Smolin letter to a string believer

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In summary, Lee Smolin has done a fair amount of string research over the years and written a bunch of string papers. His most recent contribution is a quantization of topological M theory. I think this paper could be important and by itself could justify considering Smolin a string theorist even without his other string papers. Incidentally it has been cited by two other string theorists recently. Other Smolin work has also been cited by Dijkgraaf, Gukov, Neitzke, Vafa. However, Smolin is not a string theory believer. Apparently this has the curious effect of excluding him from "the string community".
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Lee Smolin has done a fair amount of string research over the years and written a bunch of string papers. His most recent contribution is
http://arxiv.org/hep-th/0503140 [Broken]
A quantization of topological M theory
I think this paper could be important and by itself could justify considering Smolin a string theorist even without his other string papers. Incidentally it has been cited by two other string theorists recently. Other Smolin work has also been cited by Dijkgraaf, Gukov, Neitzke, Vafa. In the 1990s Smolin was one of those who developed the idea of quantum gravity as a constrained topological field theory, an idea which (whether or not he is personally acknowledged for it) is now proving influential.
But Smolin is not a string theory believer. Apparently this has the curious effect of excluding him from "the string community".

In nonperturbative QG research the situation is somewhat different and faith seems less of a prerequisite for belonging to the community of scholars. One can contribute to the development of several QG theories without being a believer in any particular one.

Anyway Smolin has noticed this distinction. some people do their work, or at least talk about it, as believers, and others don't. And he has written this letter on "cosmicvariance".
--------quote smolin------

Lee Smolin on Aug 15th, 2005 at 9:01 am
Dear Clifford,

Thanks for your piece on the landscape, which I agree is in a certain sense a very sensible view. At the same time, your stance is deeply puzzling to me. I’d like to take this opportunity to explain why, because I believe this is the core of the disagreement between those who consider themselves “string theorists” and those who like myself, remain outside the “string community”, in spite of doing some technical reserach on string theory.

You seem to reason from an unstated premise, which is that, whatever happens, string theory will turn out to be relevant for the description of nature. Even in your closing, when you contemplate different possibilities, including that string theory is just “The Next Theory” you don’t mention the possibility that string theory will just be not relevant for nature. This is also evident in the reasoning in your paragraph: “The idea began to arise that maybe not everything about our universe is fundamentally computable in string theory… I would go as far as to say that it is perfectly fine for us to accept that this might true about string theory while still remaining extremely enthusiastic about it, given its remarkable properties.” You don’t consider the possibility that nothing will be computable in string theory because it is not the right theory.

There are two logically possible styles of reasoning about string theory.

Method A: ASSUME 1) that there is a real non-perturbative theory behind all the approximate caclulations and 2) that it is relevant for nature. Then interpret various results, having to do with dualities, the landscape etc given these asumptions.

Method B: Look for evidence that the two assumptions of method A are true.

One evaluates results very differently, depending on whether one uses method A or method B. There is nothing wrong with using Method A from time to time, so long as the assumptions are made explicit, and the risks that are thereby taken on explicitly acknowledged. One can learn things that will turn out be true about the theory, if 1) is true, or about nature, if 2) is true. But one cannot do science only or even mostly by Method A, no matter how promsing an idea may seem. What I find disturbing in your essay, and in many conversations with string theorists is that they reason by Method A but they do not state expliclty their assumptions. This puts me often in the uncomfortable situation, when discussing with a string theorist, of having to add, “but there is one more possibility, the theory might be wrong.”

Many of us who seem fated to remain outside the “string community” are there becase we approach string theory by method B. We may, as I do, work sometimes on technical problems in string theory, motivated by our hope that evidence be uncovered that will show us whether assumptionss 1) and 2) are true or not. This leads to a different evaluations of results. For example, from the point of view of Method B work aimed to demonstrate the assumptions, such as attempts to prove conjectures like finiteness or the different dualities, is more highly valued than it seems to be by people whose work seems to grounded on the assumption that those conjectures are true.

I should emphasize that we are not being unfair here. Most of those who work on other approaches to quantum gravity and particle physics approach our own theories through method B. If you come to the loops05 meeting--and you are very sincerely invited--you will find that we are at least as hard on our own approaches as we are on string theory. Observing both communities, what I see is an overemphasis on self-criticism in the non-string communities, and too much reasoninng with method A in the string community.

Nowhere is the difference stronger than in the evaluation of the landscape results. From the point of view of method A, we are just following the theory to see where it leads. Since we assume beforehand that the theory is right, this is a worthy project.

But from the point of view of method B, the failure to come up with any method to make falsifiable predictions, coupled with the failure to find a fundamental, fully non-perturbative formulation of string theory, both after many years of work by many smart people, count as evidence against asssumptions 1) and 2).

I myself am drawn to the ideas of string theory, and I would be happy if they turn out to be true. But I believe an objective scientist must appraoch an untested theory by Method B rather than by Method A. The reason is that reasoning by Method A can lead to a situation where a large group of people come to irrationally believe in the existence of a theory they can neither construct nor test.

Another way to say this is that it is more scientific to work on problems, presented by nature, rather than theories. If we commit ourselves too strongly to theories before they are confirmed by having survived many attempts to falsify them, we risk wasting lots of time and careers on ideas that turn out, beautiful as they are, to be false.

Another consequence of Method A seems to be a lack of interest in other directions. Someone, perhaps Moshe, said on a blog recently that if there were good results on quantum gravity people would get excited and work on them. If by “people” was meant “string theorists” this is just not the case. There have been a continuous stream of significant, non-trivial results on several background independent approaches to quantum gravity over the last 20 years and the community of people who works on such approaches is growing fast. But we see very few string theorists taking an active interest in any of these approaches. If you think I exaggerate the significance of the results, come to loops05, or look at recent papers by the speakers there. Or just talk to someone in the field.

The problem is that if you reason from Method A, you are bound to over-evaluate results in string theory, and under-evaluate results in alternative approaches, because you are already committed to one view being right.

Perhaps you think I am being unfair in characterizing your reasoning in terms of methd A. So let me pose a question, “What would make you give up string theory? Is there a theoretical result, an experimental discovery, or the lack of such, that woud make you put your considerable talents in other directions?”

Lest you think this is unfair, I know the answer for myself, for each of the several theories I work on, and can happily answer the same question, if needed.

Thanks,

Lee
---end quote---

I would like to take a closer look at this letter of Smolin and some of the reaction to it on Cosmic Variance blog.
 
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  • #2
Thank you for this. Please post Clifford's reply if you eventually come across it.
 
  • #3
According to my grapevine, Smolins
http://arxiv.org/hep-th/0503140 [Broken]
A quantization of topological M theory
will be discussed by more than one guest speaker.
 
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  • #4
Chronos said:
According to my grapevine, Smolins
http://arxiv.org/hep-th/0503140 [Broken]
A quantization of topological M theory
will be discussed by more than one guest speaker.

thanks so much for passing along this bit of news, Chronos.
you are referring to some conference (conferences have invited speakers plus other stuff sometimes like posters and parallel sessions) but I can't tell which conference you mean.

there is Loops 05 this October
there is Strings 05 that is over now, it was middle July.
there are many other conferences and workshops, too many to mention.

