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Who are the most respected research groups in QG now?

  1. May 16, 2009 #1
    Hi,

    Just wondering who the big players in QG now, I know obviously Perimeter is huge, but what other research groups are there out there?

    Thanks
     
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  3. May 16, 2009 #2

    tom.stoer

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    I think you should check the homepages of Rovelli, Smolin, Ashtekar, Thiemann and perhaps Bojowald, to mention a few.
     
  4. May 16, 2009 #3

    marcus

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    Azrael, Tom gives you good advice.

    You should have some methods to learn this on your own and make your own assessment.

    Here is one approach. Quantum cosmology (using quantum geometry/gravity to go beyond the bang and hole singularities) is big. So do a keyword search for QC papers ranked by citation count (as a rough measure of visibility and importance.) Make it a recent search, date > 2006.

    http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29 [Broken]

    Because in this search I have selected ranking by citation count, you will see first the papers that other researchers consider the most useful and valuable.
    You will see some names that Tom S mentioned, and some others:
    Ashtekar and others of his Penn State team---Bojowald, Corichi, Param Singh.

    Another active QG research area is spin foam. And the "desy keyword" or DK which the Spires search engine uses for this is "spin, foam". You can do another keyword search, ranked by cite-count, and find out other top respected teams. Rovelli and his collaborators at Marseille will come up, also his former PhD students Freidel and Livine and Speziale. Here is the "DK spin,foam" search

    http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+spin%2C+foam+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29 [Broken]

    Probably, to answer your question, Rovelli has the largest most respected group in Quantum Gravity. His PhDs, who studied with him at Marseille are a large productive group, among the most cited, and among the most invited to speak at conferences and workshops. But you should learn to make the assessment yourself. At his personal website, Rovelli has a list of those whose PhD thesis he has guided as advisor. There are a dozen prominent names and these are the names you will often see if you look at the websites of upcoming conferences to see who has been invited to talk to the plenary session. They are former students at Marseille and they have spread out to a number of other institutions. (like Perimeter, which you mentioned, but not only there).

    Besides Penn State and Marseille there are other important centers:
    Utrecht, in Holland
    Potsdam (Albert Einstein Institute) in Germany
    Nottingham and London in the UK
    Wroclaw in Poland
    and other places in other countries. Particular Loop QG has spread out a lot. We are seeing LQG research from South America, Mexico, China, India, other European countries I haven't mentioned, and also the hosting of LQG conferences.

    I don't know what amount of detail you want. If you just want the top two teams, then you can see from citation-ranked search that they are obviously Marseille (Rovelli) and Penn State (Ashtekar). Please ask some followup questions if you want to know more.
     
    Last edited by a moderator: May 4, 2017
  5. May 17, 2009 #4
    Thanks so much to both of you, that info has helped me alot. How is Nottingham, UK regarded in general within the list you mentioned? I notice high ranked citations from Kirill Krasnov and Barret, how about Jorma Louko?
     
  6. May 17, 2009 #5

    tom.stoer

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    Barret is one of the inventors of the Barret-Crane model. In the meantime this model had to be modified - I think Rovelli worked on a "new graviton vertex" - nevertheless it is one of the most studied models for the QG path integral formalism.
     
  7. Jun 13, 2009 #6
    Hey, thanks for your replies again, sorry I've been out the country for the last few weeks so unable to reply.

    I was hoping for some advice on my potential PhD choice, basically I can either study string theory for 5 years at a mid 40's ranked US university, or go to Nottingham and study QG. Finding it quite hard to compare the two choices, as it's not exactly like for like, and I feel at this stage in my career I certaintly don't know enough about either String Theory/QG to say which will be the most fruitful path. I was hoping someone else may have some wisdom to share?

    Thanks
     
  8. Jun 13, 2009 #7
    It's very hard to get a job doing strings, and it is even harder to get a job doing non-string QG. My advice would be to choose whichever experience sounds more fulfilling, since both have slim chances of becoming a career, although string theory has much better job prospects they are still nothing to write home about.
     
  9. Jun 13, 2009 #8

    marcus

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    I think the kind of QG you would be exposed to at Nottingham has more research future than string does.

