Who are the most respected research groups in QG now?

[Azrael84]

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

 

[tom.stoer]

I think you should check the homepages of Rovelli, Smolin, Ashtekar, Thiemann and perhaps Bojowald, to mention a few.

 

[marcus]

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

I think you should check the homepages of Rovelli, Smolin, Ashtekar, Thiemann and perhaps Bojowald, to mention a few.

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.

 

[Azrael84]

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?

 

[tom.stoer]

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.

 

[Azrael84]

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

 

[ExactlySolved]

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.

 

[marcus]

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. ...

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

 

[marcus]

...harder to get a job doing non-string QG...

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?

 

[turbo]

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

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.

 

[Azrael84]

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 field in terms of my chances (especially in Europe which seems a less harsh culture than US academia, I'm just guessing though).

 

[marcus]

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.

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==

 

[Azrael84]

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 won't 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.

 

[Haelfix]

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.

 

[Azrael84]

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?

 

[ccdantas]

"making it"

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

 

[Azrael84]

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.

 

[marcus]

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.

 

[Azrael84]

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

 

[Civilized]

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.

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.

 

[Civilized]

Some people prefer to be outside the mainstream, others don't. For perspective on life in the mainstream here is the physics research being done at:

http://www.physics.harvard.edu/research/facresearch.html" [Broken]

http://web.mit.edu/physics/research/index.html"

http://www.pma.caltech.edu/GSR/physresearch.html" [Broken]

There isn't any non-string QG on any of those pages. Based on my impressions, non-string QG barely exist as far as the professors on those pages are concerned. Researching non-string QG seems like a lonely road, even by academic standards.

 

[atyy]

Some people prefer to be outside the mainstream, others don't. For perspective on life in the mainstream here is the physics research being done at:

http://www.physics.harvard.edu/research/facresearch.html" [Broken]

http://web.mit.edu/physics/research/index.html"

http://www.pma.caltech.edu/GSR/physresearch.html" [Broken]

There isn't any non-string QG on any of those pages. Based on my impressions, non-string QG barely exist as far as the professors on those pages are concerned. Researching non-string QG seems like a lonely road, even by academic standards.

http://web.mit.edu/physics/facultyandstaff/faculty/xiaogang_wen.html
http://dao.mit.edu/~wen/
http://www.rle.mit.edu/emergent/

His theory of gravity has some problems - the calculation with the right dispersion relation is handwavy, and the one which isn't has the wrong dispersion relation - but he is working on it. http://pirsa.org/08110003/

 

[MTd2]

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.

AdS/QCD is not string theory.And even though we haven't gravitational waves, we also haven't found any evidence for supersymmetry.

You are right about other parts of physics, specially condensed matter. Indeed, what condensed matter has been doing for the last 5 years is approaching the marvelous thing we that seems to be crazier than sci fi, just look at the daily torrent of articles on arxiv about graphene, superconductors and the recent stuff of topological insulators(I really want to take a look at that). And most of this research is guided by computer simulations of lattices, amazing...

But, this is a sort of forum for people who want guidance in the (speculative) high energy field, so, I don't if it will work by telling them they are out of perspective when not looking for non-stringy super gravity, because I am sure they are aware of that...

 

[Civilized]

AdS/QCD is not string theory.

I think you mean that AdS/QCD would not be beyond the standard model, but it is definitely string theory. The whole point is that strings in AdS are dual to quark pairs in supersymmetric SU(N) gauge theories, which are qualitatively similar to QCD.

But, this is a sort of forum for people who want guidance in the (speculative) high energy field, so, I don't if it will work by telling them they are out of perspective when not looking for non-stringy super gravity, because I am sure they are aware of that...

First of all, most mainstream work on physics beyond the standard model does not pertain to quantum gravity, so the title of this forum does not make anyone in the mainstream think of non-string QG. In fact, this aspect of this subforum is as skewed a conference entitled "People from China" where the attendees are anglo-saxons who have visited China.

There are three reasons why I am preaching to this choir about their being outisde the mainstream: (1) the OP asked about employability (2) it's one thing to romantically think of oneself as an independent rebel outside the mainstream, but it's something else to look at what kinds of people and places that you would be alienated from, and (3)because I personally think it is a travesty for impressionable young students to be lured into studying non-standard topics that prevent them from being a part of the broader scientific community.

