Quantum Graffiti: MEDIA COVERAGE, JOB OPENINGS & Gossip Around Loll at Utrecht

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the topic of this thread is MEDIA COVERAGE, JOB OPENINGS and other items of gossip around Loll at Utrecht and the new model spacetime continuum coming out of the Triangulations approach.

I think what Loll and CDT co-workers are doing is currently the most significant development in theoretical physics. So I want to assemble news about it off the web.

Like Loll is getting research grants to start a "Triangulations" GROUP at Utrecht and has posted job openings (for pre-doc and post-doc positions). How much, how many? What media coverage? Real life details.

And what is this European-wide network for random geometry research called E.N.RA.GE? this thread is to help keep up to date on the CDT-style triangulations quantum gravity story.
 
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Physics news on Phys.org
http://www.phys.uu.nl/~loll/Web/title/title.html

some exerpts:
"Renate Loll is an Associate Professor at the Institute for Theoretical Physics of Utrecht University. She received her Ph.D. from Imperial College, London, in 1989. In 2001 she joined the permanent staff of the ITP, after spending several years at the Max-Planck Institute for Gravitational Physics in Golm, Germany, where she also held a Heisenberg Fellowship..."

"...In December 2004, Loll won a five-year VICI award by the Netherlands Organisation for Scientific Research (NWO) to pursue her investigations into the quantum structure of space-time and strengthen her working group at the ITP. She is also in charge of the European Research and Training Network ENRAGE, which brings together 13 European research groups working on theories of random geometry, with applications ranging from..."

this information is dated 2004
here is a list of Loll's current and former students and post-docs
http://www.phys.uu.nl/~loll/Web/students/students.html
I hope by now the list has grown some!

here is a list of job openings, from 2004, related to her research group
http://www.phys.uu.nl/~loll/Web/jobs/jobs.html
(the deadline for applying was January 2005, I hope there is a new list but I do not see one)

Here is a feature about Loll in a Dutch daily called "NRC Handelsblad", the article is dated January 2005 and has some fresher news than the pages at her Uni Utrecht site.
www.phys.uu.nl/~loll/Web/press/knutselen.pdf

Here is the German translation by Karola Loll. (sounds like a daughter or other kin)
http://www.phys.uu.nl/~loll/Web/press/NRCdeutsch.htm
 
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Great short article by Adrian Cho for Physical Review focus

http://focus.aps.org/story/v14/st13

The American Physical Society has the major peer-review journals series Phys. Rev. and Physical Review Letters. And they pick out articles for highlighting journalistically in the accompanying publication Physical Review Focus.

Adrian Cho did a good job with this focus piece on Loll-type triangulations QG.

Like a good journalist he included some reaction-quotes from other scientists:

<<The researchers added up all the possible spacetimes to see if something like a large-scale four-dimensional spacetime would emerge from the sum. That was not guaranteed, even though the tiny bits of spacetime were four-dimensional. On larger scales the spacetime could curve in ways that would effectively change its dimension, just as a two-dimensional sheet of paper can be wadded into a three-dimensional ball or rolled into a nearly one-dimensional tube. This time the researchers found that they could achieve something that appeared to have one time dimension and three space dimensions--like the universe we know and love.

"It's exceedingly important" work, says Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Canada. "Now at least we know one way to do this." Des Johnston of Heriot-Watt University in Edinburgh, Scotland, agrees the work is "very exciting" and says it underlines the importance of causality. "The other neat thing about this work is that you're essentially reducing general relativity to a counting problem," Johnston says. "It's a very minimalist approach to looking at gravity.">>
 
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the title of the thread is supposed to be a pun (in case anybody didnt get it)
with "gra-FEE-tee" pronounced "GRAF-fi-ti"

here are links to some other "Triangulations" Quantum Gravity threads:

https://www.physicsforums.com/showthread.php?t=76674

https://www.physicsforums.com/showthread.php?t=57311

https://www.physicsforums.com/showthread.php?t=75472

What I keep putting off, because it looks like a lot of hard work, is making a translation into English of some exerpts from the article about Loll and CDT published in January 2005 by the Dutch daily "NRC-Handelsblad"

But morally, out of simple fairness, it should be done. In the United States we have heard almost nothing except string theory. With some occasional mention of Loop gravity. media coverage inversely proportional to importance. And ZERO coverage of Loll-type triangulations Qvantoom Graffitee. You have to be able to read GERMAN OR DUTCH if you want to follow the most significant developments in theoretical physics. At least it would seem so, if your source is the popular media!