It would be very sensible to expect that paper of Smolin hep-th/0503140
to be discussed at Loops 05 in October of this year (one of the invited speakers Robbert Dijkgraaf will almost certainly refer to it since he works in topological string theory)

is by any chance the conference you are talking about Loops 05?

(or, what would be incredible news, too much to hope for really, are you really talking about NEXT YEAR'S STRING conference? if your grapevine has advanced word about String 06, which I don't know even where it will be held, then you belong to a very advanced grapevine indeed!)
 
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  • #5
marcus said:
Lee Smolin has done a fair amount of string research over the years and written a bunch of string papers. His most recent contribution is
http://arxiv.org/hep-th/0503140 [Broken]
A quantization of topological M theory
I think this paper could be important and by itself could justify considering Smolin a string theorist even without his other string papers.
...
...
---quote from Smolin letter [on Cosmic Variance blog]---

...Perhaps you think I am being unfair in characterizing your reasoning in terms of method A. So let me pose a question, “What would make you give up string theory? Is there a theoretical result, an experimental discovery, or the lack of such, that woud make you put your considerable talents in other directions?”

Lest you think this is unfair, I know the answer for myself, for each of the several theories I work on, and can happily answer the same question, if needed.

Thanks,

Lee
---end quote---

...

I find it fascinating that Smolin has written a number of string papers and made what seems like a substantial contribution. Ironically, his may eventually be found to outweigh the contributions of some in "the string community" country club now carping at him.

It's interesting to scan Smolin's string papers:
I will pick some out of this list
http://www.arxiv.org/find/hep-th/1/au:+Smolin_L/0/1/0/all/0/1?skip=25&query_id=f0212f90c1b39164
Please let me know if I have included any that are not concerned with stringy matters.


1. hep-th/0507235:

Title: The case for background independence
Authors: Lee Smolin
Comments: Latex, 46 pages, no figures

2. hep-th/0503140:

Title: A quantization of topological M theory
Authors: Lee Smolin
Comments: 20 pages, Latex

10. hep-th/0401087:

Title: String theories with deformed energy momentum relations, and a possible non-tachyonic bosonic string
Authors: Joao Magueijo, Lee Smolin
Journal-ref: Phys.Rev. D71 (2005) 026010

18. hep-th/0212043:

Title: BRST quantization of Matrix Chern-Simons Theory
Authors: Etera R. Livine, Lee Smolin
Comments: Latex, 8 pages

20. hep-th/0201031:

Title: Matrix models as non-local hidden variables theories
Authors: Lee Smolin
Comments: 25 pages, latex, no figures
Subj-class: High Energy Physics - Theory; Statistical Mechanics

22. hep-th/0106097:

Title: A thermal instability for positive brane cosmological constant in the Randall-Sundrum cosmologies
Authors: Stephon Alexander, Yi Ling, Lee Smolin
Comments: 14 pages. The discussion on the relation between temperature and effective 4d cosmological constant is changed. References are added
Journal-ref: Phys.Rev. D65 (2002) 083503

23. hep-th/0106073:

Title: The Maldacena Conjecture and Rehren Duality
Authors: Matthias Arnsdorf, Lee Smolin
Comments: 14 pages, 1 figure

24. hep-th/0104050:

Title: The exceptional Jordan algebra and the matrix string
Authors: Lee Smolin
Comments: LaTex 15 pages, no figures
Subj-class: High Energy Physics - Theory; Quantum Algebra

25. hep-th/0009018:

Title: Holographic Formulation of Quantum Supergravity
Authors: Yi Ling, Lee Smolin
Comments: 30 pages, no figure
Journal-ref: Phys.Rev. D63 (2001) 064010

26. hep-th/0006137:

Title: The cubic matrix model and a duality between strings and loops
Authors: Lee Smolin
Comments: Latex, 32 pages, 7 figures
Subj-class: High Energy Physics - Theory; Quantum Algebra

27. hep-th/0003285:

Title: Eleven dimensional supergravity as a constrained topological field theory
Authors: Yi Ling, Lee Smolin
Comments: 15 pages+7, Appendix added
Journal-ref: Nucl.Phys. B601 (2001) 191-208

28. hep-th/0003056:

Title: The strong and weak holographic principles
Authors: Lee Smolin
Comments: Latex, 53 pages, no figures
Journal-ref: Nucl.Phys. B601 (2001) 209-247

29. hep-th/0002009:

Title: M theory as a matrix extension of Chern-Simons theory
Authors: Lee Smolin
Comments: Latex, 17 pages, no figures
Journal-ref: Nucl.Phys. B591 (2000) 227-242

30. hep-th/9910146:

Title: Holography in a quantum spacetime
Authors: Fotini Markopoulou, Lee Smolin
Comments: 16 pages, LaTeX

31. hep-th/9904016:

Title: Supersymmetric Spin Networks and Quantum Supergravity
Authors: Yi Ling, Lee Smolin
Comments: 21 pages, LaTex, 22 figures, typos corrected and references completed
Journal-ref: Phys.Rev. D61 (2000) 044008

32. hep-th/9903166:

Title: A candidate for a background independent formulation of M theory
Authors: Lee Smolin
Comments: Latex 46 pages, 21 figures, new results included which lead to a modification of the statement of the basic conjecture. Presentation improved
Journal-ref: Phys.Rev. D62 (2000) 086001

34. hep-th/9808192:

Title: Towards a background independent approach to M theory
Authors: Lee Smolin
Comments: 21 pages, LATEX, no figures. Contribution to a special issue of Chaos, Solitons and Fractals on " Superstrings, M,F,S...Theory"

35. hep-th/9808191:

Title: A holographic formulation of quantum general relativity
Authors: Lee Smolin
Comments: The Lorentzian boundary conditions have been extended to a much more general class, more details given of quantization in the Lorentzian case
Journal-ref: Phys.Rev. D61 (2000) 084007

36. hep-th/9801022:

Title: Strings as perturbations of evolving spin-networks
Authors: Lee Smolin
Comments: Latex, 18 pages, no figures
Journal-ref: Nucl.Phys.Proc.Suppl. 88 (2000) 103-113

37. hep-th/9712148:

Title: Nonperturbative dynamics for abstract (p,q) string networks
Authors: Fotini Markopoulou, Lee Smolin
Comments: Latex, 12 pages, epsfig, 7 figures, minor changes
Journal-ref: Phys.Rev. D58 (1998) 084033

39. hep-th/9710191:

Title: Covariant quantization of membrane dynamics
Authors: Lee Smolin
Comments: Latex, 21 pages, no figures
Journal-ref: Phys.Rev. D57 (1998) 6216-6223

40. hep-th/9703174:

Title: Chern-Simons theory in 11 dimensions as a non-perturbative phase of M theory
Authors: Lee Smolin
Comments: 18 pages, Latex no figures, improved treatment of reduced sector

44. gr-qc/9609031:

Title: Three Dimensional Strings as Collective Coordinates of Four Dimensional Non-Perturbative Quantum Gravity
Author: Lee Smolin
Comments: 32 pages

45. gr-qc/9505028:

Title: Linking Topological Quantum Field Theory and Nonperturbative Quantum Gravity
Author: Lee Smolin
Comments: TEX File, Minor Changes Made, 59 pages
Journal-ref: J.Math.Phys. 36 (1995) 6417-6455

47. gr-qc/9405015:

Title: The Chern-Simons Invariant as the Natural Time Variable for Classical and Quantum Cosmology
Authors: Lee Smolin, Chopin Soo
Comments: 32 pages, gr-qc/9405015, CGPG-94/4-1 (revised and extended, Oct. 94)
Journal-ref: Nucl.Phys. B449 (1995) 289-316

----------------------------

This list might still need winnowing to remove papers with no bearing on string theory, but you get the idea. Notice in the letter Smolin invites question about what would falsify string approach to QG or cause him to discard it as a research venture. Obviously he continues, for the time being, to pursue string AMONG OTHER qg OPTIONS. And he says he would be HAPPY to say, for each of the several theories he works on, what experimental or theoretical result would make him satisfied to discard that particular line of research. If I found myself at the same lunch counter with Smolin I might get my courage up and ask him what particular discoveries would rule string out for him.