And even though we haven't gravitational waves, we also haven't found any evidence for supersymmetry.

I'm not sure of your point here, gravitational waves are a much greater theoretical certainty than supersymmetry, which is itself a more bold but less certain theoretical prediction. It's also true that neither have been discovered. My point was that the state of the art in gravitational experiments has a long way to go before confirming the classical theory (e.g. gravitational waves) and so in the mainstream there is little hope of experiments which probe quantum gravity (in fantasy land there is lots of hope).

Atyy, it's interesting that you mention Wen since I actually hear people in the mainstream talking about his model as well. This is the good thing about being in the mainstream: people take Wen seriously even though his ideas are coming out of left field. I wouldn't begin to discourage anyone from studying with his group. His work is a counter example to my statements, but in my defense it is a new approach and judgement has yet to be passed. Historically there was also a mainstream interest in LQG (~1990-1995) until things panned out an it became clear to most people that it was unworkable.

 

[MTd2]

The whole point is that strings in AdS are dual to quark pairs in supersymmetric SU(N) gauge theories, which are qualitatively similar to QCD.

No need to consider strings anywhere. We are just talking about Super Yang whose coupling constant is inversely related to the the constant curvature of and AdS where and ensamble of CFT is defined. This is a mathematical device, like the use of poles when doing complex integrals.

And I don't see what is the problem of not being part of a "being a part of the broader scientific community" because there is almost no real perspective of why science that needs strings itself, aside from its collateral mathematics developments. The same reasoning goes to most of the "non mainstream" QG. The exception to the non mathematical part of strings being the small community around Cumrun Vafa that lately came up with something with predictive out of F-Theory.

But I welcome such side effects of studying models, and the more diverse they are, the better. Anyway, the non stringy QG community is growing fast, you can see on arxiv.

PS.: Most people or close to 50% of people on loops 2009 are chinese.

 

[Fra]

The topic was "the most respected research ..."...

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.

To the extent this is correct (it is at times) I'd expect anyone believing in what Christine calls capital "S" to fight this narrow minded attitude, for the same reason a medical doctor is supposed to want to try to cure diseases (and not first make profit for the owners of the hospital).

Doesn't there to be some intellectual space to distinguish between naivety and open minded creativity. Anything less than that is not respectable from my point of view, and I would not want to join such narrow minded community for money - after all, there are FAR easier ways to make money if that's the issue.

/Fredrik

 

[Haelfix]

Right now, the job market for string theorists is brutal. I know a number of brilliant grad students and postdocs in the subject that are struggling for positions and thinking about related fields instead (eg if you are a condensed matter/ADS physics, its not a bad move to simply go into CM instead). What position your school ranks is important, but then its hard for even the best harvard or princeton theorist to find a position atm as well, so take that for what its worth too.

That might change after the LHC has some data, fads in physics are definitely a big part of eventual hiring scenarios.

As for nonmainstream ideas. Its also a big risk. You pigeonhole yourself too a few research groups (that are also very competitive) and the winds have a tendency to change rapidly in those directions. If you are working on Horava gravity, (which has received a lot of attention recently) there is a high risk that you are not going to end up with a job in that field of research in 4 years.

 

[Fra]

Another philosophical reflection about goals and ambitions in life, that might not be totally irrelevant here...(?)

About risks, I see several types of "risks".

(a) The risk that you invest in something that still renders your unemployed; This is a practical problem of getting food on your table.

(b) The risk that you invest in something that will constrain your search for the answer to your questions; This is intellectual frustration.

(c) The risk that you get food on your table in ways you didn't expect; and get to search your answers in ways you didn't expect, but perhaps with much less time to spend on it than you hoped.

Which is worse when realized and what is most likely to occur?

/Fredrik

 

[ccdantas]

I think that Fredrik's points are important questions to enter Azrael84's equation.

Perhaps the most important practical advice would be: to have a "plan B". Everyone should have a plan B.

As Haelfix points out, the "job market for string theorists is brutal". At this point, it's very difficult to have guarantees on anything (well, this is often true in life!). Even if you think that you follow a path that supposedly increases your chances (and in the eventual case you are not bothered by (b)), there are no guarantees. Have your plan B anyway.

