOND model and to the predictions of the Newtonian-Kepler acceleration law."
interested to know if you've any reaction

marcus

Jun23-05, 11:23 AM

http://math.ucr.edu/home/baez/week69.html

this 1995 piece by Baez has some gossip about Loll.
She got her PhD at London Imperial (where Chris Isham is) in 1989
and Baez says she was a postdoc working with Isham at some point after that.
Baez says he met Isham, Ashtekar, and Loll in 1991 at a conference in Seattle where they all three were giving LQG papers.
I am going to try to put this jpg snapshot of Renate Loll in

there may have been an article about CDT in Nature, last October. havent found it on line but did find this
http://www.nature.com/news/2004/041004/pf/041004-17_pf.html
dated 8 October. it doesnt have the photograph I expected and seems to have been abridged
this greek-language version has the photon and is more complete (still havent found the english version online)
http://www.physics4u.gr/news/2004/scnews1631.html

the physics blogger Dave Bacon (the "Quantum Pontiff") had a short intuitive description of what happens in CDT
http://dabacon.org/pontiff/?p=706#comments
he didnt get anything much in the way of perceptive or pertinent comments unfortunately. CDT too new.

marcus

Jun23-05, 12:53 PM

http://math.ucr.edu/home/baez/week206.html

this entry from Baez "this week's finds" also has an intuitive description of how CDT works and puts it into larger quantum gravity context. It is Baez report after the Marseille Loop/Foam conference where Loll spoke.

just to keep things in perspective, here is a home movie that Peter Woit posted link to. it was taken during a 10 minute break at the 1927 solvay conference in Brussels.

http://www.maxborn.net/index.php?page=filmnews

the camera belonged to Irving Langmuir, the chemist, and the voice-over narrative is supplied by Nancy Greenspan (author of a book about Max Born)

I clicked on the "realplayer" version and it took a while to download but it was worth it. the home-moving runs around 2 and a half minutes.

http://216.120.242.82/~greensp/solvay.ram

Brian Bell

Jun25-05, 10:06 AM

The greatest obstacle to discovery is not ignorance,
but the illusion of knowledge.

Thank God there is but one infinity! or
Vertigo makes the world go 'round -

marcus

Jun25-05, 11:55 AM

Thank God there is but one infinity! or
Vertigo makes the world go 'round - says Brian

Hi Brian, I am glad the quote caught your attention! the person credited with observing that about the biggest obstruction to discovery was Daniel J. Boorstin. he was an American, born 1914, and became the Librarian of Congress---sort of the country's chief librarian. this page has some 30 more quotes from Daniel Boorstin:

http://www.brainyquote.com/quotes/quotes/d/danieljbo175243.html

In response to your saying about thanking God and so forth, I think it is a mistake to say there is just one infinity. I believe there are a lot of different infinities. But it is nothing to get dizzy about---just take a deep breath and the initial moment of surprise will pass
:smile:

marcus

Jun25-05, 01:43 PM

marcus

Jun26-05, 06:53 PM

the tentative programme schedule for July 11-16 "Strings 05" has been posted.

http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/program.html

the titles of many of the talks are listed on this separate page:
http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/speakers.html

marcus

Jun29-05, 01:41 PM

yesterday a very cautious paper by Martin Bojowald came out
http://www.physicsforums.com/showthread.php?p=618695#post618695

http://www.physicsforums.com/showpost.php?p=618695&postcount=347

the second link is in case the first one doesnt work.

in a very tentative, "oblique", way he is venturing to suggest that blackhole bottoms may connect to inflations of new branches of the universe.

Bojowald I respect as a careful scientist and he does not seem to be media-phile. he does not do the attentiongetting bold speculations routine.

so this paper is very underplayed, careful almost grudging.

BTW it is already quite risky to do Loop Quantum Cosmology, but what other quantum model cosmology is there where you can actually calculate numbers?
LQC is very close to standard cosmology Friedmann model that almost everybody uses, only quantized. And you can actually calculate stuff that people have hopes of being able to check for---Parampreet Singh is one of the experts on the observational side of LQG, look him up if interested.

anyway LQG is already risky, and LQC which involves simplifying down from the full LQG model is also risky, but at least you can calculate and run computer simulations showing how contraction leads to expansion and how inflation naturally arises.

and now Bojowald and others have begun studying the black hole contraction---but in order to calculate they have to make simplifying assumptions about symmetry. they assume what collapses is nice and round----not shaped like a potato.

who is going to dare to say that black hole looks like it might lead to big bang? I dont mean say that as a "visionary" but say it on the basis of the way the mathematical models fit together. who is going to venture to hint this not on the basis of some mental image but on the basis of how the numbers look.

i remember standing at cliff-edge at Big Sur looking at the Pacific ocean one afternoon in 1961.
one is conscious of the solid ground under one's feet
one does not make any abrupt moves

nightcleaner

Jun30-05, 10:04 AM

A beautiful and disquieting image, Marcus. I am very glad you were careful of your feet. Do you know the bar/restaurant called Nepenthes located near Big Sur? I have a close freind who worked there in the late 60's, and he never seems to tire of recalling the times he spent meditating on the ocean from Nepenthes' deck, hundreds of feet above the surf. But it seems the place is in the hands of developers now, and styles itself a resort. I wonder if the Black Angel still hangs above the gift shop door?

Well, I have been guilty of wild speculations about big bangs beyond black holes before, and I am glad to hear that the polymaths are beginning, with caution, to say it may be possible. The notion seems to me to have a beautiful symmetry. Time and space once again seem to extend themselves beyond the horizons.

Now what about tidal forces and information? I will boldly speculate that tidal forces will not be a barrior to passage of information for the simple reason that the compression is of timespace itself, and objects as we know them are completely dependent on the timespace background. If the background compresses smoothly, so will the objects embedded in it. Therefore there should be some physical conditions which would allow passage of information through the event horizon and then through the "singularity" itself.

Essentially I am speculating that the "singularity" is not a singularity at all, but merely another infinite spacetime, infinitely removed from our point of observation. All lines seem to converge at infinity, but if you translate your point of view to the infinite location, Euclid's fifth postulate still holds. Infinity, like its inverse, the singularity, is permanently shrouded in an event horizon. We are never allowed to look on G-d's naked face. It is for our own protection. If we ever evolved enough to see G-d's face directly, we would no longer exist....not that we would be ripped apart by tidal forces, but that the perfect definition excludes our imperfect existence. G-d naked is solitary, and it seems G-d is not amused by that.

I think G-d is amused when we stand upon the cliff, and pleased when we choose to step back. It is not G-d's fault, when we look down at the surf, full of doubts and fears, but our own.

Be well Marcus, and all.....

Richard

nightcleaner

Jun30-05, 10:16 AM

Oh yeah, about that potato thing. I recall reading in Kip Thorne about some Russian theorists early in the Black Hole argument (would that have been in the 1960's?) who showed that irregularites ("a mountain") on the surface of a black hole will quickly be reduced to the sphere. Of course this is part of the argument that information passing into a black hole will be lost. In a sense, the irregularities actually are the information.

However, I wonder if this smoothness is just on the outside surface of the horizon. The inside surface of the BH could be all crinkley, and we would never know, would we? The information may be lost, to us on the outside, but that may not mean it is lost, looking back on it from the inside. What would the event horizon look like from the inside? Ahem. Cosmic Microwave Background Energy.

Richard.

marcus

Jun30-05, 10:58 AM

...

Well, I have been guilty of wild speculations about big bangs beyond black holes before, and I am glad to hear that the polymaths are beginning, with caution, to say it may be possible. The notion seems to me to have a beautiful symmetry. Time and space once again seem to extend themselves beyond the horizons.

...

I've had some nice times at nepenthe's but it is expensive now.

You and Smolin. he has had similar speculations about big bangs beyond black holes.

but Bojowald is special for me because he is NOT visionary. I trust him not jump to conclusions. he still has not, about this thing.
what I like is that I can tell that from where he stands he can see it very clearly but he will not jump at it. his example steadies me.

marcus

Jul1-05, 07:29 PM

Turns out that Loll and Westra and Masters student of Loll's named Stefan Zohren will be giving a paper 20 July at the big Paris Einstein conference

http://einstein2005.obspm.fr/indexr.php

Wednesday, 20 July 2005 14h20-14h40 :
R. Loll, W. Westra, Stefan Zohren
« Nonperturbative sum over topologies in 2D Lorentzian Quantum Gravity »

Some photos from the Utrecht Inst. of Theor. Physics

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

...

Let's take a closer look at the program at this month's Paris conference, mentioned in the earlier post.
http://einstein2005.obspm.fr/indexr.php
http://einstein2005.obspm.fr/programmer.php
The abstracts of some Plenary Session talks are posted. Here is a sample:

Monday July 18
...
11h45 - 12h25: Abhay Ashtekar « Gravity, Geometry and the Quantum »

"General relativity is both sublimely beautiful and incredibly successful. But it is incomplete because it ignores quantum physics. Its satisfactory synthesis with quantum mechanics would constitute the next leap in fundamental physics. In the first part of the talk I will discuss the primary challenges we face and summarize the strategies that have been devised to overcome them. In the second part, I will focus on loop quantum gravity, a background independent approach in which the continuum picture of space-time breaks down. I will discuss a few ramifications of the quantum geometry that replaces it. The goal is to provide a few glimpses of the exciting world-view in which gravity, geometry and the quantum merge."

14h00 - 14h40: Brian Greene « The State of String Theory»

"I will briefly review the motivation for and essential ideas of string theory, and then assess the progress the theory has made in a variety of critical areas."

14h45 - 15h30: Alain Connes « Noncommutative geometry and physics»

[no abstract available yet]

15h30 - 15h45: Coffee Break

15h45 - 16h25: Fay Dowker « Causal sets and discrete spacetime. »

"In 1905 the basic question of whether matter was continuous or discrete was still controversial and it was only decisively settled by the work of J.-B. Perrin who verified the quantitative predictions about Brownian motion made by Einstein and by Smoluchowski, ending any remaining scepticism about the physical reality of atoms and molecules. In 2005 our best theory of spacetime itself is General Relativity, in which spacetime is a continuum. But there is growing circumstantial evidence that spacetime is discrete at the tiny scales at which quantum effects on spacetime can no longer be ignored. Taking that evidence seriously, one approach to "quantum gravity'' proposes a fundamentally discrete substructure for spacetime: a causal set. The only structure carried by a causal set is a microscopic notion of "before'' and "after''. A simple model of particles moving on a causal set background implies that they undergo a Brownian motion in momentum. I will speculate on whether this phenomenon may be able to provide a mechanism for the production of the high energy cosmic rays whose origin remains a mystery. If causal set phenomenology can indeed explain the origin of high energy cosmic rays, then this observational data may turn out to be the Brownian motion of our age, convincing us finally of the atomicity of spacetime itself."

...

Tuesday July 19
....
10h15 - 10h55: Carlo Rovelli «Loop Quantum Gravity »

" I review the main ideas and the main results at the basis of the loop approach to quantum gravity. This is an attempt to construct a fully background-independent quantum field theory, where space and time emerge as quantum excitation of the gravitational field. In other words, it is an attempt to fully merge quantum field theory with the lesson of Einstein's general relativity."

...

Friday 22 July

...
15h45 - 16h45: Gerard t'Hooft « Conclusion Talk »

[no abstract available yet]

----------------------------------------------

BTW here is a picture of Fay Dowker. Interesting that both her mother and father were physicists, born c. 1966 undergrad major math, married to physicist Jerome Gauntlett---physics seems to run in the family---has two children.
http://www.stp.dias.ie/events/2004/causal_sets_photos/WorkshopOnCausalSets-FayDowker-1.jpg

Fay Dowker is one of the featured (Plenary Session) speakers not only at Einstein2005 this month in Paris but also at Loops05 this October in Potsdam.

marcus

Jul2-05, 01:21 PM

...BTW here is a picture of Fay Dowker. ...http://www.stp.dias.ie/events/2004/causal_sets_photos/WorkshopOnCausalSets-FayDowker-1.jpg

Fay Dowker is one of the ...Plenary Session...speakers not only at Einstein2005 this month in Paris but also at Loops05 this October in Potsdam.

dammit nobody has remarked on how beautiful Fay Dowker is!

do I have to paste this in as an attachment?

selfAdjoint

Jul2-05, 03:13 PM

dammit nobody has remarked on how beautiful Fay Dowker is!

do I have to paste this in as an attachment?

Yeah, she's beautiful! How old are her kids? Are they headed for physics careers too? Wouldn't three generations be a record unmatched since the Bernoullis?

marcus

Jul2-05, 03:27 PM

Yeah, she's beautiful! How old are her kids? Are they headed for physics careers too? Wouldn't three generations be a record unmatched since the Bernoullis?

I agree that three generations would be highly commendable
but we have to wait and see because her kids are only 3 years old and 7 years old

marcus

Jul3-05, 07:17 PM

this lady does not stop
http://arxiv.org/abs/hep-th/0507012

it's her fourth paper this year

selfAdjoint

Jul3-05, 10:28 PM

From the abstract:
This shows that one can in principle make sense of a gravitational path integral which includes a sum over topologies, provided suitable causality restrictions are imposed on the path integral histories.

I hope this analytical work doesn't fall into the Motl trap of being accused of bad physics for ignoring acausal paths in the path integral. The CDT papers proper avoid that criticism because those paths do not exist even in theory in their model, causality is prior to their whole scheme. But it seems this new analytical work is back to ordinary spacetime.

marcus

Jul5-05, 11:26 AM

... The CDT papers proper avoid that criticism because those paths do not exist even in theory in their model, causality is prior to their whole scheme...

good point about how they avoid that trouble.
in this case they manage to retain a causally layered model (continuing to avoid that type of vulnerability) by severely restraining the jitter in the topology. In the Loll-Westra model the wormholes exist only for an "infinitesimal" period of time. They barely exist---unable to register at macroscopic scale---and yet they seem to change the effective cosmological constant.

this is what I find hard to understand. Loll-Westra hardly change the CDT model, if at all. I can hardly believe that these microscopic infinitesimally-brief topology changes are actually taking place. (they seem to 'undo' themselves before any clock has had a chance to tick).
and yet.
and yet.
even though I dont see them really existing they seem to affect the Hamiltonian! so that where there used to be a Lambda (cosm. const) term there is now a effective Lambda, somewhat smaller.

BTW in 2D the newton G is dimensionless. and spacetime volume is an area. and "density of microscopic wormholes in spacetime" being a number per unit spacetime volume has the same dimension as curvature----namely reciprocal area.

so "density of wormholes" has the same dimension as the cosm. const. Lambda.

they find that as (the 2D version of) newton G increases there get to be more wormholes, so that the "density of wormholes" is growing almost linear proportional to G!

and as G is increasing and "density of wormholes" is growing, the effective cosm. const. Lambda is tailing off----see their Fig. 4.

The Catalan numbers get into the analysis. and some Laguerre polynomials.

all in all a bit remarkable. this is how it was in 1998. In 1998 Loll and Ambjorn tested a 2D model, with a 'causal' assumption, and found it worked. But it took roughly 5 years to get it up from 2D to 3D to 4D.

now Loll and Westra have something remarkable working at 2D. but it is not obvious how to picture these infinitesimal very brief wormholes (compatible with the causal restriction of CDT) in the 3D case.

Well, it is Westra's thesis, so I hope it does not take 5 years!

http://arxiv.org/abs/hep-th/0507012
Taming the Cosmological Constant...

marcus

Jul6-05, 06:57 PM

I use these links to check activity in CDT and to see what new authors are getting into this line of research. There has been some growth in the number of papers written per year

Using this kind of keyword search, I try to edit out anything they bring up by mistake. Like Lee Smolin's 2003 survey mentions dynamical triangulations but is not really ABOUT that, so I dont count it.

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2003/0/1

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/2004/0/1

Last 12 months:
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

2003 3
2004 4
LTM 8

here are the authors who have recent CDT articles

Jan Ambjorn
Mohammad Ansari
Bianca Dittrich
Jerzy Jurkiewicz
Tomasz Konopka
Renate Loll
Fotini Markopoulou
Johan Noldus (postdoc with Loll at Utrecht)
Lee Smolin
Willem Westra
Stefan Zohren

this is probably not a complete list. it does not include all of Loll's graduate students at Utrecht,
http://www.phys.uu.nl/~loll/Web/students/students.html
and people like Arundhati Dasgupta who have written CDT papers but they were before 2003. but this is some of the people.

marcus

Jul7-05, 12:11 PM

there is a German physics newsmagazine called P.U.Z.
Physik Unserer Zeit------Physics of Our Time. I think it could be a German version of "Physics Today".
and there is this physicist Claus Kiefer at Uni Köln.
and in January 2005 there was a one-page general audience article by Kiefer about CDT, in particular about the paper "Emergence of a 4D World" by Ambjorn Jurkiewicz Loll that appeared in fall 2004 in Physical Review Letters.

I didnt yet find this online in English. Does anyone have a link?

there is a horrible scarcity of (semi)POPULAR writing about CDT. In English there is almost nothing written about CDT for general audience, at least not online.

so I am contemplating translating this page of semipopular German science writing.

first let's see if I can just paste in the German text
-----------quote Kiefer from january P.U.Z.-----
QUANTENGRAVITATION: Die vierdimensionale Welt
Die klassische Raumzeit besitzt vier makroskopische Dimensionen. In einer zukünftigen Theorie der Quantengravitation ist damit zu rechnen, dass auch die Dimension zu einer dynamischen Variable wird, für die nur ein Erwartungswert angegeben werden kann. Unabhängig davon muss sich aus Konsistenzgründen im semiklassischen Limes immer die Zahl vier ergeben. Dass dem tatsächlich so zu sein scheint, konnten Jan Ambjørn (Kopenhagen), Jerzy Jurkiewicz (Krakau) und Renate Loll (Utrecht) kürzlich im Rahmen des Pfadintegralzugangs zeigen [1].

Eines der grundlegendsten offenen Probleme der modernen Physik ist die konsistente Vereinigung von Quanten- und Gravitationstheorie. Die Hauptschwierigkeit besteht hierbei darin,dass die Allgemeine Relativitätstheorie keine fest vorgegebene Hintergrund-Raumzeit kennt,sondern eine dynamische Geometrie. Bei den anderen Wechselwirkungen,beispielsweise der Elektrodynamik,quantisiert man aufeiner Raumzeit,bei der Allgemeinen Relativitätstheorie quantisiert man die Raumzeit selbst.

Den ehrgeizigsten Versuch,zu einer Quantengravitation zu gelangen,bietet die Stringtheorie,die davon ausgeht,dass dieses Ziel nur im Rahmen einer Vereinigung aller Wechselwirkungen zu erreichen ist. Andere Zugänge versuchen,Einsteins Theorie direkt zu quantisieren. Hierzu gehören Quantengeometrodynamik und Schleifendynamik. Ambjørn und Kollegen wählten einen Zugang über das Feynmansche Pfadintegral.

In der Quantenmechanik summiert man im Pfadintegral über alle möglichen Pfade für ein Teilchen zwischen zwei Orten und Zeiten. Die meisten Pfade sind stetig,aber nirgends differenzierbar. Das Ergebnis ist eine Übergangsamplitude,welche die Schrödinger-Gleichung erfüllt. In der Gravitationstheorie ist hingegen über alle möglichen vierdimensionalen Geometrien („Raumzeiten“) zu summieren,die zwischen zwei dreidimensionale Geometrien („Räume“) passen.

Formal leicht möglich ist eine so genannte Sattelpunktsnäherung,bei der sich im semiklassischen Grenzfall als dominierende Raumzeit eine solche ergibt,die den klassischen Einsteinschen Feldgleichungen genügt. Für eine saubere Berechnung jenseits dieser Näherung muss die Summe über alle Geometrien aber zunächst definiert werden. Diese Regularisierung geschieht durch Diskretisierung und anschließenden Kontinuumslimes.Als Vorbild dienen die Gittereichtheorien für starke und elektroschwache Wechselwirkung. Dort ist allerdings die Geometrie festgelegt,die bei der Gravitation dynamisch ist.

Bisher hatte man das Pfadintegral zumeist im euklidischen Bereich betrachtet,wo nur über vierdimensionale Räume integriert wird und nicht über Raumzeiten. Dieser Zugang wurde vor allem durch Stephen Hawking populär.Allerdings ergeben sich dort Probleme unter anderem im Zusammenhang mit der Dimension. Man betrachtet den Erwartungswert für die effektive HausdorffDimension H. Dieser wird durch die Beziehung V(r) ~ <r>H definiert, wobei V(r) das Volumen einer Kugel mit Radius
r darstellt. Für einen dreidimensionalen Raum sollte sich also gerade H= 3 ergeben.

