I have a long-percolating post that I hope to finish soon (when everything else is finished!) on “Why String Theory Must Be Right.” Not because it actually must be right, of course; it’s an hypothesis that will ultimately have to be tested against data. But there are very good reasons to think that something like string theory is going to be part of the ultimate understanding of quantum gravity, and it would be nice if more people knew what those reasons were.
Of course, it would be even nicer if those reasons were explained (to interested non-physicists as well as other physicists who are not specialists) by string theorists themselves. Unfortunately, they’re not. Most string theorists (not all, obviously; there are laudable exceptions) seem to not deem it worth their time to make much of an effort to explain why this theory with no empirical support whatsoever is nevertheless so promising. (Which it is.) Meanwhile, people who think that string theory has hit a dead end and should admit defeat — who are a tiny minority of those who are well-informed about the subject — are getting their message out with devastating effectiveness.
The latest manifestation of this trend is this video dialogue on Bloggingheads.tv, featuring science writers John Horgan and George Johnson. (Via Not Even Wrong.) Horgan is explicitly anti-string theory, while Johnson is more willing to admit that it might be worthwhile, and he’s not really qualified to pass judgment. But you’ll hear things like “string theory is just not a serious enterprise,” and see it compared to pseudoscience, postmodernism, and theology. (Pick the boogeyman of your choice!)
One of their pieces of evidence for the decline of string theory is a recent public debate between Brian Greene and Lawrence Krauss about the status of string theory. They seemed to take the very existence of such a debate as evidence that string theory isn’t really science any more — as if serious scientific subjects were never to be debated in public. Peter Woit agrees that “things are not looking good for a physical theory when there start being public debates on the subject”; indeed, I’m just about ready to give up on evolution for just that reason.
In their rush to find evidence for the conclusion they want to reach, everyone seems to be ignoring the fact that having public debates is actually a good thing, whatever the state of health of a particular field might be. The existence of a public debate isn’t evidence that a field is in trouble; it’s evidence that there is an unresolved scientific question about which many people are interested, which is wonderful. Science writers, of all people, should understand this. It’s not our job as researchers to hide away from the rest of the world until we’re absolutely sure that we’ve figured it all out, and only then share what we’ve learned; science is a process, and it needn’t be an especially esoteric one. There’s nothing illegitimate or unsavory about allowing the hoi-polloi the occasional glimpse at how the sausage is made.
What is illegitimate is when the view thereby provided is highly distorted. I’ve long supported the rights of stringy skeptics to get their arguments out to a wide audience, even if I don’t agree with them myself. The correct response on the part of those of us who appreciate the promise of string theory is to come back with our (vastly superior, of course) counter-arguments. The free market of ideas, I’m sure you’ve heard it all before.
Come on, string theorists! Make some effort to explain to everyone why this set of lofty speculations is as promising as you know it to be. It won’t hurt too much, really.
Update: Just to clarify the background of the above-mentioned debate. The original idea did not come from Brian or Lawrence; it was organized (they’ve told me) by the Smithsonian to generate interest and excitement for the adventure of particle physics, especially in the DC area, and they agreed to participate to help achieve this laudable purpose. The fact, as mentioned on Bloggingheads, that the participants were joking and enjoying themselves is evidence that they are friends who respect each other and understand that they are ultimately on the same side; not evidence that string theory itself is a joke.
It would be a shame if leading scientists were discouraged from participating in such events out of fear that discussing controversies in public gave people the wrong impression about the health of their field.
Sean,
My comment about debates did explicitly refer to “physical theories”, and I think it’s true that it’s highly unusual for abstract theories about physics to become the topic of this kind of public debate (by the way, on the whole I think such debates are a good thing, modulo obvious problems with dealing with technical issues in this kind of forum). Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity). I’m quite curious to know if anyone can point to such an example.
Horgan enjoys being extreme and provocative, so some of his over-the-top comments weren’t surprising and one would be justified in not taking them completely seriously, but I do find it striking that string theorists are losing people like George Johnson, who traditionally have been quite sympathetic to what they are doing. I think one important reason is the way they have reacted to the challenge posed by my book and Smolin’s. Johnson makes it pretty clear that he was strongly struck (and not positively), by the way people at the KITP behaved in the discussion he held on the topic there.
I’ve also been kind of amazed by what a terrible job string theorists are doing of responding to criticism. The most sensible ones are pretty much keeping quiet, letting the response (at least on the web and in blogs) be dominated by some of their colleagues with less than good judgement, especially ones who think that ad hominem attacks are an appropriate response to criticism of a scientific theory.
Peter, if you look closely you’ll see that I actually linked to such an example in my post. (Today, the question of whether nebulae are galaxies or just gas clouds doesn’t seem that abstract, but in the 1920’s it was.) That’s just the most famous one; I don’t think examples are that hard to come by. The Bohr-Einstein debates about quantum mechanics weren’t carried out in front of public audiences, but they easily could have been, and it might have been a good thing.
I agree with you that the most sensible string theorists are (pretty much) keeping quiet — this post was in part an attempt to tweak them into speaking up!
You know, I promised myself I’d give up Lee Smolin for Lent (when is that, anyways?), and now you try to pull me back in.
So, I’ll just suffice with self-promotion and refer back to my review of Peter’s book where I try to do just what you say.
On the other hand, I think is is part of a natural media cycle of promotion and backlash. Once people are through proving their iconoclasm bona fides, I tend to think things will even out to a reasonably sober equilibrium.
I am not a scientist, (I don’t speak math, so that kills any scientific aspirations), but love reading and learning about what’s going on in different scientific fields. I guess you could say I’m the audience that consumes scientific dialog “for dummies”.
I could never write a paper on string theory or quantum-loop gravity, but I can certainly discuss the benefits of funding programs of discovery. So to read a statement such as “things are not looking good for a physical theory when there start being public debates on the subjectâ€, stuns me. Did these words actually come from a scientific mind? Does discussion of scientific theory constitute valid data that the theory is flawed? Or is public discussion viewed as evidence that the subject matter is too accessible to the minds of little people, and therefore not worthy of attention by great minds?
I doubt such an (ego-driven?) attitude will get real legs…at least I would hope not. The backlash from the public for such thinking would likely be similarly childish; “If you’re are unwilling to discuss it, we’re unwilling to fund it.”
As for me, I think these are heady times for scientific observers. It seems to me that we, (by which I mean you science types), have really begun to learn how to learn. That may seem offensive, but when I read about all the various data points supporting global warming and consider that “connecting the dots” has really only come together in earnest over the past ten years, you can see my pov.
