At the (K)ITP the other day there was a journalist-led discussion/presentation on the largely-media-driven “controversy” about string theory. You know my opinion on this -it’s a largely made up story based on two inaccurate chariacatures (in book form) of research in the field- told by the same journalists and editors who some time earlier brought you the glossy stories about string theory that played up the excitement and promise, and played down the often-said but often-ignored cautionary remarks. The irony of all of this seems to have been lost on most. (I’m not saying that string theorists are entirely blameless in this, but I’ve seen how hard it is to get a balanced remark -about the basic process of seeing a complex scientific program through to its end- to survive next to a glossy one-liner).
The point is that the story being told now in the press is simply the one that journalists and editors want to tell now – a David vs Goliath story. It has little or nothing to do with what is actually going on in the science research. The journalist -George Johnson- does a good job of pointing out supporting evidence for this by going through a number of stories from a decade ago and looking at their structure. (You can see the video archive, as I did, on the web here.) He points out many things, such as the fact that journalists don’t actually write their own headlines for the story and sometimes these have only a loose connection to the actual words written in the body of the article. (There were expressions of surprise from the assembled scientists at this – I find myself amazed at the very fact that they were surprised – Have they not been paying attention to any of this over the last several years?) He points out many other things about the processes involved in getting these stories to appear in the newspaper as well. Worth listening to, if you have not heard this sort of thing before. (Have a read of a report that I and another blogger did on a similar topic, presented by science writer KC Cole in a physics department colloquium a while back.)
Anyway, please have a look/listen to the archived video (find it here). Particularly interesting (in addition to the above description of things as seen from the journalist’s world) is the reaction of lots of physicists in the audience to things that he says, and particularly to a long series of comments that Lee Smolin sent to Jim Hartle that he gave permission to be projected up onto a screen. You have to listen carefully, but have a listen to remarks from Gross, Horowitz, Srednicki and others at various points about Smolin’s moving-target approach to this entire discussion (e.g. how can you claim to be “not anti-string” for the purposes of appearing to be “just wanting to have a discussion” while pushing a book with a title that explicitly links string theory to the fall of science?), and both Smolin’s and Woit’s inconsistent standards of criticism about what constitutes a good research idea that young people should be working on (as opposed to them working on the supposed string theory dead end, you see).
There’s some useful discussion here overall, with good comments from the audience both serious and humorous (I love the joke (I don’t know who called it out): “Do you need higher dimensions to be both one-sided and two-faced?”. I know I’m going to get yelled at for repeating it, but it’s just funny.)
Most importantly, I hope that George Johnson takes on board some of the remarks from the audience about what science reporting could be in the greater scheme of things, beyond the current silliness. We’ve talked about that here a lot – first and foremost, getting across a clearer idea of how science actually works. What it can and cannot do, it’s role in society, etc. But I fear that he’s heard that all before, and that there’s little to be done without changing the business model of what Science journalism is fundamentally about. The model currently has very little in it about the agenda of getting the actual science out there. Until that changes, none of this sort of misrepresentation will change. This is why some of us blog.
Overall, the lesson to take away from this discussion is -as I have said above- that there’s just a huge amount of this discussion (about 95% of it, in my opinion) that has nothing whatsoever to do with the science issues facing string theory or any other approach in this area of physics. You, a reader trying to get an impression of what is going on in the field really have to be aware of that. As usual with any reading, be careful what you read out there… question the motives of those journalists, editors, and also those scientists who are writing popular-level books.
On the latter, be *especially* careful when a scientist writes a popular-level book which is almost entirely an attack on a body of work by others, rather than a description of some new ideas that they happen to be interested in or excited about. That’s probably a big clue that the science is not really their primary concern.
-cvj
Elliot,
What you miss by not taking into account the “technical issues” is that in most of these online conversations between Lee and other more mainstream physicists, he seems to be systematically disingenuous. He dismisses well-established physics by appealing to “theorems” which, on closer examination, never say what he claims they do. He then appeals to his own work on string theory as some sort of proof that he is neutral, even while outright attacking the work of others. The “tone” is always reasonable, but it’s covering up a thoroughly unreasonable viewpoint. He may not sound like he is attacking people, but if you pay close attention to the content, he always is. His criticisms never stand up on valid technical grounds, but when people criticize his own work on valid technical grounds, he dodges the question, either making grand claims unsupported by evidence or appealing to his results as promising but not yet completely worked out. It’s annoying, and anyone with a good understanding of quantum field theory can see many reasons why Lee’s claims simply don’t make sense.
