The lack of any serious (Lubos doesn’t count) response to my book from string theorists since its appearance in the UK a month or so ago has begun to surprise me a bit. I was also suprised at how weak the defense of string theory was that the Wall Street Journal’s Sharon Begley put in her recent article. It seems that she did talk to some string theorists, but couldn’t get much usable from them (one supposedly told her that the best argument for string theory was the anthropic landscape). Peskin’s argument that string theory’s biggest success is its “explanation” of the number of generations was evidently the best he could come up with, although it’s obviously very weak.
I’ve heard that the WSJ has gotten some correspondence about this, with Jacques Distler writing in to complain about the article. In one letter from him (also signed by his two collaborators), he claims that Smolin is wrong to say that string theory is not falsifiable, since Distler has a recent paper called Falsifiying String Theory Through WW Scattering.
This paper was discussed extensively here. You can make up your own mind about it, but it’s undeniable that the calculations in the paper don’t involve string theory at all (Distler’s two co-authors are not string theorists). Pretty amazing trick to show that a theory is falsifiable without actually using the theory at all.
There are two obvious problems with the claim in the title of the paper, the first is that when one says a theory is falsifiable, one is talking about the characteristic predictions of the theory, and that’s not what the paper is about. The second is that “string theory” is an ill-defined term, and many versions of “string theory” don’t satisfy the assumptions of the paper (one of the co-authors admits this in the comment section). To fudge his way around this, in the letter to the WSJ, Distler refers to “the canonical definition of string theory” as opposed to “string theory”, although he provides no reference to what this is. Putting “canonical definition” and “string theory” into Google doesn’t turn up anything relevant.
It will be interesting to see if a referee can be found who will go along with allowing the “falsifiying string theory” claim. Most physicists, string theorist and not, that I’ve talked to about this think it’s way out of bounds. It seems to me pretty amazing that Distler would choose to take this case to the Wall Street Journal.
We’ll also see if the WSJ publishes the letter, if not I’ve asked one of the co-authors if they’ll let me publish it here.
I could certainly do a better job of defending string theory than the people Begley talked to. The strongest argument string theorists have is clearly the one that they have “the most promising approach to quantum gravity”. The problem with this is that there are plenty of people who disagree, especially those who do LQG. This is the reason that Distler has been on an anti-LQG campaign throughout the blogosphere recently. His latest posting is about this, with comment section featuring the always incoherent Lubos Motl, and the trademark Distlerian sarcastic sneering at people he disagrees with, e.g. the following comment on a paper by Thomas Thiemann:
I suppose that it is only Thomas’s natural modesty that prevented him from submitting this paper for the Clay prize.
In the first comment, someone quotes from my book something I have to say about the issue being discussed in this posting. For the record, I’m no expert on LQG, and can’t judge exactly how close they are to having a fully satisfactory quantum gravity theory, but my impression is that what they are doing is a more promising approach to quantum gravity than string theory, and the fact that they are convincing more people about this is what is getting Distler and others very worked up. I also don’t think either LQG or string theory has made any headway on the problems of the standard model, although several orders of magnitude more effort have gone into the string theory approach.
Since Distler has a whole posting and ongoing discussion in his comment section about this and I’m no expert, if you want to discuss LQG, its problems and prospects, or comparisons to string theory, please do it there, not here.
Dear Peter,
I respect your desire not to engage in discussion outside of your knowledge base… however, I encourage you to form some opinion on the alternatives to ST, since I think this is very relevant to the discussion. If there were 15 alternative approaches to QG which were even half as promising as string theory, the state of our field would be very different.
“The problem with string theory as a theory of particle physics is not that its explanatory power at the TeV scale is “weak at best”. Its explanatory power as regards particle physics is zero at any scale, up to and including the GUT scale and beyond.” –PW
I think this is unfair. We don’t know physics beyond the TeV scale, so we have no idea whether string theory could provide a useful explanation for it. String theory at least provides some pictures for what this physics could be.
