
#19
Sep1707, 12:53 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

Bojowald 652 Singh 403 Ashtekar 320 Steinhardt 302 Reuter 80 Veneziano 36 



#20
Sep1707, 04:47 AM

Sci Advisor
P: 1,047

Does Steinhard really do research on quantum cosmology, or does he work on finding a classical alternative to inflation?




#21
Sep1707, 10:42 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

But the Steinhardt work is STRINGY and it does provide one kind of BEFORE the big bang story. So some people might think of it as the principle stringinspired rival to Bojowald/Ashtekar LQC and they might think it was unfair to leave Steinhardt out. I'd like to be fairly inclusive. So even though technically Steinhardt "ekpyrotic" or cyclically crashing branes scenario doesn't look like a sensible quantum cosmology to me, I've included him. If you think this is a bad idea let me know, I'll think about dropping him. the thing I like about Steinhardt is he did some work a while ago that found inflation was incompatible with the complex arrangement of stringy extra dimensions. As he said recently in comment on paper by Tegmark Kachru et al, you either have to throw out string theory or throw out inflation. So Steinhardt set to work to find a way of getting some of the EFFECTS of inflation without actually having inflationa way to resolve the same puzzles that inflation resolves but without all that exponential expansion. And he and Turok dreamed up these colliding branes that bump each other over and over again. To me that says the guy is serioushe doesnt just sweep contradictions under the rug and ignore themand he was making a determined effort to avoid the logical necessity of abandoning string philosophy. I admire his integrity and imagination even though his scenario seems a bit farfetched to me. I'll get a link to the Tegmark Kachru work http://arxiv.org/abs/0709.0002 Searching for Inflation in Simple String Theory Models: An Astrophysical Perspective Mark P. Hertzberg (MIT), Max Tegmark (MIT), Shamit Kachru (Stanford), Jessie Shelton (Rutgers), Onur Ozcan (MIT) 24 pages, 5 figs (Submitted on 3 Sep 2007 (v1), last revised 3 Sep 2007 (this version, v2)) "...We analyze three explicit string models from the recent literature, each containing an infinite number of "vacuum" solutions. Our numerical investigation of some natural candidate inflatons, the socalled "moduli fields", fails to find inflation. We also find in the simplest models that, after suitable field redefinitions, vast numbers of these vacua differ only in an overall constant multiplying the effective inflaton potential, a difference which affects neither the potential's shape nor its ability to support slowroll inflation. This illustrates that even having an infinite number of vacua does not guarantee having inflating ones. This may be an artifact of the simplicity of the models that we study. Instead, more complicated string theory models appear to be required, suggesting that explicitly identifying the inflating subset of the string landscape will be challenging." http://space.newscientist.com/articl...inflation.html Can string theory accommodate inflation? Steinhardt is quoted in this last article. He says NO string cannot accomodate inflation, and this is what he found out some time ago which he thinks these other guys are just confirming. And I guess that was basically why he tried so hard to find an alternative mechanism to inflation, so you could chuck out inflation and keep stringat least in his subjective view of things. 



#22
Sep1907, 01:34 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

I found a better way to do the search in one case
for Parampreet Singh, it works best to use the "EA" command instead of the simple "A" FIND EA SINGH, PARAMPREET AND DATE>2002 and the current total is 405. FIND A BOJOWALD AND DATE>2002 gave 658 



#23
Sep2207, 10:53 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

This list focuses on quantum cosmology (and related quantum BH) work published in the last 5 yearscurrently publication date >2002
To save trouble only papers with 35+ cites are tallied. Here are the total number of cites as of 22 September 2007. I've included the Spires search commands in case anyone else would like to update the list. FIND A... means "find author...". Bojowald 660 FIND A BOJOWALD AND DATE > 2002 Singh 408 FIND EA SINGH, PARAMPREET AND DATE>2002 Ashtekar 327 FIND A ASHTEKAR AND DATE > 2002 Steinhardt 298 FIND A STEINHARDT AND DATE > 2002 Reuter 80 FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002 Veneziano 37 FIND A VENEZIANO AND DATE > 2002 http://www.slac.stanford.edu/spires/ 



#24
Nov3007, 11:50 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

The last time i updated this list of leading QC researchers was over two months ago, so I'll refresh the numbers. If you have someone else to suggestactive in quantum cosmology and quantum blackhole research during the past 5 yearswhom we should watch, please let me know
This list focuses on quantum cosmology (and related quantum BH) papers published in the last 5 yearscurrently publication date >2002 To save trouble only papers with 35+ cites are tallied. Here are the total number of cites as of 30 November 2007. Bojowald 716 Singh 475 Ashtekar 394 Steinhardt 344 Reuter 82 Veneziano 38 I've included the Spires search commands in case anyone else would like to update the list. FIND A... means "find author...". FIND A BOJOWALD AND DATE > 2002 FIND EA SINGH, PARAMPREET AND DATE>2002 FIND A ASHTEKAR AND DATE > 2002 FIND A STEINHARDT AND DATE > 2002 FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002 FIND A VENEZIANO AND DATE > 2002 http://www.slac.stanford.edu/spires/ It is noticeable that Bojowald, Singh, Ashtekar each picked up 5570 cites in the past 2 months, suggesting that their work is hot. Steinhardt picked up 46, which is is almost at that level. Quantum cosmology is a small field with only a few researchers working in it, so these numbers indicate considerable activity relative to the size of the community. 



