Introduction To Loop Quantum Gravity

  • #251
Xristy helpfully assembled the links to the chapters of a new book which are available in preprint form online.
https://www.physicsforums.com/showthread.php?p=2899654#post2899654
The book is a collection of talks given at George Ellis' 70th birthday celebration, called The Foundations of Space and Time. A gathering of people from Loop, CDT, String, Cosmology communities comparing notes on basic issues and each other's approaches. Ellis co-edited the book and it is to be published by Cambridge Press.
http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521114400

Some information is posted about Loops 11. It can be interesting to look down the list of plenary speakers at a major conference--it may give some idea of where the field is or where it's going. The Loops conference is held approximately biannually (once every two years) with other related conferences sometimes filling in on off-years. Here's the plenary speakers list:

Abhay Ashtekar (Penn State University, USA).
Martin Bojowald (Penn State University, USA).
Alejandro Corichi (UNAM-Morelia, Mexico).
Bianca Dittrich (Albert Einstein Institute, Germany).
Kristina Giesel (TU Munich, Germany).
Jerzy Lewandowski (Warsaw University, Poland).
Renate Loll (Utrecht University, Netherland).
Yongge Ma (Beijing Normal University, China).
Don Marolf (Univ. California-Santa Barbara, USA).
Daniele Oriti (Albert Einstein Institute, Germany).
Tomasz Pawlowski (University of New Brunswick, Canada).
Alejandro Pérez (Univ. Méditerranée, Marseille, France).
Jorge Pullin (Louisiana State University, USA).
Carlo Rovelli (Univ. Méditerranée, Marseille, France).
Hanno Sahlmann (Karslruhe University, Germany).
Parampreet Singh (Perimeter Institute, Canada).
Lee Smolin (Perimeter Institute, Canada).
Thomas Thiemann (Univ. Erlangen-Nurnberg, Germany).
Madhavan Varadarajan (Raman Research Institute, India).

The Loops 11 conference will be held 23-28 May, in Madrid:
http://www.iem.csic.es/loops11/
for comparison, here are the plenary speakers and talks of Loops 09 and Loops 07:
https://www.physicsforums.com/showthread.php?p=2296306#post2296306
http://www.matmor.unam.mx/eventos/loops07/ (links to plenary talks/abstracts)

Christine's thread about the forthcoming Hamiltonian GR textbook (applications to LQG cosmology) by Penn State's Martin Bojowald
https://www.physicsforums.com/showthread.php?t=432381
 
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  • #252
Atyy called attention to an interesting January 2010 paper by Madhavan Varadarajan
which was cited in Thiemann's latest (October 2010). This gives a good idea of what some of the plenary talks will be about at Loops 11.
Some information is posted about Loops 11... Here's the plenary speakers list:
...
...
Lee Smolin (Perimeter Institute, Canada).
Thomas Thiemann (Univ. Erlangen-Nurnberg, Germany).
Madhavan Varadarajan (Raman Research Institute, India).

The Loops 11 conference will be held 23-28 May, in Madrid:
http://www.iem.csic.es/loops11/

Rovelli's talk could draw from the October "Simple Model" paper http://arxiv.org/abs/1010.1939
Lewandowski's from his September "Gravity Quantized" http://arxiv.org/abs/1009.2445
Smolin could conceivably talk about Unimodular Gravity (and the problem of time? http://arxiv.org/abs/1008.1759 )
Thiemann's talk could draw from http://arxiv.org/abs/1010.2426
Varadarajan's from http://arxiv.org/abs/1001.3505

LQG-RELATED TEXTBOOKS etc. scheduled for release:

Christine's thread about Bojowald's Hamiltonian GR textbook (applications to LQG cosmology)
https://www.physicsforums.com/showthread.php?t=432381
Cambridge Press page about Canonical Gravity and Applications
http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521195751

Amazon page about Once Before Time, Bojowald's forthcoming Loop cosmology popularization
https://www.amazon.com/dp/0307272850/?tag=pfamazon01-20

World Scientific press page about Montani's textbook Primordial Cosmology:
http://www.worldscibooks.com/physics/7235.html

Cambridge Press page about Foundations of Space and Time (Ellisfest collection)
http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521114400

Chennai basic LQG/LQC Lectures http://arxiv.org/pdf/1004.2952
(Ganashyam Date gave a series of beginning lectures on LQG which explain certain things most clearly--only 72 pages, not a textbook but could be used as supplemental reading.)

Xristy's links to draft chapters of the Ellisfest book:
https://www.physicsforums.com/showthread.php?p=2899654#post2899654
 
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  • #253
Eugenio Bianchi will give a talk soon at Perimeter, about Loop Quantum Gravity, and it will go on the PIRSA online lecture archive
http://pirsa.org/10110052/
9 November
 
  • #254
A newcomer was asking about math prep for LQG--here are some online notes on group representation theory---if you know better online notes please say. There is quite a variety here to pick and choose from:

http://www.math.columbia.edu/~woit/RepThy/
 
  • #255
A one-year masters (MSc) program is being set up by John Barrett and colleagues at Nottingham. The first year of operation will start September 2011. We may be able to pick up some information about their curriculum, lecture notes, textbooks---get some clues from this.
http://johnwbarrett.wordpress.com/

==quote==
New MSc course
Here at Nottingham we are starting an MSc in Gravity, Particles and Fields. This is very specifically aimed at students interested in getting into relativity and particle physics research, in areas such as quantum gravity, cosmology, quantum information, etc.

The first run starts in September 2011, so we are open for applications now.
==endquote==

http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
==quote==
Gravity, Particles and Fields Masters (MSc)
Duration: 1 year full-time

The course provides an introduction to the physical principles and mathematical techniques of current research in general relativity, quantum gravity, particle physics, quantum field theory, quantum information theory, cosmology and the early universe.
The programme of study includes a taught component of closely-related modules in this popular area of mathematical physics. The course also includes a substantial project that will allow students to develop their interest and expertise in a specific topic at the frontier of current research, and develop their skills in writing a full scientific report.
The course will provide training in advanced methods in mathematics and physics which have applications in a wide variety of scientific careers and provide students with enhanced employability compared with undergraduate Bachelors degrees. In particular, it will provide training appropriate for students preparing to study for a PhD in the research areas listed above. For those currently in employment, the course will provide a route back to academic study.
Key facts
• The course is taught jointly by the School of Mathematical Sciences and the School of Physics and Astronomy.
• Dissertation topics are chosen from amongst active research themes of the Particle Theory group, the Quantum Gravity group, and the Quantum Information group
• In addition to the lectures on the course, there are several related series of research-level seminars to which Masters students are welcomed.
• The University of Nottingham is ranked in the top 1 per cent of all universities worldwide.
...
==endquote==
 
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  • #256
Does LHC Can test Loop quantum gravity or other approaches to QG?
 
  • #257
QGravity said:
Does LHC Can test Loop quantum gravity or other approaches to QG?

I haven't thought much about it. It seems to me that in this period of history new physics is often going to be revealed by the huge river of data coming from the sky---astrophysical observations by new types of instruments (many in space but also on ground.)

The importance of LHC may have been exaggerated relative to other less expensive instruments. I really don't know, it's hard to judge. But I'll mention a few things to think about besides the LHC. Some might be relevant to testing LQG and others not.

Things to be investigated include: dark energy or cosmological constant, dark matter, Gammaray Bursts, high-energy cosmic rays, early universe neutrinos, polarization and other features of Microwave Backgound, gravitational wave imprint in CMB, signals from black hole formation (unusual stellar explosions). Largescale structure of universe.

Instruments: interferometers including spaceborn, synthetic aperture telescopes, atmospheric Cherekov gammaray telescopes, CMB-mapping spacecraft beyond COBE and WMAP, X-ray astronomy using spacecraft , gravitational wave detectors, neutrino detectors like IceCube in Antarctica, Cosmic Ray detector arrays like the Auger, gammaray astronomy in space as with FermiLAT or combining orbital and ground as with SWIFT.

This is a quick impromptu list bound to leave stuff out. I'd guess that LQG testing comes in here somewhere with CMB early universe astronomy, and maybe somehow with some of the ways of gathering information.
 
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  • #258
In a sense cosmology is the "collider" for quantum gravity and unification. The main arena for testing models is going to be the early universe. It's is where the energy is, and the phenomena we have to make sense of.
So when Weinberg talked to Strings 2010 (about his "Plan B" in case string although great mathematics proved physically disappointing) he focused on applying his Plan B idea to cosmology. Its where everything has to go eventually, not just hobble on to the next particle accelerator.

So we have to watch developments in quantum cosmology and related areas. Here is a unique resource. Penrose June 2009 talk at the Institute for Gravitation and Cosmology:

The title was "Fashion, Faith, and Fantasy in the New Science of the Universe"

1.
2.
3. http://www.youtube.com/watch?v=4BtYn2Wde4o&NR=1
4. http://www.youtube.com/watch?v=zVTCaaP5Y0s&feature=related
5. http://www.youtube.com/watch?v=bQNUwHnQzvA&feature=related
6. http://www.youtube.com/watch?v=DvfRYzRgqWE&feature=related
7. http://www.youtube.com/watch?v=afsd3_PJais&feature=related
8. http://www.youtube.com/watch?v=UMi_QB0vWC0&feature=related
9. http://www.youtube.com/watch?v=tiRy07yweA0&feature=related
10. http://www.youtube.com/watch?v=5jXj1TwiFys&feature=related

http://gravity.psu.edu/events/abhayfest/
=======================================

Weinberg on Asymptotic Safe gravity/cosmology, at Strings 2010:
https://mediamatrix.tamu.edu/streams/327756/PHYS_Strings_2010_3-18-10C

A recent Asyptotic Safe gravity paper that I think will prove important (sometimes computational power enables progress as much as a new idea, it's happened before in other fields.)

http://arxiv.org/abs/1012.3081
The Universal RG Machine
Dario Benedetti, Kai Groh, Pedro F. Machado, Frank Saueressig
38 pages
(Submitted on 14 Dec 2010)
"Functional Renormalization Group Equations constitute a powerful tool to encode the perturbative and non-perturbative properties of a physical system. We present an algorithm to systematically compute the expansion...
... In a first illustrative example, we re-derive the gravitational beta-functions of the Einstein-Hilbert truncation, demonstrating their background-independence. As an additional result, the heat-kernel coefficients for transverse vectors and transverse-traceless symmetric matrices are computed to second order in the curvature."