Die Hausdorff-Dimension ist aus der Theorie der Fraktale bekannt, allerdings als klassische Größe und nicht als Erwartungswert. Da in der Quantengravitation kein Hintergrund existiert,ist H a priori ungleich der Dimension d der Bausteine, über die im Pfadintegral summiert wird. Merkwürdigerweise ergibt sich für das euklidische Pfadintegral der Wert H= 2 für d> 2.

Wegen dieses und anderer Probleme schlagen die oben erwähnten Autoren den alternativen Weg der „Lorentzschen dynamischen Triangulationen“ ein. Hier summiert man tatsächlich über Raumzeiten statt Räumen,was physikalisch vernünftiger erscheint [2]. Die Diskretisierung erfolgt durch Wahl von Tetraedern zur festen (diskretisierten) Zeit,die mit dem nächsten sowie vorangehenden Zeitschritt durch vierdimensionale Simplizes verknüpft sind. Simplizes repräsentieren also die (diskretisierte) Raumzeit. Abbildung 1 zeigt eine typische Konfiguration,die in dem gezeigten Beispiel aus 91100 Simplizes besteht. Die Summe über alle Konfigurationen im Pfadintegral erfolgt durch Monte-Carlo-Simulation.

Die Autoren betrachten den Mittelwert des räumlichen Abstandes zwischen zwei Punkten im räumlichen Volumen und finden für die oben definierte Hausdorff-Dimension den Wert H= 3,10 ±0,15. Dies ist
eine gute Evidenz für die Dreidimensionalität des Raumes (und somit für die Vierdimensionalität der Raumzeit). Hieraus folgt freilich noch nicht, dass es auf kleinsten Skalen tatsächlich einen glatten dreidimensionalen Raum gibt. Doch immerhin liefert dieses Ergebnis einen Hinweis auf die Existenz einer Kontinuumstheorie. Interessant ist noch,dass diese Methode nur bei einer positiven Kosmologischen Konstante funktioniert -- in Einklang mit Beobachtungen. Der numerische Wert wird allerdings nicht festgelegt. Die sich so ergebende dynamisch erzeugte Quantengeometrie kann dann als Hintergrund für die Quantenfluktuationen anderer Freiheitsgrade angesetzt werden.

[1] J. Ambjørn, J. Jurkiewicz, R. Loll, Phys. Rev. Lett. 22000044, 93, 131301.
[2] R. Loll, in: Quantum Gravity (D. Giulini, C. Kiefer, C. Lämmerzahl Hrsg.), SpringerVerlag, Heidelberg 2003. Claus Kiefer, Köln

ABB. 1 SIMULATION: Typische Konfiguration („Raumzeit“), wie sie in einer MonteCarlo-Simulation erscheint. Nach oben sind die Zeitschritte (hier insgesamt 40) aufgetragen, die beiden anderen Achsen sind Raumdimensionen (aus [1]).

marcus

Jul8-05, 12:54 AM

the German text by Kiefer can be found here
http://www3.interscience.wiley.com/cgi-bin/abstract/109860245/ABSTRACT
this is the HTML abstract, which has a link to the PDF file.

the Kiefer article can also be found by scanning the table of contents of the January issue of Physik Unserer Zeit
http://www3.interscience.wiley.com/cgi-bin/jissue/109860236

and also it is at Loll website
http://www.phys.uu.nl/~loll/Web/press/press.html

Because we have a shortage of general audience description of CDT in English, I translated the short Kiefer article:

--------transl. from Claus Kiefer january P.U.Z.-----

QUANTUM GRAVITY: The four-dimensional world

Classical spacetime has four macroscopic dimension. In a future theory of quantum gravity one must take into account that even dimensionality will be a dynamical variable, for which only an expectation value can be provided. For reasons of consistency the number four must arise independently in the the semiclassical limit. Jan Ambjørn (Kopenhagen), Jerzy Jurkiewicz (Krakau) and Renate Loll (Utrecht) were able to show that in the path-integral framework it actually works out that way.[1]
--------------------------------

One of the most fundamental open problems in modern physics is the consistent unification of the quantum and gravitation theory. The chief difficulty consists in the fact that General Relativity knows no fixed prior-given background spacetime, but rather a dynamic geometry.
One quantizes other interactions, for example electrodynamics, ON a given spacetime, but with General Relativity one must quantize the very spacetime itself.

The most ambitious attempt to arrive at quantum gravity has been on the part of string theory, whose point of departure is the assumption that this goal can only be attained in the context of a unification of all the interactions.

Alternative approaches attempt to directly quantize Einstein's theory. Among these approaches are quantum geometrodynamics and loop dynamics (LQG). Ambjørn and colleagues chose an approach via the Feynmanian path integral

In quantum mechanics the path integral is summed over all possible paths a particle can take from one point to another. Most of the paths are continuous but nowhere differentiable. The result is a transition amplitude, which satisfies the Schrödinger-equation. In quantum gravity, the job is to sum over all possible four-dimensional geometries ("spacetimes") which fit between two three-dimensional geometries ("spaces")

Formally, it's easy to write down a so-called saddle-point approximation which in the semiclassical limiting case is dominated by a spacetime satisfying the Einstein field equations. But to go beyond this approximation to a clean calculation, one must define the sum over all geometries. This regularization occurs by discretizing and a subsequent continuum limit. The lattice theories of strong and electroweak interactions serve as models. There, however, the geometry is fixed ahead of time, while in the case of gravity it is dynamic.

Up till now the path integral has mostly been used in the Euclidean context, where one integrates only over fourdimensional space, rather than spacetime, geometries. This approach was made popular above all by Stephen Hawking. However problems arise there, among other things with the dimension.

Consider the expectation value for the effective Hausdorff dimension H. This is defined by the relation V(r) ~ <r>H where V(r) is the volume of a ball with radius r. For a three-dimensional space this should come right out H = 3.

The Hausdorff dimension is known from the theory of fractals, however as a classical quantity and not a quantum expectation value. Since in quantum gravity there is no background, H is a priori NOT equal to the dimension d of the building blocks used in the path integral summation. Notably, in the Euclidean path integral the value of H turns out to be 2, even for d >2.

Because of these and other problems, the above-mentioned authors have introduced the alternative way of "Lorentzian dynamical triangulations". Here one actually sums over spacetimes rather than spaces, which seems physically more reasonable [2]. The discretization is accomplished by choosing, at some fixed (discrete) time, spatial tetrahedra which are then joined by four dimensional simplices to like tetrahedra at the next timestep. Thus the simplices represent the (discretized) spacetime. Figure 1 shows a typical configuration which in the example shown here consists of 91,100 simplices. The sum over all configurations in the path integral is performed by Monte-Carlo simulation.

The authors consider the mean value of the spatial separation between two points in a spatial volume and find, for the Hausdorff dimension defined earlier, the value H = 3.10 ±0,15. this is good evidence of the three-dimensionality of space (and thus the four-dimensionality of spacetime). From this it certainly does not yet follow that at the smallest scale there is actually a smooth three-dimensional space.

But nevertheless this result offers a pointer towards the existence of a continuum theory. Moreover it is interesting that this method only works with a postive cosmological constant--in agreement with observations.
The numerical value has however not been determined. The resulting dynamically produced quantum geometry can then serve as a background for the quantum fluctuations of other degrees of freedom.

[1] J. Ambjørn, J. Jurkiewicz, R. Loll, Phys. Rev. Lett. 22000044, 93, 131301.
[2] R. Loll, in: Quantum Gravity (D. Giulini, C. Kiefer, C. Lämmerzahl Hrsg.), SpringerVerlag, Heidelberg 2003. Claus Kiefer, Köln

FIG. 1 SIMULATION: Typical configuration ("spacetime") as it appears in a Monte-Carlo simulation. The time steps (here 40 in all) are upwards, the other two axes are spatial dimensions.[1]

----end quote from the Claus Kiefer article---

selfAdjoint

Jul8-05, 08:15 AM

marcus

Jul8-05, 10:01 AM

Marcus you are to be congratulated and you deserve our thanks for translating these articles. If there are no copyright issues in the way it would be nice to collect them into a permanent website for people wishing to getr some non technical info on CDT. (I like it that this article defines the Hausdorf dimension. That's something that a slightly technical public might know and respond to, from all the fractal stuff around).

constructive idea,
for starters I will check with Loll
her "press" page at her website is something of a central spot
for popular writing
she already has some translations (dutch to german, german to dutch...)
that she links to, as well as the orig.

if she thinks my translation is accurate and colloquial enough to link to, or wants to correct it, that's fine. if not then a better translation may show up.
personally I think my translation is fine, of course, but I am not a professional tech translator and it is conceivable that there's a better one out there.

I suspect copyright is not an issue because of educational "fair use".

you are right BTW that Claus Kiefer's is more "educational" than usual because he actually defines things he talks about instead of doing what journalists usually do which is not define but give metaphors and analogies, which often fry the readers brain but give everybody literary satisfactions.

marcus

Jul19-05, 11:37 PM

time to update, today (20 July in Paris) Loll's grad student Stefan Zohren is giving a paper at the Einstein 2005 conference.
here is the schedule of plenary sessions of the conference, to give an idea of the scope:
http://einstein2005.obspm.fr/programmer.php

Stefan is presenting a Loll-Westra-Zohren paper about "sum over topologies"---including topology change in the nonP quantum gravity path integral---in one of the conference's parallel sessions, titled "The Nature of Space-Time"

If things go as planned, the schedule for the Loops 05 conference should be posted within the next week or so, at this site:
http://loops05.aei.mpg.de/
believe it when i see it, since delays can happen in scheduling a large conference. the list of invited speakers is already posted here:
http://loops05.aei.mpg.de/index_files/Programme.html

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

There is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi. I would like to see another from Loll/Dittrich on Black Holes but I don't know of one in the works, and it would be exciting to get a new paper from Loll/Westra about sum-over-topologies.

Here at PF we had a thread to post predictions about whether the QG path integral including sum over topologies would be extendable from the 2D case up to 3D and 4D. the thread is here:
http://www.physicsforums.com/showthread.php?t=81626

The thread shows who predicted what. Only 36 percent of us thought that they would be able to reproduce the result in full 4D spacetime---4 out of 11 respondents. (I was one of the optimists, still not entirely comfortable with that since can't imagine how the result might be extended from 2D to higher dimension.)

This thread, Quantum Grafitti, is mainly about the people doing Loll-type quantum gravity, with random news and gossip. To get an idea of the CDT (Causal Dynamical Triangulations) scene check out Loll's website at the Uni Utrecht in Holland. Here is a list of Loll graduate students/postdocs:

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

OK I guess that is the update for now.

marcus

Jul23-05, 01:46 PM

http://www.phys.uu.nl/~loll/Web/title/title.html

I didnt hear back from Loll about this translation of the Kiefer article, guess she is busy. thinking about other places to offer (rough nonprofessional) translations. Should post (as selfAdj suggests) because there seems to be more in the european media than there is in US. where balanced QG coverage is scarce.

Loll press page has this interview with Hermann Nicolai from Die Zeit, I guess that is like the New York Times. so this is to compare with the articles by Dennis Overbye. (which tend to be "good" by Lubos Motl standards, that is what i would call onesided)

http://zeus.zeit.de/text/2005/16/Nicolai-Interview

Nicolai is a director at Albert Einstein Institute and in this interview he is critical of the German funding agencies for not giving enough support, however it is the other things that caught my attention---a research director can be expected to put in a plug.

<<Alles nur Fassade

...
DIE ZEIT: Hundert Jahre nach der Entwicklung der Relativitätstheorie haben Sie Ihre Kollegen zu einer Bestandsaufnahme ans Albert-Einstein-Institut nach Golm gerufen. Wie sieht die Bilanz aus?

Hermann Nicolai: Wir leben in spannenden Zeiten! Um es mit einem Wort des Astrophysikers Michael Turner zu sagen: Wir wissen viel mehr, aber verstehen weniger. Dank neuer Teleskope und moderner Beobachtungsmethoden ist die Kosmologie – anders als zu Einsteins Zeiten – heute eine empirische Wissenschaft. Wir haben eine Fülle von Daten über die Beschaffenheit des Universums. Doch eine umfassende Theorie, die all diese Beobachtungen erklären könnte, ist derzeit nicht in Sicht.

ZEIT: Hat Einstein das nicht mit der Relativitätstheorie versucht?

Nicolai: Diese kann zwar alles erklären, was mit der Schwerkraft zusammenhängt – die Struktur des Raumes, die Bewegung von Galaxien, Schwarze Löcher… Aber ebenso wie in der Elementarteilchenphysik fehlt uns eine fundamentale Erklärung, die sagt, woher alles kommt und warum das so ist. Warum dehnt sich das Weltall genau auf diese Weise aus, die wir beobachten? Weshalb hat es gerade diese Massendichte, warum gibt es Galaxien? Letztlich wissen wir das nicht. Das liegt auch daran, dass die Theorie fürs große Ganze – Einsteins Relativitätstheorie – und fürs ganz Kleine – die Quantenmechanik – unverknüpft nebeneinander stehen. Eine gemeinsame »vereinheitlichte Theorie« zu finden bleibt die große Herausforderung der Physik für das 21. Jahrhundert.

ZEIT: Als ein Kandidat gilt ja die Stringtheorie. Ihr zufolge gibt es keine punktförmigen Teilchen mehr, sondern nur winzige schwingende »Saiten«. Aus deren Schwingungen sollen sich sämtliche Elementarteilchen und ihre Kräfte erklären lassen.

Nicolai: Als die Stringtheorie in den achtziger Jahren aufkam, brach eine Art kollektiver Begeisterung aus, und die Physiker dachten: In den nächsten vier Wochen haben wir alles erklärt. Mittlerweile ist eine gewaltige Ernüchterung eingetreten. Seither haben über tausend kluge Köpfe weltweit an der Stringtheorie gearbeitet. Es hat wohl noch nie in der theoretischen Physik eine solche kollektive Anstrengung gegeben – doch wie die Stringtheorie schlussendlich aussehen soll, wissen wir noch immer nicht.

ZEIT: Gibt es Alternativen?

Nicolai: Eine Besonderheit des Albert-Einstein-Instituts hier in Golm ist, dass wir zwei Ansätze verfolgen: zum einen die Stringtheorie, die Einsteins Relativitätstheorie radikal modifiziert. Zum anderen die Quantengravitation, die Einsteins Theorie, so, wie sie ist, neu formulieren will – unter Berücksichtigung der Tatsache, dass die Größen der Natur nicht kontinuierlich erscheinen, sondern sprunghaft oder »gequantelt«. Allerdings wirft das gewaltige mathematische Probleme auf, die noch nicht gelöst sind. Mir kommt es so vor, als ob bei allen derzeit verfolgten Theorien eine entscheidende Einsicht fehlt, die wie ein Schlüssel ins Schloss passt.

...>>

marcus

Jul23-05, 02:39 PM

DIE ZEIT: A hundred years after the development of relativity theory, you have invited your colleagues to the Albert Einstein Institute at Golm for a status report. How does the balance sheet look?

NICOLAI: We live in exciting times! As the astrophysicist Michael Turner puts it: we know a lot more, but understand less. thanks to the new telescopes and modern observation methods, cosmology is---in contrast to Einstein's time---today an empirical science. We have an abundance of data about the origin of the universe. But a comprehensive theory, that could explain all these observations, is so far not in sight.

Zeit: Didn't Einstein investigate that with his Relativity Theory?

Nicolai: Indeed this can account for everything related to gravity---the structure of space, the motion of galaxies, black holes...But we are lacking, just as we are in elementary particle theory, a fundamental explanation that says where does it all come from and why this is so. Why is the World arranged exactly in the fashion which we observe it to be? Why does it have exactly this density? Why are there galaxies? In the end, we just don't know. That is because the theory of the big total (Einstein's relativity) and that of the totally little (quantum mechanics) are not connected.

To find a common "unified theory" remains the great challenge of physics for the 21st century.

Zeit: String theory certainly counts as one candidate. According to it, there are no point particles, but rather tiny vibrating strings. From their vibrations the elementary particles and their forces are supposed to be explainable.

Nicolai: When string theory arrived in the eighties, a kind of mass enthusiasm broke out, and physicists thought: "in the next four weeks we will have explained everthing!" Then came the shock of disillusionment. Since then over a thousand clever heads worldwide have worked on string theory. There was never before such a huge collective effort in theoretical physics---but we still don't know what string theory will finally look like.

Zeit: Are there alternatives?

Nicolai: One of the special things about the Albert Einstein Institute here in Golm is that we pursue two different approaches:
One is string theory, in which Einstein's relativity is radically modified.
The other is Quantum Gravity, which attempts to reformulate Einstein's relativity exactly as it is, but taking into account the fact that quantitites in nature appear in steps or "quantized", instead of being continuous.

Either way tough mathematical problems turn up, which are not yet solved. My impression is that in all the theories that have so-far been tried there is a decisive insight missing, a missing key that will fit the lock...

marcus

Aug1-05, 02:45 PM

a wide-audience account of CDT written in English (finally) has been commissioned by the UK based magazine Contemporary Physics
and should be appearing shortly.

the TOC of Contemporary Physics is online, but I don't think the text is available---will take a trip to the library for one or more of us.

for what its worth, here is the link to the online TOC

http://www.ingentaconnect.com/content/tandf/tcph

They havent posted the contents of the May-June 2005 issue (vol 46 no 3)
and that is the one I'm expecting to see this article in. So the link is to check periodically to see if it's out yet.

marcus

Aug3-05, 04:03 PM

this is a pretty good short essay
giving intuitive explanation of CDT
and how it arose in the context of other approaches to QG
to circumvent difficulties the others encountered

http://www.phys.uu.nl/~loll/Web/research/research.html

it is in English and also the best introduction for nonspecialist audience
I didnt realize this earlier.

marcus

Aug3-05, 04:36 PM

an effective introduction to Causal Sets is this 2004 set of lecture slides by Dowker

www.dpf2003.org/xx/qg/dowker.pdf

the title of the talk is
"Causal Sets as the Deep Structure of Spacetime"

the slides are written-out enough to understand on their own, without the talk. there is an essential reference to a paper by Sorkin et al
Ahmed, Dodelson, Green, Sorkin
http://www.arxiv.org/abs/astro-ph/0209274
and indirectly to a 1993 Sorkin talk published in 1997
http://www.arxiv.org/abs/gr-qc/9706002

from Dowker slides one gets the impression that Causets is not a quantum theory yet, it has some probabilities you can calculate but no hilbertspace and no complex amplitudes. seems conceptually nice (if you like discrete finite sets and relations defined on them) but so far not so good for calculating or for imitating General Relativity spacetime dynamics.
however it has a strong appeal for philosophers

Dowker intimates that Sorkin got an amazingly close estimate of the size of the cosmological constant (which if true might be an accident or might mean something) back in 1992 or 1993 just using Causal Sets reasoning.
Causets is still somewhat nebulous as a theory IMO, so this thing about predicting the size of the cosmological constant, even if just an order of magnitude guess, is iffy. Also it is based on a strange picture where Lambda oscillates and we just happen to be in a era when it is E-120.

but even discounting the claim of predicting Lambda, causets is a lively contender for the Nonperturbative Limelight.

marcus

Aug3-05, 05:10 PM

In case you are interested in that 1997 Sorkin paper mentioned in the previous post

http://www.arxiv.org/abs/gr-qc/9706002
Forks in the Road, on the Way to Quantum Gravity
Rafael D. Sorkin (ICN-UNAM and Syracuse University)
29 pages
Int.J.Theor.Phys. 36 (1997) 2759-2781

'In seeking to arrive at a theory of "quantum gravity'', one faces several choices among alternative approaches. I list some of these "forks in the road'' and offer reasons for taking one alternative over the other. In particular, I advocate the following: the sum-over-histories framework for quantum dynamics over the "observable and state-vector'' framework; relative probabilities over absolute ones; spacetime over space as the gravitational "substance'' (4 over 3+1); a Lorentzian metric over a Riemannian ("Euclidean'') one; a dynamical topology over an absolute one; degenerate metrics over closed timelike curves to mediate topology-change; "unimodular gravity'' over the unrestricted functional integral; and taking a discrete underlying structure (the causal set) rather than the differentiable manifold as the basis of the theory.

In connection with these choices, I also mention some results from unimodular quantum cosmology, sketch an account of the origin of black hole entropy, summarize an argument that the quantum mechanical measurement scheme breaks down for quantum field theory, and offer a reason why the cosmological constant of the present epoch might have a magnitude of around 10^{-120} in natural units.'

Sorkin is one of the invited plenary speakers at the Loop 05 conference at Potsdam in October

it could be an accident but 10^{-120} is about right.