#25
Dec1607, 03:04 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

as of 16 December 2007. Bojowald 732 Singh 475 Ashtekar 406 Steinhardt 347 Reuter 86 Hawking 70 Veneziano 39 Source: http://www.slac.stanford.edu/spires/ Search terms: FIND A BOJOWALD AND DATE > 2002 FIND EA SINGH, PARAMPREET AND DATE>2002 FIND A ASHTEKAR AND DATE > 2002 FIND A STEINHARDT AND DATE > 2002 FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002 FIND A HAWKING AND DATE > 2002 FIND A VENEZIANO AND DATE > 2002 



#26
Dec2807, 07:29 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

Here are the citation totals as of 28 December 2007. Only papers published since 2002 which have received 35+ cites are tallied.
Bojowald 737 Singh 477 Ashtekar 409 Steinhardt 351 Reuter 86 Hawking 71 Veneziano 39 Source: http://www.slac.stanford.edu/spires/ 



#27
Feb1008, 02:22 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

FIND A LOLL AND DATE > 2002 In another thread, the question came up as to which scientists study conditions just before the big bang, and the possible causes of the start of expansion. This is mainly the subject of quantum cosmology and we should be able to keep track of who the leading quantum cosmologists arecitations to recent work (published in the last 5 years.) It is time to update, and add some new names if anyone has some to suggest. This is now as of 10 February 2008. Bojowald 743 Singh 489 Ashtekar 423 Steinhardt 391 Loll 145 Reuter 88 Hawking 75 Veneziano 40 



#28
Mar3008, 09:51 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

Here is another approach http://www.slac.stanford.edu/spires/...tecount%28d%29 This takes hardly any time. I just do a search of the Spires database for DESY keyword QUANTUM COSMOLOGY and date > 2003, and ask for the papers to be ranked by citation count, so the most important papers are listed first. 



#29
Mar3008, 09:02 PM

Sci Advisor
P: 1,664

Does inflation count? What about cosmic strings/topological defects, and any number of phenomenological objects that could arise in principle from quantum cosmology.
People like Linde and some of the other big astrophysics names double or triple the citation count of anybody on that list 



#30
Mar3108, 10:30 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

You probably noticed that the DESY librarians who apply the Spires keywords do not consider Linde's papers to be quantum cosmology. Nor do they include cosmic strings. Why should this be? Apparently it puzzles you. I will try to help you understand. I think (and this is only my guess) that it is because Linde's papers about inflation are based on CLASSICAL geometry. The universe does not have a quantized geometry in all that usual inflation work. The size or scale factor is not represented by a wave function, for instance. The same is true with cosmic strings. The underlying geometric model is classical, not quantum. So none of that stuff you mention is considered to be quantum cosmology. 