    You mentioned Krasnov. Check out http://arxiv.org/abs/0905.4916
     
    Last edited: Jun 13, 2009
  10. Jun 13, 2009 #9

    marcus

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    I don't know if Azrael objects to living in Canada or Europe. I think we need some objective measure here to balance subjective impressions. Of course it's hard. The question is gauging how hard.

    Let's have a look at the list of Renate Loll's past PhD students and where they are now.
    Even more relevant is the list of Carlo Rovelli's PhD students.
    Ashtekar's have also done well.

    From looking at the publication rates and the new names I would say that people are getting into QG (quantum geometry/gravity) and into QC (quantum cosmology) at the moment. Maybe because it's newer and easier to find interesting problems to work on. For whatever reason.

    If anyone wants to check, here are some links:
    http://www.phys.uu.nl/~loll/Web/group/group.html (scroll down to former students and former post-docs)

    http://www.cpt.univ-mrs.fr/~rovelli/vita.pdf (scroll down to page 5, listing PhD-thesis supervised, it says where they are now.)

    John Barrett at Nottingham was recently (2006?) put in charge of a chunk of ESF (Euro Sci Foundation) funding to support QG (quantum geometry&gravity).
    His network supports workshops, conferences, etc and the mandate is for non-commutative geometry approaches as well as usual nonstring QG.
    Here is a major workshop/school Barrett's agency is supporting that happens this year. Anyone interested in QG should attend this if they can.
    http://www.physics.ntua.gr/corfu2009/qg.html
    Nottingham has got to be a QG nerve-center, in touch with the most active trends.
    Last year the main QG conference was in Nottingham:
    http://www.maths.nottingham.ac.uk/r...ntum_geometry_and_quantum_gravity_conference/
    Here's the main url:
    http://www.maths.nottingham.ac.uk/qg/
    I don't see how Azrael rates having the option of going there, maybe is Brit and already has a track record inside the UK system?
     
    Last edited: Jun 13, 2009
  11. Jun 13, 2009 #10

    turbo

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    You might want to look into the work of Thanu Padmanabhan, too. He is coming at the gravitation question from the classical side, but has posited that the vacuum may play a role in gravitation, as Sakharov did in the '60's. The last time I checked, he was modeling the vacuum as an elastic solid, but he was treating it as a monolithic entity, which seems to preclude a dynamic model of gravitation. If the vacuum cannot be polarized/densified/rarified by the presence or absence of embedded matter, it's hard to see how it can be an active player in gravitation, instead of a passive background against which gravitation plays out.
     
  12. Jun 13, 2009 #11
    I don't object to living in Canada or Europe (I'm from the UK originally btw), I wouldn't be working directly with Krasnov or Barrett at Nottingham also,so I don't know if that's a negative factor.

    With the US option my worries are it's only ranked mid 40's, and as has been mentioned string theory is super competitive, so not sure how I'd fair without a big name advisor. Also the fact the length of the programme is almost double that of Nottingham, and also it would have a TA load that might interfere with research, whereas Nott wouldnt. The Pros however are that it's in a place in the US that I would really like to live, and I would be travelling, seeing the world etc, so if I didn't make it into academia at least I would of had a good experience in that sense.

    Nottingham however, my worries are I've lived in cities like that all my life, so location wise pretty dull, second no (or not many) postgrad taught courses and exams, so no idea how I'm going to learn QFT, Symmetries, Topology and everything else I need to know. My worry is if I'm expected to just get going and start research I'm going to be swimming out of my depth here. Good points are that it's shorter, there are seemingly well respected members in the group at least like Krasnov/Barrett, and maybe QG would be a better feild in terms of my chances (especially in Europe which seems a less harsh culture than US academia, I'm just guessing though).
     
  13. Jun 13, 2009 #12

    marcus

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    When you have to make your choice?

    In many places it is possible to change advisor, if you develop a line of interest that matches better with some other member of the department.

    Do you know what the rule is at Nott? They could for example just automatically assign you to someone like J.L. who maybe doesn't have a lot of advisees that term. And then a year or two down the road you might have developed an interest that is more in line with K.K. or J.B. and there might be some minor bureacrat form to fill out and apply to switch advisor and presto.