Hi Aaron,
The lost theorem only talks about the uniqueness of the kinematical (prior to solving the Hamiltonian constraint) Hilbert space. Different choices of Hamiltonian constraint operator can lead to inequivalent physical Hilbert spaces. (ofcourse how to define inner product on kernel of Hamiltonian constraint in the absence of observables is a even more vexing issue.) Also as the lost theorem is based on a number of requirements (unitary-anamoly free implementation of spatial diffeomorphism being one of those), violation of any one of those could lead to an inequivalent Hilbert space (even prior to solving the constraint).
I apologise if this answer isnt pertinent.
Also on a side note, as a graduate student in lqg i find it astonishing that many people seem to think that string theorists who have studied lqg and are skeptical about it
(jaques and aaron and urs for example) are trying to undermine the field. All they do is ask genuine technical questions, & there’s absolutely no malice involved in any of it. It seems to me that there is always a bit of overselling of results going on in this field (& maybe in high energy physics in general), pointing it out, or questioning it doesnot amount to any offense at all.
Justin,
Sorry to butt in, but you said
I think this is unfair. We don’t know physics beyond the TeV scale, so we have no idea whether string theory could provide a useful explanation for it. String theory at least provides some pictures for what this physics could be.
But that’s just what it doesn’t do – things which provide accurate “pictures” (however you want to interpret that) also provide accurate physical calculations according to a precisely defined model – this is the ultimate credo of physics. Correct me if I’m wrong.
-drl
If there were 15 alternative approaches to QG which were even half as promising as string theory, the state of our field would be very different.(justin)
Any comment about why string theory papers are uploaded to hep-th instead of gr-qc, then?
Lubos seems to have removed his review of NEW from the amazon.co.uk web site.
Or maybe it did not meet Amazon standards, and they removed it themselves.
Chris Oakley said “… Lubos seems to have removed his review of NEW from the amazon.co.uk web site.
Or maybe it did not meet Amazon standards, and they removed it themselves. …”.
However, as of the time I am writing this comment, Lubos’s review is still among the 9 reviews on the USA amazon.com web page for the UK version of Peter’s book.
The USA web page seems to have listed the UK version for book resellers who have UK versions for resale in the USA. In the past, there have been a number of such books for sale on that page, but now the page says
“… THIS TITLE IS CURRENTLY NOT AVAILABLE. If you would like to purchase this title, we recommend that you occasionally check this page to see if it has become available. …”
so I guess the USA resellers are as of now sold out of the UK version.
Maybe they will restock and it can again be bought through the USA amazon.com.
Here are the 5 current customer reviewers of the UK book on the UK web site amazon.co.uk
LEJ Brouwer
J. B. Cook (UK)
Reader (Australia)
Sam “Sam” (UK)
Dr. C. G. Oakley (Dunstable, Bedfordshire United Kingdom)
Here are the 9 current customer reviewers of the UK book on the USA web site amazon.com
LEJ Brouwer
truth eker (Canada)
Knotted String
Humble Priest “String Theorist” (USA)
M. Wang “mrnexus” (CT United States)
J. B. Cook (UK)
Lubos Motl (Cambridge, MA United States)
Sam “Sam” (UK)
Dr. C. G. Oakley (Dunstable, Bedfordshire United Kingdom)
It is interesting to read all those customer reviews.
Here is an excerpt from the 5-star review by Humble Priest “String Theorist” (USA):
“… I’m a string theorist by the way, which is why I’m hiding behind a pseudonym (I don’t want to be called a “science hater” by my seniors). …”.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
PS – I think that amazon must not allow customer reviews of books not yet available, as there are no customer reviews on the USA amazon.com web page for the not-yet-released USA version of Peter’s book. However, there is a Beta-version customer discussion feature (as of now it has only one participant, me).
Lubos has posted Barton Zwiebach’s response on his blog.
http://motls.blogspot.com/2006/06/barton-zwiebach-letter-to-editor.html
In regards to Zwiebach’s response, this pretty much sums things up:
“All that is needed to rule out string theory is showing that no solution describes our universe.”
That should be easy.
(BTW, Isn’t that what led to the anthropic landscape in the first place?)
Hi all,
in Lubos’ site, today Zwiebach is quoted as saying:
“[string theory] has explained, for example, why black holes have entropy and temperature.”
Can I get some insight on this ? What is Zwiebach referring to, and what is true about it ? Sorry for my ignorance…
Cheers,
T.