Spin_Network

Aug3-05, 05:38 PM

an effective introduction to Causal Sets is this 2004 set of lecture slides by Dowker

www.dpf2003.org/xx/qg/dowker.pdf

the title of the talk is
"Causal Sets as the Deep Structure of Spacetime"

the slides are written-out enough to understand on their own, without the talk. there is an essential reference to a paper by Sorkin et al
Ahmed, Dodelson, Green, Sorkin
http://www.arxiv.org/abs/astro-ph/0209274
and indirectly to a 1993 Sorkin talk published in 1997
http://www.arxiv.org/abs/gr-qc/9706002

from Dowker slides one gets the impression that Causets is not a quantum theory yet, it has some probabilities you can calculate but no hilbertspace and no complex amplituded. seems conceptually nice (if you like discrete finite sets and relations defined on them) but so far not so good for calculating or for imitating General Relativity spacetime dynamics.
however it has a strong appeal for philosophers

Dowker intimates that Sorkin got an amazingly close estimate of the size of the cosmological constant (which if true might be an accident or might mean something) back in 1992 or 1993 just using Causal Sets reasoning.
But causets is not really a numerical theory yet, so this thing about predicting the size of the cosmological constant, even if just an order of magnitude guess, is iffy. Also it is based on a strange picture where Lambda oscillates and we just happen to be in a era when it is E-120.

but even discounting the claim of predicting Lambda, causets is a lively contender for the Nonperturbative Limelight.

What I like about the images, you can see Fay embedded into the background of the photographic paper, taking photo's! :!!) that..is she taking photo's of slide's, or is she really taking photo's of herself? :rolleyes:

I think its a deliberate action!..a precise action..a double take!

marcus

Aug3-05, 07:40 PM

Definitely deliberate. hip lady. your term "double take" is nice. I assume you saw that snapshot of Fay posing at the blackboard---had a link to it around post #54 back a ways in this thread.

http://www.physicsforums.com/showthread.php?p=665506#post665506

Let's take a closer look at the program at this month's Paris conference,
http://einstein2005.obspm.fr/indexr.php
http://einstein2005.obspm.fr/programmer.php
The abstracts of some Plenary Session talks are posted. Here is a sample:

Monday July 18
...
11h45 - 12h25: Abhay Ashtekar « Gravity, Geometry and the Quantum »
...
14h00 - 14h40: Brian Greene « The State of String Theory»
...
14h45 - 15h30: Alain Connes « Noncommutative geometry and physics»
...
...
15h45 - 16h25: Fay Dowker « Causal sets and discrete spacetime. »

Tuesday July 19
....
10h15 - 10h55: Carlo Rovelli «Loop Quantum Gravity »
...

Friday 22 July
...
15h45 - 16h45: Gerard t'Hooft « Conclusion Talk »
----------------------------------------------

BTW here is a picture of Fay Dowker. Interesting that both her mother and father were physicists, born c. 1966 undergrad major math, married to physicist Jerome Gauntlett---physics seems to run in the family---has two children.
http://www.stp.dias.ie/events/2004/causal_sets_photos/WorkshopOnCausalSets-FayDowker-1.jpg

Fay Dowker is one of the featured ... speakers not only at Einstein2005 this month in Paris but also at Loops05 this October in Potsdam.

marcus

Aug8-05, 04:07 PM

Last update was 20 july, time to update again

20 July Paris conference Zohren presented a Loll-Westra-Zohren paper about "sum over topologies"---including topology change in the nonP quantum gravity path integral

if things go as planned, the schedule for the Loops 05 conference should be posted within the next week or so, at this site:
http://loops05.aei.mpg.de/
possibly at this page
http://loops05.aei.mpg.de/index_files/Programme.html
there has already been some understandable delay.

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

There is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi. I would like to see another from Loll/Dittrich on Black Holes but I don't know of one in the works, and it would be exciting to get a new paper from Loll/Westra about sum-over-topologies.

Here at PF we had a thread to post predictions about whether the QG path integral including sum over topologies would be extendable from the 2D case up to 3D and 4D. the thread is here:
http://www.physicsforums.com/showthread.php?t=81626

This thread, Quantum Grafitti, is mainly about the people doing Loll-type quantum gravity, with random news and gossip. To get an idea of the CDT (Causal Dynamical Triangulations) scene check out Loll's website at the Uni Utrecht in Holland. Here is a list of Loll graduate students/postdocs:

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

A commissioned general audience article on CDT, in English, is expected to appear in the forthcoming issue of Contemporary Physics
and should be listed here when it comes out
http://www.ingentaconnect.com/content/tandf/tcph
(unless the publisher is forgetting to update the website)

marcus

Aug8-05, 05:45 PM

we still have a scarcity of popular English-language media coverage of triangulations gravity, compared with what's available in Dutch and German. So I translate general audience science journalism stuff sometimes.

Here is this popular Austrian magazine article from November 2004
http://science.orf.at/science/news/130119

As for the brow-level (hi-brow, middle, low-brow) get a load of this
http://orf.at/
it definitely looks Cross-section Austrian to me---sports, politics, celebrities, photomodels, online lottery, advertisments

And yet in their science section
http://science.orf.at/science/
which looks mass-audience enough
they had this thing about CDT last november.

what did Americans know about CDT last november?
Well maybe we will catch up. Something in newsweek? or the NYT? I didnt see it yet.

Anyway, I better translate at least a sample from this Austrian magazine article---anybody who wants to help, please do. Just post a chunk and I will merge it in with mine.

marcus

Aug8-05, 06:38 PM

Here is a short exerpt from the article by Robert Czepel, 11 November 2004, for ORF.at "World of Science" section, as a sample of CDT coverage in Austrian popular press. I will just translate the beginning paragraphs:
http://science.orf.at/science/news/130119

HOW TO BUILD A FOUR-DIMENSIONAL UNIVERSE

With the help of so-called Quantum Gravity, physics researchers are trying to bring the large and small alike under one roof. ["under one hat", as the hat-loving Austrians like to say]. Until now this effort has been flawed, in that the theory could not explain why the universe's spacetime exhibits exactly four dimensions. Three physicists have now, with the help of Quantum Gravity, been able for the first time to establish why that is so.

A team led by Renate Loll at the University of Utrecht has succeeded in this by integrating a simple principle of cause and effect into the equations of the model. In the medium-scale world of everyday life, it is hardly a surprise that events have causes. But applied to the model of Quantum Gravity, this principle frankly works wonders.

CAUSALITY - A DISCOVERY?

Is causality an inherent property of our universe, or only an illusion which emerges from how we interpret the world?

The Scotish philospher David Hume proposed the latter view. In his opinion, we can never do more than merely observe that two events A and B regularly follow one another, and cannot say why the cause A leads to the result B.

According to Hume's sceptical interpretation the notion of causality is an invention of our minds, which has no counterpart expressed in the real world.

[Czepel has a link to an online encylopedia of philosophy here]

LARGE AND SMALL IN A SINGLE THEORY

A current study by the three physicists comes close to suggesting that Hume might just have been a little too skeptical. Renate Loll at the University of Utrecht, together with two collaborators, has designed a model which describes space and time as an assemblage of extremely small quantum particles.

[this is not quite true but Czepel is a journalist]

This is already of considerable interest because the principles of large scale physics (General Relativity Theory) on the one hand, and small scale physics (Quantum Mechanics) on the other, have until now scarcely been brought under one roof.

The two theories, although both well verified by experiment, do not immediately let themselves be "married"---that is, combined in a single coherent theoretical concept...

...
...
[there is lots more in case anyone else is curious, or wants to translate it for us.)

marcus

Aug25-05, 12:09 PM

Last update was 8 august, time to update again

At the July Paris ("Einstein Century") conference Stefan Zohren presented a Loll-Westra-Zohren paper about "sum over topologies"---how to incorporate topology change into the nonperturbative quantum gravity path integral. Here's a snapshot of Stefan

http://www1.phys.uu.nl/wwwitf/fotopagina's/Studenten/Stefan%20Zohren.htm

there has been some delay in posting the schedule for October's Loops 05 conference. It should eventually appear at this site:
http://loops05.aei.mpg.de/
possibly at this page
http://loops05.aei.mpg.de/index_files/Programme.html

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

There is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi. I would like to see another from Loll/Dittrich on Black Holes but I don't know of one in the works, and it would be exciting to get a new paper from Loll/Westra about sum-over-topologies.

This thread, Quantum Grafitti, is mainly about the people doing Loll-type quantum gravity, with random news and gossip. To get an idea of the CDT (Causal Dynamical Triangulations) scene check out Loll's website at the Uni Utrecht in Holland. Here is a list of Loll graduate students/postdocs:

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

http://www1.phys.uu.nl/wwwitf/fotopagina's/Studenten/Stefan%20Zohren.htm

here is the whole staff of the Utrecht ITP (inst. theor. phys.) where Loll and co-workers and students are based.
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

A commissioned general audience article on CDT, in English, is expected to appear in a forthcoming issue of Contemporary Physics
and should eventually be listed here
http://www.ingentaconnect.com/content/tandf/tcph

We have a PF a thread polling people's predictions about whether the QG path integral including sum over topologies will prove extendable from the 2D case up to 3D and 4D. the thread is here:
http://www.physicsforums.com/showthread.php?t=81626

marcus

Aug28-05, 08:21 PM

this thread is to keep track of the news/current events/essential links about Loll triangle gravity. (CDT path integral)
see preceding post for basix

something interesting I just became aware of:

people who have been watching CDT (since that April 2004 paper) know that one of the surprises is that microscopically the CDT spacetime continuum has this "fractal-like" highly non-classical stucture with dimensionality going down steadily from macro 4D down to 3.5 down to 2.9 etc etc down to (at very small scale) sort of 1.9 to 2.1----roughly 2D.

this is measured by creating a spacetime by Monty Sims in the computer and then RUNNING A RANDOM WALK DIFFUSION PROCESS in that spacetime
the dimension you measure that way is called the "spectral" dimension.
to distinguish it from the "hausdorff" dimension that you measure by comparing radius and volume.

this business is summarized in the paper I've had in my sig for much of this year:
http://arxiv.org/hep-th/0505154
and also in this other short paper http://arxiv.org/hep-th/0505113

So probably others, I for one at least, were thinking it was pretty weird that Loll gravity has a fractally wrinkly feathery kinky smallscale spacetime structure.

the thing about it is that with Loll gravity you DON'T PRESUPPOSE HOW SPACETIME IS GOING TO LOOK, you set up a dynamic action principle of how little spacetime chunks arrange themselves together and stick together and LET IT RUN and SEE what kind of continuum comes out, whatever comes out that's it, and if it doesnt look and act like our space macroscopically, then you did something wrong.

so you can't be sure you are going to get a nice smooth spacetime or even something that is four dimensional! for some 10 years they were trying to do this and the dimension kept coming out really wrong. But now by the grace of nature and the coolness of Renate Loll you do get something that is largescale 4D. however as we learned earlier this year, it is kinky at microscopic scale

OK NOW SOMEONE USING AN ENTIRELY DIFFERENT APPROACH at the University of Mainz, a guy named Martin Reuter HAS ALSO FOUND A KINKY FRACTALLY MICROSCOPIC STRUCTURE

he is coming from an entirely different direction and he says he has "MADE CONTACT" with Loll results.

so I am paying attention to this and emphasizing it. I think it could be significant.
Here is Martin Reuter paper that came out today. I already put it on the Rovelli thread

http://www.arxiv.org/abs/hep-th/0508202
Fractal Spacetime Structure in Asymptotically Safe Gravity
O. Lauscher, M. Reuter
20 pages

"Four-dimensional Quantum Einstein Gravity (QEG) is likely to be an asymptotically safe theory which is applicable at arbitrarily small distance scales. On sub-Planckian distances it predicts that spacetime is a fractal with an effective dimensionality of 2. The original argument leading to this result was based upon the anomalous dimension of Newton's constant. In the present paper we demonstrate that also the spectral dimension equals 2 microscopically, while it is equal to 4 on macroscopic scales. This result is an exact consequence of asymptotic safety and does not rely on any truncation. Contact is made with recent Monte Carlo simulations."

Reuter approach is so different that the fact that the two approaches CONVERGE and actually AGREE on something makes me wonder if maybe in some sense REAL spacetime continuum could be micro-fractally, and only have the illusion at large scale, that we see, of having 4 nice dimension

in other words wondering if maybe it is not just the MODEL but the actual real continuum that is like this---but what that could mean is a relational thing. spacetime is the web of spatial relations and causalities among things and for it to be microfractally must have to do with how things can relate to each other at very close quarters---how they can be on top of each other and beside and between and inside and around, but at very small scale. these possibilities of relationship ARE space. and if Loll and Reuter picture is true (which would be pretty surprising because physics theories turn out so often to be false) then these possibilities of relation would have to be DIFFERENT at very small scale than over larger reaches.
well it is a lot of stuff to be puzzled with.

arivero

Aug29-05, 04:32 AM

The original argument leading to this result was based upon the anomalous dimension of Newton's constant.

Yep, this makes such kind of results intuitive. G is an area, as Fermi constant. All the others are adimensional.

Sam Owen

Aug29-05, 07:24 AM

What is meant by spacetime is a fractal, fractal like or has a kinky fractally structure ?

I know what a fractal is and what they look like, so is it an appearance of fracticality or actually fractal and does the reductablity of the pattern ever stop at a cut off volume ?

also how does one get half a spatial dimension or half a temporal dimension surely a half is still a whole when talking of dimensions ?

marcus

Aug29-05, 08:23 AM

In her papers (like e.g. http://arxiv.org/hep-th/0505154 and the earlier http://arxiv.org/hep-th/0505113 ) Loll says "fractal-like". and "evidence of a fractal structure" --- she never says that spacetime actually turns out to BE a fractal. I think she is speaking more carefully than Reuter---who says his picture predicts that at small scales it IS a fractal. I think he is using word in a more general sense or just being careless. but I do not know reuter work at all well, so cannot be sure. Let us assume that he also means "fractal-like"

I am starting an auxilliary thread to talk about what fractal-like
versus just plain "fractal"
could mean. That way, discussing what is a fractal or what it means to say something is "like a fractal" will not gum up this CDT news-and-gossip thread.

Here is the auxilliary thread
http://www.physicsforums.com/showthread.php?t=86751

I hope it helps get some answers about what is means to not actually be a fractal but to be "like a fractal".

marcus

Sep5-05, 09:24 PM

Hanno Sahlmann (the Sahlmann algebra is basic in LQG) is now a postdoc at Utrecht ITP
http://www1.phys.uu.nl/wwwitf/fotopagina's/Medewerkers/Hanno.htm
(earlier he was at AEI-Potsdam and at Penn State, if I remember correctly.
Here is Hanno's Penn State webpage:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml )

Sergei Alexandrov is at Utrecht as well. He has done both string and LQG research. Some of his LQG research was with Etera Livine (now at Perimeter). Sergei Alexandrov used to be at Paris. after PhD he came to Utrecht.
http://www1.phys.uu.nl/wwwitf/fotopagina's/Medewerkers/Serguei.htm

Utrecht has a capability in at least 3 kinds of quantum gravity research: string, LQG and CDT (Renate Loll's specialty). this is interesting because not very many places have this kind of diversity.

Stephon Alexander is now faculty in Abhay Ashtekar's department at Penn State (he was a postdoc at SLAC-Stanford)

marcus

Sep5-05, 09:49 PM

because of Fall term changes, here's a CDT update:

schedule for October's Loops 05 conference should eventually appear here:
http://loops05.aei.mpg.de/

These are CDT papers that have come out in the past 12 months.
http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

I believe there is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi.

http://www.phys.uu.nl/~loll/Web/students/students.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Johan.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

http://www.phys.uu.nl/~0404985/ (Stefan Zohren, alt. at Aachen)

here is the whole staff of the Utrecht ITP (inst. theor. phys.) where Loll and co-workers and many of her students are based.
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

An excellent survey article for wide audience ("The Universe from Scratch") is here
http://arxiv.org/hep-th/0509010

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

We have a PF a thread polling people's predictions about whether the QG path integral including sum over topologies will prove extendable from the 2D case up to 3D and 4D. the thread is here:
http://www.physicsforums.com/showthread.php?t=81626

It is interesting that Hanno Sahlmann is now listed as postdoc at Utrecht. Here is his earlier web page, describing his research interests, with sketches of ideas, from when he was at Penn State:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml.

marcus

Sep7-05, 10:36 PM

...It is interesting that Hanno Sahlmann is now listed as postdoc at Utrecht. Here is his earlier web page, describing his research interests, with sketches of ideas, from when he was at Penn State:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml.

Hanno Sahlmann postdoc is working for Loll (!)

http://www.phys.uu.nl/~loll/Web/group/group.html

marcus

Sep7-05, 10:53 PM

it looks like one of the best available LQG postdocs has just crossed the border over into CDT. I do not think this is bad luck for LQG, on the contrary it could be good luck.

hanno casts a wide net of ideas. the LQG uniqueness theorem associated with Lewandowski Okolow Sahlmann Thiemann actually started out with two solo papers by Hanno.

then it was picked up by Lewandowski Okolow (who called the algebra the "Sahlmann algebra") and carried further by them and by Sahlmann-Thiemann collaboration. So he is able to work at an efficient level of abstraction and connect the dots. It seems exciting to me that hanno should decide to work postdoc with Loll. things could come of it that one didn't expect. I dont want to say that he might see a connection between some variant of LQG-spinfoam and CDT because maybe that is the wrong idea to be thinking. but something valuable is likely to come from his crossing the border. I think it is a lucky move, him going to work with Loll!

OTHER NEWS BIANCA DITTRICH HAS JUST MOVED FROM POTSDAM TO PERIMETER

if she decides to do some CDT while she's there it will make a stronger CDT presence at Perimeter.

marcus

Sep22-05, 01:15 PM

an interesting group of people is assembled at Utrecht (at the ITP and the Spinoza Institute there)

Sahlmann has been giving seminars about LQG
and Saueressig about (Reuter asympt. safe) QEG

Saueressig was at Mainz working with Reuter in 2001, for instance
http://www.arxiv.org/abs/hep-th/0110054
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
M. Reuter, F. Saueressig
58 pages, 24 figures
Phys.Rev. D65 (2002)

mostly by cleverness, I suppose, the Utrecht people have assembled a Quantum Gravity group that is strong in LQG/CDT/QEG
It would be difficult to do it just by spending money.

In 2002 Saueressig went to Jena, in 2003 he was still collaborating with Reuter:
http://www.arxiv.org/abs/hep-th/0311056
Nonlocal Quantum Gravity and the Size of the Universe
M. Reuter, F. Saueressig

In spring 2004 he was still at Jena, and doing some string papers with Thomas Mohaupt, but in fall 2004 he was already at Utrecht.

some science historian could someday write how this Utrecht combination was assembled (if they get results) and by what chain of decisions.

Here are recent seminar talks there:
http://www1.phys.uu.nl/wwwitf/Seminars/seminars.html
http://www1.phys.uu.nl/spinoza/seminars.html
http://www1.phys.uu.nl/spinoza/seminars/Grafiti.html

especially in this last link notice 12 Sept Renormalization Group improved cosmologies: no strings attached by Frank Saueressig, and two seminars on Loop Quantum Gravity on 19 Sept and 26 Sept given by Hanno Sahlmann Loop Quantum Gravity, an (un-)conventional QFT

You see also that Bojowald spoke in March, and Kiril Krasnov in April, and Renate Loll in June (Kiril Krasnov, of Nottingham, does Laurent Freidel type stuff---more or less simultaneous with Freidel)

So if Loll wants to talk to someone about QEG and fractally smallscale structure of spacetime, she does not have to email Reuter at Mainz, she can just walk down the hall to Saueressig. If there is any new development in LQG, Sahlmann can tell her about it. very good place. I will get a picture of Frank Saueressig to help thicken the soup.

marcus

Sep22-05, 01:39 PM

Here is Frank Saueressig 12 September talk abstract:

Renormalization Group improved cosmologies: no strings attached

"It is generally believed that in the very early universe, at times smaller than the Planck time, quantum gravity effects play a crucial role. Since the physics in the Planck era prepares the initial conditions for the subsequent classical evolution of the universe it is desirable to gain some understanding of the quantum gravitational processes which took place immediately after the Big Bang. Based on the Einstein-Hilbert approximation of asymptotically safe quantum gravity we discuss a consistent renormalization group based framework which allows for the inclusion of such quantum gravitational effects into the cosmological field equations and applies to all stages of the cosmological evolution. The very early universe is found to contain a period of "oscillatory inflation". Later on the cosmological evolution is classical and asymptotes to a de Sitter era at cosmologically late times."

Here is a snapshot:
http://www1.phys.uu.nl/spinoza/members/Frank.htm

marcus

Sep22-05, 02:10 PM

More Utrecht gossip:

Abhay Ashtekar will be teaching a course there Spring 2006 term.
http://www1.phys.uu.nl/wwwitf/courses/main.htm

It is a regular course for credit, with exam. Now is fall semester which runs thru the first week of January. So he is teaching NEXT semester which goes
February--June 2005

The course is Black holes in fundamental physics
lectures are Wednesday 9-11, with a tutorial on Monday.
A course description is available at the above link.

what intelligence is getting all these people together? As I said earlier, I dont think you could do it with just money---no matter how well funded Harvard or Princeton are, I don't think they are currently in position to assemble such a group. Or Stanford or UCSB-Kavli. What good is cash if you hire the wrong people? It is good luck for the graduate students at Utrecht---they can see several paths to QG where progress is being made and there are suggestions of convergence.