Actually (but this is off the subject a little) I think Lolls Triangulation approach has more promise of yielding a fully nonperturbative quantum theory of gravity----more than string anyway---because it constructs an entirely new kind of 4D quantum spacetime continuum.
(mathematically very different at short scale from a 4D differentiable manifold). String spacetimes are stock differentiable manifolds, even with geometries fixed in advance. So Loll CDT breaks new ground compared to string, and has better prospects in my view. So, since Smolin ALSO works in CDT, I might ask him what theoretical or experimental discovery would convince him to give up THAT approach. The answer could be interesting.
 
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  • #6
marcus said:
Lee Smolin has done a fair amount of string research over the years and written a bunch of string papers. His most recent contribution is
http://arxiv.org/hep-th/0503140 [Broken]
A quantization of topological M theory
I think this paper could be important and by itself could justify considering Smolin a string theorist even without his other string papers.

---quote Smolin letter [Cosmic Variance blog]---

...
...

The problem is that if you reason from Method A, you are bound to over-evaluate results in string theory, and under-evaluate results in alternative approaches, because you are already committed to one view being right.

Perhaps you think I am being unfair in characterizing your reasoning in terms of methd A. So let me pose a question, “What would make you give up string theory? Is there a theoretical result, an experimental discovery, or the lack of such, that woud make you put your considerable talents in other directions?”

Lest you think this is unfair, I know the answer for myself, for each of the several theories I work on, and can happily answer the same question, if needed.

Thanks,

Lee
---end quote---

I would like to ... take a closer look at this post of Smolin and some of the reaction to it.

Here are some reactions. The names don't matter. I will just call them "second string theorist" and "third string theorist". To my ear THIRD sounded more collegial, and less sarcastic, than SECOND. Anyway here is a sample of the reaction to Smolin (whom I consider to be "first string theorist" and has already spoken)

----quote SECOND string theorist---
Hi Lee,

Thanks for your comments. And thanks for your valuable and insightful psychoanalysis of me and “the string community”.

As a member of the scientific community, I tend to use the customs of my people: We confront scientific ideas ... I thought it was clear to everyone reading this article (and the one it is the sequel to) that this is one such scientific idea. Perhaps I was wrong.
...

In my mentioning one approach to a problem, I did not realize that I have to stop and mention all the other approaches all the time. I just took it for granted that the intelligent reader (having seen the word “research” and other such phrases) can conclude that we don’t know the answers yet, and so we cannot know if we’re looking in the right place.

I’m so sorry if I was not clear.

Let me say it clearly for you and those people out there who you think might be confused:


“Research” is here taken to mean that we don’t yet know the answers. By examining a set of ideas to see if they contain the answers, we are allowing for the possibility that those ideas do not contain the answers.

I do apologize to anyone out there who was misled by my articles into thinking that the act of my describing a particular area of research implied that we already knew that it was the answer - before having completed the research.

I thank you, Lee.

...

Hi again Lee,

I forgot one thing. You’re reminding us in your comments in several places that we are not as honest and hard on ourselves as those excellent people in your community. You mention “observing” our community.

Where exactly do you make these observations? The last time I saw you at the kind of workshop where the really hard work on string theory is taking place -where the kind of self-questioning and examination of the whole endeavour is put into practice- was very very many years ago in the middle to late 90’s in Santa Barbara.

Now, I’m not asking for an attendance sheet from you. Let me be the first to say that I’ve not been to all the workshops. Not even most of them. But then, neither have you. So are you sure that you should be making such pronouncements about the motivations, character, and scientific honesty of an entire community of people based on your “observations”? If so, your clarity of vision is ….. remarkable.

Cheers!

---end quote---

---quote THIRD string theorist---
Lee was, most recently, at Strings 2005, and he does hang out with his stringy colleagues at Perimeter.

I don’t know whether that counts for you, but it does for me.

I also don’t know what the contours of the ultimate theory of quantum gravity will look like. But I do think that it is very likely that, whatever it turns out to be, it will have classical solutions about-which it is well-approximated by a perturbative string theory. (Which is not, necessarily, to say that our world is likely to be well-approximated by a perturbative string theory.)

I could explain why I think that, but, instead, I will throw out what I see as the possible alternatives:

1) quantum gravity is never perturbative, about any of its vacua
2) it does possesses perturbative vacua, but the short-distance behaviour is totally-different (non-stringy).

Discuss and enjoy …
---end quote---

---SECOND string theorist again---

Jacques,

Strings meetings are not the best measures of the activity that goes on in the field. They are reports on results. There’s never much time to have open discussions about what we’re doing, where we’re going, etc. This year’s strings did (admirably and unusually) try to have an official discussion, and that is good. But panel discussions are not what I’m talking about, I’m talking about workshops and smaller meetings, where the real work gets done.

So if it “counts” for you, that’s fine. But I don’t think that going to a few meetings, (big or small) and having some colleauges that do string theory occupy the same building qualifies one to make broad comments about the scientific integrity and motivations of an entire scientific field. Not even most of the “insiders” of the string community would do that!

Cheers,
---end quote---

I have several reactions to these voices, which represent for me a kind random sample of people doing string research. The identities are not important to the conclusions I want to draw. I see that one of them ("Third") sounds openminded and generous spirited. He wants to include Lee as one of "us" and he says Lee's participation (which he does not detail except in a light sketchy way) "COUNTS" for him.

It would seem that for Third the "string community" is not seen as an exclusive country club closed except to right-thinking boosters who talk string happy talk and attend the proper workshops. The "community" seems to have room for others: for doubters perhaps, for loners pursuing the long-shot, and for those who offer constructive criticism of a prevalent attitude. Here I don't suggest that Smolin fits any of those descriptions but merely illustrate that Third's view of the "community" seems comparatively roomy.

I don't want to imply that the actual people ARE the way they sound here.
Third, of whom I get a good impression from the quote, might be different in real life. Second might really be a sweet guy, and so forth.
 
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  • #7
Loops 05, marcus. Rumor has it should be very interesting. I don't know much about strings 06, but I do know Smolins BI paper has created a stir in the string community. Witten, for one, has even drawn a bit of fire from the right wing for commenting favorably upon it.
 
  • #8
Smolin continues

Posts #90 and #95 on the CV "Landscape" thread

------------SMOLIN REJOINS THE THREAD, POST #90-------------
Lee Smolin on Aug 21st, 2005 at 5:30 pm
Hi, if this thread is still alive, I have some comments on earlier posts:

To Aaron on background independence:

“Background independence and string theory are not in any stark disagreement.” If by this you mean that no one has proved there is no background independent formulation of string theory I agree. But this is very weak. If one exists, we should find it.