In fact, it is only by taking scientific dialog out of the lab and making it available to a broader audience that allows the “dots” to be connected. My understanding is that cosmic microwave background radiation was discovered (when it was) because a guy who knew the scientists at both Princeton and Bell Labs learned what each were working on and introduced them, thereby literally connecting the “dots”.
So I support your view that public discussion of scientific developments is a good thing. And not just because I am personally interested. Rather, I feel such dialog will bring closer the day that a room full of politicians can publicly laugh Intelligent Design right back under the rock from which it crawled. But until the public can discern between science and philosophy, (ok, string theory isn’t helping there YET), politicians will play ball with both crowds. And they make the appropriations decisions so discuss, discuss, discuss!
Sorry Sean, but I came with time to precisely the opposite conclusion. At least as far as the public blogosphere is concerned, I have no evidence of anyone ever changing their minds, or even changing any of the details of their arguments. More generally, this is a highly technical subject, inevitably any public debate will come down to who is the nice guy and who sounds more reasonable. Personally, if I had any intention of engaging in marketing I would want to get paid more for it…
Luckily, as you note, among quantum gravity experts there is a near consensus on the merits of this approach, this ought to be the important thing. Of course, technical debates among experts are going on all the time, let’s just say they have a slightly different flavor than the public debates.
(not to say that string theory should not be explained to the public, and to our colleagues, but debate and explanation are two separate issues).
Sean, thanks for your thoughtful post on my conversation with George Johnson. Just let me clarify my view of the debate between Greene and Krauss over strings. Contrary to what you imply, I don’t think a scientific theory loses credibility just because it’s debated publicly. It was the jokey tone of the Krauss-Greene debate–at least as described in one online report–that struck me as yet more evidence that strings are in big trouble. Neither Krauss nor Greene seemed to be even attempting to be serious about strings. They were just posturing, performing, for fun. In other words, they seem to tacitly agree with my description of string theory in The End of Science as “ironic science,” which is more akin to philosophy or even literature than real science and should not be taken literally. Sean, jump off the sinking ship while you still can!
God forbid scientists should have a sense of humor.
“Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity).” - Peter Woit
Einstein debated general relativity on 25 September 1920 with his Nobel Laureate Philipp Lenard:
“On September 25, the day of the debate on relativity, Born and Einstein walked out of the train station to face a changed scene: guards armed with fixed bayonets. Not trusting the scientists’ sangfroid, the government prepared for trouble, unnecessarily, as it turned out.
“In Bathhouse 8, five to six hundred eager listeners “squeezed together on seats, stood along the walls, filled the balcony … .” First came hours of invited papers, until session chair Max Planck finally opened the floor to discussion. Lenard spoke first. When Einstein followed, Planck was forced to silence heckling, perhaps orchestrated. Lenard and Einstein rebutted each other’s comments, as others in the audience asked questions and offered opinions, including Born. Then Planck, who had maintained a more dignified proceeding than many had considered possible, observed that relativity theory still had not made it possible to extend the time for the meeting and ended the discussion.
“Einstein was disappointed in his performance. “I will … not allow myself to get excited again, as in Nauheim,” he wrote Born. “It is quite inconceivable to me how I could have lost my sense of humour to such an extent through being in bad company.” Born knew that Einstein suffered under the attacks and worried that he might leave Germany. This was all the more reason for the Borns to react strongly to the swirl of publicity that surrounded Einstein and, in their opinion, made him more vulnerable to attack - publicity that the Borns and other friends such as Max Wertheimer attributed to Einstein’s good nature and Elsa’s enjoyment of the attention.”
- http://www.maxborn.net/index.php?page=excerpts
Relativity was an ad hoc explanation for existing physical concepts such as the FitzGerald-Lorentz transformation (including length contraction, time dilation, and mass increase after 1897 when J.J. Thomson showed that the mass of a charge is inversely proportional to its radius), so it’s not a good analogy to string theory. Relativity was a working theory, addressing data, straight off. String theory isn’t even a model of anything already known to exist.
A better anology to string theory is the debates concerning the Bohr-Heisenberg Copenhagen, particularly during the 1927 and 1930 Solvay Congresses, which led to the EPR paradox published in the Physics Review (1935), “Is the quantum description of physical reality complete?” In turn, this first led to Bell’s inequality and then to Aspect’s tests in 1982, so although interpretational difficulties still abound the foundations of quantum mechanics, at least the subject isn’t hyped up so much now as ending with Copenhagen. There was eventually interesting physics generated from the arguments: it wasn’t a waste of time.
Rob,
“Did these words actually come from a scientific mind?”
Yes, these words did come from a scientific mind, mine. Do you really think it’s necessary to make insulting comments like this to make your argument? The point I was making (as were Horgan and Johnson) is not that there is anything wrong with these debates, just that they are an unusual phenomenon in this particular science and thus indicate something unusual is going on. Sean has helpfully pointed to another example, from astrophysics, but it’s one from nearly a century ago. I don’t think it is in any way unreasonable to suggest that the existence of these debates suggests that something unusual is going on in this subject.
One thing that struck me in reading the transcript of the recent Smolin/Duff debate were Chris Isham’s remarks that quantum gravity is not like other subfields of physics because theoretical claims can’t at all be confronted with experiment, and scientific disagreements adjudicated through this means. This has a lot to do with the unusual current situation. Nobody was holding public debates in the early seventies about the Weinberg-Salam model and whether there were weak neutral currents. They were making models that made distinct predictions about this and evaluating them as the data came in. Maybe they should have been having public debates, and that would have been fine, but the debates would have had a different nature, with everyone looking to experimental results to sustain their points.
Again, I don’t think there’s anything at all “wrong” with these debates, actually I think their existence is great. I’m a big fan of the free marketplace of ideas, whenever it’s a free marketplace…
[...] Update: Sean Carroll has a posting about this over at Cosmic Variance entitled String Theory is Losing the Public Debate. Probably best if people join the discussion over there, which so far includes John Horgan and others. [...]
John and Aaron,
One of the things that most struck me about some of the KITP on-line videos of talks on the Landscape is the amount of nervous laughter involved. People seemed to be very much aware of the kind of ludicrous nature of some of the arguments being presented. Nothing wrong with a sense of humor, but this seemed to me something different. There’s a difference between making jokes about one’s ideas and the ideas being a joke.