This is one of the most annoying aspects of the public nature of these attacks on string theory; the debates are public but the public does not have the tools to appreciate the technical nature of what’s going on. No one has any desire to prevent people from working on other theories of quantum gravity. It’s just that there are none, so far. If there were, lots of people — including string theorists — would be excited about it! If people doing LQG have trouble getting jobs, it’s probably because their work just doesn’t make sense. For the most part, people in the community are friendly and don’t like making public comments demeaning the work of others. But when Lee is publicly attacking perfectly reasonable and competent people who are just doing their best to understand how quantum gravity works, I don’t think it’s unreasonable to point out to the public that Lee is a fringe figure whose work is not entirely sensible. Was it too harsh for people at the KITP to call him a “crackpot”? Probably. But he is not a great physicist, no matter how much he seeks to set himself up as one.
I say all of this as a field theorist, not a string theorist, to the extent that that distinction even makes sense these days. Clifford, feel free to delete my comment if it seems too harsh.
All,
I second Elliot. In addition, is “you can not judge a book by its cover” still applausable?
One of several things that has really astounded me over the last couple years is the willingness of some string theory partisans to engage in disgraceful and professionally unethical behavior, of an extremely cowardly sort. I have no idea who “anon” is, but the idea that any professional scientist would consider it acceptable behavior to launch this kind of ugly personal attack on someone from behind the protection of anonymity really boggles the mind.
Dear Anon,
Please be specific and we can discuss point by point:
-Which theorem did I quote that meant something different from what I said?
-Which of the criticisms of string theory did I make that did not stand up on technical grounds?
-Which work by LQG people “does not make sense”?
About your general characterization of my work, you might check for example, my citation record. Do you think that all the papers that cited mine were written by people who were somehow wrong about the significance of the results they cited? Then check my career, do you think that the different hiring, promotion and tenure committees, and grant referees were fooled?
And yes, I agree with Peter, it is unethical to make an unsubstantiated personal attack without identifying yourself. Beyond that, I can also assure you that it does not help your case, in the eyes of most scientists, to respond to reasonable criticism with nasty personal attacks. If you cannot take constructive scientific criticism, offered reasonably, and respond to it respectfully and professionally, it gives the impression you cannot be trusted to evaluate reliably either your own work or anyone elses.
Finally, note that I was making what in essense was a peace offering, admitting some fault for having not been able to block too provocative a cover. I still am hoping that somewhere on the other side of this debate there are people who knows how to carry on an honest and respectful discussion about differences of opinion among experts.
Thanks,
Lee
Thanks,
Lee
Blake,
I remember several of my old professors mentioning that there’s only so much stuff they can “cram” into a particular course, during the semester/quarter. In those days I was wondering why the “ground” covered by so many physics and math courses, was kind of on the flakey and/or “weak” side. Most profs just told me that if I wanted to know more about a particular thing in greater depth and detail, I should just read a particular book and/or paper and work out some of the details myself without any “grading” nor any expectations for academic credit.
At the time I didn’t know they were encouraging me to be more independent minded, and that “classroom” lectures were a very inefficient means of passing on detailed subject information. (Initially I thought they were being complete jerks!)
Zwiebach’s undergrad string course and textbook look quite impressive, in how much stuff can be crammed into an undergrad one-semester length course without being too “confusing” (along with “minimal” prerequisites). Though at times I wonder whether a course like that is really appropriate at the undergrad level.
Evidently, avoiding the technical issues is much more satisfying.
But, to return to the point of contention, we have the proposition:
Lee, in his book, asserts that AdS/CFT does not satisfy the requirements of background-independence. David Gross, apparently, asserts that Lee does so, despite having assented privately to the above proposition.