” I can’t help but think that to say that any quantum theory of gravity must be background independent smacks of hubris. Nature is going to work how it’s going to work. We certainly don’t get any say in the matter.”

Would you say the same thing about the principle of inertia? That principle is extremely well tested, but it is still possible that the quantum theory of gravity will reverse it, and return to the Aristotelian idea of a preferred state of rest. But to take the principle of inertia as something to be preserved in the next theory is hardly hubris, it is good sense to keep well tested principles unless there is a strong reason to abandon them.

But background independence has exactly the same status. It is extremely well tested at the classical level, because general relativity is background independent and its predictions are well confirmed. Were there not exactly two degrees of freedom, which is a consequence of diffeo invariance, the precise match between theory and experiment for the binary pulsar data would fail. Thus, it is only good sense to expect that this well tested principle be preserved in the next theory.

To Sean on finiteness. I’d be curious what is your understanding of the status of perturbative finiteness. Your comment seems to imply that there is very strong evidence, just short of a rigorous proof. I wish this were the case, but this is not my understanding of the situation. Perhaps you can correct me, if so I would be very grateful. My understanding is that even at a theoretical physics level of rigor all claims fall short of a complete demonstration. Either they rely on additional assumptions or do not rule out all possible sources of divergences, as in Mandelstam and Berkovitz or they go only to genus two, as in d”Hoker and Phong. Thus, this is not a typical sistuation where we theoretical phyicists have a convincing argument, awaiting only translation into a rigorous theorem. As Feynman told me in 1976 (with regard to confinement in QCD), “If lots of really smart people have tried to prove something and failed, perhaps its because it is actually not true.”

Do I personally think supersymmetric string theory is perturbatively finite? I certainly hope so, otherwise I for one have wasted a lot of time on an inconsistent theory. At the same time if after twenty years of work by really smart people, the experts on the technical issues involved have not found a complete demonstration, I don’t think we should be complacent. I would instead think we should present perturbative finiteness as a conjecture that there is some evidence for, but which remains open despite efforts to prove it. Perhaps if we emphasize that this important question is unsolved, this will motivate someone to do the hard work needed to complete the proof or find a counterexample.

[several replies skipped]
-----------SMOLIN CONTINUES. POST #95---------
Lee Smolin on Aug 21st, 2005 at 10:12 pm
Hi Aaron,

You cannot seriously mean that “It is simply not the case, however, that it is even possible to do an experimental test of it.” There is a long list of confirmed predictions of GR, some to very high precision. These strongly constrain the parameters that measure possible deviations from GR-the post Newtonian parameters.

I also can’t imagine you mean what you said: “GR has been extremely well confirmed in one particular background. There haven’t been any experiments in a different background that I know about….”

The point of GR is that the full metric is dynamical. This means that the metric emerges as a solution of the field equations. So there is no metric that is put into define the field equations, as there is for field theories on fixed backgrounds, such as Maxwell theory or free string theory. The statement that GR is background independent is, so far as the metric is concerned, equivalent to the statement that the metric is fully dynamical. A theory of a linearized tensor field on a fixed background is unable to reproduce all the predictions that GR successfully makes.

So I just don’t know what you could mean by “GR has been extremely well confirmed in one background.” This is like saying, there is a particular Maxwell field that describes the E and B fields in the universe, which happens to be a solution to the Maxwell equations, but I don’t take that as a confirmation of the truth of the Maxwell equations.

There is one solution that describes our world but it is not a background. That one solution is incredibly complex, as the observations of lensing and the precision solar system tests all show in detail, the geometry changes dynamically, partly to reflect the distribution of matter. It has no symmetries and structure on a huge range of scales. The solution that describes our world is one of a continuous infinity of such complex generic solutions. It has no other special status. There is no plausible explanation for this than that the metric of the world is a solution to the Einstein equations, at least within a certain regime.

What I am arguing for is only that the correct quantum theory of gravity preserve the key feature of the well tested classical theory of gravity, which is that the spacetime metric is fully dynamical. This rules out theories like perturbative string theories or linearized spin two fields whose equations of motion require the prior specification of a fixed background metric.

-------------JAQUES REPLY, POST #96----------
Jacques Distler on Aug 21st, 2005 at 11:24 pm
This rules out theories like perturbative string theories or linearized spin two fields whose equations of motion require the prior specification of a fixed background metric.

That perturbation theory requires a choice of background metric (about which to perturb) is a tautology. It is equally true of perturbation theory applied to GR.

Any consistent interacting theory of a massless spin-2 field must have (the full nonlinear) diffeomorphism invariance. Perturbative string theory is diffeomorphism invariant. It also has the aforementioned (and much-maligned) split into a background metric plus perturbation.

It is hard to imagine a theory that has both full diffeomorphism invariance and a perturbative split into background metric plus perturbation, which is not, in fact, background-independent. If you can construct an example, that would be interesting.

There are other arguments for background-independence in string theory; I’m sure I don’t have to repeat them.

What we don’t have, in perturbative string theory, is manifest background-independence.

I think we can all agree that manifest background-independence would be a nice thing to have. But, in a pinch, non-manifest background-independence will do.

Personally, I’m not sure that the concept of “background independence” (as you are using the term) is even relevant to the problem of finding the fundamental formulation of string theory. “Background independence” merely requires a formulation in terms of the (full) dynamical spacetime metric. But, in string theory, there are solutions which admit multiple interpretations in terms of different spacetimes, with different spacetime metrics and different spacetime topologies.

So, when one says, “… depends only on the (full) dynamical spacetime metric,” the relevant question is, “Which metric is that?”

---------------SMOLIN RESPONSE, POST #101-----------------

Lee Smolin on Aug 22nd, 2005 at 9:06 am
Dear Aaron and Jacques,

I agree that there is evidence for the existence of a background independent string theory, but this is not the same thing as to construct it. I also agree that the most convincing evidence is from the fact that a necessary condition for the conformal anomaly to vanish is that the target space satisfies the vacuum Einstein equations, to leading order and the quantum effects renormalize the metric. As to what evidence makes me think that string theory doesn’t have a metric that is fully dynamical, one is the fact that we only know the precise amplitudes for supersymmetric strings to propagate and interact in backgrounds with timelike or null killing fields, which is to say we only know that perturbative superstring theory exists, in detail, for metrics that are non-dynamical.

It may be that this limitation can be transcended. But it is good to be precise about what has been shown and what is still conjectured.

I’m heartened that we all agree that there is enough probability that a background independent formulation of string theory exists that it is worth while looking for it. So let's move on to discuss what are good strategies to look for such a theory. I know of three,

1) Construct an 11 dimensional Chern-Simons like theory. (Banados et al, Horava)

2) Construct a background independent matrix theory, and derive the existing background dependent matrix formulations of string and M theory by expanding around solutions of it (hep-th/0002009,0006137,0104050, 0212043).

3) Construct a background independent quantization of 11d supergravity (hep-th/0003285, with Yi Ling).