Here is Roberto Percacci's website index page for AsymSafe gravity.
http://www.percacci.it/roberto/physics/as/index.html
Thanks to Atyy for pointing out the new picture (Benedetti, Machado, Rahmede collaborating at the blackboard)
Percacci has a FAQ for AsymSafe, and useful links to stuff.
Someone was asking if Pedro is from Brazil or Portugal--here's his current page:
http://www.gen.cam.ac.uk/research/AMA/members/Pedro.html
 
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  • #259
The previous post mentioned some Asymptotic Safe gravity stuff (from Weinberg, Percacci, Benedetti et al...). On the same subject, one of the major figures in AS gravity, Martin Reuter, just came out with a paper formulating AS in a way that looks compatible with LQG. The Holst action, which LQG uses, and its Immirzi parameter. This could serve as a bridge between the two QG approaches.
http://arxiv.org/abs/1012.4280

Another Loop textbook coming out.
http://www.springer.com/physics/the...+computational+physics/book/978-1-4419-8275-9

This will be in the Springer Lecture Series, planned release date March 2011.
Quantum Cosmology, by Martin Bojowald
approx. 250 pages

This might serve as a companion to another textbook which Cambridge Press is bringing out
http://www.cambridge.org/gb/knowledge/isbn/item5692826/?site_locale=en_GB
Canonical Gravity and Applications: Cosmology, Black Holes, and Quantum Gravity, by the same author
approx. 310 pages

The UK Amazon says it is temporarily out of stock:
http://www.amazon.com/dp/0521195756/?tag=pfamazon01-20
US Amazon says you can pre-order, available January 2011.

It's interesting to see QG and QC take shape as academic subjects. When I started watching the field in 2003 there were, as far as I know, no textbooks. At least not for quantum *cosmology*, which (because we have so much data on the early universe) seems to be the key to the whole business.
 
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  • #260
  • #261
So I while back I asked about the relationship between quantum foam, Quantum Loop Gravity theory, string theory, and how many dimensions each theory requires in this link https://www.physicsforums.com/showthread.php?t=432962". As you may note nismaratwork helped me to understand how string theory would smear out quantum foam. He also helped remind me that String Theory require multiple dimensions but quantum foam requires only four.

However, I as I was reading your thread I realized that I assumed two things:
First, quantum loop gravity only requires 4 dimensional Minkowski Space
Second, that quantum foam actually plays a role in quantum loop gravity.

So I was hoping you could help me with the following questions:

  1. Are there any limits, such as a minimum or maximum, on the number of dimensions that quantum loop gravity, independent of string theory, would require?
  2. Is their a relationship between quantum foam and quantum loop gravity? If so, what role exactly does quantum foam play in quantum loop gravity theory? If not, does quantum loop gravity, replace quantum foam with something analogous to quantum foam purpose in solution the Klein-Gordon Equation(*)?
 
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  • #262
piareround said:
So I while back I asked about the relationship between quantum foam, Quantum Loop Gravity theory, string theory, and how many dimensions each theory requires in this link https://www.physicsforums.com/showthread.php?t=432962". As you may note nismaratwork helped me to understand how string theory would smear out quantum foam. He also helped remind me that String Theory require multiple dimensions but quantum foam requires only four.

However, I as I was reading your thread I realized that I assumed two things:
First, quantum loop gravity only requires 4 dimensional Minkowski Space
Second, that quantum foam actually plays a role in quantum loop gravity.

So I was hoping you could help me with the following questions:

  1. Are there any limits, such as a minimum or maximum, on the number of dimensions that quantum loop gravity, independent of string theory, would require?
  2. Is their a relationship between quantum foam and quantum loop gravity? If so, what role exactly does quantum foam play in quantum loop gravity theory? If not, does quantum loop gravity, replace quantum foam with something analogous to quantum foam purpose in solution the Klein-Gordon Equation(*)?

Let's start a separate thread, for discussion/explanation. I try to use this thread just to provide selected links to useful source material for people following current LQG research.
It would get unwieldy to include discussion and explanation in addition to what it's doing already.

I will start a thread for you, with your questions about LQG.
 
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  • #263
This year (first two weeks March 2011) the best ever QG school will be held at the ski resort Zakopane. It is aimed at postdocs and advanced PhD students ready to enter QG research. The school is definitive of the field, so we can learn some things from examining the schedule.

Of the lectures on LQG, those I have colored bright blue will probably be more from the manifold-free perspective----no spacetime continuum manifold. That will be about half, I guess. Those I have colored dark or navy blue will probably use the older development which starts with a 4D manifold. Talks listed in black are on other types of QG, or neutral as regards this change in LQG.

So one thing we can learn by looking at the school line-up is how this reconstitution or reformulation of LQG is progressing. Another thing to gauge is how much the Loop people are looking towards Group Field Theory, Noncommutative Field Theory, and Noncommutative Geometry for additional inspiration. I think it has to do with a sense that LQG is ready to take on matter---to rebuild QFT on a quantum geometrical basis---and they are on the lookout for ideas.

In any case here is the schedule color-coded as I described earlier:

Mar 1
A. Ashtekar 2h — Opening lecture
C. Rovelli 2h — Spin foams
K. Giesel 2h — Loop quantum gravity
H. Sahlmann 2h — Loop quantum gravity

Mar 2
K. Giesel 2h — Loop quantum gravity
H. Sahlmann 2h — Loop quantum gravity
C. Rovelli 2h — Spin foams

Mar 3
K. Giesel 1h — Loop quantum gravity
H. Sahlmann 1h — Loop quantum gravity
J. Brunnemann 2h — Volume operator
C. Rovelli 2h — Spin foams

Mar 4 Break (Friday)

Mar 5
C.Rovelli 2h — Spin foams
W. Kamiński 2h — EPRL map: SO(4) and SO(1,3), integrability
P. Singh 2h — Loop quantum cosmology

Mar 6
S. Hollands 2h — Exact QFT in curved backgrounds
C. Rovelli 2h — Spin foams
P. Singh 2h — Loop quantum cosmology

Mar 7
S. Hollands 2h — Exact QFT in curved backgrounds
S. Speziale 2h— LQG and twisted geometries
C. Perini 1h — Graviton propagator
E. Bianchi 1h — Friedmann equation from the EPRL vertex amplitude

Mar 8
T. Krajewski 2h — Group field theories
S. Hollands 2h — Exact QFT in curved backgrounds
J.B. Geloun/V. Rivasseau 2h — EPRL GFT

Mar 9 Break (Wednesday)

Mar 10
H. Steinacker 2h — Non-commutative geometry and matrix models
J. Barrett 2h — Large j limit of spin foam amplitudes
T. Krajewski 2h — Group field theories

Mar 11
H. Steinacker 2h — Non-commutative geometry and matrix models
H. Grosse 2h — Renormalisation of the Grosse-Wulkenhaar model
M. Burić 2h — Renormalisation of the Grosse-Wulkenhaar model

Mar 12
H. Steinacker 2h — Non-commutative geometry and matrix models
K. Noui 2h — SLq(2,C)
W. Fairbairn 2h — SLq(2,C) EPRLK model

Mar 13
B. Dittrich 2h — Diffeomorphisms, renormalisation and perfect action in discrete theories
J. Jurkiewicz 2h — Causal dynamical triangulations
C. Meusburger 2h — 2+1 gravity

Offhand it seems like the school lineup is about evenly balanced in respect to manifoldy/manifoldless or however you want to imagine the shifting reconstitution going on.
http://www.fuw.edu.pl/~kostecki/school3/
 
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  • #264
Short history of LQG (courtesy Inspire database)

Stanford-SLAC has a new physics database called Inspire. It improves on Spires, which has been in use for over a decade. Inspire is still in beta and being worked-on.

Here, in effect, is a history of Loop Gravity from 2005 onwards obtained simply by finding each year's papers and listing them ranked by cite count. The cites reflect the interest of the research community, so you can see what were considered (roughly speaking) the most interesting/valuable Loop papers of each year. These leading papers influence the direction that research in the field moves. You will see the focus and makeup of the top papers change over time.
(To learn more about any paper click on the corresponding "detailed record" link.)

The number of papers which appeared each year are given in parenthesis.

2005: (42)
http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

2006: (77)
http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

2007: (120)
http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

2008: (142)
http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

2009: (145)
http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

2010: (153)
http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

The keywords used are "quantum gravity: loop space", "quantum cosmology: loop space", "spin: foam".
 
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  • #265
I will try to assemble here links which can help assess the current status of LQG and LQC (loop gravity and loop cosmology)---as well as provide an introduction to the modern formulation of loop gravity using combinatorial spinfoam dynamics. This spinfoam formulation is sometimes referred to as the "full theory" as contrasted with loop cosmology which has been developed as a symmetry reduced version: made simpler by assuming some degree of uniformity in the universe. There are several points to be made about current developments, for which corresponding source links will be given.

Quantum cosmology has become observational. Here are articles mostly by early universe phenomenologists about ways of testing LQC against CMB data. Since LQC derives from LQG, this turns out to be the most accessible route to testing LQG.
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28DK+POWER+SPECTRUM+or+dk+cosmic+background+radiation%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29

Loop cosmology connects with the full (spinfoam) theory:
http://arxiv.org/abs/1003.3483
Towards Spinfoam Cosmology

The distinctive prediction of a bounce carries over:
http://arxiv.org/abs/1010.1258
Big Bounce in Dipole Cosmology

LQC bounce naturally initiates a period of superinflation even without the usual scalar ("inflaton") field. If the usual scalar field is present as well, the bounce ensures ample inflation without any further adjustments.
http://arxiv.org/abs/1103.2475
Probability of Inflation in Loop Quantum Cosmology
This is a kind of observational confirmation because it shows that LQC makes observed features of the universe associated with inflation more likely.