As “You” noted, Barton Zweibach’s letter to the Wall Street Journal editor is posted on Lubos Motl’s blog. In it, Zweibach says:
“… string theory … computations give unequivocal answers.
… All that is needed to confirm string theory is finding one solution that describes our universe. All that is needed to rule out string theory is showing that no solution describes our universe. An answer must exist. …”.
That is true.
What Zweibach does NOT say is that after two decades of work by many well-funded superstring theorists, none of them have found ANY “string theory … computation” that “describes our universe” in the sense that it gives the force strengths and particle masses of the Standard Model.
Perhaps two decades of failure to find such a solution is an indication that such a solution does in fact not exist, thus providing Zweibach’s “answer”:
conventional string theory, as a unification of gravity and the Standard Model, is probably wrong.
Zweibach also says:
“… a healthy equilibrium exists where string theory and other good ideas are explored and compete for attention …”.
However,
a competing model that allows computation whose answers (unlike those of superstring calculation) are explicitly known and consistent with experimental measurements of such parameters of the Standard Model,
is
ignored by theoretical physics institutions and and its developer (me) is blacklisted by the Cornell arXiv for physics papers and is subjected to ad hominem attacks by Harvard Professor Lubos Motl as a “… moronic … crackpot …”.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
PS – My competing model can be formulated in terms of a NON-supersymmetric string theory in which strings correspond to world-lines of particles, but Lubos Motl attacked it as not being “string theory” because it did not have conventional supersymmetry.
Maybe when the LHC collider data that is to begin to be taken around 2008 will show whether or not such supersymmetry is consistent with experiment. Peter, in his blog entry “Strings 2006”, quoted Jonathan Schock as saying, about the coming LHC experiments:
“… … if supersymmetry is found … then we all will be together [at a Strings 2009 meeting] to celebrate it and if it is not found we will be together for a collective suicidal. …”.
Tony, You say ‘That is true’ to Barton Zwiebach’s claim that “All that is needed to confirm string theory is finding one solution that describes our universe.” But is that so? If I understand Peter Woit, a theory with 10^500 possible universes is a ‘theory of anything’, unless you can specify the mechanism that singles out one of these vacuum states. If it is just something like ‘spontaneous symmetry breaking’, which sounds like pure chance to me, then it seems to me you haven’t really explained anything. Of course, as an ignorant layman, I may not have my facts straight. 🙂
Tommaso this may be helpful
http://en.wikipedia.org/wiki/Black_hole_entropy
Dear Tommaso,
I think Zweibach is referring to the emergence of the Hawking-Bekenstein entropy law from a string theory picture of a black hole. While we have very little evidence of black holes themselves, general relativity leads to a theoretical framework where there is a duality between black hole properties on one side and macroscopic thermodynamic properties, such as entropy, temperature, free energy, on the other. There is no parallel for microscopic properties from GR alone.
Using string theory to model a black hole, and imagining the microstates of a black hole to be string excitations, Strominger and Vafa, were able to find the entropy of a 5-dimensional Reissner-Nordstrom black hole from the microscopic states. The entropy calculations have been extended to a large range of black holes with success. That string theory can model the microstates of a black hole means it fulfils a necessary criterion for any theory of quantum gravity. In this sense sometimes this is (mis)referred to as an experimental test of string theory.
It is a very actove area of string theory reserach at the moment, and the string picture has lead to corrections to the Bekenstein-Hawking area/temperature law and even to the idea that the black hole has no precise event horizon when viewed from close-up – the event horizon becomes pictured as a statistical distribution, like temperature, that only makes sense when viewed from far away (in the same way that if you were riding a molecule in a gas, the temperature of the gas as a whole would be a strange concept for you, but if you were macroscopic experimenter then temperature is a very clear concept). The theoretical picture is making progress, all we need now is a black hole to experiment with…
This is, arguably, the greatest result of string theory to date. Zweibach’s wonderful purple book, Chapter 16, has an excellent introductory review.
Best wishes,
Paul
From Zwiebach’s article:
Right … so ST has explained the existence of unobserved physical properties about a possibly non-existent class of objects.