I think Jacques Distler did a very good job, explaining the Motivation(s) for string theory in this blog post.
I’m noticing that everyone here is being careful to describe the debate about string theory as a debate about its merits as a theory of quantum gravity. As someone who has always been most concerned with its merits as a supposed theory that explains things we can actually hope to observe (e.g. particle physics), I’m just wondering: is the debate on that point over?
Sean,
> The Bohr-Einstein debates
Actually, I find comparisons of the recent debate about string theory and the Bohr-Einstein debate (and other historical debates) very painful.
The contrast between the high level of discourse in the past and the low level now, often quickly degenerating into name-calling, is perhaps a major reason why string theory might be ‘loosing the public debate’.
Bohr did not call Einstein a ‘crackpot’, but tried to convince him…
Wolfgang, many string theorists can’t respond directly to criticisms because M-theory originator Ed Witten has stated in a letter to Nature that responding to criticisms may add fuel to controversies:
‘The critics feel passionately that they are right, and that their viewpoints have been unfairly neglected by the establishment. … They bring into the public arena technical claims that few can properly evaluate. … Responding to this kind of criticism can be very difficult. It is hard to answer unfair charges of élitism without sounding élitist to non-experts. A direct response may just add fuel to controversies.’ - Dr Edward Witten, M-theory originator, Nature, Vol 444, 16 November 2006.
For those who aren’t aware of Dr Witten’s view:
‘String theory has the remarkable property of predicting gravity.’ - Dr Edward Witten, M-theory originator, Physics Today, April 1996.
Wonder why he won’t respond directly to criticisms?
Moshe, it’s a shame you feel that way. I was talking, of course, about “explanation” more than “debate,” and in a broader context than just the blogosphere. But I think that too many sensible people read some pointless name-calling on blogs, and conclude that it’s a waste of time to talk to non-specialists in general. Which is a mistake.
And I should say specifically that the “it’s a technical subject” argument is missing the point in an important way. Of course, non-experts (whether they are non-scientists or other physicists) aren’t going to be adjudicate the role of polymer representations of non-seperable Hilbert spaces, or the difficulty of stabilizing moduli in a controlled large-volume approximation. But they certainly can understand the basic reasons why an approach might be promising even in the absence of direct experimental support. It’s worth making an effort to make those reasons clear. (Which I know that you, as one of the good guys, appreciate.)
It might be nice if the academic system allowed young folks to just spend 7 years in their attic — a la Andrew Wiles & Fermat’s Last Theorem — to actually work out an actual mathematically-consistent alternative to string theory… But this is fundamentally not possible with the present system (due to publication, tenure, and career pressures), thus all we get is a Soviet-style single (and untestable) choice in the matter of a quantum mechanical theory of gravity. (I don’t think many people would consider quantum loop gravity to be an alternative, at least at this point.)
Dimension is actually an operator that acts on a state.
Minkowski space is its vacuum expectation. Complete those two sentences…
What happens if one were to promote dimension to an operator? Many people have wondered about that — note that one would need to establish its commutation relations, for one thing — but no one has been able to do the resulting mathematics. So maybe that line _might_ even end up resulting in an alternative to string theory — but no one has been able to take the plunge, mostly because of academic pressures.
I think that’s unfortunate.
Peter — I was responding to the fact that Mr. Horgan seems to think of it as an indictment of a theory that people are willing and able to debate it in good humor.
As for the landscape, you know as well as I do that the debate about the landscape within the string theory community has been at least as vehement as that without, if not nearly as public.
As for the other, no attempt at a theory of quantum gravity has been able to produce a falsifiable prediction. There are various things that might be confirmatory, however. As is well-known, there are effective field theory arguments that make it extremely difficult to directly observe quantum gravitational effects. Nonetheless, there are conjectural restrictions on the sort of effective field theories that might arise out of string theory. If these could be more firmly established, they would constitute falsifiable predictions and/or retrodictions.
It seems to me that Horgan’s attack is really on theoretical high-energy physics, not on string theory. His arguments are against the whole idea of unifying quantum mechanics and relativity. The idea is that physics has gotten as far as it possibly can, and that from now on it is bound to be theology. Johnson’s praises a “pragmatic” approach of… just giving up. Why do we need a single, unified theory anyway?
That’s the saddest thing about today’s “public debate”: the people who brought string theory to the court of public opinion don’t realize that what they are sinking is their ship too. If tomorrow LQG were to become the new darling of high energy physicists, people like Horgan would be bashing it just like today they are doing with string theory, on precisely the same grounds.
I don’t suppose I will be the one who will convince these critics that they’re being short-sighted. I’ll just add that it is rarely mentioned that string theory has _already_ led to very nice progress in mathematics. Oh yea, but maybe not even geometry is a “serious enterprise”.
Peter, about your comment #13: I find it hard to understand how you can totally separate debating string theory’s promise in understanding quantum gravity from a larger debate of it’s viability. I agree that string theory seems unlikely to tell us anything about electroweak scale particle physics(except perhaps through gauge/gravitational duality as applied to QCD). But it isn’t really fair to claim that it is thus dead in water. String theory excited many theorists by providing a quantum gravity candidate and, in the end, exploring that regime will be what determines if it sinks or swims. Admittedly, that doesn’t appear like it will happen soon. But does the fact that one doesn’t know when one can test an idea make the idea unscientific?
I see my previous comment strayed a bit from what you were saying, Peter. I can’t speak for every string theorist(many will disagree with me probably), but I don’t think there’s much chance of string theory saying much about “particle physics”. I use the quotes since what is usually meant by that term is electroweak scale collider physics, where QCD is weakly coupled. But I do think string theory may provide insight into hadron physics, strongly coupled QCD etc. through dual gravitational models. This would be very different from string theory as the “theory of everything” since such a thing would be an effective model which may only apply in a certain regime.
As a string phenomenologists, I find the comments by the anti-string people that string theory cannot be tested to be somewhat insulting and completely wrong. We can now competely derive the MSSM from string theory, including the quark, tau lepton, and neutrino mass matrices and mixings (see our paper on Monday), so these people should sit down and be quiet.
I would like to see a semi-popular debate on the issues. The landscape, extra dimensions, branes/strings/particles, Maldacena conjecture would all be covered. With most pop physics books, the assumption is that the reader is a complete idiot. Yet there are plenty of pop math books that include a “lite” version of various concepts and equations. Books like Superstrings (edited by Davies) were a step in the right direction.