A definitive presentation of LQG, with some math prerequisites:
http://arxiv.org/abs/1102.3660
Lectures on Loop Gravity

A definitive presentation of LQC, as of mid-2010:
http://arxiv.org/abs/1005.5491.
The Big Bang and the Quantum

A comparatively non-technical presentation of LQG, including its historical development and evidence suggesting the theory recovers classical GR.
http://arxiv.org/abs/1012.4707
Loop quantum gravity: the first twenty five years

http://arxiv.org/abs/1101.4049
Cosmological constant in spinfoam cosmology

http://arxiv.org/abs/1101.3264
Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions

http://arxiv.org/abs/1012.1739
Lorentz covariance of loop quantum gravity

Formation of an inclusive research community of Quantum Gravity/Geometry/Cosmology is being helped by European Science Foundation "QG" events such as this year's conference at the Zurich ETH:
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start

Quantum Theory and Gravitation
Topics to be covered include:
General quantum theory, relativistic quantum theory, emergence of space(-time)
General quantum field theory, including deformations of QFTs
QFT on curved and NC space-times
Canonical quantum gravity and supergravity
Regge calculus
String theory and M-theory
Loop gravity, spin foam
Quantum cosmology

International Advisory Board
John Barrett
Harald Grosse
Hermann Nicolai
Carlo Rovelli
Roger Picken
 
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  • #266
sir my question is that is it literally impossible to prdict the volume f the previous universe or it can be pradicted with accurate theorues?please tell me sir
 
  • #267
Mehul Ahir, sir, that is a helpful question because it reminds us of how little we know. There are several different approaches to Quantum Cosmology, and on the whole they are young unformed theories. We do not know which, if any, is to be trusted.

Loop cosmology is only just beginning to be compared with real observational data. You can see in the recent Ashtekar-Sloan paper how they confront the theory with WMAP data. http://arxiv.org/abs/1103.2475 So far there are some pretty nice agreements with data but further testing could prove the theory wrong!

And even if the theory survives a number of tests and begins to be tentatively trusted, it still says very little definite about the contracting phase of the universe, before the bounce. Even if we believed the LQC theory we could still say almost nothing about the spatial volume. Only that distances were contracting in the same sense that they are now expanding.

We do not know the total spatial volume the universe has even today. We only can estimate how far away the most distant material is that we can see.

The great thing, as I see it, is that scientists are doing their job. They are supposed to construct simple TESTABLE theories that fit the data. And then their job is to derive predictions from theory that can be checked by observation---and if those predictions are not observed then the theory is disproved and one must construct a better one. The good news is not that Loop Cosmology is right (we don't know that) but that it is testable. It replaces the former singularity with a particular kind of bounce that has measurable consequences to look for in the cosmic microwave background (CMB, the ancient light).
 
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  • #268
The next biannual Loops conference, Loops 2011, will be held in Madrid the last week of May.
To date about 150 people have registered to partciipate:
http://www.iem.csic.es/loops11/

Strings 2011 will be held one month later, at the end of June, in Uppsala, Sweden.
http://www-conference.slu.se/strings2011/
The registered participants include Stephen Hawking, Juan Maldacena, John Schwarz, Michael Green, and Edward Witten:
https://www.akademikonferens.se/list.jsf?conf=strings2011
 
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  • #269
Loop cosmology linking up with early universe phenomenology is a recent development that has changed the QG picture somewhat. Here are 29 early U. phenom. papers that appeared 2009 or later:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28DK+primordial%2C+fluctuation+OR+DK+INFLATION+OR+DK+COSMIC+BACKGROUND+RADIATION%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29

The Spires search is:
IND (DK QUANTUM GRAVITY, LOOP SPACE OR DK QUANTUM COSMOLOGY, LOOP SPACE) AND (DK PRIMORDIAL, FLUCTUATION OR DK INFLATION OR DK COSMIC BACKGROUND RADIATION) AND DATE > 2008
====================
The next biannual Loops conference, Loops 2011, will be held in Madrid the last week of May.
We can get an idea of where in the US you can study Loop gravity/cosmology by looking at the list of 170 registered participants.
Only 25 are from US institutions---the US lags Europe in QG.
http://www.iem.csic.es/loops11/
Here's where the US participants come from

PSU (Penn State) 13
LSU (Louisiana) 4
UC Berkeley 2
Hamilton 1
FAU (Florida Atlantic, Boca Raton) 1
FSU (Florida State, Talahassee) 1
Utah State 1
Dartmouth College 1
Le Moyne College 1

Chris Duston, the guy coming from FSU, is doing his PhD in quantum gravity/cosmology under Matilde Marcolli (Caltech). So Caltech has a kind of spectral presence in this listing as well.
==================================
Strings 2011 will be held one month later, at the end of June, in Uppsala, Sweden.
http://www-conference.slu.se/strings2011/
https://www.akademikonferens.se/list.jsf?conf=strings2011
The three public lectures (by Stephen Hawking, Brian Greene, Andrei Linde) will feature the stringy Landscape and the Multiverse.
===================================

In between these two, in mid June, there's the Zurich conference
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
Quantum Theory and Gravitation
87 registered participants so far, ecumenical (brings together prominent people from various different approaches to QG) interesting lineup of speakers. 30 from some 5 or 6 different lines of research.
 
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  • #270
Here is a page about the new one-year MSc program at Nottingham, in Gravity, Particles and Fields
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx

==quote==
The course provides an introduction to the physical principles and mathematical techniques of current research in general relativity, quantum gravity, particle physics, quantum field theory, quantum information theory, cosmology and the early universe.
The programme of study includes a taught component of closely-related modules in this popular area of mathematical physics. The course also includes a substantial project that will allow students to develop their interest and expertise in a specific topic at the frontier of current research, and develop their skills in writing a full scientific report.
The course will provide training in advanced methods in mathematics and physics which have applications in a wide variety of scientific careers and provide students with enhanced employability compared with undergraduate Bachelors degrees. In particular, it will provide training appropriate for students preparing to study for a PhD in the research areas listed above. For those currently in employment, the course will provide a route back to academic study.
Entry requirements: At least a second class honours (2:2) BSc degree (or equivalent from other countries) in Physics, Mathematical Physics or Mathematics, or joint degrees containing substantial elements of physics or mathematics.
Other requirements: Previous knowledge of mechanics, quantum mechanics, special relativity and methods of mathematical physics (all as taught typically at BSc level 2) is required.
IELTS: 6.0 (with no less than 5.0 in any element)
TOEFL paper based: 550 (with at least 4.0 on the TWE)
TOEFL IBT: 79 (with no less than 17 in any element)
==endquote==

The main person responsible for the new program is John Barrett. His research is in several QG areas including Loop and NC-geometry. He's also director of ESF-QG the European Science Foundation setup for funding quantum gravity and quantum geometry.
Here's Barrett's Nottingham faculty page:
http://www.nottingham.ac.uk/mathematics/people/john.barrett
and personal homepage
http://johnwbarrett.wordpress.com/
http://johnwbarrett.wordpress.com/talks/
Exemplifying directions in the European QG community, here's the website of a conference that Barrett's ESF-QG agency is sponsoring this summer in Zurich.
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
It brings together Loop, NCG, String, SUGRA, QFT on Curved space---speakers chosen who the organizers consider able to talk to each other and exchange ideas. Amazing conference, first of its kind. Barrett is one of the organizers, with Carlo Rovelli, Hermann Nicolai* and some other top people.

*director of the QG+unification wing at MPI Potsdam
=================
I have some more stuff related to the Loop academic terrain and entry to the field in this other thread:
https://www.physicsforums.com/showthread.php?p=3229102#post3229102
which was started by Barak (about doing one's PhD in Loop).
==================
Incidental information about the annual Strings conference (late June, Uppsala).
http://www-conference.slu.se/strings2011/
Preliminary list of confirmed speakers (sorted by type):

OPENING TALK
David Gross (KITP, Santa Barbara) opening talk

REVIEWS and other talks
Henriette Elvang (University of Michigan) review talk
Michael Green (Cambridge University)
Juan Maldacena (IAS, Princeton)
Liam McAllister (Cornell University) review talk
Greg Moore (Rutgers University) review talk
Subir Sachdev (Harvard University) review talk
Nathan Seiberg (IAS, Princeton) review talk
Ashoke Sen (Harish-Chandra Research Institute, Allahabad)
Samson Shatashvili (Trinity College, Dublin and IHES)
Gerard `t Hooft (University of Utrecht)
Erik Verlinde (University of Amsterdam)
Edward Witten (IAS, Princeton)
Fabio Zwirner (University of Padua) review talk

SUMMARY TALK AT END
Jeff Harvey (University of Chicago) summary talk

PUBLIC LECTURES (inflation, landscape of multiverses...)
Brian Greene (Columbia University)
Andrei Linde (Stanford University)
Stephen Hawking (TBC)
 
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  • #271
Thanks to Barak for this item from Oxford University Press catalogue:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do

A First Course in Loop Quantum Gravity
Rodolfo Gambini and Jorge Pullin
280 pages | 18 b/w line figures | 246x171mm
to be released: August 2011
TOC
1: Why quantize gravity
2: Special relativity and electromagnetism
3: Some elements of general relativity
4: Hamiltonian mechanics including constraints and fields
5: Yang-Mills theories
6: Quantum mechanics and elements of quantum field theories
7: General relativity in terms of Ashtekar's variables
8: Loop representation for general relativity
9: An application: loop quantum cosmology
10: Further developments
11: Open issues and controversies

Publisher's decription:
"First book on the subject at the undergraduate level
Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
High interest currently in quantum gravity among physicists worldwide
Controversial subject which needs good, impartial introduction from respected scientists
This book provides an accessible introduction to loop quantum gravity and some of its applications, at a level suitable for undergraduate students and others with only a minimal knowledge of college level physics. In particular it is not assumed that the reader is familiar with general relativity and only minimally familiar with quantum mechanics and Hamiltonian mechanics. Most chapters end with problems that elaborate on the text, and aid learning. Applications such as loop quantum cosmology, black hole entropy and spin foams are briefly covered. The text is ideally suited for an undergraduate course in the senior year of a physics major. It can also be used to introduce undergraduates to general relativity and quantum field theory as part of a 'special topics' type of course.
Readership: Undergraduates and beginning graduate physics students, lecturers in physics."

This forthcoming undergrad Loop gravity text came up in Barak's thread here:
https://www.physicsforums.com/showthread.php?p=3226419#post3226419
https://www.physicsforums.com/showthread.php?p=3232530#post3232530
 
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  • #272
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do

EDIT: Atyy points out that Bojowald has already published a textbook in LOOP COSMOLOGY


and also one in the CANONICAL APPROACH TO GENERAL RELATIVITY.