Here, Lee responds that he never assented to the above proposition and, instead, offers a conjecture (unsupported by any evidence) that, perhaps, in the quantum theory, the anti-de Sitter algebra is deformed. Even if this conjecture were true, it — in no way — addresses the truth or falsity of the above proposition.
So am I supposed to be reassured that Lee does, in fact, believe that the above proposition is false?
Note that this is, one would have thought, a completely uncontroversial statement about gravity in asymptotically AdS spacetimes (and the requirements of global hyperbolicity, etc). It has nothing to do with the truth or falsity of the Maldacena Conjecture.
Lee’s perfectly free to poke holes in the Maldacena Conjecture, arguing that no one has proven that N=4 SYM exists as a quantum field theory (in fact, no one has demonstrated the existence of any nontrivial 4D QFT), or that, perhaps, it doesn’t really have vanishing beta function, or that Rehren’s Theorem proves that the Maldacena Conjecture cannot be correct or …
But his statement about background independence seem to me to be just plain false. And I don’t see why it matters that he ‘really believes it.’
Dear All,
Please try to return to some semblance of moderation here. Responding to a naive remark from above about us supposedly being required -as scientists- to be dispassionate, I for one do not believe that we should argue like robots, or bad science fiction chariacatures of scientists. We are human beings, like it or not, and so we have passions. I love science and being a scientist partly because of the passion and emotion that can be involved. I don’t want to eradicate that. And we should not lie to the public and cover up our humanity (well, not too much!) That said, we must be careful all the same, and strive to at least keep the ratio of substance to emotive baggage as high as we can in our comments. That way we all stay engaged in the arguments and discussions because we’ll see the worth of the whole enterprise. But the ratio will vary from comment to comment, I’m sure. Just like in regualr conversation. I don’t have a problem with that. On rules of engagement when making the stronger remarks:- Generally, if you want to go for the jugular, it does lend more weight if you attach your name to the dagger.
Dear Lee,
For what it is worth, I do not buy the “it was out of my control” argument. This is not the same as a magazine or newspaper article. If you felt so strongly about ethics, you would simply have refused to sign a contract to give the publisher control of the book if you did not like the title. Anyone can see that such a title/subtitle combination would be perceived as extremely negative…great for book sales of course, but you claim that you wanted to have a civilised discussion. That title is not a good opening move for such a discussion. It undermines the whole thing. On to ethics again, since you brought it up: Is it not damaging to theoretical physics in general, and to your own integrity as an author/scientist, to knowingly put out a title that claims tht a subfield is destroying physics when (you claim) this differs from the content of the book? You cannot wiggle out of it by saying that you did not think we would be “so sensitive”.
In short, it’s a lame excuse. This is, I suspect, part of the “moving target” aspect we all find frustrating.
As I said to Peter above (please read the comment here)…. if you want to discuss research idea alternatives, and resources, let’s do that. Preferably through the usual channels. If you must write a book, write a book that is about that… But don’t write books trying to drag down an entire research effort -trying to damage its reputation in the eyes of the public- and then claim that it is about somethign else. …. when challenged on it, claim that it is not your title choice? You have to accept responsibility for the whole book. Stand up and be counted, as it were. Are you going to start attributing things in the actual text of the book to having been put there by the copy editors, and not you? I hope not.
Thanks,
-cvj
@JC:
The introduction to Zwiebach’s book lists the chapters which the MIT class (8.251) covers, and it suggests options for different chapters to emphasize based on the time allotment and desired sophistication of the class.
I could rant much more fully about the MIT physics curriculum, but such a rant would be even less germane to this comment thread than anything else I’ve said so far, so I’ll refrain.
Clifford,
I also don’t have a problem with people arguing passionately for what they believe in but you seem to have a double standard here, attacking Lee for putting before the public some emotionally-laden negative expressions about string theory and the current state of theoretical physics, while at least seeming to excuse if not encourage the highly emotional response this has generated in some string theory partisans.