The ad hominem attacks are degrading the signal to noise ratio, but they do have a point. String theory is a technical field, thus it’s fair to question the credentials of the critics.
Easy to read papers like “A Laymen’s Guide to M-theory” (hep-th/9805177) are good idea too.
Eric,
Your paper sounds very exciting. How about a hint. What is the mass of the Higgs and the what particle is the LSP?
Eric: “derive” (i.e. “predict”) … or “construct”.
An important logical distinction…
If it’s really the former, then what is the value of delta (the Dirac CP phase)?
If you can actually predict that, and you are proven to be correct, then clearly you will have a Nobel prize waiting for you.
Eric,
Intriguing stuff but I still think there is a bit of an issue. Given the vast variety of string constructions, I don’t doubt that there is one that contains the MSSM at low energies with all of the couplings consistent with current measurements. But one expects that there will actually be many such string models which look roughly the same at low energy(since renormalization group isn’t actually a group and so isn’t uniquely invertible). Now, any given model which is consistent with SM will give unique predictions for higher energy physics. But let’s say you have one and it’s gets proven wrong by future experiments. “No big deal,” you say and move onto a slightly different model so string theory still lives. This is the feature that many people object to. That string theory won’t be falsified by the falsification of some model and doesn’t seem to give any unique predictions. The converse also seems to be true. If your model stands up to scrutiny in the next round of experiments, I’m not sure this gives much in the way of evidence for string theory, just for some effective field theory like the MSSM. To get real direct evidence for string theory, I think you probably need some data from the Planck scale, where string theory is qualitatively different from quantum field theory.
On the other hand, I think there are many channels of indirect evidence for string theory. Experimentally, finding low-energy SUSY at LHC will give a big boost of confidence that we’re on track with this set of ideas. Theoretically, things like black hole microstate counting, including higher derivative stringy corrections give (me, at least) confidence that the string program is on to something.
I don’t mean to deride your work, I think the sort of model-building you describe is important. But it seems to me mostly a “proof of concept”, like most, if not all, work in string theory.
Two things: First, I think Sean is right when he says often those manifestly opposed to string theory are those “who are a tiny minority of those who are well-informed about the subject.” It seems most anti-string theory people I meet have never taken formal courses on the matter. They form their opinions based off the opinions of others.
I don’t think it would be fair for me to judge until I have taken some formal courses so as I can judge for myself. (Only a couple of years more!
) Then I will be in a better position to have a credible opinion.
Second: It seems the more I study high energy theory the more you have to evoke whatever works. You say “well, we get this infinity so we will just do this, and, oh look we get the right answer.” It seems sometimes we just play the game of finding the math that works best. If it turns out you have to call on higher dimensions and unseen fields and so forth to get the math to work out maybe that should be okay.
But again, I am no expert yet so I’m just throwing stuff out there. I am just grateful to be going into a high energy area and exploring these effects on the Universe. Keep the debate live and well.
Like Aaron, I’ll just suffice with self-promotion and refer back to my no-go theorem for string theory.
For a presumably well-informed opinion about string theory, consider what the founder of the string theory group at Rutgers write in subsection 1.6 of hep-th/0204131.
String Theory is Losing the Public Debate
I have a long-percolating post that I hope to finish soon (when everything else is finished!) on “Why String Theory Must Be Right.†Not because it actually must be right, of course; it’s an hypothesis that will ultimately have to be tested agains…
The only blog thats even attempted to pose the question scientifically is Professor Distlers excellent series on motivation for quantum gravity (sorry dont have the link handy).
The simple arguments contained therein are more or less the prime reason people take it seriously. Namely quantum field theory doesn’t leave us many options for a consistent logical framework, and it seems the only way out leads straight smack into string theory (whether you are looking for it or not).
If string theory is wrong it nearly (but not quite) implies a massive inconsistency in the fundamental theorems of either special relativity, general relativity or quantum mechanics, and the possibiliities for an escape shrinks to an almost intractable level.
Naturally theorists took the easy way out of that problem and assumed thats not the case, rather than tackling the much harder problem of making sense of the inconsistency given that we know those three key aspects of the physical world make good sense in just about every experiment ever conducted.
“If string theory is wrong it nearly (but not quite) implies a massive inconsistency in the fundamental theorems of either special relativity, general relativity or quantum mechanics, and the possibiliities for an escape shrinks to an almost intractable level.” -Haelfix.
Jacques Distler’s defence of string theory ends with the following comment about LQG:
“Urs is right that LQG isn’t, strictly, a discretized model, though the use of the spin-network basis does introduce a fundamental length scale into the theory. It’s, more properly, a continuum theory, quantized in a Hamiltonian framework (albeit, a very, very unconventional one). The words I wrote above were geared to a Lagrangian formalism. It’s not hard to adapt them to a Hamiltonian one.” - Dr Distler’s Musings blog
LQG isn’t complete, so this sort of dismissal is unhelpful. LQG is far more economic than string theory. It introduces questions about special relativity on the quantum scale, hence “doubly special relativity”. Because there is a fundamental grain size in LQG, the Lorentz contraction can’t make that smaller due to motion, so the grain size is a fixed size irrespective of motion. This limits the scale of application of special relativity.
Maybe you think string theory is right because there are no alternatives and string is consistent with special relativity, etc? M-theory is claimed to be a self-consistent theory of quantum gravity. However, self-consistency in a totally speculative framework isn’t so stringent: what counts is consistency with facts.
The immense number of speculative, uncheckable assumptions involved in string theory: gravitons, 6/7 extra dimensions, supersymmetric partners for all observable particles, Planck scale unification, branes, etc., make it clear that it is not consistent with what is known. Ockham’s razor tells you that LQG is closer to reality. The path integral in LQG is the sum of all interaction graphs in the Penrose spin network. The result of this gives Einstein’s field equation. It’s not really a continuum, because each interaction graph is a quantum interaction. So Dr Distler is being misleading.
Much as I admire the fine physicists who collaborate to produce this blog, it seems to me that Sean unjustifiably and unfairly caricatures Peter Woit’s position when he flippantly claims:
“Peter Woit agrees that `things are not looking good for a physical theory when there start being public debates on the subject’; indeed, I’m just about ready to give up on evolution for just that reason.”
To put it bluntly, this verges on deliberate deception because Woit’s statement is taken so far out of context. What Peter Woit is clearly saying is that that “Things are not looking good for a physical theory when there start being public debates on the subject between recognized credentialed scientists about whether the theory even qualifies as either scientific or a theory.