Timbuqtu

Sep23-05, 11:20 AM

marcus

Sep23-05, 02:41 PM

.. And I really enjoy the courses taught at the moment (QFT, Statistical Field Theory, GR) :

interesting, if you go to GR lecture at 9 Thursday morning then you may be hearing classical GR from someone who has an idea of what could replace it.

Spin_Network

Sep23-05, 08:02 PM

I would give anything to get into the lecture by :prof. dr.ir. P. Grassberger,:NS-TP450M: Kramers course: Phase transitions and anomalous scaling in non-equilibrium systems

then:NS-TP453M: Soft condensed matter theory:lecturer : dr. R.H.H.G. van Roij,

Great place to be!

marcus

Sep24-05, 01:38 PM

Timbuqtu, I have a suggestion for you
the October 10-14 conference at potsdam could be historically significant
it might IMHO be of interest to you later to have been there and seen it.
I suggest you consider doing this:
go to Loll, or Westra and say "can you get me in as an observer to this conference? I know the registration is past, but i think it might be
a memorable conference and I would like to have seen it. would that work?"
http://loops05.aei.mpg.de

marcus

Sep24-05, 03:52 PM

Perimeter is inviting applications for postdoc positions for 2006
http://www.perimeterinstitute.ca/index.php?lang=en
application must be done online (they supply a link)
and the deadline---in November 2005---will be extended until
all positions are filled.

Timbuqtu

Sep24-05, 06:39 PM

interesting, if you go to GR lecture at 9 Thursday morning then you may be hearing classical GR from someone who has an idea of what could replace it.It is interesting :smile:. But let me ask you something else: can you imagine Gerard 't Hooft, being one of the big string opponents, teached String theory for couple of years (until 2003/2004) here?

Timbuqtu, I have a suggestion for you
the October 10-14 conference at potsdam could be historically significant
it might IMHO be of interest to you later to have been there and seen it.
I suggest you consider doing this:
go to Loll, or Westra and say "can you get me in as an observer to this conference? I know the registration is past, but i think it might be
a memorable conference and I would like to have seen it. would that work?"
http://loops05.aei.mpg.deProbably it's too late now (Potsdam is not exactly around the corner). But there will be enough oppurtunaties to see (some of) these people around here I think. And I guess I wouldn't understand a lot of what they are saying. But it sure must be impressive to see all these guys together.

marcus

Sep28-05, 04:31 PM

It is interesting . But let me ask you something else: can you imagine Gerard 't Hooft, being one of the big string opponents, teached String theory for couple of years (until 2003/2004) here?

Yes Timbuqtu!
I think Gerard 't Hooft should be the perfect person to teach a course about String ideas.

I think that to all approaches to bring quantum physics together with GR he would be encouraging them to do their best. but I think he is also realistic and I like the quote where he is explaining that String ideas are not yet a Theory----that there is so far no scientific theory called String Theory, that makes predictions by which it can be tested---and he says in his book In Search of the Ultimate Building Blocks:

Actually, I would not even be prepared to call string theory a “theory” rather a “model” or not even that: just a hunch. After all, a theory should come together with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions for them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?

http://www.physicsforums.com/showthread.php?p=755232#post755232

http://www.physicsforums.com/showthread.php?p=761411#post761411

My impression of 't Hooft (please tell me if I am way off the mark) is that he wants people to get a quantum theory of spacetime, AND HE DOES NOT CARE WHO, OR HOW, OR BY WHAT METHOD IT COMES. So he is not protecting the interest or prestige of this method or that method, or the authority of this person or that person. I like to imagine that 't Hooft says to all the methods "go for it! go get 'em". And if this is his attitude and also the attitude of De Wit, then those people stand a good chance.]

marcus

Sep28-05, 04:35 PM

here is a general question to anybody

Renate Loll has a new snapshot of herself at her website

http://www.phys.uu.nl/~loll/Web/title/title.html

and she is holding a doll.

Identify this doll.

Dimitri Terryn

Sep28-05, 04:39 PM

Isn't that the Einstein action figure they realised for the 2005 World Year of Physics?

marcus

Sep28-05, 04:58 PM

Isn't that the Einstein action figure they realised for the 2005 World Year of Physics?

Thank you Dimitri! Stupid me, I could tell it was Einstein but I didn't know there was an Official Horrible Taste Kitsch doll created especially for the World Year of Physics. what will they think of next.

marcus

Sep28-05, 06:10 PM

selfAdjoint

Sep28-05, 08:02 PM

Seems more like the chip on her shoulder is aimed out at the viewer rather than at the Einstein doll. Like "Yes, I have an Einstein doll. You wanna make something of it?"

Spin_Network

Sep28-05, 08:25 PM

this photo troubles me

maybe it is a good photo. what do you think? anybody.

what I see in the person at that moment is a mixture of
dignity and impudence

and maybe the picture is iconic, or symbolic of a true relationship, that already at this moment we (in combination with her) hold Gen Rel in the palm of a new model.
and that Gen Rel is the artifact of the quantum theory we watch developing

The photographer ( likes to put something "extra" into his images, for instance here:http://www.fjodor.nl/manipulation_mariecarmenoudendijk_gb.html

His webpage here:http://www.fjodor.nl/biografie_gb.html

I do not think Loll would have just picked up the Doll,that was just laying around in the room she was having her picture taken, and holding Einstein thus?

She is reaching out to Einstein?..Holding Einsten in the palm of her hand?..or just simply, she is holding out a "model of Einstein", wherby she is symbolically an "extension" of Einstein?

marcus

Sep28-05, 08:41 PM

She is reaching out to Einstein?..Holding Einsten in the palm of her hand?..?

her theory, CDT, is aimed at comprehending and containing Einstein Gen Rel. if it were right then she would be the "super-Albert"

and CDT would provide a dynamical principle by which spacetime operates at very very small scale
and this quantum dynamical principle, by operating everywhere at very small scale, would GIVE RISE at large scale to the behavior described by the Einstein equation of general relativity.

so Gen Rel would come out of Loll CDT as a large scale limit.

you know this Spin_N, I just want to have it explicitly said. this is what CDT aims to do. It aims to have a micro-scale dynamic principle that DOES NOT EVEN ASSUME THAT THE MACRO-SPACETIME IS FOUR DIMENSIONAL. Even something as basic as the dimensionality is supposed to arise from the working of a simple planckscale mechanism.

So if one can make CDT work, then one "explains" Einstein Gen Rel. One has a model that can reproduce it from something simpler and more basic.

the photo concept, symbolism (even tho daring), layout and composition is OK, what bothers me is the absurdist streak of the photographer, because the doll is such a Barby caricature of Einstein. But I am gradually getting over the shock and will be all right soon

Spin_Network

Sep28-05, 10:02 PM

her theory, CDT, is aimed at comprehending and containing Einstein Gen Rel. if it were right then she would be the "super-Albert"

and CDT would provide a dynamical principle by which spacetime operates at very very small scale
and this quantum dynamical principle, by operating everywhere at very small scale, would GIVE RISE at large scale to the behavior described by the Einstein equation of general relativity.

so Gen Rel would come out of Loll CDT as a large scale limit.

you know this Spin_N, I just want to have it explicitly said. this is what CDT aims to do. It aims to have a micro-scale dynamic principle that DOES NOT EVEN ASSUME THAT THE MACRO-SPACETIME IS FOUR DIMENSIONAL. Even something as basic as the dimensionality is supposed to arise from the working of a simple planckscale mechanism.

So if one can make CDT work, then one "explains" Einstein Gen Rel. One has a model that can reproduce it from something simpler and more basic.

the photo concept, symbolism (even tho daring), layout and composition is OK, what bothers me is the absurdist streak of the photographer, because the doll is such a Barby caricature of Einstein. But I am gradually getting over the shock and will be all right soon

Marcus, I left the reply for a while hoping that you would re-look at the Loll/Einstein MODEL picture?

Take another look?....what do you see?..specifically, what pose/stance is the Einstein Model Loll is holding in?..look really closely! :wink:

Scale Model :approve:

marcus

Sep28-05, 10:45 PM

...

Scale Model :approve:
maybe I understand you Spin_N. if you had been the photographer then the Albert doll would have his left hand extended palm up supporting a tiny figure of newton. and newton would have been in a similar stance...

well, here is the link, in case anyone else is curious
http://www.phys.uu.nl/~loll/Web/title/title.html

marcus

Sep30-05, 08:29 PM

Peter Woit flagged a talk by Eric Laenen about theoretical physics in the Netherlands

http://www.nikhef.nl/recfa/Presentations/RECFAEricLaenen.ppt

it is in powerpoint but somehow my computer digested it and produced something I could read. of particular interest were pages 14 thru 18.

Theoretical physics in the Netherlands and how the different institutes and researach programs fit together and what are some important developments. Helps to put Utrecht in perspective with other Dutch universities.

marcus

Oct2-05, 08:09 PM

That talk Peter Woit mentioned, by Eric Laenen, on the organization status current activity of theoretical physics in the Netherlands---here is Eric Laenen
http://www1.phys.uu.nl/wwwitf/fotopagina's/Medewerkers/Eric.Laenen.htm

A few posts back I mentioned that Hanno Sahlmann (who was postdoc at Penn State) is now postdoc with Loll at Utrecht

Artem Starodubtsev (who was working with Laurent Freidel at Perimeter) is now also postdoc with Loll at Utrecht

http://www.phys.uu.nl/~loll/Web/group/group.html

Also there is Joe Henson---I thought he did causal sets. Perhaps I am confusing him with someone else.
[EDIT: yes he has been at UC San Diego and worked in causal sets and coauthored with Rafael Sorkin]

marcus

Oct2-05, 08:16 PM

here's an update:

schedule for October's Loops 05 conference is here:
http://loops05.aei.mpg.de/

Here is an imperfect keyword search for CDT papers that have come out in the past 12 months. It can get non-CDT papers by mistake.

http://arxiv.org/find/grp_physics/1/OR+OR+abs:+AND+triangulations+AND+Lorentzian+dynam ical+abs:+AND+triangulations+AND+causal+dynamical+ ti:+AND+gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

I believe there is a paper in the works by Loll with Dario Benedetti and Francesco Zamponi.

Here is Loll's group:
http://www.phys.uu.nl/~loll/Web/group/group.html

Here are some snapshots mostly from the Utrecht Inst. of Theor. Physics:

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Renate.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Willem1.jpg

http://www1.phys.uu.nl/wwwitf/fotopagina's/foto's/Dario.jpg

http://www.phys.uu.nl/~helios/commissies.php#kas (Jaap)

http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml.

here is the whole staff of the Utrecht ITP (inst. theor. phys.) where Loll and co-workers and many of her students are based.
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

Here is Loll homepage:
http://www.phys.uu.nl/~loll/Web/title/title.html

A clear brief non-technical description of CDT approach, written by Loll for general audience is here
http://www.phys.uu.nl/~loll/Web/research/research.html

A survey article commissioned by Contemporary Physics for wide audience ("The Universe from Scratch") is here
http://arxiv.org/hep-th/0509010

CDT coverage in press here:
http://www.phys.uu.nl/~loll/Web/press/press.html

We have a PF a thread polling people's predictions about whether the QG path integral including sum over topologies will prove extendable from the 2D case up to 3D and 4D. the thread is here:
http://www.physicsforums.com/showthread.php?t=81626

Hanno Sahlmann is listed as postdoc at Utrecht. Here is his earlier web page, describing his research interests, with sketches of ideas, from when he was at Penn State:
http://cgpg.gravity.psu.edu/people/igpg_hsahlmann.shtml.

Also Artem Starodubtsev, who coauthored with Smolin while at Perimeter, and with Freidel.
To find Artem's page at Perimeter go here
http://www.perimeterinstitute.ca/people/index.php
click on "graduate students", advance to the second page.

Also Joe Henson, I believe he has been working in causal sets and and has coauthored with Rafael Sorkin and Fay Dowker. I think Henson was most recently at the physics department of UC San Diego.

I have not heard anything about the location of next year's Loops 06 conference but I think it will be at Utrecht.

Remember that Ashtekar (whom one is used to identifying with Penn State) is going to be at Utrecht at least for half of 2005-2006 academic year. He is teaching a black holes course there in the spring term. It would be a reasonable choice with such a confluence of QUANTUM GRAVITY researchers (nonperturbative, background independent QG of course :smile: ). So maybe they will have it there, who knows?

this url is for the Spinoza Institute
http://www1.phys.uu.nl/spinoza/People/Members.html
this is for the Utrecht ITF
http://www1.phys.uu.nl/wwwitf/Members/members.staff.htm

marcus

Oct19-05, 02:47 PM

It's good to hear such positive things about Utrecht. I'm one of the students who enrolled in the Master's programme in Theoretical Physics in Utrecht this year. And I really enjoy the courses taught at the moment (QFT, Statistical Field Theory, GR) and I'm looking forward to next semester's courses (Cosmology, String, Black holes, Standard model, etc.). Certainly I will attend Ashtekar's course next semester.
Keep up the good work, Marcus! Your announcements are really useful. :smile:

Thanks for the encouragement Timbuqtu,

I have something in Dutch that I would like to see (at least portions of) in English. It just came out this month in the Utrecht University weekly newspaper Ublad.

Think if you might consider picking out one or two paragraphs and translating them. I would greatly appreciate the help. This is the article,
from the 13 October issue of Ublad (vol 7 no. 37)

http://www.ublad.uu.nl/WebObjects/UOL.woa/4/wa/Ublad?id=1022717

HERE IS A PART THAT I WOULD SKIP, AT THE BEGINNING

Renate Loll (43) werkt nu vier jaar in Utrecht. In die tijd heeft ze zich ontpopt tot eminent wetenschapper en een enthousiast pleitbezorger voor meer vrouwen in de wetenschap. Ze kreeg drie miljoen euro uit Brussel voor een Europees netwerk en sleepte eind vorig jaar een vici-premie van 1,25 miljoen euro in de wacht. Geld genoeg om te blijven zoeken naar de heilige graal van de fysica.

HERE IS A PART HALFWAY DOWN THAT I AM CURIOUS ABOUT:

Waarom heeft een Duitse onderzoeker een aanstelling aan een van de gerenommeerde Max Planck Instituten in haar geboorteland eigenlijk verruild voor een positie als universitair hoofddocent in Utrecht?

Loll: "Ik ben in eerste instantie naar Utrecht gekomen, omdat ik hier een vaste aanstelling kon krijgen en wellicht op termijn hoogleraar kon worden. Maar ik heb zeker ook voor Utrecht gekozen vanwege de reputatie van dit instituut en vanwege Gerard 't Hooft. Niet dat ik nauw met hem samenwerk, want Gerard werkt met niemand samen. Zijn wonderbaarlijke kracht is zijn volstrekt individuele stand alone manier van denken. Hij is superkritisch en uiteraard zijn we het lang niet altijd eens over het probleem van de quantumgravitatie, maar wat ik heel bijzonder vind is dat hij niet alleen naar colloquia en seminars gaat, maar ook naar praatjes van masterstudenten en daar met hen in discussie gaat. Noem mij maar eens een andere Nobelprijswinnaar die dat doet dat. Gerard maakt echt deel uit van the spirit of the place. Dat maakt het extra motiverend om hier te werken."

Timbuktu, you see what I am getting at. It has a quote that looks possibly interesting. I would be glad if you, or anyone here who speaks Dutch, would translate.

Timbuqtu

Oct21-05, 11:02 AM

marcus

Oct21-05, 11:55 AM

I read this article last week. Here are the translations you requested (don't mind my English):
Renate Loll (43) has been working in Utrecht for four years now. She has become an eminent scientist and an enthousiastic advocate for more women in science. She received three million euro from Brussels for a Europian network and also a vici-prize of 1.25 million euro last year. Enough money to keep searching for the holy grail in physics.... thanks! I will try to extend this using Babelfish. I will just tack on some more sentences to what you have already:

UPDATE: a translation of the whole article into English is now at
http://www.physicsforums.com/showthread.php?p=796410#post796410

-------this is what we started with earlier today: some improvements have been made----
"There were years of struggle until I first got the idea that what many theorists had lost sight of was the need to include causality---cause and effect---in the picture at very small scale. So I put that in as an absolute requirement in my calculations. then I worked for several years with a Danish and a Polish colleague to work out the consequences of that idea.

And it succeeded, because in an article last year we showed that a realistic four-dimensional universe does indeed arise, under the condition of causality, from miniscule bits of four-dimensional quantum-foam.
I can still remember vividly how it felt when we saw that that outcome appearing. It was a magical moment."

The article by Loll and her colleagues was received worldwide as a breakthrough on the way towards a better grasp of the structure of spacetime. It is still a question in many people's minds whether it offers insight into the long-awaited theory of quantum gravity.
It is clear however, that the leadership at the Spinoza Institute made a good bargain, with this appointment.
Why did a German scientist swap an appointment at one of the renowned Max Planck Institutes in her native country for a position as senior lecturer in Utrecht?
Loll: "Initially I came to Utrecht because I could get a permanent appointment and possibly later become a professor. But I certainly also chose Utrecht because of the reputation of this institute and because of Gerard 't Hooft. Not that I closely cooperate with him, for Gerard doesn't work together with anyone. His remarkable power is his totally individual stand alone way of thinking. He's very critical and we of course don't always agree on the problem of quantum gravity, but what I find very special about him is that he does not only attend colloquia and seminars, but he also visits talks by master students and he participates in their discussions. You name me another Nobel laureate who does such things. Gerard is really a part of the spirit of the place, which makes it extra encouraging to work here."

marcus

Oct23-05, 01:58 PM

Dimitri Terryn, a physics Masters student at Brussels
Vrije Universiteit has kindly supplied a full translation into English of this article by Eric Hardeman from the 13 October issue of Utrecht's university newspaper, the Ublad (vol 7 no. 37):
http://www.ublad.uu.nl/WebObjects/UOL.woa/4/wa/Ublad?id=1022717
The article is a two-page profile of Renate Loll.
Thanks to others, Timbuqtu and Andre, who also took part in what became for a short time a PF group effort.
Dimitri's original post is at
http://www.physicsforums.com/showthread.php?p=797984#post797984

Looking for the holy grail

Renate Loll is looking for movement in the smallest particles

Renate Loll (43) has been working for four years in Utrecht. During that time she has become an eminent scientist and an enthusiastic advocate of women’s involvement in science. She has received more then three million Euros from Brussels for a European network, and last year she got a 1.25 million Euro vici-grant. More than enough money to continue looking for the Holy Grail of physics.

A vacuüm that isn’t empty; spacetime that consists of little pieces of foam; and our three-dimensional universe that is a four-dimensional one. The reality that Renate Loll is studying, is full of paradoxes and contradictions. In her office in the Minnaetbuilding the German shows understanding for the confusion of her interviewer. “It’s not easy to explain what my research consists of. Very concisely put, I am looking for the structure of spacetime, but in order for you to understand what I mean by that, you first need to distance yourself from the common sense view that we live in a space of three dimensions, where a clock ticks in the same way for everyone. For our daily lives this is a very useful assumption, but Einstein has made it clear to us exactly one hundred years ago with his theory of relativity that there is no strict fundamental separation between space and time. Something that someone sees as a piece of time, another sees as a piece of space. Actually we live, according to Einstein, in a fourdimensional reality: spacetime.”

“Suppose that we would investigate spacetime with an imaginary microscope. You would expect that on very small scales, beyond the last known elementary particles, there would be an absolute void. But quantum theory, that was developed in the twenties in order to explain what happens on this very small scale, tells us a very different story. According to this theory the vacuum is in reality an extensive “sea” , where particles are constantly created and destroyed. These so-called quantum fluctuations happen on scales that are millions of times smaller than the size (10-19 m) of quarks, the smallest known elementary particles. We still do not have a precise idea of how they behave themselves, but it appears that on the so-called Planck scale of 10-35 m they begin to deform spacetime itself. It’s not easy to determine this experimentally. Our particle accelerators will never be able to show us what happens on such a small scale, and the theory of relativity does not say anything about what happens on this scale.”

In fact, the great and still unresolved paradox in modern physics is that there are two theories, that both decribe in a very elegant manner a part of our physical reality. They are however based on so different principles that they are utterly incompatible. For many years theorists are looking for the holy grail of physics, the so called theory of quantum gravity that will resolve this paradox by describing the behavior of large structures in the universe (explained by relativity) and that of the smallest particles (explained by quantum theory) in the same framework.