While passion has its place, it must be constrained by intellectual honesty. I think both Lee and I wrote books that are passionately felt and also rigorously honest. We both took great care to get facts right and to make arguments for which we believe we have strong evidence. Quite possibly we’re each wrong about some things. I certainly don’t agree with some of what Lee wrote and I’m sure he feels the same about my book. I’ll be glad to argue with anyone about what’s actually in my book and doubtless Lee feels the same way about his. What I’m seeing far too much of is people who want to argue about the covers and jacket copy of books they haven’t read, instead of dealing with the serious and important issues these books address.
Peter, I’m pretty sure you can tell the difference between passion on the one hand, and an untruth on the other. Consider this in re-reading your first paragraph. Consider this in re-reading your recent post on your blog where you just decided to make up random facts about me in an effort to undermine my reputation. That’s not being passionate.. that’s just making stuff up. I am not encouraging that.
With regards your book being “rigorously honest”, I have to disagree. Recall that on the last thread where we had a discussion about the central argument of your book … the main reason people will take it off the shelf to read -that string theory is wrong, that it can make no contact with experiment- you found yourself, after being asked again and again, unable to supply us with the “well known” (your words) evidence of this. You’re confusing your personal gut feelings, which you are entitled to, with a fact. You should be clear about that with your readers.
As to the issue of the serious and important issues…. We talked about what seems to be the main issue at hand – it has nothing to do with string theory and is more about the career path in physics in general…perhaps all of science. Sure, lets have a discussion….. I’ve said some things above that you did not respond to on this point… would you like to pick up the baton and carry it on….? Also, you did not respond to the comment of one or more of the very young people that you’re so concerne about. Would you do that please?
Thanks,
-cvj
Clifford,
Thanks for that. About the cover, if I feel there is an atmosphere of good faith I’d be glad to further discuss the circumstances, which were long since the contract had been signed. But good faith would mean I sensed a willingness to actually read my book and respond to the arguments written in it.
For the present, it seems I have just to repeat myself. Jacques writes: “Lee, in his book, asserts that AdS/CFT does not satisfy the requirements of background-independence. David Gross, apparently, asserts that Lee does so, despite having assented privately to the above proposition.”
It seems that Jacques did not read my first post to this thread, so let me repeat here the substance:
On page 189 I wrote : â€â€¦if the strong form of the Maldacena conjecture turns out to be true —which is also consistent with the present evidence — then string theory provides good quantum theories of gravity, in the special case of backgrounds with a negative cosmological constant. Moreover, those theories would be partly background-independent, in that a nine-dimensional space is generated from physics in a three-dimensional space….There is other evidence that string theory can provide a unification of gravity with quantum theory…â€
and on page 240 I repeated the point: “In a certain limited sense, if the strong form of the Maldacena conjecture (see chapter 9) turns out to be true, a nine-dimensional geometry will emerge out of a fixed three-dimensional geometry. It is thus not surprising to hear Edward Witten say, as he did in a recent talk at the Kavli Institute for Theoretical Physics at UC Santa Barbara, that “most string theorists suspect that spacetime is an ‘emergent phenomenon,’ in the language of condensed matter physics…â€
OK, get it: I did in the conversation with David in July agree to what was already in the final text of the book, which is that there is limited or weak sense in which, were the strong form of the Maldacena conjecture true, it would satisfy a certain weak form of background independence. So I did not contradict myself, and I think I am owed an acknowledgement of that.
Jacques wants to argue about something else, which is what should be the right form of background independence in different circumstances, I am happy to continue that discussion but it is irrelevent to answering the charge that I contradicted myself and I would prefer to have this settled first. If I get some acknowledgement that what I wrote is indeed consistent with what I said, and perhaps even an apology for having my integrity questioned, then I would be happy to continue to discuss the science. But first things, first.
Thanks,
Lee
Clifford,
You’re the one engaging in untruth here. I’ve repeatedly explained to you that I wrote a very long posting on my blog responding to your question as to what are the problems with making contact between string theory and experiment, again, see:
http://www.math.columbia.edu/~woit/wordpress/?p=473
Remarkably, string theorist Michael Dine recently gave a talk at the KITP entitled “Prospects for a string phenomenology” (see http://online.itp.ucsb.edu/online/bblunch/dine/) in which he accurately explained what the problems are with getting particle physics out of string-based unification. His conclusion was that the only possible way to do this would be by the statistical calculations he is pursuing, and he then explained what Witten’s arguments were for why this won’t work. I’m with him on the first part of this Witten on that issue.