I’d be curious as to your view of these approaches and what other ideas you have about how to go about finding the background independent formulation of string theory.
--------END QUOTE--------

For convenience, i have expanded the above arxiv references into links:

2) Construct a background independent matrix theory, and derive the existing background dependent matrix formulations of string and M theory by expanding around solutions of it
http://arxiv.org/hep-th/0002009 [Broken]
http://arxiv.org/hep-th/0006137 [Broken]
http://arxiv.org/hep-th/0104050 [Broken]
http://arxiv.org/hep-th/0212043 [Broken]

3) Construct a background independent quantization of 11d supergravity http://arxiv.org/hep-th/0003285 [Broken] with Yi Ling.
 
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  • #9
Yep, it seems that Lee is looking for public discussion with people who is expected to understand string theory. In a first reply it seems that Aaron is refusing confrontation, or at least refusing to follow topic as Lee suggests it should be followed. Let's see Jacques.
 
  • #10
arivero said:
Yep, it seems that Lee is looking for public discussion with people who is expected to understand string theory. In a first reply it seems that Aaron is refusing confrontation, or at least refusing to follow topic as Lee suggests it should be followed. Let's see Jacques.

Arivero, I was hoping that Jacques would engage more but stuff just ricochets off him. Or how do you see it? But Moshe has started to discuss with Smolin and he seems more interested in engagement of ideas.
We are getting this realtime. Smolin just posted this about 15 minutes ago:

--------SMOLIN POST #109-----
Lee Smolin on Aug 22nd, 2005 at 6:49 pm
Hi Moshe and Aaron,

First, I agree that the focus on asymptotics is at least partly because it allows an easier class of observables to be studied. I also agree with Banks that different choices of asymptotic conditions define different classical phase spaces and hence distinct Hilbert spaces.

In classical theories, whether GR, supergravity or topological field theories this is completely clear, and can be understood in detail. The reason is that the choice of asymptotic conditions break the diffeomorphism and gauge invariance on the boundary, and this gives rise to easy versions of local physical observables defined on the boundary. Furthermore, whenever there are boundary or asymptotic conditions, boundary conditions have to be imposed and boundary terms have to be added to the action, otherwise the action is not functionally differentiable and the field equations are not defined. These boundary conditions and boundary terms then become part of the kinematical specification of the phase space. There is no phase space that unifies them. If one follows standard quantization rules they lead to distinct quantum theories.

There is also a subtle interplay between what is gauge and what are physical symmetries, whose details depend on the boundary terms and conditions. This leads to a clear separation between constraints that generate gauge invariances and observables such as energy, charge and momentum, that are defined by surface integrals at the boundary. There is more to say, but the best way to learn this stuff is to work carefully through the case of GR with different boundary terms and asymptotic conditions to see how it goes. One good, careful source is Ashtekar’s World Scientific book on the new variables. (btw the calculations are much simpler in Ashtekar variables than in ADM variables.)

The analysis leads to an understanding that the formulations with boundary or asymptotic conditions are truncations of the full theory in which the added conditions reflect the presence of external sources and currents. These can be interpreted as coming from situations we observers set up, when we wish to isolate and study a part of the universe. If we then extend this wisdom from the classical theory to our conjectured background independent quantum theory we would conclude that the basic formulation will be the one without asymptotic or boundary conditions. Once this is in closed form, it is likely that models of isolated systems can be constructed, as in the classical theory, by imposing boundary or asymptotic conditions.

Hence, I believe we only have to make one theory, and it is one without boundary or asymptotic conditions. If we can do this, we should be able to invent appropriate truncations to represent isolated systems, when needed.

Thanks,

Lee
--------END QUOTE-----
 
  • #11
Is he just saying that background independence gives rise to a finite universe that can be observed and that is preferable ?
 
  • #12
Reading prep for this thread

to follow the discussion in this thread I guess the main homework prep would be to read the first 3 pages of the introduction section of
http://arxiv.org/hep-th/0507235 [Broken]
The Case for Background Independence

these are pages 3, 4, and 5

(pages 1 and 2 are just the abstract summary and table of contents, they can be skipped)
 
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  • #13
thanks Marcus

having read that i think i can safely answer my own question which is...yes

however it is not their discussion i was intent on following. The intent was to intitate our own discussion here.

I think he made a good enough case for background independence just to fit the observables in 3d+time but he couldn't rule out the possibility of a background against which time and space is played out in
 
  • #14
Sam Owen said:
The intent was to intitate our own discussion here.

If you want a different discussion, please make a separate thread, Sam. My aim in this thread is focused on what Smolin is writing and I don't want to clutter it with side conversations like this.
 
  • #15
I do want the same discussion. You don't want to discuss what he is writing, just quote it ?

Why then not just post the link to the source and join in the discussion there otherwise i don't see the point in posting up the transcript if not to inspire discussion in this thread ?

kinda voyeuristiclly creepy

"I think he made a good enough case for background independence just to fit the observables in 3d+time but he couldn't rule out the possibility of a background against which time and space is played out in"

do you agree ?...discuss
 
  • #16
Sam Owen said:
You don't want to discuss what he is writing, just quote it ?

See Marcus's post #10 on this thread. He does want to discuss, he just wants to hold down the empty speculation and BS. Those are not appropriate on this subforum. RTF paper and keep your discussion on topic and cogent.
 
  • #17
I did RTF paper and this is what i got from it...

Smolin is basically saying deal with quantum gravity using what is here in our 3+1d universe in terms that fit what can be observed and tested without positing extra dimensions or conditions but allow for hidden variables that may crop up like non locality which means sorting out this time business for all of the theories as that is where they all break down

he stops just short of positing extra dimensions to account for non locality in any hidden variable theory but it seems implied though not in a stringy compacted sense

The paper raises more questions than it answers
 
  • #18
I believe it is time to continue the story with another installment.

To recap about Smolin, he is an interesting figure partly because by his research output he qualifies as a string theorist, with a track record for getting onto ideas early and having a nose for fruitful lines of investigation in several fields. Another asset he has is an outsider viewpoint, something that can be important at certain junctures.

Recently he has posted this preprint: hep-th 0507235 "The Case for..." which could turn out to be influential. perhaps in combination with hep-th 0503140.

The main thesis of "The Case for...", italicized on page 5, is actually a piece of advice to other string theorists, and can be freely paraphrased as
try making it more background independent and see what happens.

The context for this thread is that the stringtheoretical research program is in trouble, especially where there has been concentrated over-investment in that one approach instead of a diversified strategy. The crisis (which may well be resolved and prove only temporary) is shown by declining objective signs of vitality and by expressions of worry and defensiveness. We have other threads where this can be discussed and I shall not discuss it here. This thread is intended for readers who are already aware of the troubled string situation and interested in Smolin's ideas on what to do about it.

Recently, on the CV blog, Smolin ADDED to his message to string theorists and contributed another piece of advice. This can be paraphrased as follows:
"Don't assume string theory will turn out to describe nature." He finds that some, perhaps more than just a few, theorists have gotten into the mental habit of assuming that string theory is right and will eventually evolve into a successful, predictive, testable theory---empirical based. This assumption can distort one's thinking, like putting blinders on, he suggests. He particularly pointed out how it can make researchers less alert to developments on the margin, neighboring quantum gravity fields, essentially a case of complacency dulling periferal vision.

One can like something a lot (as Smolin string) and find the ideas deeply appealing, yet still remain skeptical. (Of course this part of the message is not unique to Smolin but is a time-honored part of good science.)