As you can see, this completely blows Sean’s grossly distortive quip that “indeed, I’m just about ready to give up on evolution for just that reason” out of the water.
There is NO debate among serious credentialed scientists about whether the theory of evolution qualifies as either scientific or a theory. None. Zero. Zilch. Nada. Zip. Diddly.
What we get in regards to the theory of evoluiton is a bunch of phoney staged pseudo-controversies in which people with no qualifications and no credentials and no expertise in biology, people without degrees in biology, people without PhDs in biology, people who have never published any papers on evolution in recognized peer-reviewed professional academic journals, stand up and make long-debunked claims which the biologists who have published countless articles in peer-reviewed professional academic journals then shoot down in a few seconds. The biologists typically respond to these kinds of canards by remarking, “This is the fallacy of the second law of thermodynamics, which reflects a misunderstanding of the definition of a closed system and was original raised in [year X] and was definitively rebutted in [year Y].”
This is the same kind of pseudo-controversy you get when a flying saucer cultist stands up and makes wild claims, and skeptics debunk them by pointing to Project Blue Book and citing case after case after case where previous claims for the existence of flying saucers turned out to be hoaxes or lenticular clouds or lens caustics in cheap cameras.
Let’s be clear. That’s not a “debate.” It’s one kook spouting gibberish, and a scientist debunking it.
That’s no debate. An actual debate occurs when person X stands up and provide facts and logic to support his claim, and then person Y rebuts those facts and logic and provides facts and logic for hi/r own contrary assertion.
String theorists have no facts to support their assertion that string theory is science. They don’t have a single experimental result to support their contention that string theory is either scientific or a theory.
Consequently, all string theory “debates” (so-called) twixt serious scientists thus far have taken the following form: skeptical scientist A points out that a theory isn’t scientific and isn’t a theory if it can’t make any testable predictions and if no testable predictions have been adduced to support it. Credulous scientist B, a string theory supporter, indulges in hand-waving and blows a lot of smoke up everyone’s hoo-ha to disguise the fact that s/he cannot provide even one (1) testable predictions from string theory, and cannot provide even one (1) piece of experimental data published in the peer-reviewed professional physics literature to support the assertion that string theory is either scientific or a theory.
You tell me. Is that a debate?
No, that’s one scientist demanding that the so-called “theory” make predicitons and that experimental physicists provide evidence to back those predictions up. Then another guy waves his hands in the air and tries to distract attention from the hard cold provable fact that there are no testable predictions and there is no hard scientific evidence for string theory. None whatsoever.
To see how badly distorted and how fundamentally deceptive Sean’s false analogy with evolution is, let’s compare evolution with string theory:
If any scientist like Woit or Smolin demands hard experimental evidence for string theory, the string theorists provide nothing but hand-waving.
By contrast, if any scientist _were_ to demand that evolutionists provide testable predictions (no reputable scientist does, because evolution is so well-established and backed up by so much evidence the very question would be foolish), the evolutionists could deluge ‘em with testable predictions. Let’s just run through 10 testable evolutionary predictions off the top of my head — first, evolution would predict that vaccines would gradually become ineffective as viruses and bacteria mutate over time. We have tested this prediction and it has proven irrefutably true. Second, evolution predicts that mammalian males will be generally larger than females because of selective pressure for males to battle other males over mates. Once again, this prediction has been extensively tested and has proven true. Third, evolution predicts that we’ll get the ratios Gregor Mendel found in his plant breeding experiments. This prediction has been tested and has proven true. Fourth, evolution predicts intermediate stages in the fossil records. While a few gaps exist, we have so many examples (such as Archaeopteryx) that this prediction has also proven true. Fifth, evolution predicts that developed characteristics cannot be inherited — i.e., Lamarckism isn’t correct and the children of people who exercise and build up their muscles are not born with larger muscles. This prediction has been tested and has been found true. Sixth, evolution predicts that because of the problems caused by inbreeding in humans, selective pressures will tend to favor the differentially greater reproduction of individuals with an innate aversion to incest. This prediction has been tested and has been found to be true in interesting studies which show that unrelated children raised together are not sexually attracted to one another, while related children raised apart can and sometimes do become sexually attracted to one another. Seventh, evolution predicts a common ancestor for all current forms of life. This prediction has been tested with DNA sequencing, most spectacularly with mitochondrial RNA sequencing, and has been proven true. Eighth, evolution predicts vestigial organs (Dollo’s Law). Once again this prediction has been tested and found true. Ninth, evolution predicts anatomical and molecular parahomology. This has been tested and found true by both paeloanatomists and by molecular biologists. Tenth, evolution predicts statistical support for phylogenies. The stats have been run on many different cases, and in each case cladistic analysis supports virtually completely and almost perfectly the known phylogeny.
To hammer this point home and demonstrate the thoroughly slipshod and inexcusably sophistical nature of Sean’s faulty analogy twixt string theory and evolution, there exist literally hundreds of websites which pile up mountains of evidence from the peer-reviewed scientific literature to support evolution as a scientific theory. Sites like
http://www.talkorigins.org/faqs/comdesc/
http://www.bartleby.com/65/ev/evolutio.html
http://www.txtwriter.com/backgrounders/Evolution/EVcontents.html
http://www.gate.net/~rwms/EvoEvidence.html
http://www.talkorigins.org/faqs/evolution-research.html
http://books.nap.edu/html/creationism/evidence.html
http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_01
http://www.evolutionpages.com/
Googling for the phrase “evidence for evolution” produces 1,130,000 pages containing that phrase. You could literally spend the rest of your life reading the gigantic mountain of evidence that has been published supporting predictions made by the theory of evolution, and you would still not reach the end of it.
Now let us compare with string theory.
Name me one peer-reviewed scientific journal, Sean, which has published a single experimental result predicted by string theory.
Name me one.
Just one.
You can’t. Because string theory makes no testable predictions.
Okay, Sean. Now show me the 1,300,000 websites contains peer-reviewed published evidence for string theory.
Show ‘em to me, Sean. I want to see all those websites. Let me see ‘em.
Whoops! There aren’t any.
Not ANY.
On the one hand, the theory of evolution, with more than a million pages citing peer-reviewed scientific literature chock full of evidence directly supporting it…
…And on the other hand, string theory — with not a single web page citing a single peer-reviewed piece of scientific literature directly supporting it.
Are they comparable?
You tell me, folks. Is Sean’s analogy valid, or is he being deliberately and flagrantly deceptive?