These are serious scientific arguments, not my gut feelings.
As for “youngonion”, he wasn’t even claiming to have read my book, much less trying to argue with what is in it. Sorry, but life is short, and responding to hostile personal attacks from anonymous people on your blog is not high on my list of priorities, so I’m going to pass on dealing with that one.
As for any thing I may have written anywhere about you that is not accurate, it’s certainly possible that I’ve made such a mistake. However so far you haven’t bothered to explain what precisely I’ve written that is inaccurate. It might be a good idea for you to privately contact me and inform me exactly what the problem is, and I’ll be happy to make any appropriate corrections of what I wrote.
Peter,
What you’ve explained is your dislike for the approach. You have not presented “well known evidence” that the approach cannot work. THe research has not even been finished yet…the theory only partly developed. How on earth can you know? I’ve pointed this out before.
I have not looked at Michael Dine’s talk, and so cannot comment on it. I hope that others might be able to. I repeat my comment that the theory is very poorly developed right now. I cannot imagine how anyone can make a sweeping statement about string theory’s prospects without understanding it better. I’m betting that Dine’s remarks are not as sweeping as yours. I could be wrong.
Funny that you’ve said nothing about your bizarre accusations about me. How so?
Cheers,
-cvj
In defense of the book title thing, it really is (as far as I know) a pretty standard thing to sign away a large part of the rights concerning the promotion of the book. Journalists don’t write their titles, Authors don’t pick their titles. It’s really not that controversial.
“Actually, the books rarely carry Phil’s original titles, as the editors usually wrote new titles after reading his manuscripts. Phil often commented that he couldn’t write good titles. If he could, he would have been an advertising writer instead of a novelist.”
– Philip K. Dick’s wife on why the film adaptations of his work often have different titles from the books
Maybe there is an ethical concern but this is how things often are done. The practice really is quite similar to the academic practice of senior researchers putting their names on the papers of junior members of their research group even if they were only marginally involved in the work; which they do for what might be called ‘marketing’ reasons.
TheGraduate:- Thanks. But this is not about the entertainment industry, it is about (supposedly) and academic discussion about research. Or at least, I thought it was. I’m not so sure any more. Maybe it is all entertainment…..
-cvj
Lee, EVERYTHING is negotiable in a book contract. I know, I negotiated one last year (for a textbook, but the principle is the same). If one publisher won’t agree to your terms, find another (it helps to negotiate with two at once); if none will, post it online yourself, and forgo the money. And issuing an apology for the cover of your book deep in the comments section of someone else’s blog does not really do much to change the situation.
For what’s it worth, I do not endorse, and explicitly repudiate, the childish name distortions that were employed at George Johnson’s seminar. (In real time, I was wincing at their mention, but did not speak up and say so.) As for the “crackpot” comment, here is what happened (not fully captued on audio/video). Johnson said something like “No one thinks Smolin is a crackpot.” I raised my hand. This was intended as a joke (and indeed produced the round of laughter that can be heard), but was also intended to convey the point that (in my opinion) the various flavors of loop quantum gravity do not have anywhere near the intellectual heft of string theory, and that Johnson was wrong (in my opinion) to assume (based on what he read in your book) that they did. Bottom line: I do not think you are a crackpot, and I apologize for conveying that impression. However, I do believe that the line of research that you are persuing is extremely unpromising.
I also deny in the strongest possible terms that I am “blind to” or “dishonest” about the “naked prejudice” against women and blacks in physics. No, you don’t mention me by name, but I surely must be among the sort of people you had in mind when you wrote page 336.
.
Clifford,
It’s completely hopeless to try and discuss this topic with you, you just ignore everything I write, characterizing it as being about what I personally “like” or “dislike”. This has nothing to do with that, this is about the technical reasons that no one is able to produce testable, falsifiable predictions about particle physics out of string theory. The problem is not that string theorists are lazy and more graduate student years are going to get it done. You’re welcome to believe that some future new understanding of string theory will change the current situation and testable predictions will become possible. That is something that seems to be purely based on feelings, yours.