Among physicists there is the commonly-held view that the key to this theory lies in an adequate description of the structure of spacetime, but the solution is being sought in many different directions. Many colleagues of Renate Loll think that superstring theory is the best candidate to reconsile relativity with quantum theory, but she sees more promise in an approach that does not make it nescessary to assume that there are more than four dimensions.

“I try to build a model that describes both on the quantum scale as on the larger scale the structure of spacetime in an accurate way. Now it is believed that on the smallest scale that there are high energy fluctuations, that spacetime is curved to a high degree there. But that is only conceivable if we assume that it is extremely warped or even ripped apart in uncountably many pieces of so-called quantum foam. The big problem is that there is no theory that can explain how the sum over all those little shards of quantum foam gives us our nice continuous four dimensional reality on macroscopic scales. All attemps to formulate such a theory have failed until now. Sometimes the sum gave us a two dimension world, sometimes it came out as a world with infinitely many dimensions.”

“Years ago I first got the idea that maybe the problem lay in the fact that many theorists had lost sight of the requirement that at those very small scale there must also be a notion of causality, of cause preceeding effect. I took this to be an absolute condition for my calculations. After that, I have worked for years with a Danish and a Polish colleague to calculate all the consequences of that idea. And succesfully, because last year we showed in an article that computersimulations on the basis of minuscule pieces of quantumfoam, under the condition of causality, we indeed got a four dimensional universe. I can still remember vividly how it felt when we saw the outcome of the calculations appear. That was a very magical moment.”

Loll’s article has been received worldwide as a breakthrough towards a better understanding of the structure of spacetime. If it also offers prospects towards the long awaited theory of quantum gravity, is for many people still an open question. It is clear however that the management of the Utrecht Spinoza institute have made a good move in approving here. But why did a German researcher let pass an appointment at the reknowned Max Planck institutes in her native country in favour of the position of professor at Utrecht?

Loll : “I went to Utrecht in the first place because I could get tenure and a probably a professorship soon. But in part I also chose for Utrecht because of the reputation of this institute and because of Gerard ‘t Hooft. Not that I work closely with him, because Gerard does not work with anyone. His wonderful strenght is his utterly individualistic stand alone way of thinking. Hij is extremely critical and naturally we do not always agree on the problem of quantum gravity, but what I find very special is that not only does he go to colloquia and seminars, but also to the talks of masters students and discusses things with them. Name me one Nobel Prize winner who does that. Gerard truly is part of the spirit of the place. That makes it extra motivating to work here.”

In the four years since her appointment in Utrecht, Renate Loll has shown herself to be not only an eminent scientist, but also an enthousiastic advocate for a higher degree of women in science. “Women’s position is very important to me. I find the situation in the exact sciences in the Netherlands absolutely shocking. In Germany things were pretty bad, but it’s much worse here. Not only is the thought that girls could be good at exact science completely absent. Worse is that there isn’t even a realisation that there is a problem. My male colleagues are very dear to me, and it’s not that they are opposed to women, but they have no idea how masculin the system is in which they function and how it disadvantages women.”

As coordinator of the so-called Enrage (European Network of Random Geometries) network of the European Union Renate Loll has found a way to give female scientist a little support, she tells us. “It’s about a network of scientist who use the same geometric techniques that I use in QG in different fields. One of the goals of the network is to increase the participation of women in the exact sciences. You can have different views on Europe, but the EU has some very enlightened ideas about women in science. They are more progressive in Brussels then in any of the member states”

“In all European programs attention for women’s position is an explicit criterion. But did you think that anyone cared about it? Usually it comes down to writing somewhere at the end of a sixty page research proposition by the way, we have someone in our network who is responsible for the women. Completely ridiculous. In my network I’ve been trying to integrate this more. Of the thirteen groups in Enrage we have three where women play a prominent role. I gave all three of them an extra PhD grant.”

Renate Loll herself has had to conquer obstacles herself. “I was one of those young girls that was pulling radios apart, to see how they work but I had to think long about what I was going to do at university. Then I thought : Why not take up physics, it could never hurt. My parents were fine with this, but from the rest of my enviroment I got little or no support, not only during my studies but afterwards as well. I really had to struggle as a woman to make it in science. That I only got a permanent position at age 39 says a lot about that.

Superstring Theory

According to superstring theory the most elementary particles in the universe do not consist of points, but of a kind of vibrating ellastic bands, whose vibrations manifest themselves as particles, like electrons or photons. Although the theory initially seemed to be a promising candidate to bridge the gap between relativity and quantum theory, it seems to be more and more clear that the theory has her own share of problems. The most serious complication is that according to this theory our world is part of a ten dimensional universe, without us noticing in our everyday lives. Possibly is our threedimensional universe floating through higher dimensions, in the same way as a two dimensional flying carpet is flying throug three dimensional space, separated from a shadowworld that may be only a few tenths of a milimeter away, as Spinoza winner Robert Dijkgraaf recently decribed.

Altough Renate Loll is careful with her formulation as to not antagonize any of her colleagues, it is clear that she does not think much of this line of research. “Initially, superstring theory looked to be very simpel and therefore attractive, but graduately there emerged more and more complications, making me to find it quite a far fetched theory now. In addition it is unclear wether the string approach will lead us somewhere. That’s why I favour my own approach. That at least has produced some concrete results.”

Gerard ‘t Hooft, just like Renate Loll, isn’t at all convinced by string theorists. But whether the approach of his colleague from Utrecht is correct, is still a question according to him. “It is clear that Renate has made progress the last few years, but she’s not there yet. It’s even a question whether she is on the right track concerning QG. Although personally I tend to look in the direction of black holes, I think that string theory still has the best hand. We have hit a number of obstacles, but none the less is that approach still more concrete and structured than other attemps to reconcile GR and QT. But that doesn’t mean that Renate couldn’t be right. My philosophy is, let everyone muddle on. She should continue with what she is doing, because the resolution of this problem will probably come from an unexpected direction.”

marcus

Oct25-05, 01:00 AM

the last time I mentioned this was post #79
this thread is to keep track of the news/current events/essential links about Loll triangle gravity. (CDT path integral)

in other words it's basically for CDT gossip----that means Utrecht, Loll's group and related matters.
There was some favorable comment about CDT on SCI.PHYSICS.RESEARCH earlier this month. I will copy a Baez post in here. It is short and sweet.
The context was that someone named EvT started a thread about how are things going in various approaches to QG. On 3 October Baez posted this:
----quote---
27. John Baez Oct 3, 4:55 pm
In article <20050905174410.33275.qm...@web32010.mail.mud.yahoo .com>,
EvT <vantu...@yahoo.com> wrote:
>According to some physicists (for instance John Baez
>and Peter Woit), both string theory and loop quantum
>gravity have not made much progress recently.
>How active are other approaches like noncommutative
>geometry, euclidean quantum gravity, discrete
>approaches (Lorentzian, Regge calculus, ...), twistor
>theory, topos theory, supergravity, Ads/CFT, emerging
>properties (Robert Laughlin)...?
Ultimately what matters most is not whether an approach
is "active", but whether it's getting somewhere. A big
bandwagon can make a lot of noise just by spinning its wheels
in the mud.
As far as I'm concerned, the one approach that's making
the most progress now is Causal Dynamical Triangulations,
which is a variant of the Regge calculus.
Not many people are working on this yet, in part because
it requires computer simulations, and most researchers
in quantum gravity still prefer pencil-and-paper work.
But, the results so far are impressive. They've numerically
simulated quantum gravity, and found something surprising:
their spacetimes act 4-dimensional at large scales but
2-dimensional at small scales!
The three main people working on Causal Dynamical Triangulations
are Ambjorn, Jurkiewicz and Loll. Here's a nice simple review
article:
http://arxiv.org/abs/hep-th/0509010
and here's a more technical one:
http://arxiv.org/abs/hep-th/0505154
Sophisticated work on perturbative quantum gravity by Lauscher,
Reuter and others adds evidence for this idea that quantum gravity
makes spacetime effectively 2-dimensional at short distance scales.
For a review with lots of references, try:
http://arxiv.org/abs/hep-th/0508202
So, technically speaking, the old problem of the nonrenormalizability
of quantum gravity may be solved by an ultraviolet fixed point of
surprising kind!
Of course I'm optimistic that this 2d small-scale behavior
is ultimately due to a spin foam model: imagine a bunch of
"soap bubbles" (2d surfaces) forming a "spacetime foam" that
mimics a 4d continuum at length scales much larger than the
Planck length. But, this is just speculation at this point.
I hope there will be some discussion about this idea when I
talk about it at Loops '05 next week, where Loll will also be
speaking:
http://loops05.aei.mpg.de/
------endquote------
http://groups.google.com/group/sci.physics.research/browse_frm/thread/96746bb106e7a2f9/3bece53891b06e6d#3bece53891b06e6d

John Baez gave one of the invited talks at this month's Loops conference and his talk is available online at his website. The talk is more complicated than this statement here. I'm quoting it because someone whose views are a good guide in Quantum Gravity is saying where the progress is happening and he does not make a complicated statement of it, he simply says that as far as he's concerned what's making the most progress is CDT.

marcus

Oct25-05, 11:04 AM

Today I saw a related post from Baez at Not Even Wrong. In this post he answers the riddle of why we didnt immediately hear an announcement that Loops '06 would be held in Utrecht. It looked like an obvious choice that next year conference of NONPERTURBATIVE QUANTUM GRAVITY research would be in Utrecht. It has people there from several of the main QG lines of development and it hasnt hosted such a conference whereas other major QG centers have.

----quote----
John Baez Says:
October 24th, 2005 at 9:38 pm

dan said:

will there be a Loops ‘06?

Probably; the idea of calling it Loops ‘05 was to make this an annual thing. However, we need someone to agree to run Loops ‘06 - and I don’t think it’s gonna be me!

Some obvious possibilities include Penn State, the Perimeter Institute, and Marseille, but they’ve all run conferences like this quite recently. So, Mexico and Utrecht are being mentioned.

I’m not sure Renate Loll will want to run something called Loops ‘06, since she considers her own approach - causal dynamical triangulations - quite distinct from loop quantum gravity, and more successful! Personally I think this year’s conference should have been called something like QG ‘05, since there were talks on almost every approach to quantum gravity. Or maybe NOT VERY MUCH STRINGS ‘05.

Anyway, we’ll see what happens.

dan said:

incidentally, shouldn’t all LQG researchers work on the semiclassical limit problem, for if it doesn’t reduce to GR, then it is not a viable theory of QG?

I think all loop quantum gravity researchers should work on this problem. That’s why I keep talking about it every time I get a chance! I spoke about it at Marseille, at the Perimeter Institute, and at Loops ‘05. However, it’s hard to get people to work on a very hard problem, when there are easier problems out there.

Similarly, I think all string theorists should be working on a background-free approach to this theory, and on finding a way for it to make specific predictions about particle physics. But at any given moment there are lots of easier things to do.
-----endquote-----

http://www.math.columbia.edu/~woit/wordpress/?p=279

marcus

Oct25-05, 08:46 PM

http://www.phys.uu.nl/~loll/Web/jobs/jobs.html

postdoc openings
Loll has announced some job openings recently. She has one or more postdoc positions starting "Autumn 2006 or earlier". She is asking for applicants who have some experience with Monte Carlo computer simulations as well as knowledge of quantum gravity.

They are not yet taking applications. It says there will be an official announcement in EARLY NOVEMBER, at the above "jobs" URL, and this will also give the deadline and details on how to apply.

predoc openings
Also there will be at least one more PhD student slot starting in 2006, where you get teaching work to do and some support for up to 4 years. Applications for that can be submitted NOW. It is explained how to apply:

"Applications, preferably in electronic form (text-, postscript- or PDF-format), can be submitted at any time to loll@phys.uu.nl with subject line "QG predoc 'your name'". The application should consist of a cover letter, CV, transcripts of university grades and degrees, a statement of research interests and reasons for undertaking doctoral research at the ITP, as well as the names of at least two senior scientists who are in a position to judge the applicant's suitability for a PhD in theoretical physics. Applications will be considered until the position is filled."

It sounds simple to apply for the "PREDOC" position, but to get it one would probably need the right combination of qualifications. She seems to need people with experience with Monte Carlo simulations because there is a lot of computer work to be done. If one had a Masters in Statistical Physics and also the right computer background----I am just guessing----one might have a chance. Exciting place to be right now, if one can get invited to the party.

marcus

Oct29-05, 12:12 PM

A new graduate student has joined Loll's group. He is Pedro Machado, a PhD student from Copenhagen NBI (niels bohr inst.)

marcus

Nov12-05, 07:30 PM

postdoc openings
Loll has announced some job openings recently. She has one or more postdoc positions starting "Autumn 2006 or earlier". She is asking for applicants who have some experience with Monte Carlo computer simulations as well as knowledge of quantum gravity.

They are not yet taking applications. It says there will be an official announcement in EARLY NOVEMBER, at the above "jobs" URL, and this will also give the deadline and details on how to apply.
...

applications are now being taken for one or more postdoc positions in Loll's group.
directions about how to apply are at the jobs webpage
http://www.phys.uu.nl/~loll/Web/jobs/jobs.html

the deadline for applications is January 2006

"...preference will be given to young researchers with expertise in Monte Carlo simulations, one of the backbones of the approach of Causal Dynamical Triangulations..."

===================================

For anyone interested in Causal Dynamical Triangulations it would be worth listening to the recording of the talk by Martin Reuter 12 October at the QG conference. Because Reuter's approach (assymptotically safe renormalization) has some significant points of agreement with CDT (microscopic fractal-like 2D structure of spacetime) but also significant differences. The second half of Reuter's talk discusses the contact made between his approach and CDT.

Here is Reuter's abstract page with links the slides and the recorded talk
http://loops05.aei.mpg.de/index_files/abstract_reuter.html

the video recording of the talk
http://loops05.aei.mpg.de/index_files/Video/reuter.wmv

the slides/lecturenotes
http://loops05.aei.mpg.de/index_files/PDF_Files/reuter.pdf

the slides serve as complete notes for the lecture, and go very well together with the talk.
there were no technical problems with the recording of this talk.

however with Loll's talk the same day the audio sometimes goes out. Here is a link
http://loops05.aei.mpg.de/index_files/abstract_loll.html

marcus

Dec4-05, 11:44 AM

Loll's talk of 18 November 2005 at Perimeter Institute is quite good.
It is organized and clear and gets a complete overview of CDT into 45 minutes. Technically the recording worked out better than it did at Loops '05.

This link should get the video and the slides, in a split screen format, to run in synch.
on the Emergence of Spacetime in Quantum Gravity
split screen slides and video
http://streamer.perimeterinstitute.ca:81/Mediasite/Viewer/Viewer.aspx?layoutPrefix=LayoutTopLeft&layoutOffset=Skins/Clean&width=800&height=631&peid=ae9950c3-33b8-46f3-a248-52d17f97bb86&pid=bba3089f-6509-485b-9ffd-379e4b8ffdf0&pvid=1&playerType=WM64Lite&mode=Default&shouldResize=true
Allow a few minutes for it to download, before it starts to play. You shouldnt have to do anything except click on it.

If the link doesnt work for any reason, try going to the menu:
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?cid=a9b1d20a-efa7-485f-8d5d-3b62fb7d3e4c&shouldResize=False

scroll down the sidebar menu on the left and click on
"Emergence of Spacetime Workshop", which gives a
page with recordings of 6 talks. Loll's is
"Emergence of quantum spacetime from causal dynamical triangulations"

Some PF posters, like Spin_N, have already watched many of these PI recorded talks and know about the exceptionally good format----which I only just found out about.

Loll's talk was part of a 3 day workshop. I assume the essential thing of this weekend workshop was not the 40 minute talks on the first day, but the discussions between the 6 visitors and Perimeter people over the next two days.

marcus

Dec16-05, 12:26 PM

this thread is for news and gossip about the QG scene at Utrecht, and esp. Loll's group

BTW Loll just gave a seminar talk at Göttingen on 13 December, I think some QG research interest is germinating at that university.

We have another Dutch text from the Utrecht newspaper "Ublad"
http://www.ublad.uu.nl/WebObjects/UOL.woa/2/wa/Nieuws?id=1023382

Looks like Loll or her team has been nominated for an annual Dutch science-communication prize

Loll kanshebber Academische Jaarprijs

Prof.dr. Renate Loll is de Utrechtse kanshebber op de eerste Academische jaarprijs. Een jury maakte vrijdag bekend welke projecten in aanmerking komen voor de prijs voor de beste vertaling van wetenschappelijk onderzoek naar een breed publiek.
De Universiteit Utrecht had zeven wetenschappers laten meedingen naar de prijs van 100.000 euro, een nieuw initiatief van NRC Handelsblad in samenwerking met NWO en KNAW. De jury vond dat het voorstel ‘waarom bestaat de ruimte uit drie dimensies?’ van Renate Loll, werkzaam op het gebied van de theoretische fysica, de beste Utrechtse inzending was.

De wetenschappers was gevraagd een plan te maken om de waarde en relevantie van excellent wetenschappelijk onderzoek duidelijk te maken aan het Nederlandse publiek. De inzendingen mochten zeer verschillend van aard zijn, zo kunnen er plannen zijn voor tentoonstellingen of voor lesprogramma’s.

Voor elke universiteit is nu een project aangewezen dat kans maakt op de hoofdprijs. Op de slotmanifestatie op 1 juni wordt de winnaar gehuldigd. De winnaar mag het geld gebruiken om zijn of haar ideeën te realiseren.

-------
thanks to FLORINE for this lead! she is a physicist at utrecht who has a blog
http://www.phys.uu.nl/~fmeijer/wordpress/
-----
it is interesting that in Holland a scientist could get a prize for how clearly and accurately they COMMUNICATE their work to the public. I dont think that they are rewarding work like Brian Greene which confuses and excites---it is not a advertizing prize but more an education prize. I think. If it is a prize for responsible communication to the public about science, not for geewhiz hype, then I think it is a good idea. Scientists should do more of that. so it should be recognized and good performance honored.
---------
HERE IS WHAT THE CRAZY BABELFISH SAYS

Loll kanshebber academic Jaarprijs
Prof.dr. Renate Loll are the Utrechtse kanshebber on the first academic jaarprijs. A jury made Friday confessed which projects qualify for the prize for the best communication of scientific study into a broad public.
The university to Utrecht to seven scientists would have let compete to the price of 100,000 euro, a new initiative of NRC trade booklet in association with NWO and KNAW. The jury found that the submission "Why does space consist of three dimensions?" by Renate Loll, working in the field of the theoretical fysica, was the best Utrechtse entry.

NICE BABELFISH LINK:
http://www.systransoft.com/index.html

marcus

Dec16-05, 03:27 PM

this thread is for news and gossip about the QG scene at Utrecht, and esp. Loll's group

...thanks to FLORINE for this lead! she is an experimental physicist at utrecht who has a blog
http://www.phys.uu.nl/~fmeijer/wordpress/
....

each of the competing teams will prepare a WEBSITE WITH A BLOG
the competition between the different entries (from each of a dozen Dutch universities)
has just begun, so the Utrecht entry doesnt have much at their site yet

http://www.academischejaarprijs.nl/utrecht/

When the websites are up, if you want you can GO TO THIS SITE AND VOTE:

http://www.academischejaarprijs.nl/nl/index.php

a vote for Utrecht in the poll is a vote for Loll's team as doing a good job explaining their research results to the general public.

Personally I would vote for Loll because i think those people do a good job in explaining to the public what they are doing, and they do it in a solid way with less hype and more integrity.

also check out Florine Meier's blog
so far she showed good taste in poetry, for a physicist.
scientists should have blogs----the practice should be encouraged
here is Florine's homepage at the Center for Science Education
http://www.cdbeta.uu.nl/instituut/medewerkers.php?id=23
I gather she is a theoretical physicist, by training, who has specialized in how to teach physics in Dutch schools---quantumphysics in particular. Here again is her blog
http://www.phys.uu.nl/~fmeijer/wordpress/

the Dutch are not bad in physics education. Gerard 't Hooft has a website with a great set of online materials for the aspiring young physicist. One of the best physics reading lists I've seen.

marcus

Dec18-05, 03:04 PM

the dutch call this website science communication contest
(teams from 13 universities competing) a "Battle of the Universites"

frankly, as a serious mathematician, I can't see how Loll could stand being involved leading a website development team, in a "competition" even.

here is the menu of the 13 websites:
http://www.academischejaarprijs.nl/nl/weblogs.php

hmmm the sites are all supposed to be BLOGS

maybe Loll can delegate the work to her master and PhD students
but she is trying to make creative physicists out of them in a short time, it could be frustrating to have a distraction like this Battle.
one does not want to waste one's students time.