    That's something you could find out about if you have time.

    If you have to have made up your mind by next week then it's too late to investigate such fine points.

    If you have, say 6 months before you must make your choice, then it's different. In that case I would urge you to attend the Corfu School this September. John Barrett's QG network funded it, and it lasts one week. All the hot topics in QG are represented.
    You have one week to network with bright insider post docs (the most hip people career-wise). Here is the Corfu lineup:
    http://www.physics.ntua.gr/corfu2009/qg.html
    If the Corfu school is too advanced for you, write me a PM and I may be able to suggest other ideas.
    If the Corfu school is unaffordable, they plan to put the lectures online so at least that part is free online.
    Alejandro Sachs who blogs was at Nott, working with J.L. at one time, maybe still is. You might email him and get some advice.
    Frank Hellmann who sometimes posts here at PF is or was at Nott, I don't know which advisor. You could PM/email him and you might get some advice.

    ==quote from Corfu lineup==
    School main lecturers and topics:
    Prof. Abhay Ashtekar
    Title: Loop Quantum Gravity
    Abstract
    This set of lectures will provide an introduction to loop quantum gravity through the simpler setting of loop quantum cosmology. The goal will be to provide a concise summary of the conceptual framework, salient results and open issues. The time limitation will not permit me to give detailed proofs and technical details for which I will provide a guide to literature.

    Table of Contents

    Background independence and non-perturbative methods.
    General relativity in terms of connection variables.
    Loop quantum cosmology: Kinematics.
    Loop quantum cosmology: Dynamics.
    Principal results and open problems of loop quantum gravity.
    ************

    Prof. John Baez
    Title: Categorification in Fundamental Physics
    Abstract
    Categorification is the process of replacing set-based mathematics with analogous mathematics based on categories or n-categories. In physics, categorification enters naturally as we pass from the mechanics of particles to higher-dimensional field theories. For example, higher gauge theory is a generalization of gauge theory that describes the parallel transport not just of particles, but also strings or higher-dimensional branes. To handle strings, we must categorify familiar notions from gauge theory and consider connections on "principal 2-bundles" with a given "structure 2-group". One of the simplest 2-groups is the shifted version of U(1). U(1) gerbes are really principal 2-bundles with this structure 2-group, and the B field in string theory can be seen as a connection on this sort of 2-bundle. The relation between U(1) bundles and symplectic manifolds, so important in the geometric quantization, extends to a relation between U(1) gerbes and "2-plectic manifolds", which arise naturally as phase spaces for 2-dimensional field theories, such as the theory of a classical string. More interesting 2-groups include the "string 2-group" associated to a compact simple Lie group G. This is built using the central extension of the loop group of G. A closely related 3-group plays an important role in Chern-Simons theory, and it appears that n-groups for higher n are important in the study of higher-dimensional membranes.

    Table of Contents

    Connections on abelian gerbes.
    Lie n-groups and Lie n-algebras.
    Multisymplectic geometry and classical field theory.
    Higher gauge theory, strings and branes.
    ***************

    Prof. John Barrett
    Title: Spin networks and quantum gravity
    Abstract
    The series of lectures will be devoted to explaining techniques of spin networks and outlining their use in models of quantum space-time and quantum gravity. The lectures will start with the classical SU(2) spin networks, explaining the diagrammatical techniques and the construction of the Ponzano-Regge model of 3d quantum gravity. Then the q-deformation of spin networks and the Turaev-Viro model are constructed, together with an explanation of the completion to a topological quantum field theory. Next, observables are introduced in these models, and some related models of quantum space-time are also mentioned. Finally, there will be an introduction to some four-dimensional models, both the topological ones, and, briefly, an outline of four dimensional gravity models.
    *******************

    Prof. Vincent Rivasseau
    Title: Renormalization in Fundamental Physics
    Abstract
    Renormalization was first invented to cure the short distance singularities in quantum field theory. Simultaneously constructive field theory developed combinatoric tools to also attack the neglected divergence of perturbation theory. It was later understood that the renormalization group is the correct tool to track the change of physical phenomena under change of observation scale. Then it was realized that the correct notion of scale is not always naively related to short or long distance phenomena, but rather to the spectrum of the propagator. This allowed in the recent years to understand how to renormalize noncommutative field theory, and to attack with a fresh look and new hopes the problem of renormalizing quantum gravity.