As for the “bizarre accusations”, again, you seem to have trouble reading the words I write here, here they are again:
“As for any thing I may have written anywhere about you that is not accurate, it’s certainly possible that I’ve made such a mistake. However so far you haven’t bothered to explain what precisely I’ve written that is inaccurate. It might be a good idea for you to privately contact me and inform me exactly what the problem is, and I’ll be happy to make any appropriate corrections of what I wrote.”
The Maldacena conjecture does not “satisfy a certain weak form of background independence.” It satisfies the strongest possible form of background independence consistent with quantum gravity in asymptotically anti-de Sitter spacetimes.
Perhaps, David Gross gave you credit for having said something more sensible than what — you say — you actually told him back in July. Not having been a party to the conversation I am not in a position to judge.
Personally, though, I tend to be relieved when my physics mistakes are “corrected” by the faulty recollections of my interlocutors.
But that’s just me …
Peter, don’t you find it a little questionable to make accusations and then state that it is the responsibility of the accused to correct them if they are wrong? That’s not exactly civil discourse….
anon.:
I think what he said was that he did his best to make sure it was accurate but if it isn’t let him know and he’ll fix it.
(There is enough to disagree about in this debate without picking at the small potatoes don’t you think?)
Reasonable people have been known to disagree. It’s someting to keep in mind.
Peter… ok.. No progress on the first paragraph then. Fine. You believe there is “well known” evidence for the failure of a research program that is still ongoing. Ok.
And yes, I missed what your last paragraph was about. Did not mean to ignore. Anyway, I agree with anon. You get to just make random stuff up out of whole cloth about someone, and it is up to them to come out and correct you? You really believe that is the way things are supposed to be done? Wow. Are these the same standards you use to judge that string theory is wrong?
-cvj
TheGraduate:- What did he do to make sure it was accurate? He made something up about me, something I was supposed to have done….and then put it on his blog. Is that his best!? That’s utterly ridiculous. And certainly not reasonable, I hope you agree.
-cvj
Jacques,
“The strongest possible form of background independence consistent with quantum gravity in asymptotically anti-de Sitter spacetimes.” according to you, does not satisfy the standard definition of background independence (or in Greene’s terms, manifest background independence) which is that no classical metric and no global symmetries are required to state the laws of the theory. But it does satisfy something weaker than that and because I respect the facts I have been careful in speaking and writing to state clearly the situation. I don’t argue from my feelings, when there is a clear logical case for something I acknowledge it and try to state it clearly. It seems like the pay back I get for trying to be accurate about the facts and precise in my characterization of them is to get insulted and slammed by people who deliberately twist a subtle distinction to make it look like a contradiction. I am still waiting for someone to acknowledge that they had the impression that I did not mention in the book that the Maldacena conjecture could satisfy some (any!) form of background independence, and that, having read the quote from the book, they recognize that impression was wrong. I would like to get some recognition of the fact that on many issues, including this one, my book describes the factually correct situation.
Dear Mark,
I accept your apology, I hope you can accept mine. In fact, one cannot walk away from a contract signed years earlier a few weeks before publication over a dispute over advertising copy, without being in breach of contract. But please be assured that I was not referrring to you or making any terrible accusations towards you or anyone in particlar, in my brief discussion of prejudice in hiring. I was only saying that we all have at some point in our career observed some unconscious prejudice in action, whether in ourselves or in some-but by no means all of our colleagues in physics.
Thanks,
Lee
Mark,
Sure everything is negotiable if you prepared to walk… But in good faith negotiations there is give and take.
What is very clear to me is that this thread itself is not “background independent”
Elliot
‘When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean—neither more nor less.’
Sorry, Lee, but unlike Humpty Dumpty, Physics does not allow us to choose what “background independence” in asymptotically anti-de Sitter spacetimes is supposed to mean. If what is allowed by the Physics doesn’t accord with your “definition”, then that is an inadequacy of your definition.