OK so these ideas come up in the little multipart "essay" or "letter" on CV blog. But they are scattered around in a huge number of other posts and by now almost impossible to find. You can't link to individual comments.
So I have gathered them together, and I guess it is time to add another chapter.

If you have physics questions of a general nature, feel free to start a separate thread---this will then not distract from our focus on this Smolin "essay".
 
  • #19
the next part is written in an oblique style, I take it this is because the author is making a gigantic effort not to ruffle anyone's feathers and not to appear to blow his own horn, these being things YOU CAN DO IN A BOOK but are risky to do on someone else's blog

interesting to notice how media can affect style

quite a lot of water under the bridge since the last installment, and the conversation moved over to another thread.

courteous restraint so predominates as to make the piece seem written in a kind of "code". I guess I will try, in a little while, to decode some. but first I will just copy in the text:

------quote Smolin on CV blog------
... I am happy also to acknowledge that the main points you have been arguing for are correct: there are critics of string theory who are not as informed as they should be, and they do under estimate the breadth and variety of views and approaches within the string community.

But I would ask to impose just a bit more on your hospitality here to say something I think is terribly important, that exchanges on this and other blogs have illustrated. Let us call the range of views that can be heard from people who live in the string community R. My observation is that, however wide this is, it is a proper subset of another set P, which is the possible range of views that could reasonably be taken on various issues, which are as well supported by the evidence from calculations and from nature as are the views in R. I will call the views in P but outside R, O. I also observe that among those who are considered outsiders by string theorists, there are some who are in fact familiar with many of the technical details, and who could, and in some cases do, contribute research to string theory. Let me call such people the “competent outsiders”. Now here is what I think is so important:

-One draws different conclusions about the possible futures for string theory, given views in O than in R. Thus, it matters a lot for physics, which views are correct. The importance of the competent outsiders is that they sometimes hold views in O.

-Occasionally a view is moved from O to R. One illustration of this was the significance of 11 dimensional supergravity and the 11d supermembrane for string theory, which was moved from O to R in 1995.
Another example is the view that the connection between string theory and nature will involve a landscape of equally possible theories rather than a unique, single theory, which was moved from O to R in the last few years. In these and other cases there were competent outsiders who had been insisting on the importance of these views, that were not listened to by insiders.

-These examples illustrate the importance of O, as it can have a big effect on the direction of research when a view is moved from O to R.

-Nevertheless, at anyone time, insiders are often not aware of the views currently in O or, if they are, they do not accord them much interest. Even when a view is moved from O to R, some insiders think of it as a new invention and do not appreciate that the view has been held for some time by competent outsiders.

-There remain views in O that may still turn out to be important. Among these I would put the fact that there are a range of possible versions of the AdS/CFT conjecture allowed by the evidence and the view that string theory cannot succeed unless a truly background independent formulation is found.

So, while I agree that the breadth of views in R, held by insiders is sometimes unappreciated, I hope you can appreciate that some outsiders have a valid point when they remark that the range of views allowed by the evidence is wider than that usually heard within the string community.

These stories raise several questions for me, that I am thinking about as I try to write a kind of intellectual history of the subject. First, wouldn’t it have been better if the views I mentioned that moved from O to R had been all the time included within the range of views discussed and considered by insiders? Does this imply that progress would be faster if the range of views considered seriously by string theorists were broadened?

There are also some general questions about how science works. Is the situation I’ve described common, or is it special to string theory? Is R always narrower than P, and why? Is there commonly a class of competent outsiders? Related to this, why is R at anyone time narrower than P? And why are insiders sometimes not aware of, or dismissive of views in O? Are strong divisions between research programs, such as we see between the different approaches to quantum gravity, generally good or bad for the progress of science?

---end quote---
 
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  • #20
people with a knowledge of the classics may detect echos of the Gilbert and Sullivan number, "If I were fortune, which I'm not," from the Mikado.

We must ever strive to be worthy of the ancients.

Even though obliquely worded, the piece may still have been a satisfaction to write, just to get it down in pixels. I will put a key here, for convenience:

R: range of viewpoints inside a loyal support group or research "community".

P: possible range of intelligent informed views-----P contains R

O: competent outside viewpoints --- R is properly contained in P and O = P \ R


Notice that Smolin indicates that one of his projects is some INTELLECTUAL HISTORY writing, maybe a book or a longer essay like his "Scientific Alternatives to the Anthropic Principle". I would guess that the topic is essentially "the String Adventure of recent decades and what we can learn from it about conducting science"

he has been well positioned to observe, chronicle, and draw conclusions, so it might be an interesting book
 
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  • #21
it might be useful to collect some bibliography for this thread---articles to click on that relate to what Smolin is saying. I've already mentioned some of the references several times

the main paper is "The Case for Background Independence"
http://arxiv.org/hep-th/0507355 [Broken]

a recent suggestion for b.i. formulation of stringy theory is
http://arxiv.org/hep-th/0503140 [Broken]

reference to other proposals for b.i. formulation were given in Smolin's CV comment #101 which I quoted earlier. Here is an expanded version giving the full URLs.

"2) Construct a background independent matrix theory, and derive the existing background dependent matrix formulations of string and M theory by expanding around solutions of it
http://arxiv.org/hep-th/0002009 [Broken]
http://arxiv.org/hep-th/0006137 [Broken]
http://arxiv.org/hep-th/0104050 [Broken]
http://arxiv.org/hep-th/0212043 [Broken]

3) Construct a background independent quantization of 11d supergravity http://arxiv.org/hep-th/0003285 [Broken] with Yi Ling."

Just for carefulness, I want to repeat the CONTEXT in which Smolin gave these links. It may help clarify what to expect from them, and what not to.

--------quote comment #101---------

Lee Smolin on Aug 22nd, 2005 at 9:06 am
...
...
I agree that there is evidence for the existence of a background independent string theory, but this is not the same thing as to construct it. I also agree that the most convincing evidence is from the fact that a necessary condition for the conformal anomaly to vanish is that the target space satisfies the vacuum Einstein equations, to leading order and the quantum effects renormalize the metric. As to what evidence makes me think that string theory doesn’t have a metric that is fully dynamical, one is the fact that we only know the precise amplitudes for supersymmetric strings to propagate and interact in backgrounds with timelike or null killing fields, which is to say we only know that perturbative superstring theory exists, in detail, for metrics that are non-dynamical.

It may be that this limitation can be transcended. But it is good to be precise about what has been shown and what is still conjectured.

I’m heartened that we all agree that there is enough probability that a background independent formulation of string theory exists that it is worth while looking for it. So let's move on to discuss what are good strategies to look for such a theory. I know of three,

1) Construct an 11 dimensional Chern-Simons like theory. (Banados et al, Horava)

2) Construct a background independent matrix theory, and derive the existing background dependent matrix formulations of string and M theory by expanding around solutions of it (hep-th/0002009,0006137,0104050, 0212043).

3) Construct a background independent quantization of 11d supergravity (hep-th/0003285, with Yi Ling).

I’d be curious as to your view of these approaches and what other ideas you have about how to go about finding the background independent formulation of string theory.
--------end quote--------

Now there is something else interesting that I wanted to get by way of bibliography. It is work that Smolin mentions in the last installment BUT DOESNT GIVE THE urls. This is in the part about R, P, O and the occasional effectiveness of outsider viewpoint. He refers to some articles obliquely. I am curious as to which ones they are.