That’s good enough for me. I’ll now go and remove all the negative things I have said about ST from my web site.
The “it has many sollutions” paradigm is already a change to what, for example Lubos Motl was arguing a while ago, that is, that it’s essentially unique.
As such it is of course not a theory of anything. Newtons formula F = ma is of course completely unspecified until you define F in terms of x, yet few would argue that it’s therefore vaccuous.
String theory is unique in getting a relationship between the effective QFT picture and Gravity. There is no other theory that can do this at the moment (some loopy results might be getting there, but it’s not here yet). At the same time it’s hard to see how to answer the hard conceptional questions from the String theory PoV precisely because it is so tightly tied to the effective field theory picture.
JDs critizism of LQG is that it does not relate to the effective field theory picture, well yes, that’s the point. It’s not a local field theory.
Why claim that black holes do not exist? Hawking (+ Penrose?) proved long ago that GR must have singularities. I believe there is expt observation of black holes, see this from HST
http://hubblesite.org/newscenter/newsdesk/archive/releases/1994/23/
As Benjamin said, I said “… ‘That is true’ to Barton Zwiebach’s claim that “All that is needed to confirm string theory is finding one solution that describes our universe.” …”,
and
Benjamin asks “… But is that so?
… unless you can specify the mechanism that singles out one of these … 10^500 possible … vacuum states …[other than]… pure chance …
then it seems to me you haven’t really explained anything. …”.
Benjamin, I think you do have your facts straight.
When I said “That is true” I was assuming that Barton Zweibach’s “… finding one solution that describes our universe …” would be based on his finding some sort of reasonable uniqueness criterion, not based on something like a pure chance random search.
So, I stand corrected. I should have said:
Zweibach says:
“… string theory … computations give unequivocal answers.
… All that is needed to confirm string theory is finding one solution that describes our universe.
All that is needed to rule out string theory is showing that no solution describes our universe.
An answer must exist. …”.
Zweibach’s first alternative should be divided into two possibilities, giving a total three:
1 – finding one solution that describes our universe, and finding that it has unique characteristics (other than just happening to correspond to the properties of our universe) that single it out from all other (about 10^500) possibilities, would confirm superstring theory;
2 – finding one solution that describes our universe, but finding that it has no uniquely distinguishing characteristics from all other (about 10^500) possibilities, would show that superstring theory is Not Even Wrong;
3 – finding that no solution describes our universe would show that superstring theory avoids being Not Even Wrong by in fact being Wrong.
Among those three alternatives, I think that “An answer must exist”.
Thanks, Benjamin, for pointing that out.
My personal guess as to which alternative is true is still that superstring theory is Wrong (my third alternative), because failure to find a solution (in ANY way, random or not) by two decades of work by many hundreds of very (techically) smart, well-funded people indicates to me that such a solution is unlikely to exist, thus providing the “answer”:
conventional string theory, as a unification of gravity and the Standard Model, is probably wrong.
My conviction as to my guess is supported by the attitude of people like Jonathan Schock, who (according to Peter’s quote) said that at Strings 2009, “…if supersymmetry is … not found [by LHC] we will be together for a collective suicidal. …”.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
I just wrote a new posting about the Zwiebach letter. Please continue discussion of it there.
Sunderpeeche,
You’re twisting Chris Oakley’s words. He’s not claiming black holes don’t exist. Just saying it hasn’t been proven they do. That’s true.
The NASA page you point to describes a dark, supermassive object in the M47 galaxy. There are GR alternatives that predict such things (see http://www.arxiv.org/abs/astro-ph/0606489) without black hole singularities.
There’s also a dark, supermassive object, Sgr A*, in this galaxy. But a close look shows it or something nearby radiates at long wavelengths.
Sorry for the typo. That should read M87, not M47.
Peter,
Sorry again. Missed your last comment.
Peter and others,
since we are discussing quantum gravity., I urge all of you to read this nice
preprint which appeared just yesterday gr-qc/0606120 (which talks about possible
experimental tests). I am surprised no one has discussed it in the blogosphere/
Cecil,
http://www.people.fas.harvard.edu/~math21a/exhibits/unknotting/index.html
And, what Tony said.
-drl