Neither is explicitly an undergrad text in LQG, but the former treats the application of LQG to cosmo which is pretty close.
And the latter although mainly it is not about QG it has a chapter at the end, I recall.

======================
The question is: should we call the Oxford Press book the "First undergrad LQG text"?

I think yes, because for one thing that is what OUP calls it:
==quote==
Publisher's decription:
  • First book on the subject at the undergraduate level
  • Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
  • High interest currently in quantum gravity among physicists worldwide
==endquote==

And for another thing Bojo book about Hamiltonian formulation of GR is not directly aimed at LQG. It does not start out talking QG. It puts it in as a last chapter.

The Gambini Pullin is explicitly aimed. It starts out with chapter 1 "Why quantized gravity?"

And it is TITLED as a textbook for LQG, not just as a GR text with apps.
 
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  • #273
marcus said:
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do

Not Bojowald's, or is that not undergarduate? https://www.physicsforums.com/showthread.php?t=432381
 
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  • #274
atyy said:
marcus said:
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do

Not Bojowald's, or is that not undergarduate? https://www.physicsforums.com/showthread.php?t=432381

Atyy, good question! I edited so as to respond in the appropriate place, right after the OUP publisher's blurb. I think in fact that the Gambini IS the first explicitly LQG undergrad text!
The Bojo text is on Canonical GR, with several applications. It could be used as a text but doesn't have the clear focus on LQG.
Oxford press says Gambini is the first LQG text for undergrads. And they are right. If you look at the title and TOC of the Bojo books you will see what I mean.

New page, so I will make the update post here for easy reference:
It hasn't been done for over a month so it's probably time to redo the regularly updated links post to give an introductory overview of the Loop program.
==================================

BRIEF OVERVIEW OF THE LOOP QG PROGRAM

Loop Gravity is a small growing field. It has had regular biannual conferences only since 2005 (Loops '05 was held at Potsdam.) Attendance at the biannual (Loops '11 Madrid) is now up to about 170.

Because centers of LQG research are spreading rather rapidly, jobs and postdoc positions seem currently to be ample compared to the number of new PhDs. It's hard to predict the future, but at least for now job prospects seem pretty good. Most new PhDs are out of Marseille,Penn State, AEI-Potsdam, and they all get placed. There are starting to be more PhDs now out of other places: Nottingham, Erlangen, Lyon, Cambridge, London...hard to give an exhaustive list.

First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do

Newly established Masters program aimed at Loop and other QG research (among other paths) starting at Nottingham in 2011:
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx

Survey for non-specialists, historical development and indications the theory recovers classical GR.
http://arxiv.org/abs/1012.4707
Loop quantum gravity: the first twenty five years

Definitive presentation of Loop gravity, with some math prerequisites:
http://arxiv.org/abs/1102.3660
Lectures on Loop Gravity

Loop cosmology, as of mid-2010:
http://arxiv.org/abs/1005.5491.
The Big Bang and the Quantum

Since Loop cosmology derives from LQG, this turns out to be the most accessible route to testing LQG. Here are 32 or more articles mostly by early universe phenomenologists about ways of testing LQC against CMB data,
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28DK+PRIMORDIAL%2C+FLUCTUATION+OR+DK+INFLATION+OR+DK+COSMIC+BACKGROUND+RADIATION%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29
which have appeared since 2009.

Some other papers of possible interest:

http://arxiv.org/abs/1101.3264
Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions

http://arxiv.org/abs/1012.1739
Lorentz covariance of loop quantum gravity

The European Science Foundation "QG" network is encouraging development of a broad-base research community by events such as this year's QG 2011 conference in Zurich:
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start

Topics to be covered include:
General quantum theory, relativistic quantum theory, emergence of space(-time)
General quantum field theory, including deformations of QFTs
QFT on curved and NC space-times
Canonical quantum gravity and supergravity
Regge calculus
String theory and M-theory
Loop gravity, spin foam
Quantum cosmology
===============================

The biannual Loops conference starts 23 May: Loops 2011 in Madrid.
http://www.iem.csic.es/loops11/
Click on "scientific program" in the menu on the left to see the list of talks. Abstracts of most talks are now available, just click on the title.

Many of the talks are about early universe pheno---the prospects for testing/constraining the theory.
Emerging challenges to the current formulation of Loop gravity are also represented at the conference and include "Shape dynamics" (see the session devoted to that on 23 May) and "Relative locality" (see talks by Laurent Freidel and Lee Smolin).

One of the signs of growth is the number of "parallel session" talks scheduled for Loops 2011, last time I checked there were 99 such. Younger researchers and newcomers to the field normally give talks in these parallel sessions.
=========================

Other signs of growth in the field:
  • the number of institutions now hosting Loop gravity (+ related phenomenology) research, and where one can do a Loop PhD
  • citations in the relevant categories (gr-qc, quantum cosmology, e.g. a growing share of "top 10 or top 30" papers)
  • simply the increased number of research papers coming out. Approximately doubled since 2006.

Code: 
Loop gravity papers, by year 
2005    41
2006    81
2007   121
2008   142
2009   141
2010   154
Code: 
Loop cosmology papers, by year 
2006    21
2007    39
2008    46
2009    45
2010    57
The current Loop cosmo formulation (Ashtekar et al) only appeared in 2006 so I start with that year.
Here are the relevant Spires searches, and links, if anyone wishes to see how the listing looks.

FIND DK SPIN,FOAM OR QUANTUM GRAVITY, LOOP SPACE OR QUANTUM COSMOLOGY, LOOP SPACE AND DATE = 2005
FIND DK QUANTUM COSMOLOGY, LOOP SPACE AND DATE = 2006
2005:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2005+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2006:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2006+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2007:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2007+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2008:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2008+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2009:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2009+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2010:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3D+2010+&FORMAT=WWW&SEQUENCE=citecount%28d%29
 
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  • #275
A new PF member asked "what exactly is LQG?" and requested a non-mathematical (effectively high school level, I think) answer. Tom Stoer supplied the following which then got some editorial attention from Ben Crowell and Redbelly (who suggested copying it here.) I think it's an unbiased informative account:

==quote tom.stoer post==

What exactly is LQG?

It's difficult w/o math.

The problem with quantum gravity is that naive mechanisms to quantize gravity (which have been applied successfully to other fields) fail for gravity. That means that something fundamental has to be changed for quantum gravity.

There are different approaches to solve these problems, e.g.
a) string theory
b) asymptotic safety
c) loop quantum gravity (LQG)

I don't want to comment on a) and b) here.

Essentially LQG does the following: it introduces new variables which replace the (in GR) well-known metric that describes spacetime + curvature. This is pure math, so I don't want to go into details here, but what happens is that these new variables are rather close to fields that we know from gauge theory like QED and QCD. Indeed in a certain sense gravity looks rather similar to QCD, but there is one additional property of gravity that allows one to apply a second mathematical trick which essentially replaces the fundamental fields with something like "fluxes through surfaces" or "fluxes along circles". These surfaces and circles are embedded into spacetime.

The next step is again rather technical and it becomes possible due to so-called diffeomorphism invariance: one can get rid of the the embedding of circles and surfaces into spacetime. Instead one replaces these entities with a so-called spin network, i.e. a graph with nodes and links between nodes where each link and each node carries some numbers which represent abstract entities from which certain properies of spacetime can be reconstructed. You can think about spacetime as made of cells (I will soon tell you that you can't :-); each cell has a certain volume carried by a node; each cell has certain surfaces and the link between different nodes (sitting inside these cells) carry the areas of the surfcaes.

The problem with this picture is that one might think about these cells as sitting in spacetime - but this is fundamentally wrong: this picture is only due to the construction, but basically there is no spacetime anymore; all there is are nodes and links (and certain numbers attributed to nodes and links). Spacetime is no longer fundamental but becomes an entity emerging from the more fundamental graphs with their nodes and links. The graphs are called spin networks b/c the numbers they are carrying have properties well-known from spins. But this is a mathematical property only, it does not means that there are real spinning objects.

Compare this emerging spacetime to a water surface of a lake. We know that it consists of atoms, and as soon as we get this picture it is clear that there is no water between the atoms; the surface is only an emerging phenomenon, the true fundamental objects are the atoms. In the same sense the spin networks are the fundametal entities from which spacetime, surfaces etc. and their properties like volume, area, curvature etc. can be constructed. Dynamics of spacetime (which was curvature, gravitational waves etc. in GR) is replaced by dynamics of spin networks: within a given graph new nodes with new links can appear (there are mathematical rules, but I don't want to go into detail here).

The last puzzle I have for you is the fact that such a spin network is not a mechanical object which "is" spacetime. Instead quantized spacetime is a superposition of (infinitly many) spin networks. This is well-known in quantum mechanics; there is no reason why an atom should be in a certain state; we can achieve that via preparation or measurement, but in principle a single atom can be in an arbitrary complex quantum state which is a superposition of "an atom sitting here, an atom moving in a certain direction over there, an atom moving in this or that direction, ...".

So classical spacetime is recovered by two averaging process: first there seems to be a regime were this superposition of spin networks is peaked around a single classical spacetime, i.e. where one network dominates the superposition of infinitely many spin networks; second from this single spin network one can reconstruct spacetime in the same sense as one can reconstruct the water surface from the individual atoms. But there may be different regimes (e.g. in black holes or closed to the big bang) where is classical picture and this averaging does no longer work. It may be that in these regimes all there is are spin networks w/o any classical property like smooth spacetime, areas, volume etc. It's like looking at a single atom: there is no water surface anymore.

Eventually this is why one started with this stuff: the classical picture of spacetime seems to become inconsistent when one tries to quantize it, i.e. when one defines these superpositins etc. These inconsistencies do not bother us as long as we talk about spacetime here, in the solar system etc. But they become a pain in the a... when we talk about spacetime near a singularity like a black hole or like the big bang. In order to understand these new non-classical regimes of spacetime a fundamentally new picture is required. This is what LQG (and other approaches) are aiming for: construct a new mathematical model from which well-known classical spacetime (like in GR) can be reconstrcuted, but which does not break down in certain regimes but remains well-defined and consistent.