#31
Mar3108, 10:48 AM

Astronomy
Sci Advisor
PF Gold
P: 22,808

Of course the imagined exotic matter field, like any matter field, would be a quantum object. But this does not mean that the 1923 cosmological model they plug it into is quantum! So let's try to understand better what is considered to be quantum cosmology. Stanford SLAC has this wonderful Spires database that everybody seems to use and the papers are tagged by a bunch of librarians in Germany, at the DESY. They tag papers by string theorists as quantum cosmology when they actually are quantum cosmology. Or so it seems to me. For example they tagged a paper by Cumrun Vafa, and Hirosi Ooguri, and Erik Verlinde as QC. Let's check and see what they tag. And by the way the Spires people are not necessarily right! I think they omit Renate Loll who obviously does QC because she models quantum universes in the computer! It is clearly a QC path integral. The universe is being modeled with a totally quantum geometry. But so far DESY overlooks that work. Nevertheless, let's try to see how the Spires librarians think. I will copy their list of the mostcited recent QC papers. 1) Background independent quantum gravity: A Status report. Abhay Ashtekar (Penn State U. & Potsdam, Max Planck Inst. & Schrodinger Inst., Vienna) , Jerzy Lewandowski (Warsaw U. & Penn State U. & Potsdam, Max Planck Inst. & Schrodinger Inst., Vienna) . Apr 2004. 126pp. Published in Class.Quant.Grav.21:R53,2004. ePrint: http://arxiv.org/abs/grqc/0404018 295 2) Loop quantum cosmology. Martin Bojowald (Penn State U. & Potsdam, Max Planck Inst.) . AEI2005185, IGPG0616, Jan 2006. 104pp. Published in Living Rev.Rel.8:11,2005. ePrint: http://arxiv.org/abs/grqc/0601085 103 3) HartleHawking wavefunction for flux compactifications. Hirosi Ooguri (Caltech) , Cumrun Vafa (Harvard U., Phys. Dept.) , Erik P. Verlinde (Amsterdam U.) . CALT682543, HUTP05A005, ITFA200505, Feb 2005. 37pp. Published in Lett.Math.Phys.74:311342,2005. ePrint: http://arxiv.org/abs/hepth/0502211 89 4) Quantum nature of the big bang. Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh (Penn State U.) . IGPG0621, Feb 2006. 4pp. Published in Phys.Rev.Lett.96:141301,2006. ePrint: http://arxiv.org/abs/grqc/0602086 74 5) Quantum Nature of the Big Bang: Improved dynamics. Abhay Ashtekar (Penn State U. & Utrecht U. & Newton Inst. Math. Sci., Cambridge) , Tomasz Pawlowski, Parampreet Singh (Penn State U.) . IGPG0672, Jul 2006. 40pp. Published in Phys.Rev.D74:084003,2006. ePrint: http://arxiv.org/abs/grqc/0607039 71 6) Quantum Nature of the Big Bang: An Analytical and Numerical Investigation. I. Abhay Ashtekar (Penn State U. & IUCAA, Pune & Newton Inst. Math. Sci., Cambridge) , Tomasz Pawlowski (Penn State U.) , Parampreet Singh (Penn State U. & IUCAA, Pune) . IGPG06032, Apr 2006. 59pp. Published in Phys.Rev.D73:124038,2006. ePrint: http://arxiv.org/abs/grqc/0604013 65 7) Loop quantum cosmology: Recent progress. Martin Bojowald (Potsdam, Max Planck Inst.) . AEI2004017, Feb 2004. 17pp. Plenary talk given at 5th International Conference on Gravitation and Cosmology (ICGC 2004), Cochin, India, 510 Jan 2004. Published in Pramana 63:765776,2004. ePrint: http://arxiv.org/abs/grqc/0402053 58 8) Baby universes in string theory. Robbert Dijkgraaf (Amsterdam U.) , Rajesh Gopakumar (HarishChandra Res. Inst.) , Hirosi Ooguri (Caltech) , Cumrun Vafa (Harvard U., Phys. Dept.) . CALT682557, HUTP05A019, ITFA200514, Apr 2005. 39pp. Published in Phys.Rev.D73:066002,2006. ePrint: http://arxiv.org/abs/hepth/0504221 53 9) Oscillatory universes in loop quantum cosmology and initial conditions for inflation. James E. Lidsey, David J. Mulryne, N.J. Nunes, Reza Tavakol (Queen Mary, U. of London, Math. Sci.) . Jun 2004. 6pp. Published in Phys.Rev.D70:063521,2004. ePrint: http://arxiv.org/abs/grqc/0406042 52 10) On the Hamiltonian constraint of loop quantum cosmology. Kevin Vandersloot (Penn State U.) . Feb 2005. 28pp. Published in Phys.Rev.D71:103506,2005. ePrint: http://arxiv.org/abs/grqc/0502082 42 11) Genericity of big bounce in isotropic loop quantum cosmology. Ghanashyam Date, Golam Mortuza Hossain (IMSc, Chennai) . IMSC20040729, Jul 2004. 4pp. Published in Phys.Rev.Lett.94:011302,2005. ePrint: grqc/0407074 40 12) Creation of a compact topologically nontrivial inflationary universe. Andrei Linde (Stanford U., Phys. Dept.) . Aug 2004. 8pp. Published in JCAP 0410:004,2004. ePrint: http://arxiv.org/abs/hepth/0408164 40 I have written the currenct citation number in bold. I see that Linde has a paper that the database DOES treat as quantum cosmology! I will have to take a look and see in what sense it qualifies. this is interesting. Maybe we should add Linde to the list. 



#32
Mar3108, 08:50 PM

Sci Advisor
P: 1,664

Some of the LQG 'inspired' models are semiclassical treatments, so its not clear what the criteria actually is, it seems to me rather arbitrary.




#33
Mar3108, 10:52 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

What do you mean by semiclassical in this context? I'd like to understand better what you are trying to say. 



#34
Apr208, 08:25 AM

Sci Advisor
P: 1,664

I don't really know what the DESY librarians mean when they say a paper is QC. WHat they most certainly do not preclude (since some are listed), are semiclassical treatments like inflation and some of say Bojowalds 'effective bounce' papers.
Its a very fine line ultimately akin to the difference between theory and phenomenology in particle physics since it seems (if I had to guess) that its just a question of how much pure quantum gravity theory perse is involved in the paper relative to the amount of text exploring the consequences for the classical cosmological limits (+ modifications). 



#35
Apr208, 03:11 PM

Astronomy
Sci Advisor
PF Gold
P: 22,808

As I said before, I would appreciate it if you would give me a link to a particular paper which Spires database classifies as quantum cosmology, which you do not think is quantum cosmology in your sense of the word.
The reason is, I'm curious about what your idea of quantum cosmology is, and I need to see it applied at the level of a specific paper or two. 


Register to reply 
Related Discussions  
The Quantum Configuration Space of Loop Quantum Cosmology  Beyond the Standard Model  1  
Loop Quantum Cosmology  Beyond the Standard Model  1  
Researchers Develop Quantum Processor  Quantum Physics  3  
Help about quantum cosmology  General Astronomy  6 