I think that (c) is the most likely outcome, in general cases. And it is often *the* plan B! Point (a) is too idealistic when you grow older and have responsabilities with your family. But it can work for a while if you are young and single. Even then you need a plan B in order to have a minimum of survival. Or you can be like Garrett Lisi...

Azrael84 mentions: "I just don't want to finish my PhD and be high and dry and flung back into industry". Not necessarily so, but perhaps you should consider being a university professor/teacher. This would not give you full time for research but it is a possibility for your plan B.

Bottom line is: what do you really *want* to do with your life? Make a decision on what you *really* like and go for it. With your plan B in the pocket.

 

[Civilized]

No need to consider strings anywhere.

I don't know where your getting this, the basis of the duality is that strings in the bulk AdS space have their endpoints on the boundary of the space. The endpoints of the strings correspond to the quarks in the CFT that lives on the boundary. The whole point is to do string calculations in the AdS bulk to learn about the properties of quarks on the boundary. This is a non-perturbative tool, you say:

We are just talking about Super Yang whose coupling constant is inversely related to the the constant curvature of and AdS where and ensamble of CFT is defined.

But AdS with a curvature constants and no strings is only dual to a CFT with an inversed coupling constant but no quarks. In other words, without strings you can only describe the trivial solution where the CFT fields vanish. If you want the CFT to have quarks in it so that something interesting happens, then you have to put strings in the AdS bulk to get some dynamics.

This is a mathematical device, like the use of poles when doing complex integrals.

I disagree, poles in the complex plane were not invented and studied by physicists, and they have no physical properties by themselves. String theory is a physical theory, it describes the physics of relativistic strings, essentially strings with infinite tension. The strings in AdS are not fundamental constituents of matter, but they are an exact description of quark gluon pairs in CFT. You might notice that two quarks connected by a gluon flux tube are very similar to a string with nearly infinite (over some range of distances) tension. There is much more to the correspondence than a mathematical device.

The topic was "the most respected research ..."

in QG, which made me think of Vafa and other top string theorists. But of course I came into the thread and it was all about non-standard QG. It is really sad to me that some people use plain 'QG' to refer to non-standard physics in a forum where students might get the wrong impression, which I am trying to counteract.

And I don't see what is the problem of not being part of a "being a part of the broader scientific community" because there is almost no real perspective of why science that needs strings itself, aside from its collateral mathematics developments.

When you say "almost no real perspective" I don't think you are referring to top research universities. These people know the Witten-Weinberg theorem, so they know that any other theories of quantum gravity besides string theory are one of (1) not lorentz invaiant (2) non-renormalizable and (3) not quantum field theories. Furthermore, they know that string theory can already describe quantum gravity and that the theory is finite to all orders in pertubation theory (no need for renormalization). Science needs string theory because within our current scheme of conceivable physical theories it is the only possible way to extend QFT to a UV-completion and build a quantum theory of gravity.

To the extent this is correct (it is at times) I'd expect anyone believing in what Christine calls capital "S" to fight this narrow minded attitude, for the same reason a medical doctor is supposed to want to try to cure diseases (and not first make profit for the owners of the hospital).

Believe me, the mainstream is not narrow minded, but they are somewhat judgemental. What allows them to be judgemental is mathematics, since this separates viable theories from inviable ones more quickly and more definitely than intuition, fantasy, etc. As I stated above, the mainstream accepted LQG until it was found to violate Lorentz-invariance and then they moved on. The LQG people claim to have reformulated themselves so that they are no longer lorentz violating, but now its not even a QFT and the mainstream perspective is that not being a QFT puts you back in the dark ages and is unacceptable for the concievable future.

Oh, who is Christine and what is captial S?

But I welcome such side effects of studying models, and the more diverse they are, the better. Anyway, the non stringy QG community is growing fast, you can see on arxiv.

OK, but the people who have developed 20th century physics do not welcome the side effects of studying these models, since in the mainstream they have already been falsified in so far as they are coherent.

Also, since most non-string QG papers do not get peer-reviewed, looking at amount of activity does not give you any indication of whether it is being done in a professional or scientific way. Every now and then someone needs to take a bunch of rapid communications results and bundle them into a review paper that actually gets peer reviewed, but non-string QG doesn't do that.

Rewriting and reformulating everything every six months is nothing like the way that mainstream science is done, but it is a good way to prevent your theories from being outright falsified (keep rewriting them, obsfucate the details) and this is what I see in non-string QG.