He must so to speak throw away the ladder, after he has climbed up on it - Ludwig Wittgenstein
=====endquote=====

Original post:
https://www.physicsforums.com/showthread.php?p=3319185#post3319185
 
  • #276
  • #277
I'm trying out this Spires search to keep track of Loop early universe phenomenology papers (studying ways to test Loop cosmology.)
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29

It is a reworking of a search I was using earlier--what gets typed into the search terms box is:

FIND (DK LOOP SPACE AND (QUANTUM GRAVITY OR QUANTUM COSMOLOGY) ) AND (GRAVITATIONAL RADIATION OR PRIMORDIAL OR INFLATION OR POWER SPECTRUM OR COSMIC BACKGROUND RADIATION) AND DATE>2008

Just now when I tried it, the search came up with 42 items--papers that appeared 2009 or later.

The proposal of ways to test LQG---in particular the effects of the bounce at the start of expansion (which is a robust feature)---is an important development, I think. Another development is represented by this year's Quantum Theory and Gravitation conference ("QG11") which brings several QG communities together for comparison, sharing ideas, and discussion.
It is a mixed QG conference. We will see if the idea catches on. I have color-coded the list of talks to give an idea of the mix.

Causal Dynamical Triangulations(CDT)
Spectral Action (Connes Noncommutative Geometry)
LQG (incl. Group Field Theory)
Asymptotic Safety
Foundations-general considerations
String
======
Ambjorn: CDT, a quantum theory of geometry
Arnlind: Poisson Algebraic Geometry and Matrix Regularizations
Ashtekar: Quantum Cosmology and the Very Early Universe
Bachas: The problem of localization of gravity
Baez: Higher gauge theory, division algebras and superstrings
Barrett: State sum models and the spectral action
Beisert: Symmetries and Integrability for Scattering Amplitudes in N=4 Super Yang-Mills Theory
Blau: String Theory as a Theory of Quantum Gravity: a Status Report
Bodendorfer: Towards Loop Quantum Supergravity
Bossard: Toward the consistency of N=8 supergravity as a quantum field theory
Chamseddine: The Spectral Action
Compere: The translation anomaly of asymptotically flat spacetimes
Craps: Cosmological singularities in string theory
de Goursac: Renormalizability of noncommutative quantum field theories
Dixon: Ultraviolet behavior of quantum (super)gravity through four loops
Elvang: Symmetry constraints on the UV behavior of N=8 supergravity
Freidel: The principle of relative locality
Giulini: Very basic issues concerning quantum mechanics and gravitation
Hollands: Quantum field theory correlators on manifolds at very large and very short distances
Hoppe: Fundamental Structures of M-brane Theory
Jacobson: How general is the generalized second law?
Lechner: Covariant and local deformations of quantum field theories
Lewandowski: Canonical LQG: soluble models and other advances
Litim: Renormalisation group and the Planck scale
Loll: Nonperturbative highlights on quantum gravity from CDT
Longo: Boundary Quantum Field Theory and Conformal Field Theory
Morton: Extended Field Theories and Higher Gauge Theories
Mukhanov: Massive Gravity
Nicolai: Infinite-dimensional symmetries and the Wheeler-DeWitt equation
Oriti: Group field theory: a brief survey of recent developments
Reiterer: A class of gauges for the Einstein equations
Reuter: Einstein-Cartan Theory and Asymptotic Safety
Rovelli: Loop quantum gravity: the covariant dynamics
Shaposhnikov: Scale-invariant alternatives to general relativity
Speziale: Spin networks as twisted geometries
Steinacker: Matrix models, noncommutative gauge theory and emergent geometry
Wulkenhaar: Ward identities in matrix models arising from noncommutative geometry

I I'm not sure what Nicolai's talk is going to be about but just as a guess classify it "foundations-general considerations"--a potentially important topic suggested on the front page by the organizers.
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:programme
 
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  • #278
  • #279
Marcus,

About Causal Dynamic Triangulation, there still hasn't been much published out in layman's land. In the above discussion of LQG those terms almost describe an engineering model using an element system (something like a hydraulic model using links and nodes). Does this suggest that LQG acts like a secondary field much like eddy currents within an electromagnetic field (solved using a matrice)?

When looking at spin states 2D respresentation seem like "Fractals" as you described previously. How does CDT model or resolve loop gravity?
 
  • #280
Peter McKenna said:
Marcus,

About Causal Dynamic Triangulation, there still hasn't been much published out in layman's land... How does CDT model or resolve loop gravity?

Have you seen the SciAm article on CDT? It's well-written as an introduction for wide audience, and it has links to further reading, some of which is pretty accessible. I keep the URL to the SciAm article in my signature (check the end of this post). It is the "signal lake" link.
http://www.signallake.com/innovation/SelfOrganizingQuantumJul08.pdf

In the above discussion of LQG those terms almost describe an engineering model using an element system (something like a hydraulic model using links and nodes). Does this suggest that LQG acts like a secondary field much like eddy currents within an electromagnetic field (solved using a matrice)?

When looking at spin states 2D respresentation seem like "Fractals" as you described previously...

I'm not sure I can respond adequately. Maybe one of us will start a separate thread specifically to discuss these ideas. This thread does not have much discussion--it is mainly used to provide quick access to selected source material on Lqg.
 
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  • #281
I try to use this thread primarily as a place to keep the best current source material on LQG, including its phenomenology (ways of testing) and application to cosmology.

It should provide quick access to the latest review articles and survey talks.

Here is a search intended to dig up LQG/LQC pheno papers. It now gets 44 articles
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+INFLATION+OR+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=ds%28d%29

To see the latest, change the ordering from "by cite count" to "by date" and repeat the search.

The May 2011 Loops conference in Madrid had some great review talks. Video and slides PDF are available online. It can be useful to download both because you can scan through the slides and then drag the timebutton of the video to a part of the talk where you wish to focus attention. Also the video shows both slide and speaker and may sometimes cut off a part of a slide you want to read. So it may work best to download both and do your own split-screen. Ashtekar and Rovelli gave great survey talks:

Ashtekar's talk (for a Loop cosmology review):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=181
Rovelli's talk (for status and open problems of the full LQG theory):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76

Peter McK expressed an interest in Causal Dynamical Triangulations, and Renate Loll gave a CDT review at the same conference. It's a good way to hear the latest.
Loll's review of CDT:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=182

For the listing of all the talks (linked to an abstract for each):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=75

I'll include Frank Wilczek's Uppsala talk because I think it is a reality-based view of particle physics unification prospects. He gives the most likely picture of matter's future--- that which LQG spacetime geometry is apt to join up with.
Wilczek video: http://media.medfarm.uu.se/flvplayer/strings2011/video24
Wilczek slides: http://www-conference.slu.se/strings2011/presentations/4%20Thursday/1140_Wilczek.pdf
 
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  • #282
I'm currently having difficulty getting some of the videos of the Madrid talks.
The link to Rovelli's talk is:
http://www.iem.csic.es/departamentos/qft/grupos/gravitacional/loops11/Archives/Plenary-Lectures/Videos/Carlo-Rovelli_The-covariant-version-of-Loop-Quantum-Gravity-definition-of-the-theory-results-open-problems.mp4
That works fine. And the link to video of Ashtekar's talk works:
http://www.iem.csic.es/departamentos/qft/grupos/gravitacional/loops11/Archives/Plenary-Lectures/Videos/Abhay-Ashtekar_Recent-Advances-in-Loop-Quantum-Cosmology.mp4
But I believe the link to, for example, Renate Loll's talk is currently broken.
You can try various ones and see what luck you have. Here is the program:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=75
If you click on a particular talk you get a one-page summary with further links to the slides and (in the case of plenary talks given in the morning session) a link to the video, or what looks like one.
For example here are two summary pages:
Ashtekar's talk (for a Loop cosmology review):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=181
Rovelli's talk (for status and open problems of the full LQG theory):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76

Click on Loll's talk and you get the summary page all right:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=182
And you can get her slides PDF. But the link to the video is given as:
http://161.111.24.61/loops11/Archiv...avity-from-Causal-Dynamical-Triangulation.mp4

And that doesn't work. My first guess was that the links to video which are broken are the ones that begin
"161.111.24.61". The talks seem to be archived at two separate locations and one of the systems might be down. But that guess was wrong. If you have any current experience with getting videos of the talks, please share it. I'd like to know what luck others have had. Fortunately I downloaded a number of the talks before this problem developed (but I didn't happen to do that with Renate Loll's)
 
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  • #283
marcus said:
Currently the best review of LQG is this video talk:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76
The talk was given 25 May 2011 in Madrid, at the biannual Loops conference.
...

When I posted that, a few weeks ago, the new version of its written counterpart, Zakopane Lectures, had not yet appeared. Now the new version is out. It has been expanded by an additional 10 pages or so, and rewritten in parts. It's now an excellent tutorial, aimed at advanced grad students ready and wanting to get into Loop research.
http://arxiv.org/abs/1102.3660
The Loop people have introductory winter "schools" for grad students and postdocs. This year they had a two-week school at the Zakopane ski resort. This paper is a condensed version of the series of lectures Rovelli taught at that that school. It has examples and exercises to work out. It reviews the open research problems, some where progress has recently been made. It presents the theory concisely, and also gives an overview of the various approaches that converged to it from different directions.

For a printed journal-style review article, try http://arxiv.org/abs/1012.4707 which appeared December 2010. Ths is not as pedagogical as the other. It is more for nonspecialists who just want a general status report and overview, with some historical background. It is not aimed at people who want to get their hands on quantum geometry and do some research in it.
 
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  • #284
QG growth in France has been remarkable in the past few years. It's interesting to examine what shape this is taking and to try to figure out why.
There are now many active centers of QG research:
Marseille (Rovelli's group)
Paris-Sud (Rivasseau's Orsay group)
Lyon (Livine's group)
Montpellier (Alexandrov, Roche)
Tours (Noui)
Ecole Polytechnique (Gabriel Catren)

http://www.rivasseau.com/
http://en.wikipedia.org/wiki/École_Polytechnique
http://en.wikipedia.org/wiki/Paris-Sud_11_University
http://www.polytechnique.edu/home/about-ecole-polytechnique/awards-and-honors/erc-starting-grant-awarded-to-gabriel-catren-62493.kjsp?RH=1282806775110

Paris-Sud has 4 Fields Medalists and 2 Nobel prizewinners. By Usa standards it is "Ivy", I guess.
The Paris Ecole Poly is like the French MIT---a small elite tech school. These are distinguished places.
It's interesting that Gabriel Catren should get a 5 year European Research Council (ERC) grant to set up a QG research team at the Ecole Poly. The emphasis of that research is on the foundations---the ontology of space and time---a more philosophical approach to basic questions in physics. You can read what he has to say about it at the above link.