However it could be very interesting if the Loll CDT team put up a lot of COMPUTER GRAPHICS of spontaneously selfcreating and evolving spacetimes-----by Monte Carlo----and of RANDOM WALKS being taken in these randomly generated assemblages of building blocks

showing a graphic of a random walk could communicate the idea of how they measure the dimension of random simplicial manifolds. one sees how easy it is for a wanderer to get lost and never return----averaged over all the places he can begin his walk----and the lower the dimension the harder it is for him to get lost.

the website of the Utrecht team could have some amusing graphics and perhaps animations or visual stories.

thinking up these graphics and animations could acutally help the students learn CDT and understand it better, so it would not be totally wasted time

I also like "Monte Carlo moves" very much. there is a menu of just a few moves and one can entirely transform a simplicial complex by doing these moves one after the other, as one shuffles a deck of cards by repeating simple shuffle operations. I wonder if they could put up an interactive visual teacher of the Monty Moves----say in 3D

If I remember the 4D moves are almost the same or analogous to the 3D, so it is very helpful to be able to picture 3D.

Anyway, at present the Utrecht team does not have anything at the site but there is still a lot of time before the judges or whoever decide

marcus

Dec25-05, 09:11 AM

...
here is the menu of the 13 websites:
http://www.academischejaarprijs.nl/nl/weblogs.php
...

here is all it says, so far, at the Utrecht team's blog
http://www.academischejaarprijs.nl/utrecht/

24 december, 2005
Welkom op onze weblog!
Welkom op de weblog van het team van de Universiteit Utrecht. Momenteel genieten we van onze vakantie, maar het is de bedoeling dat de weblog begin januari echt van start gaat. Tot dan!
----------------

because of similarity between Dutch and English it is not hard to guess what it means:

Welcome to our blog!
Welcome to the weblog of the team of Utrecht U.
At the moment, we enjoy our vacation
...[I can't guess the next few words]...
that the blog really starts off [goes from start] beginning January.
'Til then!

-------------
Guess I'd better check my guess with Babelfish.
http://babelfish.altavista.com/tr

Babelfish says:
"Welcome on the web-unwieldly of the team of the university Utrecht. At present we enjoy our holiday, but it is the intention that the web-unwieldly beginning January real of start goes. To then!"

===========================
BTW here is a link for Utrecht ITF (inst. theor. fysik)
http://www1.phys.uu.nl/wwwitf/

here are the two seminars that Loll organizes
http://www1.phys.uu.nl/wwwitf/Seminars/Grafiti.htm
http://www1.phys.uu.nl/wwwitf/Seminars/Quist.htm

you can see what various people have been giving talks about: Hanno Sahlmann, Joe Henson, Frank Saueressig, Artem Starodubtsev

some of the titles have links to abstracts---but not to slides or video (as in Perimeter case)

here are upcoming seminars at Utrecht ITF, probably an incomplete list
http://www1.phys.uu.nl/wwwitf/seminars.htm

the ITF is organized in two programs

The research In the Utrecht Institute is organized in two programs:

Quantum Gravity, Strings and Elementary Particles (QGSEP)

Condensed-Matter Theory, Statistical and Computational Physics

"QGSEP Mission statement

The main areas of research of the program are quantum gravity, quantum field theory, string theory and - since 2004 - cosmology. A common theme of much of our work is the investigation of nonperturbative properties of fundamental physical theories at very high energies, with and without supersymmetry. This concerns physical phenomena at or near the Planck scale, which cannot be adequately described by studying fluctuations around flat space-time. Within recent years, new conceptual insights, accompanied by the development of new mathematical tools, seem to have brought us closer to an understanding of the physics at these very small distances, although a complete theory is still lacking."

the institute has some snapshots of people, and some homepages online. anyone interested can poke around and see what there is:
http://www1.phys.uu.nl/wwwitf/People.htm

==============

Hanno Sahlmann just won the annual physics prize of the German Academy of Sciences at Göttingen. I saw earlier that he gave a talk at Göttingen in mid-November but I didn't know the occasion for the talk was receiving the prize.

marcus

Jan14-06, 12:39 PM

Today the Utrecht team began to compete for the prize in the Dutch "Battle of the Universities"

they have posted their first page of their pedagogical competition website---which is to be about Quantum Gravity and especially the triangulations path integral approach being developed at Utrecht.

It strikes me as curious that an obscure line of research like this could compete against a dozen other university websites with possibly more accessible and readily visualized topics! I wonder can Utrecht catch up with the others----several of the other teams have already been putting up stuff for several weeks (a month I think) and have gotten many votes.

I wonder what Utrecht will put up on their site, and if it can make an impression. Well, as usual I will try to use BABELFISH to translate what the Dutch webpage says:

======original=========

Welkom op de weblog van het team van Renate Loll. Wij zijn jong, gevarieerd en gemotiveerd en op deze weblog zullen we u de komende maanden meevoeren naar de diepste krochten en langs de grootste mysteries die ons universum te bieden heeft. Ons onderwerp? Heeft u zich wel eens afgevraagd waarom de ruimte 3 dimensies heeft? Hoe zijn ruimte en tijd eigenlijk ontstaan? Kan het zo zijn dat de ruimte om ons heen, die zo gauw bekeken leeg lijkt, toch een diepste structuur heeft? Met andere woorden: wat is dat ding eigenlijk dat wij ruimte noemen?

Iedereen kan dit soort simpele vragen stellen. Wat velen echter niet weten is dat deze vragen een grote rol spelen in de zoektocht naar een van de laatste missende verbindingen in het hedendaagse onderzoek naar de fundamentele werking van de natuur. Het probleem is dat men geen idee heeft hoe het universum beschreven moet worden op de kleinst denkbare schaal. Theorieën die op astronomisch grote schaal, op menselijke en ook op atomaire schaal perfect hun werk doen, spreken elkaar tegen wanneer ze elkaar ontmoeten op de kleinste schalen die ons universum kent. Er is een massale zoektocht ingezet naar een theorie die dit gat zou moeten opvullen, een theorie die nu door het leven gaat als de kwantumtheorie voor de zwaartekracht.

De onderzoeksgroep van Renate Loll en haar collega’s is bezig met het ontwikkelen van zo’n theorie. Zij construeren ruimte en tijd uit kleine driehoekige bouwstenen. Dit wiskundige model heeft als ultiem doel een goede beschrijving op te leveren van hoe ons universum werkt op de kleinst mogelijke schaal.

Een van de grote doorbraken van de theorie was dat ze op grote schalen een ruimtetijd laat zien zoals wij deze kennen (3 ruimte- en 1 tijdsdimensie). Sindsdien heeft haar theorie vele subsidies in de wacht gesleept. De laatste en meest verbazingwekkende resultaten zijn dat het universum waarin wij leven op de kleinste schaal juist niet noodzakelijk vierdimensionaal is, maar dat hoe verder je inzoomt op een klein stukje ruimte, hoe meer het er op begint te blijken dat er slechts 2 dimensies overblijven.

Ons team bestaat uit 7 enthousiastelingen. Renate Loll is hoogleraar in de theoretische natuurkunde. Willem Westra is derdejaars AIO en werkt samen met Renate aan deze theorie. Sweitse van Leeuwen en Arjon van Lange zijn actief als bestuursleden van de studievereniging A-Eskwadraat. In ons midden hebben zich ook drie tweedejaarsstudenten zo moedig getoond zich in het stof der ruimtetijd te bijten, te weten Philip Klop, Quirine Krol en Egbert Rijke (natuur- en wiskunde).

De komende maanden zullen we stap voor stap afdalen naar de onmetelijke diepten, in de verbazingwekkende, maar bovenal die prachtige woeste zee van ruimtetijd, waarvan steeds meer verrassende aspecten aan het licht zullen komen. We zullen de weblog gebruiken om u de verhalen te vertellen achter een van de grootste zoektochten binnen de natuurkunde van vandaag, we zullen u vertellen hoe het er allemaal werkelijk uit ziet en vragen waarop u misschien niet eens het antwoord verwachtte zullen helder uitgelicht worden, en tot slot zal langzamerhand duidelijk worden wat u allemaal te wachten staat. Houd ons dus in de gaten!
============================

marcus

Jan14-06, 01:09 PM

here is the first draft of the translation from dutch to english:

Welcome on the weblog of the team of Renate Loll. We are young, varied and motivated and on these weblog we you will sail too the coming months to the deepest krochten and along the largest mysteries universum has us which to offer. Our subject? Why has the space 3 sometimes wondered you dimensions has himself? How do its space and time in fact arise? Can it be this way that the space for our gone, which examined this way rapidly empty seems, nevertheless a deepest structure has? In other words: what is that thing in fact that we call space? Everyone can ask simple couples to this type. What many however do not know is that these questions play a large role in the search to of the last missing connections in the contemporary study into the fundamental functioning of nature. The problem is that one has no idea how the universum must be described on the smallest conceivable scale. Theories which do on astronomically large scale, at human and also on atomic scale perfectly their work, speak each other against when they meet each other on the smallest scales which our universum has. A massive search has been used to a theory which this breach would have fill up, a theory which goes now by living as the kwantumtheorie for the gravitation. The research group of Renate Loll and its colleagues are busy with developing such a theory. They construct space and time from small triangular construction toes. This mathematical model has as an ultimate aim a good of producing description of how our universum works on the smallest possible scale. Of the large openings of the theory was that she lets a space time know on large scales see such as we these (3 spaces - and 1 time dimension). Its theory has dragged a lot of subsidies in the guard since then. The last and most surprising results are that the universum in which we live on the smallest scale correctly not necessary four-dimensional is, but that how further you zoom in on a small bit space, how starts more it there on appear that dimensions there only 2 remain. Our team exists from 7 enthousiastelingen. Renate Loll are hoogleraar in theoretical physics. Willem Westra are derdejaars AIO and cooperate with Renate to this theory. Sweitse van Leeuwen and Arjon van Lange is active as governing board members of the study association AES2. In our middle Second year students also three this way in the substance of the space time to bite itself, namely know have bravely shown Philip Klop, Quirine Krol and Egbert Rijke (nature - and maths). The coming months we will descend inch by inch to the immense depths, in the surprising, but above all that splendid savage sea of space time, of which more and more surprising aspects will come to light. We the weblog uses will tell the tales you behind of the largest searches within physics of today, we will tell you how it sees all really and asks on which you perhaps not even expected the answer will clearly be taken out, and finally gradually clear will become what you all to wait state. Watch us therefore!

=========
note that Krol means "caterwaul" and so babelfish translated the name of one of the team members

this is not bad, congratulations babelfish for saying this:

above all that splendid savage sea of space time...

the dutch original does not have such force:
"maar bovenal die prachtige woeste zee van ruimtetijd"

marcus

Jan14-06, 08:00 PM

mygod the team is young!

look at Quirine Krol

and
Philip Klop

http://www.phys.uu.nl/~sons/erg

Pietjuh

Jan16-06, 05:06 PM

I'm from the Netherlands, so I will try to give a translation of the text. But beware, my english grammar isn't that good as you guys :rolleyes:

--------------------

Welcome to our weblog:

Welcome to the weblog of the team of Renate Loll. We are young, varied and motivated and on this weblog we shall take you the next few months to the deepest places and along the biggest mysteries our universe has to offer us. Our subject? Have you ever wondered why space has 3 dimensions? How where space and time actually created? Could it be that the space around us, which at a glance seems empty, has a deepest structure? In other words: what is it that we call space?

Everyone could ask these kind of simple questions. What many do not know however, is that these questions play a big role in the search to one of the last missing connections in contemporary research on the fundamental workings of nature. The problem is that no one really knows how to describe the universe on the smallest possible scale. Theories that work perfectly on astronomical scales, on human and on atomic scale, contradict each other when they meet at the smallest scales which exist in our universe. There's a massive search started to find a theory which should fill up this hole, a theory that's now called quantum gravity.

The research group of Renate Loll and her colleagues works on the development of such a theory. They construct space and time out of small triangular building blocks. The ultimate purpose of this mathematical model is to give a good description on how our universe works at the smallest possible scale.

One of the greatest break-throughs of this theory was that it showed a spacetime we knew on large scales (3 space and 1 time dimension). Since then her theory has collected many fundings. The last and most awe struck results are that the universe we live in doesn't neseccary have to be 4 dimensional on the smallest scale, but the more you zoom in on this small piece of space, the more it starts to like there are only 2 dimensions left.

Our team consist of 7 enthousiasts. Renate Loll is a professor in theoretical physics. Willem Westra is a third year PhD and works together with Renate Loll on this theory. Sweitse van Leeuwen and Arjon van Lange are active as members of the board of the student association A-es kwadraat. In the middle we also have 3 second year students, brave enough to try to study spacetime, namely Philipe Klop, Quirine Krol and Egbert Rijke (physics and mathematics).

In the following months we will descend step by step into immense depths, into the most amazing, but foremost into the beautiful wild sea of spacetime, from which more and more surprising aspects will come to light. We shall use this weblog to tell you the stories of one of the greatest voyages in physics to this day, we shall tell you what it really looks like, and questions on which you might even haven't got a clue, shall be clearly explained, and it should be clear by now what's in store for you. So watch this site!

------------------------

There is also a famous wheatherman in the netherlands called Erwin Krol. But I don't they are family.

Pietjuh

Jan16-06, 05:11 PM

mygod the team is young!
look at Quirine Krol
and
Philip Klop
http://www.phys.uu.nl/~sons/erg

It's not that those 2 are already doing the heavy stuff. They are only second year students. In Utrecht I see it's the case where they have to follow a course for which they have to do a small research project in one of the research groups at the university, but which is really simplified, but still very interesting for them.

marcus

Jan17-06, 08:42 PM

I'm from the Netherlands, so I will try to give a translation of the text. But beware, my english grammar isn't that good as you guys :rolleyes:
...
There is also a famous wheatherman in the netherlands called Erwin Krol. But I don't they are family.

Pietjuh your english grammar is fine (at least by my simple standards!) that is a highly readable translation. THANKS. it helps to have a real translation instead of babelfish

About one of the team, called Quirine Krol, there is a dutch professional SCULPTOR by the name of Krol. I think perhaps it could be Quirine's mother. It doesnt matter except that in some kind of physics it could help to have a very strong 3D imagination and memory, as one might inherit from a scuptor parent.

Perhaps you should visit their site :smile:
leave them a message. They are already answering the blog at:

http://www.academischejaarprijs.nl/utrecht/

In other Utrecht news, Joe Henson, most recently from California, now a postdoc working for Renate Loll, has posted his first SOLO research paper on arxiv and gotten it accepted for publication.

He posted it today
http://arxiv.org/abs/gr-qc/0601069
Constructing an interval of Minkowski space from a causal set
Joe Henson
8 pages, one figure; accepted for publication in Classical and Quantum Gravity Letters
"A criticism sometimes made of the causal set quantum gravity program is that there is no practical scheme for identifying manifoldlike causal sets and finding embeddings of them into manifolds. A computational method for constructing an approximate embedding of a small manifoldlike causal set into Minkowski space (or any spacetime that is approximately flat at short scales) is given, and tested in the 2 dimensional case. This method can also be used to determine how manifoldlike a causal set is, and conversely to define scales of manifoldlikeness."

In the past, Joe has co-authored with Fay Dowker and Rafael Sorkin among others.

Chronos

Jan18-06, 01:36 AM

Chess is four dimensional, so this does not seem to be a terribly complicated contest.

marcus

Jan25-06, 06:25 PM

the climate for Quantum Gravity seems to be subtly different in Europe from what it is in the USA. Earlier we had a translation of an interview with Hermann Nicolai in the German newspaper DIE ZEIT (analog of the NY Times)

One reason to keep track of the general audience press is to understand better the surroundings and situation of the European QG community (Loll at Utrecht, Rovelli at Marseille, their groups, and others).

Today Peter Woit had links to a couple of new things in German.

Here is DIE ZEIT interview with Martin Carrier, philosopher of science.
http://zeus.zeit.de/text/2006/05/N-Interview_Carrier

Here is a DIE ZEIT article by Max Rauner
http://zeus.zeit.de/text/2006/05/Kosmologie

marcus

Jan25-06, 06:40 PM

Out!
Physics is in the crisis: The dream of the world formula burst, the new theories is hardly more examinable. Does it at all still concern in the cosmology science?

by Max Rauner

Free love, LSD, anti-war demo. Leonard Susskind took part in all that "and still more", as he stresses. Afterwards it became a physics professor at the American elite university Stanford, in the heart remained it a rebel. Now Susskind wrote a book, which shifts its colleagues in riot. If it keeps right, is physics at the end. Or completely at the beginning.

Originally Susskind was taken off to find the world formula a all-comprehensive theory, which describes the Big Bang just like the nano-world. For a long time it waehnte itself close to. With the most brilliant physicists and mathematicians he developed the stringer theory in the eighties, the best candidates for a world formula. Before six years the hope of the physicists got a first tear, when it showed up that this theory supplies many solutions almost infinitely. Now Susskind Ernst makes: In its book it postulates The Cosmic Landscape the fact that the theoretical solutions are not an excrescence of mathematics but to material in each case would correspond existing university verses.

However would be called: There are innumerable other worlds beside our well-known universe – and in everyone this own laws of nature apply for university verses. Thus however the search according to the world formula would be led ad absurdum. More badly still: Whether actually it exists to other university verses or not, leaves itself practically to never examine. And then the question arises whether such a physics can be considered at all still as natural science.

No miracle that among physicists a violent discussion was inflamed. In the controversy it goes over the relationship of theory and reality, over coincidence and necessity, physics and Metaphysik. Go around exploding, shrinking, and one on the other hitting worlds – and around the question whether the physicists have still all cups in the cabinet

To the cosmological offense now a heavy depression comes

Cosmological principle debates shook always also the self understanding of humans. Before 500 years Nikolaus Kopernikus fell the geocentric conception of the world and set the sun into the center of the universe. Driving out of the navel of the world described Sigmund Freud later than "cosmological offense" of mankind. Soon it became clear that the sun is only one star in the backyard of the Milky Way and the Milky Way only one of but billions other galaxies in the universe. The fact that the physicists doubt now also still the however position of our universe appears there only consistent.

According to Susskind we live "in an infinitely small bag in an enormous Megaversum". Our world would be therefore only a kind philanthropic niche, besides however gives it innumerable other university verses. Some of them are empty and boring, others exist for a few milliseconds, a hand fully stars, planets and even lives brought out. This conception of a multi or mega+verse around gives it of course longer. New it is however that meanwhile not only a few philosophically inspired crank in it believe, but to a certain extent the guidance elite of theoretical physics. Leonard Susskind, and other one with it, is anyhow safe itself: If philosophers and physicists look back in one hundred years, they will describe the today's time as that period, in which the concept of the only universe was replaced in favor of the conception one multi-verse around.

But if Kopernikus’ Theory an offense was, is the Multiversum a heavy depression. Thus mankind would pull itself back on a completely insignificant, coincidental island in the cosmic ocean. Us only the comfort remains that there are nevertheless organisms on this island, which are intelligent enough to argue about it.

Scientifically seen, that is hauptproblem of this conception however their examinableness: From where are we to know whether the theory of the multiple worlds is actually correct? Even if there were many other university verses really, we could never throw a view of it. Still is science? Or does physics thereby approach the Esoterik, in which much is only maintained, but nothing proven or refutable is? The philosopher Karl Popper set up once to the maxim that scientific theories should be so constituted that one disproves it in principle, therefore falsifizieren can. If one gives this guiding principle up, a grundpfeiler of the natural science comes into the wanken.

The criticism at Susskinds theses is accordingly hard. "I consider the beginning dangerous", say Paul Steinhardt of the Princeton University. "the science would come to a depressing end." The stringer theoretician Brian Greene feared, the idea can hold scientists to look for more deeply lying explanations. And the cosmologist Lee Smolin of the perimeter of institutes in Waterloo, Canada, grumbles: "Lenny Susskind errs, and he will see that he errs." One can present gladly ideas, "however if one a theory has, which predicts neither something avowedly nor something, then stops one making science."

But the multi-verse around theory has just as prominent advocates. "our whole universe is a fruitful oasis within multi-verse around", says the astrophysicist Sir Martin Rees, president of the venerable British Royal Society. Andrei lime tree of the Stanford University, to which its colleagues sometimes with charm-cheat maintains, already simulated the Multiversum on the computer and placed pictures of it on its Website ("Kandinsky Universen"). Even the Nobelpreistraeger steven vineyard, a solid, highly estimated theoretician, shows up openly. "I am not convinced yet of the Multiversum, but I take the possibility seriously."

The controversy was overdue. Because with all success physics to today no answer to the fundamental question has: Why is the world straight so constituted, how we find it? Or, in the words of Einstein: "could God have created the world also differently?" In the meantime we know that laws of nature and natural constants are so finely adjusted that the smallest deviations would have fatal consequences, anyhow for the existence of humans. But an explanation of this be astonished-worth phenomenon physics did not come more near.