    Table of contents

    Renormalization in ordinary QFT.
    Constructive Field Theory Primer.
    Noncommutative Field Theory.
    Noncommutative Renormalization.
    Towards renormalizing Quantum Gravity.
    ******************


    Prof. Carlo Rovelli
    Title: Covariant loop quantum gravity and its low-energy limit
    Abstract and content

    I present a new look on Loop Quantum Gravity, aimed at giving a better grasp on its dynamics and its low-energy limit. Following the highly succesfull model of QCD, general relativity is quantized by discretizing it on a finite lattice, quantizing, and then studying the continuous limit of expectation values. The quantization can be completed, and two remarkable theorems follow. The first gives the equivalence with the kinematics of canonical Loop Quantum Gravity. This amounts to an independent re-derivation of all well known Loop Quantum gravity kinematical results. The second the equivalence of the theory with the Feynman expansion of an auxiliary field theory. Observable quantities in the discretized theory can be identifies with general relativity n-point functions in appropriate regimes. The continuous limit turns out to be subtly different than that of QCD, for reasons that can be traced to the general covariance of the theory. I discuss this limit, the scaling properties of the theory, and I pose the problem of a renormalization group analysis of its large distance behavior.

    ==endquote==
     
    Last edited: Jun 13, 2009
  14. Jun 14, 2009 #13
    Thanks again, have to make the choice ASAP so no time to ask extra details, pretty sure my advisor would end up being JL throughout though (due to my background mostly).

    The blog from Alejandro Satz was a really helpful insight. The one worry I have about Nott now is that presumably unlike US gradschools I wont have any taught grad courses, so I wonder how on earth I'm going to learn the finer points of QFT, groups, topology and more advanced things still. I do worry with the US school though, that somewhere only ranked in the 40's isn't going to be well renowned enough for me to succeed in String theory.
     
  15. Jun 16, 2009 #14

    Haelfix

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    The job market right now is very bleak for theoretical physicists in general, much less specific fields like string theory or quantum gravity.

    Theres really no way to sugercoat it, no one has seen it this bad or this competitive in their lifetime. Hopefully things will be better in a few years, but there are no guarentees.
     
  16. Jun 16, 2009 #15
    So would the general consensus be that one would have a better chance of "making it" doing QG at Nottingham, than doing Strings at mid 40's ranked US gradschool? I know that question is quite hard to answer since it depends on so much, I mean Nottingham seems to have some good people and hosts lots of conferences/workshops were the likes of Rovelli can be found. On the other hand String theory is much more mainstream, and jobs could potentially be found all over the US.

    Another issue that worries me is the education one would get doing a PhD in the US vs the UK, by which I am referring to the fact in the US almost two years would be dedicated to lectures on things from QFT, groups & symmetry, Gauge theories, String theory etc, whereas I'm not sure how you are expected to learn these things in a UK PhD (presumably you are told what books to read and are sent away to read them?? alongside doing your research in the daytime). Maybe someone whose done a UK PhD in a similar already could negate these fears?
     
  17. Jun 16, 2009 #16
    Please define the latter.

    Are you making plans to see yourself at a certain situation in, say, 10 years from now? What is this "certain situation" that you aim at?

    It appears that you are tracing the best route possible in order to get a tenure track or permanent position doing research in quantum gravity, is this correct?

    Well, I have no experience in the situation in those countries that you mention, so I will not offer advices on them. However, I will offer a general advice: you will have to work hard, very hard, in whichever choice that you make now in order to have a career in theoretical physics. Also, you will have to decide whether you are willing to do Science or science ("S" or "s"). My blog has a recent comment section that explain these.

    Best
    Christine
     
  18. Jun 16, 2009 #17
    Yeah, I guess my definition of making it would be a tenured position, or at the very least in the short term to come out of a group that is respected enough to ensure that (provided I've made a good job of the PhD) I can secure a decent postdoc position. I just don't want to finish my PhD and be high and dry and flung back into industry I suppose, no matter how much work I do in it.
     