I didn't know of Catren. Here is a bit more information:
http://www.crea.polytechnique.fr/LeCREA/fiches/Catren.htm
Perimeter video lectures:
http://pirsa.org/index.php?p=speaker&name=Gabriel_Catren
 
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  • #285
A little over 3 months ago, in post #274, I reported that the job situation (if postdoc fellowships are included) looked fairly good for new loop PhDs from Marseille, Penn State, and AEI Potsdam. This needs to be corrected or qualified by reservations.

The job situation is difficult (as with other areas of theoretical physics). Permanent positions are scarce, so what we are keeping track of are postdoc and other temporary positions.

For one thing, the new PhDs used to be mostly out of Marseille and Penn State, and now several new centers have emerged (Erlangen, Lyon, Beijing Normal, Florida Atlantic, Asia Pacific CTP in Korea, Morelia, Louisiana State, Sydney...to name a few) so it is more difficult to keep track. And it adds to the potential competition.

About all I can do is keep an eye on two or three main centers (Marseille, Penn State, Potsdam AEI) and from those I see new PhDs continuing to be placed, for the most part, but in temporary positions. I'd be glad to get other people's impressions and more accurate assessments based on direct experience.

To hazard a guess just as a casual onlooker (and this could be completely wrong) at this point if you are a new loop PhD to have a good chance at a 2 year postdoc contract or better your advisor should be Ashtekar, Rovelli, or Thiemann. I would be delighted to be corrected on that score.


The journal General Relativity and Gravitation has published a special issue containing written versions of talks at the 2nd QG school and workshop held at Corfu.
http://www.springerlink.com/content/473t7416228530w1/fulltext.pdf
The editors were:
Konstantinos Anagnostopoulos · Paolo Aschieri · Martin Bojowald · Harald Grosse · Larisa Jonke · George Zoupanos
Much of the special issue is restricted access ("pay per view") but John Baez' article is open access ("free") and there may be other stuff like that.
I think the editorial I linked to just now is free.

The main lecture series at the Corfu school were given by Abhay Ashtekar, John Baez, John Barrett, Vincent Rivasseau, Carlo Rovelli. Some of these were lectures were written up and included, along with some of the individual talks.
Here is the TOC for GRG Volume 43 Number 9
http://www.springerlink.com/content/p513t4384471/
This has links to all the ABSTRACTS---just click on the title of the talk. But the full text is in general not freely available.

Editorial
Noncommutative quantum field theory and gravity
Konstantinos Anagnostopoulos, Paolo Aschieri, Martin Bojowald, Harald Grosse, Larisa Jonke & George Zoupanos

Review Article
An invitation to higher gauge theory
John C. Baez & John Huerta

Research Articles
Non-perturbative QEG corrections to the Yang–Mills beta function
J.-E. Daum, U. Harst & M. Reuter

Geometry and observables in (2+1)-gravity
C. Meusburger

Asymptotics of 4d spin foam models
John W. Barrett, Richard J. Dowdall, Winston J. Fairbairn, Henrique Gomes, Frank Hellmann & Roberto Pereira

Braided algebras and the kappa-deformed oscillators
Jerzy Lukierski & Mariusz Woronowicz

Equivariant dimensional reduction and quiver gauge theories
Brian P. Dolan & Richard J. Szabo

Open multiple M2-branes I: quantum geometry of the M5-brane in a C-field
Chong-Sun Chu & Douglas J. Smith

Noncommutative geometry in string and twisted Hopf algebra of diffeomorphism
Satoshi Watamura

Renormalizable noncommutative quantum field theory
Harald Grosse & Raimar Wulkenhaar

Gravitational anomaly and fundamental forces
J. J. van der Bij

UV/IR duality in noncommutative quantum field theory
André Fischer & Richard J. Szabo

Curved space (matrix) membranes
Jens Hoppe

The Coulomb solution as a coherent state of unphysical photons
Glenn Barnich

Gauge symmetry breaking in matrix models
Harald Grosse, Fedele Lizzi & Harold Steinacker
 
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  • #286
Bianca Dittrich has accepted a tenure-track position at Perimeter.
There's an interview with her in Physics Today:
http://www.physicstoday.org/daily_edition/singularities/searching_for_a_theory_of_quantum_gravity

In the course of conversation with Atyy and others, in the Current Status of LQG thread, we came up with four papers which taken together can serve as a review as of August 2011:
https://www.physicsforums.com/showthread.php?p=3485140#post3485140

==quote==
That would make the combined essential "current status" review be
1102.3660 + 1108.2258 +1105.2212 + 1108.0832
Zakopane lectures+Emergence of gravity+Cosmological constant + On the structure
Rovelli + Magliaro Perini + Han + Rovelli
33 pages +6 pages +6 pages + 7 pages
==endquote==

For a video lecture affording an overview of LQG as of May 2011:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76

For Loop Quantum Cosmology status report:
http://arxiv.org/abs/1108.0893

For an index of research activity:

LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)

2005 http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (134 as of 16 Sept, annualized > 180)

http://howlonguntil.net/ 258 since 1 January
The annualized rate in this case 134*365/258 = 189

========================
Two links I want to keep handy relating to the cosmological constant problem:
http://arxiv.org/abs/1002.3966
http://arxiv.org/abs/1103.4841
=========================
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
 
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  • #287
http://www.physics.ntua.gr/cosmo11/Naxos2011/sci_prog.html

Called a "Summer School" but from the looks of the program it was more a high level workshop. The list of participants was mostly experts already established in various fields, not grad students! Interesting mix of Loop gravity, String, Loop cosmology, Asymsafe gravity, Triangulations gravity.

Just concluded. It ran last week 12-17 September

The topic was "Quantum Gravity and Quantum Cosmology"
Morning hour lectures by the likes of Ashtekar and Rovelli (Loop) and Kelly Stelle (String) and
Joe Silk (Latest Obs. Dark Matter) and Robert Brandenberger (Unconventional Cosmology)
Reuter (AsymSafe) Woodard (QG and Inflation) Bachas (String) Tsujikawa (Latest on Dark Energy) Wetterich (Spinor gravity), and so on.

And then after lunch there were 30 minute and 15 minute presentations. Also covering a broad mix of active approaches to QG and QC. To me the program looks like people getting down to business. Cosmology is the ultimate testing ground and whether they struggle or join forces, the different teams have to know each other accurately in depth and confront observations together.

One can say that representative folks from Loop, String, and other innovative approaches to gravity/cosmology were FRATERNIZING on the Aegean island of Naxos. Including major people, leaders in various fields. Nice to see that.

BTW Munich is hosting Strings 2012 and they have already set up their website:
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings.html
We will see if they move a bit in the ecumenical direction of acknowledging the competition (Strings 2008 at CERN had a talk by Rovelli, 2010 at TexasA&M had one by Weinberg on AsymSafe cosmology, 2011 Uppsala had talks by Frank Wilczek and Erik Verlinde)
 
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  • #288
Also in September there was a 3 week workshop about QG at CERN.
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/THInstitutes/2011/QG11/QG11.html
Hermann Nicolai's talk was at 2PM on 21 September and was followed by a scheduled period of discussion that concluded the day. It was titled: Quantum Gravity: Where do we stand?
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/THInstitutes/2011/QG11/talks/QGCERN.pdf

There were 28 slides, each normally repeating as points were added.
Slide 13(3 repeats) was Background Independence
Slide 14(6 repeats) was Canonical Quantization
Slide 15(5) was Geometrodynamics [i.e. original quantum grav. eqn. Wheeler-DeWitt]
Slides 16-18(7) was a sequence of "Numerous Questions..." in which slide 17 posed an unexpected question with some humor/mild shock value.
Slide 19(6) was Loop Quantum Gravity
Slide 20(1) Quantum geometry according to LQG
Slide 21(1) Spin Foams
Slide 22(1) Spin Foam Models
Slide 23(5) Quantum gravity and experiment?
Slide 24(8) A Key Issue: Non-Uniqueness
Slide 25(1) The future of quantum gravity? [humorous illustration]
Slide 26(9) Waiting for news from the LHC.
Slide 27(9) Prospects I
Slide 28(6) Prospect II
 
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  • #289
First introductory LQG textbook went on sale 1 November 2011.
I checked today to see how it's doing. Earier books have covered related topics: canonical GR, application to cosmology etc. this is first wholly devoted to intro Loop.
A First Course in Loop Quantum Gravity
Rodolfo Gambini, Jorge Pullin
Oxford University Press.
https://www.amazon.com/dp/0199590753/?tag=pfamazon01-20
I found several things---one is that you get to browse online. You can look inside the book.
Another is that at least at 7PM Pacific time 3 November it is doing rather well for a textbook:
Amazon Best Sellers Rank: #62,638 in Books
#26 in Books > Professional & Technical > Professional Science > Physics > Mathematical Physics
So it is #26 on the Mathematical Physics bestseller list.

Here's the Oxford Press description:
This book provides an accessible introduction to loop quantum gravity and some of its applications, at a level suitable for undergraduate students and others with only a minimal knowledge of college level physics. In particular it is not assumed that the reader is familiar with general relativity and only minimally familiar with quantum mechanics and Hamiltonian mechanics. Most chapters end with problems that elaborate on the text, and aid learning. Applications such as loop quantum cosmology, black hole entropy and spin foams are briefly covered. The text is ideally suited for an undergraduate course in the senior year of a physics major. It can also be used to introduce undergraduates to general relativity and quantum field theory as part of a 'special topics' type of course.
  • First book on the subject at the undergraduate level
  • Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
  • High interest currently in quantum gravity among physicists worldwide
  • Controversial subject which needs good, impartial introduction from respected scientists
Readership: Undergraduates and beginning graduate physics students, lecturers in physics.​

Masters program at Nottingham, including Loop and other QG research
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx

Some papers:
Loop quantum gravity: the first twenty five years
Survey for non-specialists, historical development and indications the theory recovers classical GR.
http://arxiv.org/abs/1012.4707

Lectures on Loop Gravity
Definitive presentation of Loop gravity, with some math prerequisites:
http://arxiv.org/abs/1102.3660

The Big Bang and the Quantum
Loop cosmology, as of mid-2010:
http://arxiv.org/abs/1005.5491.