This has nothing to do with the correctness (or completeness or whatever) of Maldacena’s Conjecture. Maldacena’s Conjecture could be completely wrong. That still would not pave the way for a “more background independent” theory of quantum gravity in asymptotically anti-de Sitter space.
If you want to insist that any theory of quantum gravity in asymptotically anti-de Sitter space obeys only a “weak form of background independence,” go right ahead. But to insist that AdS/CFT suffers from this defect (with the implication that some alternative theory would not) is dishonest.
That is not meant as a slam, or as an insult.
If David Gross misrepresented (or misremembered or misinterpreted) your conversation in July, that’s unfortunate, but it’s something you’ll have to take up with him. It doesn’t change the physics one iota. And, I have to say, I am rather disappointed at the arc of our conversation about the latter.
Dr. Johnson,
Sorry, I really didn’t mean to interfere too much. I was just hoping to promote some good faith discussion.
Please interfere…. not a problem. It is ok for us to disagree on the previous, if you wish.
Cheers,
-cvj
Sorry, maybe somebody can clarify things for me. It seems to me that LS is saying that any theory that insists from the outset on using asymptotically AdS spacetimes is not *completely* background-free, which seems pretty reasonable until you ask: what would a completely background-free description of this situation look like?
Relatedly: I keep seeing the words globally hyperbolic. AdS isn’t globally hyperbolic, so I don’t quite see what is being claimed.
Lee, I do accept your apology. Of course I would not expect anyone to walk away from a signed contract, but I agree with Clifford that each of us is responsible for the ultimate results of contracts we sign. And just to be clear, the issue is not “advertising copy”, but rather the subtitle of the book, a subtitle that amazon, barnesandnoble, and bordersstores all display as part of the title itself.
As for prejudice in physics, you wrote that “blatant prejudice” is responsible for the relatively small numbers of women and blacks, and that anyone who claims (as I do) not to have seen “naked prejudice” in action is “blind” or “dishonest”. You now seem to be backing off from these claims, using the rather milder phrase “unconscious prejudice”. Precision in language in discussing hot-button issues is something we should all strive for.
Exactly the point!
If you don’t nail down the asymptotic behaviour of the metric, you don’t have a well-posed initial value problem, even classically. Once you specify appropriate boundary conditions, however, you obtain a hyperbolic problem.
You can have a theory that is background independent, to the extent that you don’t have to specify a background metric (over the “interior of AdS”). But you can’t avoid the necessity of specifying the asymptotic behaviour of the metric. This requirement, which is basic to the formulation of AdS/CFT, is generic to any would-be quantum theory of gravity in asymptotically AdS space.
“If you don’t nail down the asymptotic behaviour of the metric, you don’t have a well-posed initial value problem, even classically. Once you specify appropriate boundary conditions, however, you obtain a hyperbolic problem.”
I’m not sure I get you, sorry. The initial value problem in GR asks you to specify a metric, energy density, extrinsic curvature etc. *everywhere* on an initial slice. [I know you know this, just stating it so we are not talking about different things.] A typical spatial slice for AdS would be a 3D space of constant negative curvature. Now it seems to me [wrongly?] that what you are saying is that it is ok to deform this metric deep in the interior, provided that the 3D metric still has approximately constant negative curvature far away. Then the system will evolve to something like “AdS deformed deep in the bulk” but still asymptotically AdS; intuitively, the conformal boundary of the 3D negatively curved space evolves into the timelike conformal boundary of the deformed AdS.
But is all this really true? Won’t the evolution lead to a Big Crunch, generically? The point is that non-globally-hyperbolic spacetimes like AdS *cannot* usually be obtained by the usual evolution from initial data. The existence theorem guarantees the existence of an essentially unique *globally hyperbolic* solution of the field equations, but that unique solution won’t be the spacetime we want, except in the case of *exact* AdS [where the maximal Cauchy development can be analytically continued to all of AdS]. Note that the singularity theorems apply here!
Actually all this is what I had in mind when I asked Prof Smolin what he could possibly mean by a *fully* background free formulation of the AdS/CFT setup. Background-free here can’t mean what he wants it to mean, because you can’t treat asymptotically AdS spacetimes as if they were cosmological models. The best you can do is to agree at the outset that you are only going to talk about spacetimes with timelike conformal boundaries — which I think is what you are saying.