To compare the theory of evolution, which is supported by a vast Himalayan mountain range of evidence that vasts up so high that if you printed it all out, it would reach to the moon and well beyond, with the idle unsupported speculations of string theory which have not yet made a single testable prediction after 30+ years and for which not a single scrap of peer-reviewed published experimental evidence exists…it’s insulting.
Sean, there is little doubt that you are a lot smarter than I am. You’re almost certainly a lot smarter than 99% of the human race. But don’t piss on my leg, Sean, and tell me it’s raining.
I know the difference between a scientific theory for which a colossal pile of peer-reviewed experimental physical evidence exists, and a set of idle speculations which have never succeeded in making even a single testable prediction and for which not one single peer-reviewed journal article can be found adducing experimental evidence in support of those idle speculations.
Don’t insult my intelligence, Sean, by even _trying_ to compare string theory with the theory of evolution. Just as there is NO debate among ANY members of the serious scientific community about whether Darwin’s theory of macorevolution constitutes a scientific and testable and thoroughly-supported theory, there is NO debate among ANY members of the serious scientific community that there current exists not a single currently testable prediction made by string theory.
Even string theorists admit that they have no testable predictions. Lubos et al. resort to claiming that string theory’s prediction will become testable someday…or they resort to claiming that if we run enough stats on the cosmic background we might someday find circumstantial evidence which ambiguous relates to the landscape hypothesis. In short, even the string theorists themselves can only provide a vague hope that someday, somewhere, over the rainbow, enough stats or sufficiently novel tech might (somewhere, over the rainbow) provide some kind of ambiguous circumstantial evidence in favor of some part of string theory.
Guess what?
That’s not hard evidence. That’s a wish and a pipe dream. “Somewhere, over the rainbow.” Let’s give every string theorist the benefit of the doubt. Let’s assume they’re right. Someday, maybe we’ll get some kind of vague circumstantial evidence for some parts of string theory.
We don’t have it now.
Right now, we have nothing. And science isn’t about what somebody might find someday, somewhere over the rainbow. Science is about what we can find evidence for right here, right now. If we can’t find hard evidence for it, Occam’s Razor says throw it out. Hypotheses non fingo. Dump it. Junk it. Don’t need it. Phlogiston? Press the eject button. Luminiferous ether? Outa here. Vital animistic fluids? History. Theory of humours? Toast.
I’m sorry to say it, but even the deceptive and profoundly sophistical effort to _try_ to compare the massively-well-grounded theory of evolution (for which enormous amounts of scientific evidence exist) with a flimsy tissue of speculations and numerology like string theory is insulting. It’s an insult to my intelligence and it’s an insult to the intelligence of every thinking person reading this blog.
Look, I have nothing against string theory. Maybe it’s right. Maybe it isn’t. I don’t know. No one does. What string theory ISN’T right now is testable. Hand-waving about the landscape just makes the problem worse because as Woit and Smolin and any number of other folks with common sense point out, the landscape predicts everything you could ever possibly observe. Just plug in the fudge factors (AKA “parameters”) and voila! There you go. The universe we see around us.
That’s not a testable prediction. A theory that predicts everything you could possibly observe, as Woit and Smolin et al. have pointed out, actually predicts nothing.
To put it bluntly, the landscape is no different from the con job that phoney psychics sometimes try to pull on the Amazing Randi when they claim that their conjuring tricks no longer work because Randi’s skepticism interferes with the alleged delicate psychic energies involved in parapsychology. Catch-22 — as long as Randi is around being skeptical, the alleged parapsychological phenomena never seem to occur. Likewise, as long as we plug in the proper fudge factors into our landscape, we always get the universe we observe..but, unfortunately, since we can’t observe other universes, we can’t ever test the landscape hypothesis. What a wonderful Catch-22! As with the phoney psychic, the null hypothesis can never be tested.
Let’s turn Sean’s flippant and egregiously false analogy around. If Sean can practice the most outrageous kind of sophistry, so can we.
For Sean to compare the theory of evolution with string theory is like a ufologist claiming that astral projection disproves Einstein’s theory of general relativity because people who project themselves astrally travel faster than the speed of light.
That’s not a serious argument. Consequently Sean is not engaging in a genuine debate, he’s playing word games.
People who want to engage in a serious debate about string theory are going to have to bring more than deceptive and contemptibly casuistical verbal calesthenics to the table. They are going to have to bring testable predictions made by string theory, and experimental results published in the peer-reviewed physical literature to back up those testable string theory predictions.
Ball’s in your court, Sean. Let’s have ‘em. Right now, on the table. Experimental results backing up testable predictions made by string theory. Show them to us right here, right now. Journal name, author(s), issue number, page numbers.
Josh,
The problem with string theory as a way to unify particle physics is not just at the electroweak breaking scale. It doesn’t predict anything at any scale up to the GUT scale, and only vague predictions even above that.
Eric,
Is your comment an April Fool’s joke? Honestly, I can’t tell. Seems to be hard to tell when string theorists are joking…
I suspect the Eric Mayes remark is in reference to a follow up paper to hep-th 0612087, but I could be wrong.
It would be nice if a skeptic (e.g. Woit), a neutral person and a strong advocate write a big article together, similar to this article about the number of dimensionful constants
John Horgan said: “Sean, jump off the sinking ship while you still can! ”
I don’t get it. John Horgan does not claim that the ship is sinking but rather that the whole ocean (of science) is drying.
(Is the Horgan’s suggestion for scientists is to go work on wall-street?
)
Eric Mayes (22): You might have forgotten that Cosmic Variance is on Central time, so you’re post appeared a few minutes before it was officially April 1.
mclaren (32): If you brush up on your reading comprehension, you’ll notice that I never compared the evidence for evolution with the evidence for string theory, about which you rant at such length. So your intelligence is somewhat self-insulting.
Eric,
if hep-th/0703280 is the paper you refer to, then it seems that there is a little bit of work left (perhaps as homework assignment for the reader).
E.g. on p.4 we learn that the electron mass comes out 6.5 times larger than it should be and the muon is 40% lighter.
But it seems that another paper is coming, which will fix this.
By the way, I thought that Volker Braun et al. already derived the MSSM from heterotic string theory some time ago, so there seems to be more than one way to do this.
Josh wrote
So far (Eric’s paper, which I haven’t read, aside), there aren’t any. Finding one would be significant progress.
Now, it’s true that, if you find one, you may be able to find others.