Until today two large theories stand next to each other like marriage partners, who sleep in separate beds: _ Einstein relativity theory and the quantum theory. With the one can one space, time and cosmological structures compute, with the other one the behavior of atoms and elementary particles. Both are extremely efficient in their range, but they do not find simply to each other. In the Big Bang they fail, too extremely are conditions in the Big fear for. And why light is fast approximately 300000 kilometers per second and a hydrogen atom weighs straight 1.67 time 10-27 gram, the theories cannot explain also. Dozens of such natural constants must insert the physicists quasi by hand into the equations.

"as young physicists hoped I to find beauty and elegance in the laws of nature", remembers Leonard Susskind. As his father as plumbers shifted the pipes, right-angled, parallel, somehow aesthetically, then he imagined physics. "instead I found a depressing disorder." That was end of the sixties. In the seventies the situation improved, in the Achtzigern became the physicists euphorically. A new theory made hope, it for them described elementary particles no longer than punctiform particles, but than swinging strings or threads. These stringers are too small, in order ever directly to be observed to be able (approximately 10-33 centimeters), but with this trick could mathematical infinities in the equations be avoided. Even the gravitation strength from relativity theory found its place in the abstract thought building. So far however the stringer theory is so complicated that many characteristics lie multi-verse around in the dark. For example it postulates eleven dimensions, by which some are microscopically "rolled up", so that we notice only three space dimensions.

Michio Kaku compares the stringer theory in its new book in the parallel universe with a small, beautiful pebble, which the physicists find with a migration by the desert: "as we the sand aside sweep, state we that it concerns in reality the point of an enormous pyramid, which lies buried under tons by sand. After decades we discover mysterious hieroglyphics, hidden chambers and tunnels. A daily we will penetrate on the lowest level and the gate will finally up-push."

Which formulates Kaku so blumig, is the dream of the world formula. But that is now burst – says Susskind, which in the meantime a white beard and a Halbglatze decorate: "the beauty became the beast." After Susskinds computations the stringer theory has at present 10500 solutions, which is practically infinite. Until Susskinds appears book The Cosmic Landscape on German, still some powers of ten at university verses could come. Instead of talking from a pyramid to, the Stanford professor sketches now the picture of a boundless imaginary landscape, which our cosmos same. In this landscape there are mountains, valleys and hochebenen. And in each valley another universe lies. Some look like ours, most exist only briefly, before in the valley again a new universe is born. Only unfortunately: One does not come from a valley into the other one. Whether actually exist to possible other university verses, one can never determine.

Such not examinable theories drive the physicist Lee Smolin the cold sweat on the forehead. If physics gives the principle up of the examinableness, then Smolin warns, comes it into the proximity of religious theories as for instance the creation teachings of intelligently the Design. "the danger lies directly before our entry door", says Smolin. The catholic church again the many world theory is not religion compatible enough. Thus the Viennese cardinal Christoph beautiful fount geisselte with his much considered attack on the evolution theory in the past year explicitly also the hypothesis of the Multiversum. It contradicts the overwhelming vouchers for purpose and Design of nature.

If there are sufficient university verses, one of it must be habitable

Hard-boiled physicists such as Steven Weinberg leave such church attacks cold. "it is beautiful that cosmology is now also getting a little of the attention, which evolution theory enjoys these days" comments Weinberg (the expression of beautiful sounds sarcastic. Straight one on atheistisch gesinnte scientists such as Weinberg exercises the speculative thesis of the Multiversum a special attraction. They struck themselves so far in vain with the question around, to bring out why the cosmos seems as created, in order stars, planets and sometime also intelligent life. The almost unbelievable fine tuning of the natural constants in favor of a habitable universe dissolves in the multi-verse around theory however in well-being favours. According to it the existence of a philanthropic universe is a pure consequence of the statistics: Under 10500 university verses must be simple ours thereby, six correct ones as somebody in the Lotto taps, if enough people along-play. Martin Rees compares the Multiversum with a large dress business. "if the selection of dresses enough is large, is not not surprised we to find something fitting" – indeed our own universe.

Could God have created thus the world also differently? Yes, the multi-verse around theoreticians answer and set still one drauf: It used its clearance extensively. Stupidly only that this conception leads to an almost inflationary arbitraryness in the description of the reality.

How thus does it continue in physics? Who not so that contently give may myself the fact that either our universe is pure coincidence or the dear God has all straight so hang-curved, as we find it, has the choice between three possibilities.

The principle hope. Finally is the stringer theory still for a long time not finished, perhaps the physicists somewhat surveyed. "it is much too early, to give up", says Princeton professor Paul Steinhardt, who set up its own theory of an eternally returning, cyclic universe. Who knows, perhaps still everything turns to the good one at the end, and an extended stringer theory describes a daily exactly a universe, i.e. ours.

The escape forward. We existed really accept, the Multiversum. Then are appropriate for other university verses outside of our own, and even the best telescope could never see it. Perhaps but other forecasts can be derived from the theory, which one could examine a daily, at least in our universe, empirically. At the European research lab CERN in Geneva 2007 the Large hadron Collider (LHC) is to go into enterprise. Perhaps this gigantic particle accelerator finds a reference to the hidden space dimensions, which the theory predicts.

Finally the possibility of the mistake remains. "the stringer theory is simply and simply wrong", believes for example Peter Woit. The mathematician of the Columbia University in New York operates the anti-stringer Web log emergency even wrong and demands: "a correct theory should have a limited number of solutions." As alternative candidates for such a theory some researchers discuss the loop quantum gravitation in such a way specified, which is developed among other things at Albert-Einstein-Institut in potsdam. According to it space-time from tiny pellets is developed. It gets along without the many dimensions and university verses of the stringer theory. The problem is bare: Also this theory supplies so far no empirically examinable forecasts.

After 2500 years physics seems again arrived at the beginning

German physicists play almost no role in the heated debate over the Multiversum. Perhaps the Sozialisation of the Bronx is missing to them, where Leonard Susskind and Steven Weinberg attended the same High School. But in this country philosophical analysis is maintained. R. Hedrich of the University of Giessen got a request at the German research council granted, in order to arrange the arguments of the physics debate. Who calls the philosopher, classical music in the background hears. "the theory of the Multiversum is reasonable in its logic", says Hedrich, "however not reasonably enough to be around science." The research program reminds it of that the Vorsokratiker in the old Greece: It is "metaphysical thinking about nature".

Did physics arrive with it after 2500 years again with its beginnings? Lee Smolin, joint founder of the loop quantum gravitation, swears to its colleagues not to go to the multi-verse around theory on the glue: "the progress of the science in the last 400 years is based on a few ethical basic rules, and Falsifizierbarkeit is one of it." One must absolutely maintain Poppers requirement of the refutableness in principle. Leonard Susskind is there fundamental different opinion: "follows property scientific practice no abstract set of rules, which for us a few philosopher prescribes, maintains" he in a hostile exchange with Lee Smolin on the Website edge.org. Smolin plays itself like an arbitrator over good and bad science up. "the natural science is the horse, which pulls the truck of philosophy. Do not let us the truck before the horse stretch."

Smolin has by the way its own theory of the universe. University verses could come as baby university verses in black holes to the world and afterwards a kind Darwin selection process subjected be. That is even refutable, insures Smolin, by the observation of neutron stars so mentioned. But again different researchers doubt that.

"Hypothesis non fingo", said Newton, I make no hypotheses. His current professional colleague is less restrained. It almost seems as if inventing new universes serves as pastime, or a kind of finger exercise, until the LHC finally starts operating. However, simply to dismiss the bizarre world-pictures of the cosmologists and stringer theoreticians however simply as craziness would be too easy. "As long as no one has a better idea, one must keep trying this," says the Giessener philosopher of Reiner Hedrich, even if the premise seems paradoxical, "trying out, even knowing that it doesn't work this way."

Until the cosmologists have again firm soil under the feet, one will have to be content provisionally with another measure for the reliability of a theory: Royal Society president Martin Rees would BET HIS DOG on the thesis of the Multiverse, and Andrei Linde of Stanford University would even bet his life. And Steven Weinberg announced in November in an essay with the title Living in the Multiverse, he has already has enough confidence in the theory, "to bet both Andrei Linde's life and Martin Rees’ dog on it".

THE TIME 26.01.2006 NR.5

05/2006

marcus

Jan25-06, 06:43 PM

"there the familiar categories dissolve"

With the conception of infinitely many universes did Physics cross the border into Metaphysics? A discussion with the science philosopher Martin Carrier

DIE ZEIT: How many universes do you believe in personally?

Martin Carrier: One!

DIE ZEIT: Can you prove its uniqueness?

Carrier: No, but to me the earlier conception of a universe seems more reliable than what is accepted by stringer theoretician. Every one of their innumerable solutions would correspond to its own universe.

DIE ZEIT: Why do you doubt the stringer theory?

Carrier: There is a set of quality criteria for scientific theories. For instance the explanation of up-till-now not understood experiments and the forecast of new phenomena. The stringer theory fares there rather badly, because it – so far at least – simply offers no connection to concrete, understandable experiences.

DIE ZEIT: May one call then still natural science? Or did physics thereby cross the border into Metaphysics?

Carrier: We no longer make the strict distinction between science and Metaphysics, that used to be made in former times. Often there have been theories, which at first did not seem testable – but which sometime later achieved great empirical success. Take for example the conception of atoms: It was around since the ancient Greeks, but only after 1800 was it successfully confirmed by facts. Therefore one should hold back oneself with categorical statements about it, which now is strictly scientific and which not.

DIE ZEIT: Nevertheless there must be criteria for good and bad science.

Carrier: Surely. Those are quality benchmarks such as explanatory and predictive power, which I just mentioned. There is today a whole spectrum of such requirements, and one judges the efficiency of a theory by how well it fares on this multiple scale.

DIE ZEIT: That applies also to religiously motivated theories as for instance for the Christian creationism?

Carrier: Exactly. We do not say: "that is not science." Separate we determine: The explanation achievement of the creationism – which fossil finds or mismatchings of organisms concerns – pitifully badly, the reliability is miserable.

DIE ZEIT: Could be said not also about the stringer theory?

Carrier: Yes and no. Their explanation achievement is indeed rather poor. On the other side it that could still change. Also the kinetic heat theory in 19. Century was terribly unsuccessful long time. The theoreticians afterwards-ran only the experiences and tried to build somehow well-known phenomena into their theory to – exactly like the stringer theoreticians today. Only as 1905 Einstein the Brownian molecular movement explained, new effects was predicted, and thus their break-through succeeded to the theory.

DIE ZEIT: According to stringer theory the world has eleven dimensions. That understands nevertheless no more humans.

Carrier: The demand for understanding bar of modern physics is unfortunately futile nostalgia. It is correct that whole classical physics up to the beginning 20. Century of the idea was certain, the world was understandable. But this conception failed with quantum physics. The bizarre world of the quanta is completely unanschaulich, and the more we into it penetrate, understand we them the less.

DIE ZEIT: But perhaps it is only one question of the time, until we understand it.

Carrier: Reliably the understanding develops itself further. Take only the revolution of the Coperinican conception of the world. Which the contemporaries had at that time for difficulties to imagine a movement of the earth. Those could not notice it nevertheless at all! Also the further arsenal physical dimension such as atoms or fields blew up the imaginative power of a layman – today that is more or less common property/knowledge. But we did not digest the paging of quantum physics yet. There the familiar article categories dissolve, and we do not find appropriate terms for it.

DIE ZEIT: Is there a realization border in principle for humans?

Carrier: In the long run we do not know whether the world is understandable. Most physicists assume that the science successfully describes the reality and that we approach to the basic modules of the world. At the end the science would exhaust nature to a certain extent. It would be in addition, conceivable that behind each level of apparently elementary things a still more fundamental level opens itself.

DIE ZEIT: What do we make with a theory, which refers to innumerable further university verses, without being able to make them accessible for the experience?

Carrier: There is a way out. We take general relativity theory: Also we can examine their philosophy, the Geometrisierung of the gravitation, not directly. But we measure their consequences – Red shift, clock slowing down – and believe therefore also in the basic principle. We think ourselves capable of even statements about it, which happens, if an astronaut falls into a black hole – even if we that will empirically never be able to examine.

DIE ZEIT: We accept, we would be in the middle in a scientific revolution, like at times of Copernicus or Einstein. What could we notice that?

Carrier: That is difficult to say. It takes every now and then decades, to scientific pagings in the scientific community recognition is often still longer and, until it accepts the public. Darwinism was accepted only a half century after the formulation by Darwin in the science. Sometimes revolutions are also broken off, and one returns to old conceptions. Contemporaries notice frequently nothing from the revolutions, which take place before their eyes.

DIE ZEIT: Could we be with that infinitely many universes likewise? Will this conception our grandchildren appear completely natural?

Carrier: That would be possible. Perhaps the stringer theory comes sometime to meaningful successes, and then – history will show – one could accept quite also consequences, which are not accessible to the direct experience. But in any place we need a confirmation. Never in the history of the science a theory was accepted, which would have brought not also empirical progress.

Max Rauner and Ulrich Schnabel were the interviewers.

DIE ZEIT 26.01.2006 NR.5

===============
EDIT, my comment is that I think Max Rauner and Ulrich Schnabel are working for Die Zeit and that they did the interview with Martin Carrier.

selfAdjoint

Jan26-06, 04:27 PM

Do I dare conjecture that Rauner means "carrier" in German?

marcus

Jan26-06, 05:19 PM

Do I dare conjecture that Rauner means "carrier" in German?
:biggrin:

Isn't babelfish awful. I love how bad the translation is and almost don't want to edit and repair it.

Actually here is a picture of Prof. Dr. Martin Carrier
http://www.uni-bielefeld.de/ZIF/Personen/Taetigkeiten/carrier.html
he is real
not a phantom of babelfish

marcus

Jan30-06, 12:48 PM

Finally yesterday someone posted a real translation into English of the Max Rauner article. Peter Woit noted it.

http://rabett.blogspot.com/2006/01/lost-this-is-something-of-new.html

The translator is Eli Rabett. He did not post a translation of the interview as far as I know.

marcus

Feb7-06, 07:01 PM

the Utrecht team competition website now has some content
as of 6 February
http://www.academischejaarprijs.nl/utrecht/

IT'S ALL IN DUTCH, I CAN'T UNDERSTAND IT!!!

hey, click on "meer", cartoon drawings by Renate Loll and also by TL, and by ER

http://www.academischejaarprijs.nl/utrecht/?p=4#more-4

I guess ER is Egbert Rijke

Loll draws pretty good cartoons.

marcus

Feb14-06, 12:06 PM

Smots

Mar1-06, 05:30 AM

Daniele Oriti, of Cambridge, gave the Quantum Gravity Seminar talk at Utrecht yesterday (13 February)

Renate Loll will give the Physics Colloquium talk at her University on 24 February, so says her website.

It would be interesting to hear about these talks from anyone who is in Utrecht---like PF poster Timbuktu and others---and who happens to attend.

I was at the talk by Renate on February 24th, and it was pretty interesting! The whole lecture room was packed to the max, with people sitting on stairs and standing against the walls :-). The talk gave me some more insight in what Loll has done and how she has done it. I tried reading her two latest papers, but got lost in terminology half-way through the paper :rolleyes: . One of the people of the audience asked: 'So how is this any different from say, astrology?'. That was pretty funny.

Also, another person asked if she had now unified quantum gravity and relativity.

marcus

Mar1-06, 08:40 AM

I was at the talk by Renate on February 24th, and it was pretty interesting! The whole lecture room was packed to the max, with people sitting on stairs and standing against the walls :-). The talk gave me some more insight in what Loll has done and how she has done it. I tried reading her two latest papers, but got lost in terminology half-way through the paper :rolleyes: . One of the people of the audience asked: 'So how is this any different from say, astrology?'. That was pretty funny.

Also, another person asked if she had now unified quantum gravity and relativity.

thanks, Smots!
It's great to have a first-hand report.
I would have liked to be there, to hear both the main talk and her response to the audience questions.

One thing Perimeter Institute has over Utrecht ITP is that they put talks like that up on the web---for anyone to watch. they have a talk by Loll, given last year actually, in case anyone is interested.

=====================

I see the Utrecht team has more up at their competition website:

http://www.academischejaarprijs.nl/utrecht/?p=5#more-5

http://www.academischejaarprijs.nl/utrecht/?p=7#more-7

the second link is to material they just put up today (1 March)
among other things, cartoons by Egbert Rijke

marcus

Mar7-06, 09:37 AM

The Utrecht team is making a kind of book. the book has charming funny drawings by Egbert Rijke
It comes in chapters, which (if I understand the dutch word) they call "Uploadings"

So they have Uploading 1, and Uploading 2, and Uploading 3, and more to come.

to me it sounds better to say "Installment"

Installment 1 (6 February)
http://www.academischejaarprijs.nl/utrecht/?p=5#more-5

Installment 2 (1 March)
http://www.academischejaarprijs.nl/utrecht/?p=7#more-7

Installment 3 (5 March)
http://www.academischejaarprijs.nl/utrecht/?p=8#more-8

this could become a hardcopy illustrated book which would be a good present to give a young person----highschool or college student---as an enjoyable intuitive introduction to the classical and quantum ideas of Spacetime.

the fact is Egbert Rijke has talent and the drawings have a fresh, not-too-serious, light-hearted character. And we have seen already for over a year that Loll is a good writer. She has a conceptual clear style and choice of metaphor that engages the reader's attention. Personally I only know how she writes in English, but thanks to several people we have translations of interviews and other writing that gives some idea that she comes across at least as strong in Dutch as she does in English.

so these installments could, if it works out, become a useful and delightful little book. Someday we may see an English version

I remember from my childhood a funny book of history and/or geography by a Dutchman, with his own drawings. I think his name was Van Loon, or something like that----I remember it sounded loony. Informal illustrated lighthearted account of otherwise daunting subjects is a genre.

Yes! I just checked. Remembered the name right! he was Hendrik Willem van Loon and his 1921 book The Story of Mankind won the very first Newberry Medal for Children's Lit ever awarded, in 1922.
http://en.wikipedia.org/wiki/Hendrik_Willem_van_Loon
I see that it is available in electronic version from the Gutenberg project
http://www.gutenberg.org/etext/754

Actually there were two books, the history and another called Van Loon's Geography which came out in 1932. I may only have seen the Geography, can't remember.

Smots

Mar11-06, 04:07 PM

VEry nice! Thanks for that nice book :).

marcus

Mar16-06, 04:50 PM

Hey Quirine!
just saw you were here visiting us at PF!
arent you the physics student on Loll's team, who has a sculptor in the family?
sculpture is good background for physics---concrete and visual!
any news from the website competition?

===================
I better update the Loll/Utrecht news:

Loll just posted two papers that I didnt record here yet. here is one with Dario Benedetti
http://arxiv.org/abs/hep-lat/0603013
Unexpected Spin-Off from Quantum Gravity
D. Benedetti (U. Utrecht), R. Loll (U. Utrecht)
10 pages, 4 figures

"We propose a novel way of investigating the universal properties of spin systems by coupling them to an ensemble of causal dynamically triangulated lattices, instead of studying them on a fixed regular or random lattice. Somewhat surprisingly, graph-counting methods to extract high- or low-temperature series expansions can be adapted to this case. For the two-dimensional Ising model, we present evidence that this ameliorates the singularity structure of thermodynamic functions in the complex plane, and improves the convergence of the power series."
============

here is one with Willem Westra

http://arxiv.org/abs/hep-th/0603079
Nonperturbative sum over topologies in 2D Lorentzian quantum gravity
R. Loll (U. Utrecht), W. Westra (U. Utrecht), S. Zohren (U. Utrecht, RWTH Aachen)
10 pages, 4 figures. Talk given by S. Zohren at the Albert Einstein Century International Conference (Paris, July 18-22 2005)

"The recent progress in the Causal Dynamical Triangulations (CDT) approach to quantum gravity indicates that gravitation is nonperturbatively renormalizable. We review some of the latest results in 1+1 and 3+1 dimensions with special emphasis on the 1+1 model. In particular we discuss a nonperturbative implementation of the sum over topologies in the gravitational path integral in 1+1 dimensions. The dynamics of this model shows that the presence of infinitesimal wormholes leads to a decrease in the effective cosmological constant. Similar ideas have been considered in the past by Coleman and others in the formal setting of 4D Euclidean path integrals. A remarkable property of the model is that in the continuum limit we obtain a finite space-time density of microscopic wormholes without assuming fundamental discreteness. This shows that one can in principle make sense out of a gravitational path integral including a sum over topologies, provided one imposes suitable kinematical restrictions on the state-space that preserve large scale causality."