----here's the quote from the recent piece---

-Occasionally a view is moved from O to R. One illustration of this was the significance of 11 dimensional supergravity and the 11d supermembrane for string theory, which was moved from O to R in 1995. Another example is the view that the connection between string theory and nature will involve a landscape ... which was moved from O to R in the last few years.


In these and other cases there were competent outsiders who had been insisting on the importance of these views, that were not listened to by insiders.
...
...

-There remain views in O that may still turn out to be important. Among these I would put the fact that there are a range of possible versions of the AdS/CFT conjecture allowed by the evidence and the view that string theory cannot succeed unless a truly background independent formulation is found...

---end quote---

I've seen a paper where Smolin was discussing a landscape of possible physics, back in around 1995 if I remember. the landscape idea only seems to have gotten popular among "insider" theorists recently. I will try to retrieve the link.

More interesting, to me, than the origins of the landscape picture would be a link that illustrates this:

"...significance of 11 dimensional supergravity and the 11d supermembrane for string theory, which was moved from O to R in 1995."

anyway, will try to assemble a few more relevant links




__________________
 
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  • #22
Smolin continued today, this this installment is on Woit's blog:

-------quote Smolin 3 September post--------
Lee Smolin; September 3rd, 2005 at 10:03 am

Dear Peter,

Thanks for this. It is good to lay out the strengths and weaknesses of all the approaches. It is true that the big challenge facing all background independent approaches is showing that the classical spacetime geometry is recovered in the low energy limit. But my own view is that John is too pessimistic. There have been for years results which show that LQG has semiclassical states, and that predictions, such as for the possible deformation of Lorentz invariance, can be gained by studying their excitations. (See summary and references in section 4.5 and 5.1 of hep-th/0408048.) So it is wrong to give the impression there are no results supporting the conjecture that the low energy limit of LQG is GR. And we should not forget the rigorous results that show that LQG and spin foam models are finite theories, so the question of the low energy limit is well posed, something not achieved in earlier theories.

Of course if the theory is right--and we never assume so--we must show more. We must show that the ground state is semiclassical, by solving the dynamics. This is a hard problem, analogous to showing that the ground state of water is a solid. But as this is the focus of attention there are beginning to be significant, non-trivial results on how classical spacetime can emerge from a background independent quantum theory. The best so far are not in LQG, they are the Ambjorn-Jurkiewicz-Loll results on CDT, http://arxiv.org/hep-th/0404156 [Broken]. More is coming, I know of 3 papers in preparation by different authors that contain interesting new approaches or results on this problem. So stay tuned and (to John) don’t loose heart.

Having said this, I should also say that my own view is that it is not likely that LQG, CDT or anything else now on the table will simply be the right thing. I believe these are all models, necessary steps from which we learn how to do non-trivial calculations in background independent, diffeomorphism invariant quantum field theories. As we gain control over them we are beginning to use the new language and tools gained to address not only quantum gravity but the other big problems such as unification and quantum cosmology. The right theory will solve all of these. And I believe it will do so by featuring a genuine emergence of classical spacetime geometry from something more fundamental.

As for string theory being the unique UV completion, the claimed uniqueness requires imposing two physically unjustified assumptions, 1) that it makes sense to an arbitrarily high energy to separate the spacetime geometry into a fixed background and gravitons of arbitrarily high energy and 2) those graviton states transform under the ordinary Poincare transformations, no matter how high the energy. The first appears false in any consistent non-perturbative unification of gravity and quantum theory including CDT and LQG. The second is much less compelling since we learned that Poincare invariance may be deformed, as in deformed or doubly special relativity theories. These allow the relativity of inertial frames to be consistent with energy and/or momentum cutoffs. At least in 2+1 gravity coupled to matter, we know this is how the theory achieves consistency. And there are indications (far from proofs) that the same will be true in 3+1 when we get the low energy limit sorted out.

Of course, the best news is that AUGER and GLAST will in only a few years tell us the fate of Lorentz invariance. The need to firm up our predictcions before the experiments report is what keeps us working hard on these problems.

-Lee
------end quote------

----Woit replied, quote----

Peter Woit; September 3rd, 2005 at 11:55 am

Lee,

Thanks for your comment, it’s very interesting and helpful. The contrast between the evangelism and refusal to acknowledge problems that characterizes many string theorists, and the much more straightforward and scientific attitude of the LQG community is really remarkable.

----end quote----

-------Wolfgang Beirl, the Austro-Bahaman blogger, inquired quote----
Wolfgang; September 3rd, 2005 at 1:34 pm

Lee,

Lubos Motl wrote a long comment to the same two opinion pieces by John Baez and Jacques Distler on his own blog. Would you dare to comment on Lubos’ remarks against LQG, especially the argument(s) that it cannot get the BH entropy right ?

Thank you,
Wolfgang

---end quote---

-----Smolin replied, quote----

Lee Smolin; September 3rd, 2005 at 2:59 pm

Hi Wolfgang,

Thanks for asking. It is always good to have critics and a few of the points Lubos mentions are correct. But not most. I ‘ll avoid the temptation to get into a point by point rebuttal and would just ask those interested to read the section on frequently asked questions in my review http://arxiv.org/hep-th/0408048 [Broken], which covers most of the points. On recent developments, he appears to mischaracterize Rovelli’s new paper, http://arxiv.org/gr-qc/0508124 [Broken], which is to my understanding significant progress. There is a lot in that paper and it also depends on a series of technical developments that directly address some of the issues Lubos raises, for example about observables, that Rovelli and his collaborators have carried out over the last few years. Rovelli et al impose a boundary to define a convenient set of observables, but this is not, as Lubos seems to think, the same as giving up background independence.

The situation with regard to black hole entropy, Immirzi, and quasi normal modes is still evolving and I don’t think Lubos’s characterization is correct. My own current understanding is contained in a new version we just posted of http://arxiv.org/hep-th/0409056 [Broken].

I agree that background independent quantum theories of gravity, including LQG, must address the problem of unification. We have some new ideas and results about this that I’m pretty excited about which will be announced at the Loops 05 conference.

-Lee

---end quote---

In the above, I have expanded arXiv numbers to links, for convenient access. I have also bolded an interesting passage where with remarkable frankness, regarding "results on how classical spacetime can emerge from a background independent quantum theory", Smolin says:
"...The best so far are not in LQG, they are the Ambjorn-Jurkiewicz-Loll results on CDT..."

I am trying to imagine a string thinker saying something comparable: "Hey, you know...as far as making progress towards a workable quantum model of spacetime? It seems that actually the nonperturbative QG people..."

but don't hold your breath :smile:

Anyway we should analyze and discuss these recent Smolin installments. He is giving a kind of cumulative perspective on current progress in quantum gravity.
 