In orientifold flux compactifications, the visible gauge and its matter content are localized on some brane(s) at some singularity of the CY. Varying the fluxes elsewhere on the CY wll change the cosmological constant. But the properties of the SM couplings will relatively insensitive to changes made elsewhere on the CY.
It is far from clear that you will be able to “tune all of the knobs” (corresponding to the 100+ couplings of the MSSM) independently. I rather doubt that you will. Every knob that “can’t be tuned independently” is a prediction, and there’s no more reason to believe that number is zero than there is to believe that all 100+ parameters are uniquely determined.
But the real point is that I (and everyone else who opines on this question) is, at this point, simply speculating. We just don’t know, and expressing our personal prejudices on how this will work out is not a scientific argument.
If only it were that easy …
If you discovered proton decay tomorrow, would that give evidence for GUTs? After all, proton decay (and any other particle physics effect you could ever hope to measure) is completely adequately described by an effective field theory.
It seems to me that, if you find a microscopic explanation for certain relations between couplings in the low energy effective theory (in the case of GUTs, for instance, sin^2 of the Weinberg angle), you don’t say “Oh, that’s not evidence for anything about short-distance physics. All we’re doing is learning about properties of some effective field theory.
Sean,
You contemptuously dis mcclaren’s reading ability, but somehow managed to miss his central points - that you willfully distorted Peter Woit’s statement, and that the status of evolution and string theory are hardly comparable. You are the one who made this comparison, so it’s disingenuous of you to blame it on mcclaren. Moreover, you made the comparison on the basis of a distortion of Peter Woit’s statement.
Jacques,
I agree that the sort of model-building that Eric brought up is important and I said so explicitly. It would indeed be progress to find a model with exactly the SM in it at low energy, with all couplings and phases right. And maybe it would give evidence for string theory if such a model made a very surprising prediction for some slightly higher energy phenomena which is then verified at LHC; especially if this prediction is very natural in a string/brane setup up but not expected from field theory reasoning. Nature may surprise us and maybe it won’t.
You are right that we are speculating here, but I don’t see that as bad or necessarily unscientific as long as we recognize what we’re engaged in.
You have a good point in your analogy with proton decay and EFT. My only real point regarding EFT was that what we would really like to see is evidence of physics which can’t be captured by quantum field theory but is found in string theory. I could be wrong, but it seems like this would require near Planck scale experiments.
Peter,
I was just using the electroweak scale as an example since this is basically the region we are probing currently. I agree that there doesn’t seem to be specific, unique predictions at even much higher energies. My point was just that the motivation for string theory is really anchored in its candidacy as a theory of quantum gravity, and so I don’t expect it will be properly tested until we can test that regime somehow. If we also learn about particle physics that would be icing on the cake, but string theory’s fortunes do not rise and fall based on its implications for particle physics. Just my view though.
Gina asked:
Is the Horgan’s suggestion for scientists is to go work on wall-street?
If they ever get the LHC working and furter findings of nothing particularly interesting are further confirmed, then there will be a very long line of PhDs at ‘the Wallstreet employment office’, becauses stubborn pride will pretty much kill the whole field before it can be rebuilt from WAY BACK when they first started *believing* that ad hoc and theoretically flawed assumptions are proven facts…
“The End of Particle Theory” JoAnne Hewett sets the Date
Horganism and John Baez
Except, CIP, that I did not distort anybody’s statement; the bit about “debates among credentialed scientists” was an interpolation on mclaren’s part, not part of what Peter or John originally said. If either of them would like to clarify, they are welcome to do so; it wouldn’t change the truth-value of what they are saying, but it would render the evolution example inapplicable.
I never compared the status of evolution and string theory, because that would be silly; the cases are not remotely comparable. What I did was to point out that the existence of public debates about a subject says nothing whatsoever about the status of that subject among people who are familiar with the details; evolution is the most obvious example.
The truth is, there is a long and honorable history of public debates about legitimate scientific questions between respectable scientists, and I think that’s a good thing.
Sean: You are going to get into the same very tedious loops that frustrated
Clifford on Asymptotia. One very trivial and peripheral comment of yours mentioning evolution generates a “War and Peace” length irrelevant rant.
The Horgan/Johnson dialogue is almost content-free. And, from what I have seen, arguing with Peter is like trying to hold quicksilver.
Peter,
As you are aware, I did misunderstand (4) your position from what was presented. Having now caught up with the comments, (39 as I write), I see that I am not unique in that.
It appears to me that there are actually multiple issues at play here which make miscommunication inevitable. On one level is the issue of whether string theory is is right or not, and on another level is the issue of whether string theory is even a scientific theory, since it cannot yet be tested. I interpret your statement:
…as reference to the position mclaren takes in (32):
It seems inevitable that the grow of our scientific foundation will lead to theories that exceed the testable reach of current instrumentation. I don’t view that as a bad thing, though I understand it may be decidedly uncomfortable to see the clear line between science and philosophy tested on both sides, (e.g. string theory as scientific philosophy and ID as philosophy pitched as science).
But there appears to be a third aspect of this discussion which elevates the tension for both issues mentioned at the top, (string theory’s veracity and whether or not it is even a scientific theory). That issue is how the scientific profession identifies winners.
In business and political blogs the participants often claim to want people who are willing to think creatively and take risks. But “risk” inherently means there are more losers than winners, so the question becomes “what happens to risk takers who lose?”
In poker losing the pot will get you invited back. In the science profession, if you bet the pot and lose, your career is typically taken out back and shot.
So public debate of unproven theory is risky, and dangerous to ones career. But is that good for science (and scientists)? Wouldn’t we all be better off by encouraging debate, and the attendant creative thinking, while reducing risk to the participant’s career?
Sean,
Ouch! Mea culpa. My apologies.
I looked, and you are right. I trusted mcclaren’s version of the quote and it’s not what Peter has up and it’s not what Horgan & Johnson said.
Never mind.
I will shut up now.
Josh wrote:
Absolutely!
As long as we’re clear about what’s speculation, and what’s established, this is a very useful conversation to have. The problem arises when people (not you) put forward their speculations and personal prejudices as established facts.
Unless we get extremely lucky (large extra dimensions), some effective field theory description is likely to be valid up to very high energies. So, yes, direct observation of non-field-theoretic (”stringy”) behaviour is rather too much to hope for. There are people thinking hard about indirect manifestations of non-field-theoretic behaviour — in cosmology, for instance — so, even there, it is possible that we may get by without a Planckian accelerator.
CIP, no problem.