Testing:
Loop cosmology derives from LQG and this provides the most accessible route to testing. Here are articles mostly by early universe phenomenologists about ways of testing LQC against CMB data,
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
These articles appeared 2009 or later. As of 3 November there were 45 of them.

Loops 2011 the biannual Loops conference was held in Madrid.
http://www.iem.csic.es/loops11/
Click on "scientific program" in the menu on the left to see the list of talks. Abstracts and slides pdf of most talks are now available, just click on the title. Videos of the plenary session morning talks are online. There were about 100 parallel session talks.

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

Research trends, as of 3 November:

http://howlonguntil.net/ day 307
162*365/307 = 193
816*365/307 = 970

LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2005 http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (162 found, annualized 193)

STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2005 http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (988 found)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1132 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1046 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (816 found, annualized 970)
 
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  • #290
There is currently a broken link in the Nottingham webpage given in the previous post:
Masters program at Nottingham, including Loop and other QG research
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx

The link to "the Quantum Gravity group" near the bottom of the page should be to:
http://www.nottingham.ac.uk/mathematics/research/groups/mathematical-physics/quantum-gravity.aspx
=======================================

Francesca has created a world map of places where LQG research is being done or where you can do a PhD in Loop.
http://maps.google.com/maps/ms?ie=U...985216139270436.0004843830d27f3e6c50e&t=h&z=0

It does not have UC Davis but on the whole it is remarkably complete. It's hard to keep such a map up to date.
As confirmation that Carlip is advising LQG research as well as other QG, see:
http://arxiv.org/pdf/1111.2107v1
 
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  • #291
I want to assemble some information and links about the Quantum Geometry/Gravity program at Erlangen. It is getting to be quite a strong program. They have TWO QG groups, one in the Physics department led by Thiemann and now a second group in the Math department led by Meusburger. The intent is to have several postdocs in each, plus PhD students.

Here is about Meusburger:
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/research-group.html
A postdoc in Meusburger's group is Winston Fairbairn whom we know of as a Rovelli PhD and co-author. There is another postdoc opening. Prof Meusburger recently sent out this email announcement:
==excerpt==
A postdoc position will be available in the quantum gravity group within the algebra and geometry group at the Department of Mathematics, University of Erlangen-Nürnberg in Erlangen, Germany...
==endquote==
for more information:
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/positions.html

Here is about the quantum gravity group in the Physics Department led by Thiemann:
http://theorie3.physik.uni-erlangen.de/people.html

This group has grown by the addition of some strong people who have had experience with various "new models" approaches. Maïté Dupuis comes there from Lyon, for example.
She has co-authored a lot with Etera Livine, who was her PhD advisor, and also one paper with Freidel.

Enrique Borja, who has co-authored with Etera Livine (several) and Freidel (one)

Emanuele Alesci, a Rovelli PhD and coauthor.

It's also interesting that John Baez' student Derek Wise is there.αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
 
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  • #292
Here are results of an InSpire search is designed to turn up observational test-related Loop gravity/cosmology papers. In conjunction with LQG/LQC, the DESY search categories are gravitational radiation, inflation, power spectrum, cosmic background radiation, primordial.

Loop pheno papers (increasingly observational test-related)
Code: 
2000-2003     2004-2007     2008-2011
    6              27           46

Here's for the 4-year stretch (2008-2011)---as of today we get 46 papers.
http://inspirehep.net/search?ln=en&...Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb

If we look at the earlier 4-year stretch (2004-2007) using the same categories, we get 27 papers.
http://inspirehep.net/search?ln=en&...Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb

Here's the same search for the previous 4 years (2000-2003 inclusive), 6 papers found.
http://inspirehep.net/search?ln=en&...Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb

There is a small amount of overlap in the time segments because InSpire counts a paper as having appeared in a certain year, say 2006, if either it was published in professional journal in 2006 or posted as a preprint on arxiv in 2006.
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
 
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  • #293
Research trends, updated as of 25 November:

http://howlonguntil.net/ day 329/365
180*365/329 = 200
855*365/329 = 949

LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2005 http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (200 annualized, from 180 found)

STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2005 http://inspirebeta.net/search?ln=en...2y=2005&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (988 found)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1132 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1046 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (949 annualized, from 855 found)

αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
 
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  • #294
One way to keep track of current developments in LQG is to watch the ILQGS online seminar list. I've shortened some titles for brevity.
ILQGS SEMINAR SCHEDULE SPRING 2012
(All seminars will held at 9:00 AM Central Time)

Code: 
DATE       Seminar Title                                    Speaker(Institution)
1/31  [B]Physics of Bianchi models in LQC[/B]	                   Parampreet Singh(LSU)
2/14 [B] Classical limit of SF on arbitrary triangulation[/B] Claudio Perini(PennState)
2/28  [B]Continuous formulation of the LQG phase space[/B]  Marc Geiller(Paris-Diderot)
3/13  [B]Black hole evaporation in LQG[/B]                        Jacobo Diaz-Polo(LSU)
3/27  [B]BH entropy in LQG new insight from local perspective[/B]    A.Perez(Marseille)
4/10  [B]Effective Field Theory QG from Shape Dynamics[/B]     Tim Koslowski(Perimeter)
4/24  [B]Path integral measure and triangulation independence[/B]      S.Steinhaus(AEI)
5/8    TBA

http://relativity.phys.lsu.edu/ilqgs/schedulesp12.html
Audio files and slides PDF are made availble online at the ILQGS website.
http://relativity.phys.lsu.edu/ilqgs/
The site's blog has commentary by other LQG researchers and background notes.
Note that the 2/28 topic is the Freidel Geiller Ziprick paper, currently leading in our MIP poll. The 4/10 talk is on the topic of the current MIP runner-up.
Two of the talks are concerned with triangulation independence, an important issue, and one deals with the classical limit of spinfoam LQG. Pretty much all are topics of current interest.
==================

For convenience I'll gather some potentially useful links:
Here is Rovelli's group at Marseille
http://www.cpt.univ-mrs.fr/~quantumgravity/

Here's the QG bunch at Perimeter
http://www.perimeterinstitute.ca/Scientific/Research/Quantum_Gravity/

Here is Thiemann's group at Erlangen
http://theorie3.physik.uni-erlangen.de/people.html

Here is Meusburger's group at Erlangen
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/research-group.html

Here is Dittrich's group at AEI
http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/index.html
http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/members/index.php

Here is Oriti's group at AEI
http://www.aei.mpg.de/english/research/teams/microscopicQuantumStructure/members/index.php

Livine's QG group at Lyon
http://www.ens-lyon.fr/PHYSIQUE/index.php?langue=anglais&page=equipe4&souspage=gravite

Pullin's QG group at LSU is part of overall gravity physics, no separate page
http://relativity.phys.lsu.edu/

Ashtekar's Institute for Gravitation and the Cosmos
http://gravity.psu.edu/
see the QG partBy now anyone who follows QG will be familiar with the strong research group at Marseille, so I won't list names there. Perimeter has a lot of well-known people, among the younger researchers: Eugenio Bianchi, Valentin Bonzom, Razvan Gurau, Tim Koslowski, Cecelia Flori, Joseph Ben Geloun. Thiemann's group currently includes Maïté Dupuis, Derek Wise, Emanuele Alesci, Enrique Borja among others. Meusburger's group includes Winston Fairbairn. Dittrich's AEI group incudes Dario Benedetti, Song He, James Ryan, Sebastian Steinhaus (giving the ILQGS presentation this semester), Wojciech Kaminski,...
Oriti's group includes Fotini Markopoulou (as visitor), Matteo Smerlak, Isabeau Premont-Schwarz, Gianluca Calcagni, Lorenzo Sindoni,...
Livine's group at Lyon includes Johannes Tambornino
QG at LSU incudes Jorge Pullin, Parampreet Singh, and Jacobo Diaz-Polo

I should also ennumerate the QG bunch at Penn State. There is a lot to keep track of. Maybe in a later post.

αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
 
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  • #295
To continue the above list:
In the above I should have noted that Kristina Giesel has joined the faculty of Thiemann's group at Erlangen. Also in the above Perimeter QG bunch I should have included Steffen Gielen. This month he moved from AEI (Dittrich group) to Perimeter. http://www.aei.mpg.de/~gielen/

Barrett's QG group at Nottingham
http://www.nottingham.ac.uk/mathematics/research/groups/mathematical-physics/quantum-gravity.aspx (faculty: John Barrett, Kirill Krasnov, Jorma Louko)

More detail on QG at Penn State
http://cft.igc.psu.edu/
(besides many well-known faculty, younger members include Elena Magliaro, Claudio Perini, William Nelson, Adam Henderson, Ivan Agullo---David Sloan until recently of this group is now at Utrecht, Ed Wilson-Ewing has moved on to Marseille, Jon Engle is now faculty at Florida-Atlantic, Param Singh now faculty at LSU)

I shouldn't forget to mention two divisions of the University of Paris: Orsay (Vincent Rivasseau is there) and Paris-Diderot (Marc Geiller). Geiller is giving the February 28 ILQGS talk mentioned in the preceding post, on the Freidel Geiller Ziprick paper.

Hanno Sahlmann has started a QG group at the AsiaPacific CPT (Pohang University of Science and Technology)

Some resource links:

Loops 2011 (many videos and slides pdf of the talks)
http://www.iem.csic.es/loops11/

Undergrad LQG textbook
https://www.amazon.com/dp/0199590753/?tag=pfamazon01-20
A First Course in Loop Quantum Gravity
Rodolfo Gambini, Jorge Pullin
Oxford University Press.