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  • #23
Lee Smolin recently posted again on the group blog Cosmic Variance.
This thread is serving as a place to collect some of these posts, which otherwise are hard to recover once one forgets when and where one saw them.

the following is comment # 91 here:
---quote Smolin Cosmic Variance 10 November---
Lee Smolin on Nov 10th, 2005 at 12:47 am

Dear Clifford, Lubos and everyone,

I would like to make some constructive suggestions, as I strongly agree with you about the need for fair debate, done honestly and with integrity. There is likely to be more debate in the next months and years. Do you really think claims that by people like Susskind and Weinberg that the methodology of science should be changed rather then give up a theory that makes no falsifiable predictions should not be met with vigorous debate? So before it gets any worse could we try to agree on some ground rules for the debates ahead:

-Stick to the issues raised. If someone raises a criticism, whether its done according to your standards of rhetoric or not, just answer the substantial science issue. Don’t waste our time with discussion about anything else. Don’t respond to a criticism on a specific point by changing the subject.

-No personal attacks, absolutely none. If someone has a Ph.D., then they are credentialed. Discuss with them in good faith and with respect.

-Let’s strive to agree on facts before discussing interpretation. Insist on precision and honesty, don’t allow exaggeration, and admit it gracefully when you are wrong or when the evidence does not support something you would like to be true. If someone questions the status of a claim, don’t say “everyone I respect believes X is true.” Say, X is in fact unproven, but there is evidence for it, which is exactly the following….

-Listen carefully to those professional colleagues who read the evidence differently from you, and try to understand sympathetically and in good faith, why they do so.

-Restrain your own communities. Make it clear that it is not acceptable to you when those in your committee insult others or publish or post things that are exaggerated or false. If someone insists on behaving badly, it is up to their community to restrain them. Make it clear that repeatedly treating colleagues disrespectfully in a public forum amounts to professional misconduct. The same is true for repeated cases of knowingly exaggerated or misleading statements in a public forum.

If we can all agree to some basic rules like this I am optimistic that we-and science- will come out better from the debates ahead.

Thanks,

Lee
----endquote---

the following is comment #13 here:
http://cosmicvariance.com/2005/11/07/krauss-on-intelligent-design-religion-and-string-theory/

---quote Smolin on CV 8 November---

Hi everyone,

Peter says, “At the moment there seems to be no plausible idea about how to get a falsifiable prediction out of the landscape…”

Can I mention that there is a precise proposal for how to make falsifiable predictions given a landscape of fundamental theories, it was presented in my first book Life of the Cosmos (OUP, 1997) and related papers, going back to 1992. (For what it's worth these were where the term “landscape of theories” originated.)

The key point is that to make falsifable predictions you need a mechanism that generates an ensemble of universes that a) is very far from random and b) within which our universe is a typical member. This is very different from the anthropic context in which the ensemble is random and our universe is very atypical. Once our universes is atypical it can be anything and there is no falsifiability. But if our unvierse is a typical member of a highly non-random ensemble you can find falsifiable predictions. You do it by finding a property of typical universes in the ensemble that is testible but not known to be true (so it is NOT a consequence of our existence.)

The cosmological natural selection proposal is an example of this methodology. Among the falsifiable (and not yet falsified) predictions is that neutron stars have kaon condensate cores so the upper mass limit is 1.6 solar masses. This is not new, the first paper was “Did the universe evolve?” Classical and Quantum Gravity 9 (1992) 173-191.

By the way the reason for the term “landscape of theories” was to suggest the connection to “fitness landscapes” from population biology, which was where the methodology was copied from.

To my knowledge, those papers and book were the first place in which it was argued in detail that string theory would have to lead to a landscape of theories. The rest of the book went on to explore the implications, particularly for how science could continue to make falsifiable predictions. Other implications, having to do with the connection between the realization that explanation in particle physics becomes “envirnomental” and the need for theories of spacetime to be background independent, were also discussed in detail.

I wonder if I can then gently suggest that those who now, more than ten years later, finally agree about the need for a landscape of string theories, might want to consider the arguments which led to the idea originally.

Finally, in case it still needs to be said, Lawrence is absolutely right that it must be possible to kill a theory by an experiment for it to be part of science. We all must be willing to abandon our favorite theories, no matter what is invested in it, if it does not yield falsifiable predictions.

Thanks,

Lee
----endquote---

this was followed a few days later by post #78

----quote Smolin on Cosmic Variance---

Lee Smolin on Nov 13th, 2005 at 12:37 pm
Dear Arun,

Wow, these debates are perhaps finally getting somewhere. But if I can suggest something-there is no conflict between having a good, honest, respectful debate over the open questions and presenting the science to the public. In my experience the best way to present what science is and how it works to the public is simply to carry out such debates in publically accessible forums like this-as well as in books and public talks. The public is smart and savy and they want the real thing. Many of them would rather look over our shoulder as we talk to each other than listen to something specially prepared for them.

And, if I may add one point on the science side: the debate is not about whether it has been useful to do research in string theory, LQG, dynamical triangulations, causal sets, twistor theory etc. Everyone (or averyone who takes a respectful view of what their colleagues do) can see that these programs have produced lots of non-trivial results. The question is where it is worthwhile, as individuals and as a community, to invest our efforts in the future. The question to be asked about each theory is, have we learned enough about it yet to regard it as unlikely-by itself-to be the right theory and, if so, shall we take in the lessons learned, positive and negative, and move on. Move on means try to invent new theories that have the strengths of those investigated without the weaknesses.

For sure there is a right theory of quantum gravity and beyond the standard model physics out there. My view is that we should spend less of our time investigating theories and ideas already on the table, because if one of them was the right theory we would know it by now. We should instead spend our time trying to invent new, better theories.

I also am very sure that when we find the right theory it will provide us with lots of new, surprising and falsifiable predictions. So I’d rather spend my time looking for that theory than arguing over whether we can live without such predictions.

Others may certainly disagree. But this is where I see the important questions are.

Thanks,

Lee
----end quote---

this was welcomed by the Cosmic Variance host who had initiated the thread
---quote cvj---
Clifford on Nov 13th, 2005 at 1:08 pm
Lee Smolin said:

"there is no conflict between having a good, honest, respectful debate over the open questions and presenting the science to the public. In my experience the best way to present what science is and how it works to the public is simply to carry out such debates in publically accessible forums like this-as well as in books and public talks. The public is smart and savy and they want the real thing."

cvj says:

Yes! Yes! this is what I’ve been getting at on the other thread, (whereas people seem to get distracted and think I’m defending string theory).

-cvj
----end quote---

it was a long thread and difficult to read thru the whole thing but it seems to have reached a friendly state of collegiality, at least at the moment
 
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1. What is the Smolin letter to a string believer?

The Smolin letter to a string believer is an open letter written by physicist Lee Smolin to string theory proponents, challenging the validity and usefulness of string theory in understanding the fundamental laws of nature.

2. Who is Lee Smolin?

Lee Smolin is a theoretical physicist and a founding member of the Perimeter Institute for Theoretical Physics. He is known for his contributions to quantum gravity and cosmology.

3. What is string theory?

String theory is a theoretical framework in physics that attempts to reconcile the theories of general relativity and quantum mechanics by describing the fundamental building blocks of the universe as tiny, vibrating strings instead of point-like particles.

4. What are some criticisms of string theory?

Some criticisms of string theory include its lack of experimental evidence, its reliance on unobservable extra dimensions, and the fact that it has yet to make any testable predictions.

5. Why is the Smolin letter significant?

The Smolin letter sparked a debate within the scientific community about the validity and usefulness of string theory, and has prompted some physicists to explore alternative theories that may better explain the fundamental laws of nature.

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