 

[marcus]

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

Hi Azrael, up to now I don't think I've given you any definite advice, just given general views and info and tried to elicit some more detail. Now I will say I (since you have asked repeatedly for advice) that I think the US 5-year option is better suited to your needs.

I say this not because I think a string Phd is better than nonstring Phd at this point in time but because you have just these two specific options that you described and frankly you don't want to live in Nottingham. Wouldn't be happy there. You want the California coast.
And in 5 years the job market may have changed. So if you have a secure grad school berth for 5 years in a nice place go for it. Also you need those US grad level courses, you are not the independent self-study type.

But I have also more higher-level reasons besides immediate security and happiness.
Let's say that the "mid-40s" California school is UCSC which in physics ranks 45 in USNews listing.
It has Tom Banks, it has Tony Aguirre (in cosmology), it has Stefano Profumo (young, brilliant, fun particle physics and cosmology). It has a great older guy Joel Primack who both helped put together the Standard Particle Model in the 1970s and then moved into cosmology.

UCSC has name people who have shifted from particle over into astroparticle and cosmo---which is a smart move. And whose guidance is going to be smart and insider-wise. And whose recommendation letters are the kind that open doors. It is a very very good place. So even tho it ranks 45 with USNews, in physics, it is intrinsically distinguished.

So let's say you are talking about a UCSC option. Then don't worry, go where you feel secure and happy and be confident that a good PhD from there will get you started on a career.

Also UC grad schools have some leeway for changing research line. The stringy folks at UCSC are very close to the cosmology folks, some even could be seen as line crossers or as wearing two hats.

Stefano Profumo is teaching the basic grad level QFT course that you have to take. He likes bicycling and sailing on SFbay and outdoors stuff. He is into astroparticle and cosmology. You will inevitably get to know him because you have to take QFT.
If you have even one friend you can probably get out of straight string theory and into a more interdisciplinary line. String has applications to trying to understand dark matter and cosmology. Get into applications, and you already have an exit if the field goes bad.
They like interdisciplinary stuff at UCSC.

Tom Banks is even something of a shape-changer himself. More interesting and less predictable than the run-of-mill big string name.
He is a noted string/M person but has moved into cosmology and helped establish string cosmology as a line of research.

Tony Aguirre is co-director of a highprofile private research foundation called FQXi. He is inside as all get-out.

Now it is just speculative hypothesis that your mid-40 school is UCSC, which I just take as an example, because it is mid-40. Suppose not. Suppose some other institution on the California coast. The details may differ but the fundamental reasoning still applies.
Wherever it is, there are going to be some good aspects, so look on the brightside, stay flexible, work enthusiastically, and you can very well luck out. Plus who really knows what the picture will be 5 years out.

http://scipp.ucsc.edu/~profumo/
Research Interests:
Astro-particle Physics
Particle Dark Matter Searches and Model Building
High Energy Astrophysics
Theoretical High Energy Physics
Particle Physics Beyond the Standard Model
Models for the Generation of the Baryon Asymmetry in the Universe
Phenomenology of Supersymmetric and Extra-Dimensional Models

http://scipp.ucsc.edu/personnel/profiles/primack.html
"...In the 1970s, Primack helped to create what is now called the Standard Model of particle physics; for example, in 1972, with Ben Lee and Sam Trieman he did the first calculation of the mass of the charmed quark using renormalizable electroweak theory. Primack's recent research has concentrated on the nature of the dark matter that comprises most of the mass in the universe. He and Heinz Pagels were the first to suggest that the dark matter might be the lightest supersymmetric partner particle. He also investigated the possibility that some of the dark matter might be light neutrinos (hot dark matter). He and his students and other collaborators have analyzed many variants of CDM - especially CDM with less than a critical density of matter and a compensating cosmological constant (CDM) - and confronted the predictions of these models with a wide range of observational data..."

http://scipp.ucsc.edu/theory/banks.html [Broken]

http://physics.ucsc.edu/people/faculty/aguirre.html

 

[MTd2]

Civilized, concerning the top universities, this is pointless, as well as citing any no-go theorem because they do not rule all possible situations, and you can always counter with a nice trick such as supersymmetry did to Coleman Mandula theorem to the trivial combination of poincare symmetries and internal ones.