Master's program at Nottingham
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx

Latest review papers
http://arxiv.org/abs/1201.4598
Introduction to Loop Quantum Gravity (Abhay Ashtekar)
and
http://arxiv.org/abs/1108.0893
Loop Quantum Cosmology: A Status Report (Abhay Ashtekar, Parampreet Singh)

Searches for Loop and String/M papers by year (results for 2011 now appear complete):
LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (203 found)
2012 http://inspirebeta.net/search?ln=en...2y=2012&sf=&so=a&rm=citation&rg=25&sc=0&of=hb

STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2006 http://inspirebeta.net/search?ln=en...2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en...2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en...2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en...2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1133 found)
2010 http://inspirebeta.net/search?ln=en...2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1044 found)
2011 http://inspirebeta.net/search?ln=en...2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (928 found)
2012 http://inspirehep.net/search?ln=en&...2y=2012&sf=&so=a&rm=citation&rg=10&sc=0&of=hb

A great series of Perimeter video lectures going back to 2003
PIRSA QUANTUM GRAVITY SERIES
http://pirsa.org/S005
select "semester"=all and "year"=all.
Among the more recent are talks by Eugenio Bianchi, Elena Magliaro, Edward Wilson-Ewing, Aristide Baratin, Philipp Höhn, Maïté Dupuis, Muxin Han, Matteo Smerlak
This recent talk by Joseph Ben Geloun was for some reason not catalogued in the QG series
http://pirsa.org/12010132/ so it does not show up in the above search. (topic GFT, tensor field theory)

ινξςυφΓΘΛΞΠΣΦΨ⋅ℤℕ
 
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  • #296
Phenomenology issues affecting various models, which may already be ruled out, are part of the general QG phenomenology picture http://backreaction.blogspot.com/2012/02/no-evidence-for-spacetime-foam.html that we need to keep track of.
Although the observations discussed here seem not relevant to LQG specifically. In LQG space is not in a simple or naive sense "grainy". Its network states are quantum states of geometry (i.e. refer to relations among geometric measurements)---they're not imagined to be "what space is made of". Lorentz violation such as energydependent speed of light or the blurring of images one might get with a grainy substance are not predictions. One way to say it is QG is not about what space IS but rather it is about HOW IT RESPONDS to measurement. Analogous to basic quantum theory in other areas.

==quote Bee, above link==
...the authors have presented an analysis of the images of 157 high-redshift (z > 4) quasi-stellar objects. They found no blurring. With that, also the holographic foam model is ruled out. Or, to be precise, the parameter α is constrained into a range that is implausible for quantum gravitational effects.

As it is often the case in the phenomenology of quantum gravity, the plausible models are difficult, if not impossible, to constrain by data. And the implausible ones nobody misses when they are ruled out. This is a case of the latter.
==endquote==
 
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  • #297
I read a lot of Three Roads to Quantum Gravity last night. I found a free, legal, online pdf source if anyone wants to check it out too. Kinda for laymen, but it filled in the blanks for me :)
 
  • #298
Three Roads is certainly one way to get an introduction to QG. Right now I want to focus on the TESTING issue which has surfaced fairly recently. Bee Hossenfelder is a QG phenomenologist and she has just posted a paper written with Leonardo Modesto that discusses a completely new mode of QG testing.

It sounds weird to me and dubious but I respect Bee a lot and maybe I have to get used to it.

It is based on Modesto's 2008 paper that CLAIMS that in LQG a black hole will not have a singularity but will open up out the bottom to make a new spacetime region.
Maybe this could be tested and proved wrong without it showing the whole theory to be wrong.
Maybe it is not an airtight case, maybe he made some special assumption or did not derive it correctly from the full LQG theory.

Anyway it gives an opportunity to test SOMETHING, and Bee is involved. So here is Modesto
s original 2008 paper:
==quote==
http://arxiv.org/abs/0811.2196
Space-Time Structure of Loop Quantum Black Hole
Leonardo Modesto
In this paper we have improved the semiclassical analysis of loop quantum black hole (LQBH) in the conservative approach of constant polymeric parameter. In particular we have focused our attention on the space-time structure. We have introduced a very simple modification of the spherically symmetric Hamiltonian constraint in its holonomic version...
=endquote==
NOW HERE IS THE NEW PAPER:
http://arxiv.org/abs/1202.0412
Emission spectra of self-dual black holes
Sabine Hossenfelder, Leonardo Modesto, Isabeau Prémont-Schwarz
(Submitted on 2 Feb 2012)
We calculate the particle spectra of evaporating self-dual black holes that are potential dark matter candidates. We first estimate the relevant mass and temperature range and find that the masses are below the Planck mass, and the temperature of the black holes is small compared to their mass. In this limit, we then derive the number-density of the primary emission particles, and, by studying the wave-equation of a scalar field in the background metric of the black hole, show that we can use the low energy approximation for the greybody factors. We finally arrive at the expression for the spectrum of secondary particle emission from a dark matter halo constituted of self-dual black holes.
15 pages, 6 figures

I LIKE THIS BECAUSE it is a way to DISPROVE the existence of these weird double-mouthed black holes by looking for, and not finding, their distinctive radiation. It's empirical. And if they actually found some matching radiation it might be quite surprising. So good either way.
 
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  • #299
A good introduction to the topic of LQBH (loop quantum black holes) Modesto-style is
http://arxiv.org/abs/0905.3170
Self-dual Black Holes in LQG: Theory and Phenomenology
Leonardo Modesto, Isabeau Prémont-Schwarz
(Submitted on 20 May 2009)
In this paper we have recalled the semiclassical metric obtained from a classical analysis of the loop quantum black hole (LQBH). We show that the regular Reissner-Nordstrom-like metric is self-dual in the sense of T-duality: the form of the metric obtained in Loop quantum Gravity (LQG) is invariant under the exchange "r ↔ a0/r" where "a0" is proportional to the minimum area in LQG and "r" is the standard Schwarzschild radial coordinate at asymptotic infinity. Of particular interest, the symmetry imposes that if an observer at "r" close to infinity sees a black hole of mass "m" an observer in the other asymptotic infinity beyond the horizon (at "r" close to "0") sees a dual mass "mp/m" ("mp" is the Planck mass). We then show that small LQBH are stable and could be a component of dark matter. Ultra-light LQBHs created shortly after the Big Bang would now have a mass of approximately "10-5 mp" and emit radiation with a typical energy of about 1013 - 1014 eV but they would also emit cosmic rays of much higher energies, albeit few of them. If these small LQBHs form a majority of the dark matter of the Milky Way's Halo, the production rate of ultra-high-energy-cosmic-rays (UHECR) by these ultra light black holes would be compatible with the observed rate of the Auger detector.
18 pages, 32 figures. Extra Plot, Improved Numerical Results

I think the more recent paper I'll call HMP http://arxiv.org/abs/1202.0412
Emission spectra of self-dual black holes refines and corrects some of these estimates. Here is an excerpt
==quote Hossenfelder Modesto Prémont-Schwarz (HMP)==
Integrating the inverse of dM/dt to obtain the lifetime, one finds that the time it takes for the black hole to completely evaporate exceeds the lifetime of the universe for m >~ 10−5mp. The primordially produced black holes with masses of about 10−3mp thus would still not have entirely decayed today. Moreover, they would have an average temperature of T ≈ 10−9mp ≈ 109 TeV, which is about in the energy range of the ultra high energetic cosmic rays (UHECRs) whose origin is still unclear. We thus see why the self-dual black holes can make for an interesting phenomenology. However, to arrive at observational consequences we have to make this rough estimate more precise. For this, we take ...
==endquote==
 
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  • #300
One way to see where a field is going is to check the conferences, what speakers and themes emerge as important. We've done that in the past in this thread. 2011 was a big year for Loop, in terms of research output and conferences, so 2012 is likely to be comparatively quiet. One upcoming event is this June Prague Relativity and Gravitation conference:
http://ae100prg.mff.cuni.cz/program
Here are excerpts from the invited speaker list.
...
Abhay Ashtekar (Institute for Gravitation and the Cosmos, Penn State University, University Park )
T.B.A.[my guess is Loop cosmology: inflation, initial conditions at the bounce, power spectrum]
...
Julian Barbour (Department of Physics, University of Oxford, Oxford)
Prague and the conception of general relativity: Kepler, Mach and Einstein
...
Karel Kuchař (Department of Physics, University of Utah, Salt Lake City )
Canonical quantum gravity: Einstein's posthumous anathema
Jerzy Lewandowski (Department of Physics, University of Warsaw, Warsaw)
Loop quantum gravity: The status report
...
Hermann Nicolai (Albert-Einstein-Institut Golm, Potsdam)
Quantum gravity: the view from particle physics
...
Misao Sasaki (Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto)
Inflation and birth of cosmological perturbations
...
Bernard Schutz (Albert-Einstein-Institute Golm, Potsdam)
Gravity talks: observing the Universe with gravitational waves
Alexei Starobinsky (Landau Institute for Theoretical Physics, Moscow)
f(R) gravity--the most straightforward generalization of the Einstein gravity
Robert Wald (Enrico Fermi Institute, University of Chicago, Chicago)
T.B.A.
Clifford Will (Department of Physics, Washington University, St. Louis)
Testing general relativity: Centenary highlights and future prospects

================
Ashtekar has new quantum cosmology results with coauthors Agullo and Nelson, that have not been posted yet but were presented in seminar by Nelson
http://relativity.phys.lsu.edu/ilqgs/nelson101811.pdf
http://relativity.phys.lsu.edu/ilqgs/nelson101811.wav
http://relativity.phys.lsu.edu/ilqgs/nelson101811.aif
and which will be the subject of an invited presentation by Agullo at the April American Physical Society meeting.
They are important results so it seems possible that Ashtekar will feature the new paper in his Prague talk this June.
================
This year's Marcel Grossmann meeting (July, in Stockholm) has these relevant parallel sessions:
http://www.icra.it/mg/mg13/parallel_sessions.htm

L. Quantum Gravity
QG1 Loop Quantum Gravity, Quantum Geometry, Spin Foams (Jerzy Lewandowski)
QG2 Quantum Gravity Phenomenology (Giovanni Amelino-Camelia)
QG3 Asymptotic Safeness and Symmetry Breaking in Quantum Gravity (Eckehard W. Mielke)
QG4 Loop quantum gravity: cosmology and black holes (Jorge Pullin, Parampreet Singh)
for more information: http://www.icra.it/mg/mg13/
================
 
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