  19. Jun 16, 2009 #18

    marcus

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    You mentioned that the US medium-grade university is in a nice place where you would like to live, and this enters into the decision. I'm curious, what place or region?

    I'm guessing it's the west coast. A lot of people want to live in or around SF, or down the coast in places like Santa Cruz, Santa Barbara, San Diego.
    Personally I don't like the LA area much, but lots of people do obviously.

    You mentioned several times that in the US system you get graduate level courses (with lecture and homework problem sets) to guide your learning. In UK, not so much, apparently. That might be decisive. The attractive environment and the structured learning might be an over-riding consideration for you.
     
  20. Jun 16, 2009 #19
    Yeah, it is California (perhaps I have an idealized image of this place, but at the very least it will be new and I think a good experience for me to live somewhere like this. If I was just comparing two identical PhDs one in Nott, one in CA I would definitely take the latter). Also yes the structured nature of the course, with it's graduate lectures also appeals to me (but of course this also means it will be almost double the length to completion). But I would sacrifice both location and course structure if I thought academically Nott was going to be better for me than the other gradschool (after all I can always do postdocs and things in nice locations later in life).

    So to break it down, US gradschool:
    Pros:
    Location/Travel/Lifestyle
    Graduate lectures
    Cons:
    Only mid 40's, is this kind of ranking good enough, respectable for career in ST?
    5-6 Years in length, vs just 3 in the UK

    Whereas Nottingham:
    Pros:
    Seems respectable to me, well known people like Krasnov/Barrett. Also conferences with the likes of Rovelli plenary speaker etc.
    3 years in length
    Cons:
    Location doesn't excite me at all being from the UK myself anyway.
    I worry about how I am going to learn advanced topics such as QFT/Gauge/Topology, without the rigorous lecture struct. Will it be just independant book reading alongside research etc.

    Think that sums it up, my open questions are is a mid 40's US gradschool good enough to make it (by which I mean as I defined earlier) in ST? and in regard to Nottingham, will a UK PhD give me the support to learn advanced topics, given that I've never taken formal lectures in these before?

    Cheers
     
  21. Jun 16, 2009 #20
    I don't know much about faculty positions outside the US, but as you say string theory is much more mainstream than non-string QG and there are a much larger number of departments with positions availible in particle theory, nuclear theory, and now even condensed matter theory for people who do strings. In general quantum gravity is not a mainstream research topic, in the mainstream we already have a theory of quantum gravity (string theory) and so the big theoretical goal is no longer outstanding, and since no one has any good mainstream proposals for testing gravity in a quantum regime (needless to say we have yet to detect classical gravity waves) I would say that the interest in QG itself is pretty low throughout mainstream research.

    Right now mainstream people are much more interested in understanding non-equilibrium non-perturbative QCD, and right now strings are the only tool for doing this. An understanding of this physics will help us to observe quarks more directly than ever in the jets that will be produced at the LHC, and to better understand the phase diagram for QCD e.g. a confining phase (which is a big part of the the Yang-Mills Clay Institute millenium prize problem), asymptotically free phase, quark-gluon plasma, color superconductivity, these are all very active research topics in particle/nuclear/condensed matter theory that are currently being researched only by string theorists and experimentalists and are pressing questions because this events will be going on at the LHC.

    I hate to say it, but non-string QG is hardly distinguished from outright crackpottery by most mainstream theorists. The typical reaction of a particle theorist faculty when a graduate student says "I heard this idea that spacetime can be modeled out of these simplexes/foams/whatever and I was wondering..." is to fight back a cringe and change the subject. A major part of the graduate school experience is to reduce naivete, so that the student knows the difference between a real research problem and a bowl of noodles, and frankly an interest in non-string QG or other non-standard Arxiv items is taken by many theorists as a sign of immaturity in this regard.

    If you one day want a tenure-track position my advice is to not do non-string QG, only do string theory if you absolutely must (and even then don't insist on researching QG), and take a look out how much interesting physics there is beyond the undergraduate level. Condensed matter theory in particular employs all of the mathematics that is found in particle theory (e.g. QFT and gauge theory), and some of the mathematics of string theory, but with much better job prospects.
     
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