Non stringy QG is peer reviewed, I don't know where you get that. As for reformulating everything every 6 months is simply not true. Besides if one can expose your ideas, work with other researchers, goes to conferences, be financially supported,this person can be sure that it has accomplished its primary objective to be a researcher "on the market".

Any way, what matter is experiments. The day CERN people like Tommaso Dorigo accepts these things as truth, I will take their word, otherwise, Cumrun Vafa and Edward Witten are just, crudely speaking, mathematicians working as physicists. If you want to speak in terms of status quo, Witten and Vafa are not as trustworthy as Tommaso Dorigo when it comes to real physics.

Concerning the strings on AdS, I don't really see the need for strings. The action used for every CFT interpreted as low effective action from strings, or their correction due to different ways of connecting string with N branes can be just seen as ad hoc assumption. As usual, it *seems* one can get anything out of strings. What is really working here is the mathematical method, which is: finding an action with inverse coupling in the AdS or CFT side that reproduces the other's sides physics. And then, proceed with calculations, afterall, one do not need AdS/CFT more than other than to simplify calculations.

I know what I told you won't convince you. Well, at least you should really rest becaue you know cannot do much to avoid the growth of non stringy QG. Just relax and enjoy the show :).

 

[Civilized]

Civilized, concerning the top universities, this is pointless, as well as citing any no-go theorem because they do not rule all possible situations, and you can always counter with a nice trick such as supersymmetry did to Coleman Mandula theorem to the trivial combination of poincare symmetries and internal ones.

But the yet-to-be-created trick you are counting on is nothing more than a fantasy at this point. There is no substance to support the possible existence of such a trick.

Non stringy QG is peer reviewed, I don't know where you get that.

Show me a peer-reviewed review paper published in the last 6 or 12 months.

If you want to speak in terms of status quo, Witten and Vafa are not as trustworthy as Tommaso Dorigo when it comes to real physics.

Of course this statement is a joke to me, but I don't except proof by authority in any case so it doesn't matter.

Concerning the strings on AdS, I don't really see the need for strings. The action used for every CFT interpreted as low effective action from strings, or their correction due to different ways of connecting string with N branes can be just seen as ad hoc assumption.

First of all, I already explained why we physically would expect the confining phase of an SU(n) gauge theory to be described by strings with super-high tension, so I don't know what you mean by "ad hoc", except in the sense that every hypothesis in science is "ad hoc" until it is put to proven use.

What is really working here is the mathematical method, which is: finding an action with inverse coupling in the AdS or CFT side that reproduces the other's sides physics. And then, proceed with calculations, afterall, one do not need AdS/CFT more than other than to simplify calculations.

Now I think I see the problem, and it has to do with the naive viewpoint that the CFT is what actually exists and the dual description in terms of AdS string theory is just a mathematical tool. This naive realist viewpoint is a major thing that separates mainstream researchers from crackpot amateurs who think it is possible or desirable to describe the things that really exist. Mature theorist realize that we are just building models to describe nature, and to say that one model 'exists' but that the completely equivalent dual model does not is to be participating in a discourse that is at a lower level than real physics research.

Well, at least you should really rest becaue you know cannot do much to avoid the growth of non stringy QG. Just relax and enjoy the show :).

I'm not worried about the growth of non-stringy QG, I am worried about students receiving misinformation that leads to the end of their studies in physics. At the university, I never mention non-string QG and neither does anyone else, it's only on this forum where non-string QG is vastly over represented as a legitimate field of physics research that I fear that students will become confused. I know people are going to call my comments off topic, but the main reason I'm in this thread is to combat the impression that "Who are the most respected research groups in QG now?" should be entirely about non-string non-standard research. In the mainstream QG is a subset of string theory, and so when I saw that the tone of the thread was contrasting string theory and QG I had to step into clean up the misinformation. According to the physics forums guideline we are trying to give students an accurate knowledge of mainstream physics, and this thread was working against that goal.

 

[MTd2]

Civilized, your hipocrisis civilized me. I ran out of arguments... You are totally right :).

 

[Civilized]

Civilized, your hipocrisis civilized me. I ran out of arguments... You are totally right :).

Although I suspect your post is sarcasm, that would really serve no purpose in a mature discussion forum, and so I am forced to conclude that you are entirely sincere.