Quirine

Mar16-06, 05:09 PM

Hi there,
Yes I'm indeed a member of the team
First I want to apologize for the very bad English,
It is really funny to read that some of you are following our weblog,
I red that there were a few questions about my name. So I'll give a quick answer to them.
No I'm not related to the famous (well in the Netherlands he is) weather man Erwin Krol. Also my mother is not a sculptor. I'm just an extract of a two musicians, nobody ever heard of.
You also wanted to know who TL was? It stands just for Team Loll. All the drawings are in fact made by Egbert Rijke. We are lucky to have him in our team.
The three youngest of the group (me included) are not following any course for this project,we are just interested in Renates theory and we do all this in our spare time. I'm really glad to have this upportunity.
so if there are any questions, ask them, I'll see what I can do,
greetings,
Quirine

marcus

Mar16-06, 05:24 PM

Hey People!
this is great! we have a Physicsforums contact with Loll's team of Utrecht students.
Hello Quirine,
no I dont have any questions just now, but please look in from time to time---maybe I or somebody will think of some things we want to know that you can tell us!

several of us here also, like you, are interested in Loll's CDT approach to exploring the fundamental nature of spacetime

also Renate Loll kicks butt-----and she writes pretty good English too.

is it alright to post this SONS link
http://www.phys.uu.nl/~sons/index.php?option=com_content&task=view&id=16&Itemid=56
it has your student organization photo so we can have an idea how you look
if this is not OK, say and I will erase the link

(it is all right to be from musicians family, I am right now listening to a clarinet quintet in A major by Mozart, he liked the clarinet and used to play it himself and he wrote some sweet music for it)

marcus

Mar16-06, 05:37 PM

Quirine, I just had a thought. Is there anything you would like US to think about or try to explain? you have indicated that we could ask you questions about Team Loll and your website competition, and you would try to answer.

we can reciprocate and say is there anything you would like us to try to explain? (we might not be able to but we could attempt it:smile: )

For example. I find Willem Westra work on topology-change very interesting. It allows spacetime to be frothy, like beer. or seltzer water.
you, Quirine, could ask us to explain WHY we think modeling microscopic very brief topology change in the Loll path integral is interesting. We could try to explain.

It is just an idea, maybe it would not work (after all, I am just an interested observer, not a QG expert).

Quirine

Mar16-06, 05:47 PM

that would be great, because for me it's only an vage intuition why this all makes sense.
Eversince I was a kid Triangles were very interesting. From Pyramids to geometry on secundary school. There was also a course where you must build our own dream house.. geuss what? Mine was build of tetrahedrons... Then I went to the University of Utrecht and there was suddenly Renate Loll with her triangulations, it catched my eye immediately.
So if you would be very kind to explain some things it would be really great

marcus

Mar16-06, 05:54 PM

...so if there are any questions, ask them, I'll see what I can do,
greetings,
Quirine

actually I have a question.
I am very curious to know something, if it is not awkward or inappropriate to be asking

I want very much to know how Willem is coming in the project to extend the topology-change result from 2D to 3D (or, if we could be so fortunate to 4D!)

my feeling is that it will be very hard to extend the result! I would like to know if there is any progress

Quirine

Mar16-06, 06:21 PM

well, I'm afraid I can't answer this technical questions myself, I would ask Willem to do so, but we all are running out of time, especially Renate en Willem, so I think you have to wait for that kind of answers. Maybe next year I will understand a bit of this all, but I think you can't wait for that...
In this case I will ask Willem tomorrow for a answer that I can understand and which I can tell you... Do you want to know it mathematically? Or Physically?
Renate explains this thing to other people, she uses a piece of paper which she crumples. It depends on how deep you look how many dimensions you measure/calculate. The strange thing about it is that you can also have solutions that varies from 2 till 3 dimensions, but I think you knew this already

marcus

Mar16-06, 06:27 PM

So if you would be very kind to explain some things it would be really great

it probably is not efficient for me to try to explain the basics of Loll's approach, you can get better teaching close to home!

but I can talk about some aspects, like why is Westra's work so interesting.

AFAIK (abbreviation for As Far As I Know) there is no other quantum model of spacetime that can handle the appearance of microscopic suddenly appearing and vanishing holes and bubbles in space.

Other QG models I think can only handle a spacetime that is like a continuous block-----the block can have a changing geometry, like Jello, that can bend and tremble-----but it cannot suddenly get a hole

in other QG models you cannot have suddenly tiny holes and tunnels that suddenly come into existence and then flicker out of existence.

but in Loll QG, if it is simplified down to a 2D world, you CAN have!

like a little bubble that appears for a moment and then goes away

the word that I think of is FIZZY, a space that is fizzy, like I remember my first drink of ginger ale, or so-called "sparkling water" the tiny bubbles are like sparks. you feel them prickly on the tongue

if Loll and Westra do not succeed in extending this fizziness to higher dimension that will still be OK-----the CDT is still a very good interesting approach

but if they succeed, then that would be a way in which the CDT approach is special, it would make it stand out before all others (AFAIK)

having holes and bubbles and tunnels that are very tiny, and which exist only for a moment, is an example of something that is called TOPOLOGY CHANGE
and so one can look back in the ARXIV (a kind of electronic online library) and find the 2003 papers of Loll and Westra about topology change in the 2D version of CDT.

they call it "topology change" because this sounds more serious than if they call it "fizzy spacetime"

be careful, maybe i am wrong or giving you the wrong idea.
check with Westra if this is the right picture

I am listening to an old recording of MOZART figaro sung in german by anneliese rothenberger, hermann prey and walter berry and the dresden philharmonic it is ABSOLUTELY FANTASTIC

marcus

Mar16-06, 07:22 PM

Do you want to know it mathematically? Or Physically?
...

Physically!

but actually, dont worry
if you are running short of time, dont bother with my question
just focus on what you have to do, the rest will easily wait

(sorry did not see your post until just now)

it is late at night there, yes?

marcus

Mar23-06, 08:51 PM

the Utrecht team has put up another chapter

http://www.academischejaarprijs.nl/utrecht/?p=9#more-9

with more of Egbert's drawings.

marcus

Mar24-06, 12:47 PM

Loll has an interview in the March 2006 Dutch edition of the Scientific American

http://www.phys.uu.nl/~loll/Web/press/RLoll_in_Sciam.pdf

4 pages, photographs, popular style writing (staple SciAm)

I wish we had a translation, of at least some highlights. It's all in Dutch
and babelfish usually doesnt do a very good job of automatic translation *gloom* :(

Pietjuh

Mar25-06, 12:17 PM

marcus

Mar25-06, 12:44 PM

If I find the time tonight, I will try to create a decent translation of it all. It's a long interview, so perhaps I will do it in a few installments.

(perhaps I should promote myself to Loll-translator) :rofl:

WOW THAT WOULD BE SO GREAT!!!!!

Don't be afraid to be selective either. If you are willing to translate even some----the parts you find most interesting or entertaining---that is also a big favor to us. Thanks!

Pietjuh

Mar29-06, 10:32 AM

The bubblebath of the cosmos

Madame Loll, why hasn't the physics at the planck scale used causality earlier on?
There was a good reason to do it. It considerably hard to build models of spacetime. By ignoring causality, the job became a lot easier.

A typical case of intellectual laziness?
Oh no, not at all. By simplifying the task, people were suddenly able to do calculations which were impossible before. From this one could also get very meaningfull results, despite taking assumptions you can't completely justify. This is always better than doing nothing at all. You should ofcourse look back at a certain moment en question if that simplification is still justifiable.

You thought that ignoring causality is no langer justifiable.
Doubting causality is ultimately just whishful thinking. Stephen Hawking hasn't made much progress in the last 25 years working on his research about the quantumstructure of spacetime -- and that's not even a controversial statement from myself!

Why do we need quantum foam?
On lower and lower scales quantumfluctuations will become increasingly intense. Some people say that these fluctuations will go look like a bubblebath, or even that they can rip spacetime apart. Although these are just metaphores. Realize that quantumfoam is a very vague concept! It isn't a classical phenomenon. We know that on the smallest scale something violent is happening to spacetime, and this unknown phenomenon is given the name quantumfoam.

Driehoekjes

You are constructing your model of quantumfoam with triangles. Why choose this shape?

The shape isn't that important actually. It's just a tool to build a model of spacetime. Eventually it doesn't matter which shape you use - triangles, squares or other shapes. My building blocks are in fact just imaginary substructures and are often misinterpreted. Consider that my building blocks are much smaller than the planck scale.

You are saying that to do chemistry experiments, you don't need a precise model of the structure of protons and neutrons.
Exactly. Besides, the choosing of the building blocks isn't the most difficult task. For example, I can create all kinds of structures with Lego bricks, that's fairly easy. But to create a moving structure is already a lot harder. That's also the case with the creation of a model of spacetime.
The building of such a structure is one thing, but to find out how such a structure quantumfluctuates is a lot harder. We have good reasons to assume that the dynamics of spacetime don't depend much on the type of building block.

How do you calculate such a model of spacetime?
We don't do a straightforward calculation, but use the principle of superposition. Imagine you want to know how a special little particle moves aroung - a particle so small that quantumeffects play a role. You can't assume that the particle just moves in a straight line from A to B. We therefore must describe the movement as a scala of possible routes such a particle may take - say a probability cloud of the movement. The sum of all those paths eventually gives you a good quantumdescription of the particle. In principle we do the same with spacetime. We take a large sum of all possible spacetimes. But naturally spacetime is much more complex than the movement of one particle.

By Thor! How does such a result look like?
You certainly have to ask yourself really good what kind of questions you ask, what you eventually want to calculate. And that's not an easy excercise. For example, you can ask yourself how you can determine the number of dimensions of the object you are calculating. There are several methods to do this. We can put, for example, extra building blocks in the model, to see how they spread in spacelike directions, but also in timelike directions. The dimensionality of the object follows from this spread.

marcus

Mar29-06, 12:54 PM

(perhaps I should promote myself to Loll-translator) :rofl:

Yes! Congratulations on your promotion! I hope you have some idea what a help it is. I like what Loll is saying here. It gives a fuller perspective on her research than what one gets by only looking at the journal articles. This is what the Scientific American magazine is good for! Many thanks, Pietjuh.

Here is the original Dutch SciAm article link, if someone wants to see the photographs or puzzle over what is the dutch word for "bubble bath" and stuff like that.

http://www.phys.uu.nl/~loll/Web/press/RLoll_in_Sciam.pdf

BTW I can read a few words, so I see from the bio-box that she was born in 1962 and studied in Freiburg and London, and has a son.

Also I see that in some of the un-translated parts she is talking about string theory, but I cannot quite tell what she is saying about it.

Pietjuh

Mar29-06, 03:49 PM

Also I see that in some of the un-translated parts she is talking about string theory, but I cannot quite tell what she is saying about it.

The interviewer asks what the link is between string theory and CDT, and specificaly about the difference in dimensions. She answers that the 2 theories have totally different starting points, and she doesn't want to elaborate on the experimental verification of string theory and CDT.

Then the interviewer asks if she believes there could be 11 dimensions. The answer is a bit vague, she thinks there might be some positive outcome from theories with extra dimensions because people have been working on it for so long.

The final part on the interview is mostly about things Loll doesnt know. They ask her how energy is incorporated in her theory. She says she simply doesnt know it yet, but she hopes that in the future she might be able to use CDT to explain dark matter.

marcus

Apr1-06, 05:05 PM

thanks Pietjuh!
for the summary as well as the translation.
I see you are at Leiden. this spring Loll had two talks scheduled at Leiden (8 March and 3 May). I dont remember if you said about this---did you happen to attend the 8 March?

I see that Laurent Freidel is talking at Utrecht on 1 May.
If anybody here can make it please do. You will not be disappointed he is doing exciting research and has a clear focused delivery.

Also if you go then please report to us some highlights of the talk or what the general message is. It is time for Freidel to be saying something about the 4D case, can he extend some of his 3D results.
Some weeks back, he had a paper with Baratin in the works, some implications for QG from feynman diagrams IIRC. Maybe he will refer to this paper in his talk.
=================
this month, April, Frank Saueressig (the name is easy to remember because it means sour vinegar) is giving a talk at Utrecht. Saueressig has co-authoried with Martin Reuter, who does QEG (quantum einstein gravity, asymptotically safe gravity) and who has found lower dimension at planck scale.

Possibly Saueressig could say something about QEG in his talk. Notice that both Jacques Distler (hostile comments) and John Baez (not so hostile) have discussed Reuter's work. Baez talked about it in TWF #228 just this past month (mid March). Baez said as it stands the work depends on a rough approximation and so some conclusions might be wrong, but that it was interesting and should be studied some more. Maybe one can improve the approximation and see if the conclusions still hold.

To anyone at Utrecht: if you hear Frank's talk on 27 April, please tell us what it is about.
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Renate Loll is now giving talks at various universities at a rate of about one per month:
Feb 24 Physics colloquium Utrecht University, The Netherlands

Mar 8 Conference talk Workshop "The World a Jigsaw - Tesselations in the Sciences", Lorentz Center, Leiden, The Netherlands

Apr 4 Conference talk ENRAGE Network Conference-cum-Workshop, International Centre for Mathematical Sciences, Edinburgh, UK

May 3 Ehrenfest Colloquium Leiden University, The Netherlands

Jun 8 Conference talk Theory CANADA 2 Conference, Perimeter Institute, Waterloo, Canada

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It is interesting that Loll will give a talk in June at the CANADA conference. It suggests that she will be based at Perimeter sometime this spring or summer, on a working visit.

the Canada conference is not an international conference. One would not invite someone to come from Holland just to give a talk. But Bianca Dittrich who is from Germany HAPPENS to be currently a postdoc at Perimeter and so she is giving a talk at this conference. Since Loll will be speaking I tend to assume that she will be temporarily based there and doing some work at Perimeter around that time.

Pietjuh

Apr10-06, 07:21 AM

I wasn't able to attend the talk in march, because I didn't know she had one! Thanks for pointing out she's also giving one at the general colloquium in may. I certainly plan to visit it!
I'm also seriously considering to apply for 'graduate school' at the university of Utrecht, because of the really interesting research that is being done there in theoretical physics. Here in leiden it's more oriented on condensed matter physics and biophysics.

marcus

Apr10-06, 09:41 AM

...Here in leiden it's more oriented on condensed matter physics and biophysics.

condensed matter is a growth area in physics research
and so (I think) must be applied physics related to bio, and medicine.
maybe the Leiden people are practical and smart, so they focus on areas that have plenty of career satisfaction and growth possibilities.

I am retired, and don't have to worry about these things. Also have idealistic non-practical tendencies. To me, investigating the fundamental nature of spacetime-and-matter is a great adventure. like going to the North Pole, or the South Pole used to be. but I would never ADVISE a young person to go into it----only if they have a passionate interest already and must do it.

otherwise I would say
1. astrophysics
2. condensed matter
3. bio and medicine-related
not necessarily in that order.

How did you get to become a reptile caretaker? I suppose that could mean either one of two things, that you are a reptile who takes care (possibly of humans) or a human who takes care of reptiles :smile:

I envy you because you live in Holland, which seems like a nice place, and are near Utrecht.

How long a drive is it from Leiden to Utrecht?

Laurent Freidel's talk at utrecht (at the Grafiti seminar that Loll organizes) on 1 May could turn out to be an important talk.

here is Loll website, and the seminar page:
http://www.phys.uu.nl/~loll/Web/title/title.html
http://www.phys.uu.nl/~loll/Web/seminars/seminars.html

It says that the Grafiti seminar is in room MG 401
and scheduled for Monday at 2PM

I think the next 5 years of advances in QG (including matter) will have a lot to do with computer simulation
"monte carlo" (which means randomized) simulation of histories of toy universes-----or random histories of chunks of spacetime-and-matter.
Loll has be one of the first to do these monte carlo simulations.
but they may also be done with OTHER kinds of models----like those that Laurent Freidel is investigating

Loll says that "Grafiti" stands for "Gravity-and-Fields-Tea"
so there is probably some tea to drink before or after the talk

Pietjuh

Apr10-06, 10:08 AM

condensed matter is a growth area in physics research
and so (I think) must be applied physics related to bio, and medicine.
maybe the Leiden people are practical and smart, so they focus on areas that have plenty of career satisfaction and growth possibilities.

The slogan here at the physics department of leiden is "Van meten tot weten", which roughly translates into "From measuring to knowledge". Here they don't concern themselves much with the fundamental issues of nature, but are a bit more down-to-earth in their research topics. We have a pretty large condensed matter group, mostly consisting of experimental groups and a small theory group. We also have a pretty good astroparticle physics group led by Ana Achucarro (she is also my advisor for my bachelorthesis on representation theory in elementary particle physics)

There are also many advantages for staying in leiden to do my masters degree, because here I'm garantueed to get a place, and I will not lose my job at the university as a teaching assistant (i need the money to pay my violin lessons).

How did you get to become a reptile caretaker? I suppose that could mean either one of two things, that you are a reptile who takes care (possibly of humans) or a human who takes care of reptiles :smile:

I envy you because you live in Holland, which seems like a nice place, and are near Utrecht.

How long a drive is it from Leiden to Utrecht?

I've always been interested in animals and seriously considered to persue a degree in zoology, or marine biology. Last year I discoverd there was a small reptile/amphibian zoo in Delft, so I contacted them for a volunteering position. It's really a great "job", you get to know a lot of animals and how they behave and experience handling them.

Holland certainly is a nice place, but a bit too crowded in the area of the major cities. The east on the contrary, bordering germany or luxenburg/belgium is a nice landscape, with lot's of wildlife! (with the only poisinous snake species in the country!).

The drive to Utrecht isn't that far. If I take the train it takes about 35 minutes to get to the central station, and then i think about 10 minutes by coach to the faculty. Leiden is pretty central to most cities, like amsterdam, den hague and rotterdam. Amsterdam and rotterdam are all about 30 minutes with the train, and den hague is just 10 minutes from Leiden (in summers it's nice to take the bike and cycle across the dunes to den hague :) ) Leiden is also a pretty small town, with aproximately 100.000 citizens.

marcus

Apr11-06, 03:30 PM

Yesterday I was looking at the current list of seminars at the Utrecht ITP
and it came to me why I approve of Renate Loll---two reasons why.

1. she gets young people to volunteer to take responsibility for things
2. she is a team player

look at the evidence. Loll's QG line is dynamical triangulations and, in Fall 2005, she had 3 postdoc positions to give

shall she give out these postdocs to people who will do Loll-type Triangles gravity? or shall she give them out in a way that is good for the whole field of QG?

watch.

the most outstanding young person in the Causal Sets line is Joe Henson.
the most outstanding young person in canonical Loop line is Hanno Sahlmann

if you compartmentalize, you think Hanno should be at Golm or Penn State, you think Joe should be in London with Fay Dowker. You would think neither would be any good to Loll, in a narrow Triangulations sense.

But in Fall 2005, Loll surprises you and invites Henson and Sahlmann to Utrecht (share the job of supporting the young researchers in a field-wide way, don't be parochial) and now what happens?

heh heh.

Now, Spring 2006, every week at the Utrecht ITP, Henson and Sahlmann are teaching a seminar on SPIN FOAMS. that is what is so funny. neither of them have done research on that. how did they get the idea? maybe Loll suggested to them that they should learn that approach. or maybe the two of them just got the notion to do it.

Spinfoam is the approach that Laurent Freidel uses, and Etera Livine and Daniele Oriti, and lately Carlo Rovelli (to make graviton propagators). And UTRECHT DOES NOT HAVE ANY spinfoam people.

All right Joe and Hanno, you be our spinfoam people. this tickles me. I am amused and delighted by it. they dont just serve the house brand at Utrecht. they bring canonical Loop and Causal Sets people in for postdocs and then they have them do yet another thing: spin foam. Probably it is very hard for those two postdocs, which is good for them. they are better off there than in Berlin or London, I think.

I would not be surprised if in their seminar they are studying the new Freidel Baratin paper. And they will be ready when Freidel comes to utrecht to give a talk on 1 May.

This is why non-string non-perturbative quantum gravity is ONE FIELD, instead of several separate little fields---social behavior like this makes it one field.

I first saw this aspect of Loll's behavior when she was invited to give a paper at the Paris July 2005 Einstein Centennial Conference. She sent an UNDERGRADUATE named Stefan Zohren to deliver a paper which is essentially the THESIS research of another student of hers named Westra. So she was pushing her youngest up to the firing line. And then, that Fall, she packed Zohren off to spend time with Fay Dowker and Chris Isham in London.

Loll could have given a major paper of hers at Paris. Instead she spun off from Westra's thesis a paper with three authors: Loll, Westra, Zohren---and she had the most junior author deliver it. And then go off to grad school at London Imperial. this has to be a good people-policy.

BTW in case anyone is curious about the paper Zohren gave in Paris, it was just posted last month on arxiv
http://arxiv.org/abs/hep-th/0603079
Nonperturbative sum over topologies in 2D Lorentzian quantum gravity
R. Loll (U. Utrecht), W. Westra (U. Utrecht), S. Zohren (U. Utrecht, RWTH Aachen)
10 pages, 4 figures. Talk given by S. Zohren at the Albert Einstein Century International Conference (Paris, July 18-22 2005)