Hello Dr. Srednicki:
On the issue of disparaging views of minorities and women held by physicists at good universities, you can take a look at the following if you wish (also I suggest reading the comment section):
[Links to motl's blog removed by cvj]
I think, if Dr. Johnson has some kind of spam detection, it might kill my post if I add any more links so I will stop here.
I am, indeed, going to restrict myself to spacetimes with timelike conformal boundaries. And one is, indeed, (severely) restricted in what initial data can be evolved forward without leading to a big crunch.
All of these feature are incorporated in the AdS/CFT conjecture, as clarified by Witten and by Gubser-Klebanov-Polyakov, following on Maldacena’s original suggestion.
Of course, I’m not (just) interested in things which have a semiclassical description in terms of smooth supergravity solutions.
One generalization is to consider boundary conditions which correspond to relevant perturbations of the boundary CFT. Even semiclassically, these do not give rise to smooth interior geometries. But they can have interesting descriptions in the full string theory.
And if the magnitude of the cosmological constant is not small (in Planck units), then, even in the case of an exactly conformal boundary, the bulk theory is far from being well-described by semiclassical supergravity.
But, before wandering off into such topics, one should — at least — have a formalism which, in an appropriate limit, reproduces known features of the semiclassical physics.
And, like you, I don’t see how such a formalism could possibly be “background independent,” in the sense Lee would like to use the term.
Dr. Johnson,
About the links, I didn’t know there was a policy about that sort of thing. Can you tell me what your policy is?
When it comes to matters of race and gender, among other topics, I find myself unwilling to look at, or to point others in, the direction of rather deliberately objectionable writings on the subjects. I’d rather not have links to that sort of material either.
I don’t have a policy against links in general.
Best,
-cvj
To Jacques Distler,
Have you read Lee Smolin’s or Peter Woit’s book?
To Mark Srednicki,
Have you read Lee Smolin’s or Peter Woit’s book?
I am just curious to what extend one side of the debate knows the position of the other side.
I’ve read all of Peter Woit’s book. I’ve also read chapters 16,18,19,20 of Lee Smolin’s book and skimmed the rest.
It’s worth pointing out that both Lee and Peter have participated in these various internet fora for a while now, so it’s not as if either of their positions on various subjects are unknown.
Clifford,
Again: I acknowledge that I sometimes make mistakes, and if that’s the case here, I’m more than willing to try and correct the record and issue any appropriate apologies. I can’t do this if I don’t know what it is that you are claiming that I got wrong. In this case you continue to be unwilling to communicate to me what the mistake in question is supposed to be and instead seem intent on pursuing it purely as a way of tarring me as dishonest, in particular using it to claim that my criticisms of string theory are dishonestly made. This tactic strikes me as, well, dishonest.
JZ, I’ve read through the parts of Lee’s book that are relevant to the debate, and skimmed the rest. (I believe that, for example, I know the history of particle physics well enough not to need to read Lee’s version closely.) I have also heard Lee and othes working on LQG speak many times, read a number of their papers, and followed some of the recent technical debate at the String Coffee Table and Jacques Distler’s blog. I have not read Peter Woit’s book, and have not commented on it, here or elsewhere.
Clifford, you said “… When it comes to matters of race and gender, among other topics, I [Clifford] find myself unwilling to look at, or to point others in, the direction of rather deliberately objectionable writings on the subjects. …”.
Isn’t failing to “look at … objectionable writings” an ostrich head-in-the-sand approach?
If you don’t “look at” the bad stuff,
and also
don’t “point others … in the direction of” the bad stuff to show them that it exists and how bad it is,
then
aren’t you aiding the bad guys by hiding from them instead of confronting them ?
Or, are you just trying to protect your fellow superstringer Harvard Professor Motl by trying to limit discussion about what he is saying on his blog ?
Tony Smith
http://www.valdostamuseum.org/hamsmith/
Tony Smith,
Please think what you want about my policy.
Thanks.
-cvj