I will try a bit of this Handelsblad article by Dirk van Delft.
It may sound dumb (because of my translation and also because that's how the popular media can often sound) but let's try:
 
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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 couldn't 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 I am 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 I am 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.“>>
 
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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.“>>
 
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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 I am 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. I am 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. I am 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 I am 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 I am 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.
 
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  • #10
another piece of the Dirk van Delft article about Renate Loll

<<Die große Herausforderung, die noch vor Renate Loll und ihrer I am 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 I am 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 acquire 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
 
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  • #11
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 don't count it.

http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/2003/0/1

http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/2004/0/1

Last 12 months:
http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/past/0/1

Code: 
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.
 
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  • #12
The Dynamical Triangulations Sex Manual

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
https://www.physicsforums.com/showthread.php?p=589732#post589732
which is not only about core LQG but lately has also a Causal Triangulations section.)
 
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  • #13
including topology change

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.
 
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  • #14
how can LQG accommodate Loll-style "Triangulations"?

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 accommodate 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 https://www.physicsforums.com/showpost.php?p=591375&postcount=11 ) has been

Code: 
2003   3
2004   4
LTM    7
 
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  • #15
Hermann Nicolai perspective

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
 
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  • #16
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...gravity+AND+Lorentzian+quantum/0/1/0/2003/0/1

http://arxiv.org/find/grp_physics/1...gravity+AND+Lorentzian+quantum/0/1/0/2004/0/1

Last 12 months:
http://arxiv.org/find/grp_physics/1...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
 
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  • #17
marcus said:
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
 
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  • #18
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.

https://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 don't 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.
 
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  • #19
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 anyone 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
 
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  • #20
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---
 
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  • #21
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 doesn't 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.
 
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  • #22
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
 
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  • #23
marcus said:
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.
 
  • #24
arivero said:
... 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.
 
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  • #25
arivero said:
... 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?
 
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  • #26
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".
 
  • #27
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 into spoil their nice plans.

Thanks,

Richard
 
  • #28
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 doesn't 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.
 
  • #29
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 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 "
 
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  • #30
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.

 
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  • #31
4-page Smolin reply on Woit's blog

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...)
 
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  • #32
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?
 
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  • #33
selfAdjoint said:
... 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.
 
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  • #34
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.
 
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  • #35
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  • #36
Thank you Marcus!
 
  • #37
selfAdjoint said:
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
 
  • #38
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 can't 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.
 
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  • #39
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/
 
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  • #40
91 teraflop computer should help with simulating spacetime

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;_ylu=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl
 
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  • #41
marcus said:
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"
 
  • #42
marcus said:
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.
 
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  • #43
ohwilleke said:
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 haven't 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
 
  • #44
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. haven't found it on line but did find this
http://www.nature.com/news/2004/041004/pf/041004-17_pf.html
dated 8 October. it doesn't have the photograph I expected and seems to have been abridged
this greek-language version has the photon and is more complete (still haven't 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.
 

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  • #45
Baez column on CDT (from May 2004 Marseille conference)

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
 
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  • #46
limits

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 -
 
  • #47

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:
 
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  • #48
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

If anyone is at the Paris conference 18-22 July, and is interested in quantum gravity, keep an eye open for them. The CDT paper that deals with topology change in the spacetime path integral context is in the session called "The Nature of Space-time"

some mathematicians who need to visualize several dimensions in geometry on their computer screens use funnylooking R/B 3D goggles. Also biochemists use those 3D goggles, in this picture Loll is wearing funny goggles
http://www.phys.uu.nl/~loll/Web/title/title.html

here is a list of Loll students and postdocs
http://www.phys.uu.nl/~loll/Web/students/students.html

This thread is mostly about CDT-people (causal dynamical triangulations approach to quantum gravity) and random information, gossip, conferences etc.
But also there are other important parts of "QGATS" (quantum gravity alternatives to string) and one part is what Laurent Freidel and co-workers do (like the recent Freidel Starodubtsev, Freidel Livine, Freidel Louapre papers). So I should keep track of this link of a good snapshot of Freidel.
http://cosmos.nirvana.phys.psu.edu/online/Html/Seminars/Spring1999/Freidel/freidel.jpg
 
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  • #50
yesterday a very cautious paper by Martin Bojowald came out
https://www.physicsforums.com/showthread.php?p=618695#post618695

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

the second link is in case the first one doesn't work.

in a very tentative, "oblique", way he is venturing to suggest that black hole 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 don't 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
 

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