“Pushed” (on both sides) would have been a better choice of word than “tested”…particularly in a science forum
Would it be accurate to say that the arguments in favor of string theory all boil down to the following?
(A) It has passed various consistency checks that could potentially have doomed it
(B) Every other proposed theory of quantum gravity suffers from more serious (arguably fatal) problems
That’s how it seems from this (non-high energy) physics student’s perspective. Based on (B) I can understand why a person studying quantum gravity would choose string theory over an alternative. What I don’t understand is why string theorists seem so convinced that the theory is correct. Should we be very surprised if string theory turns out to be both self-consistent and wrong? Or if the correct theory happens to be one we’ve never thought of?
I guess what I’m asking is: Why do string theorists seem so certain that this is the only possible answer? (Or am I overestimating their sense of certainty based on message board rhetoric?)
Oh good grief, if Paul Davies and John Wheeler are correct, then evolutionary theory is missing a key piece to the purposefully structured puzzle that only creationists and semi-religious foundations, like the templeton organization, support, so don’t pretend that Lynn Marguilis doesn’t call extremists among her own peers, “neodarwinian bullies” because she thinks that the Dawkins mentality isn’t equally over the antifanatical top!
Doncha just love how they only see the other side’s dogma?
Just to bait the readers here — nobody has answered my question: what does one end up with if one promotes dimension to an operator? There are good reasons to think that dimension may be more than just a constant — for example: as energy density increases, the gravitational manifold couples to itself more and more strongly — one could think of this as a “cloud of virtual gravitons” around a point mass, for example — and those virtual gravitons themselves perturb the manifold (no longer a manifold) further (as they are energetic), resulting in more “virtual gravitons”, etc, etc, effectively resulting in a fractal pattern type distortion of the “manifold” in regions of very high energy density. This “fractal” distortion thus changes the Hausdorff dimension in a local region around a point mass.
So one might thing that dimension is in fact an operator related in some way to Hamiltonian density.
What happens if this is done?
To quote James Thurber: Fools rush in where angels fear to tread - but many fools are alive, while all the angels are dead.
So, let me risk being a fool and pose the following question: What’s the physics motivation for String Theory?
I’m serious - what is the physics that is driving this train?
At the start of the 20th century, physicists made theoretical proposals that were at least as unconventional and counter-intuitive as anything in String Theory. A key difference is that physicists were trying to explain experimental observations for which classical physics could not account, which drove the development of quantum mechanics.
What is the experimental observation that is motivating String Theory, that can not be explained with conventional physics? By the way, I personally am in the Feynmann camp. That is - while I think it would be cool if quantum mechanics and gravity could be reconciled into a single theory - until such a theory is developed, that accounts for the observed world, I’m agnostic on whether or not such a theory even exists.
My reference to Feynmann refers to an interview he gave, wherein he was asked about the latest trends in HEP Theory, that seemed to use mathematical elegance as a guide. He allowed that while in the past, physical theories that turned out to be correct were indeed mathematically beautiful, there is no reason to suppose that this would continue, and that it was perfectly possible (in his opinion) that peeling matter down to the next layer might reveal something mathematically complex, lacking all elegance. For what does Nature care whether we find the equations pretty or not?
Now - here’s where my ignorance may have led me int a trap. Is it that, from our understanding of the Big Bang and the evolution of the universe, that at some point in the distant past - for the merest fraction of a second, gravity and QM MUST have been the same? Is that the motivation? (I’m not trying to be snarky - I don’t know). [My own research field is in Experimental Condensed Matter - developing materials for solar cells and doing some collaborating with a Neuroscientist - where we may have found something relevant for understanding of Parkinson's].
If that is the only physical motivation (that at some point in the early universe gravity and QM must have been joined), then this seems to be thin soup.
Sean, you mention String Theory as being promising. And I agree, it is. But when we hire a promising assistant professor, we give him or her seven years to pay off on their potential. At some point the plug gets pulled. What would you agree to be a fair timeline for String Theory? Eventually I imagine the field will vote with their feet, and researchers will move on.
Some of my colleagues are concerned about blowback. There was a great deal of attention when high temperature superconductivity was discovered, but its now 20 years and the trains still do not levitate. Some early promises have had to be abandoned. String Theory has been presented to a considerable subset of the non-physics professor community. I think many do not recognize the provisional nature of the theory. If it all turns out to be a false approach (of which there have been many in physics, and it is after all how we get to correct theories, crawling over the corpses of incorrect ones) will there be a backlash with the public?
Well, I have to go pick up my son. I think I’ve embarassed myself enough with this post.
And I see that while I was writing, Tim G two posts above gets at my point in 1/4 the space, and better.
There are many very good reasons to believe that string theory has something to do with quantum gravity in the real world. That’s why so many smart people are devoting their professional lives to working on it. It’s much better behaved at short distances than conventional field theories; it has proven fruitful in shedding insight on longstanding problems (such as a microscopic understanding of black-hole entropy); and by dualities it is part and parcel of our understanding of field theory itself. More details will have to wait for the post foreshadowed above — or until more string theorists decide to try harder to explain themselves.
Jim:
That’s a good question. One experimental observable that I think any quantum gravity theory should probably explain would be the value of the cosmological constant (or the properties of dark energy).
None have done so yet. (Model constructions .. not predictions! … aside).
Another example is so ubiquitous people often just forget that it is an experimental observable. That is the fact that, at least macroscopically, our universe has 3+1 dimensions. I think any quantum gravity theory should explain _why_, at macroscopic scales, Minkowski space is the appropriate metric (again, not as a possible construction/”compactification”, but an actual prediction).
Hi Jim.
The problem with quantum mechanics and gravity is not that they’re separate; it’s that they are incompatible. You need to turn quantum mechanical matter into classical gravitation and nobody knows how to do that. Now, maybe the problem is just too hard to solve without experiments to guide us, but the problem is there, and it has to have a solution.
Ellipses:
You raise two excellent observables. Now, I’m not, by any stretch, an expert on String Theory. Is this what the theorists are trying to explain? I thought that rather than account for our 3 + 1 dimensions, we are to take seriously the existence of higher dimensions, which are hiding in very small or very large length scales.
[The geek in me loves the notion that the exctra dimensions may be vary large. I call that the Good Omens Hypothesis - in Neil Gaimen and Terry Pratchets book of the same name, they explain why psychics were unable to detect the "aura" around the son of the Devil - they couldn't see it for the same reason that you can't see England when you're standing in Hyde Park]
Sean:
You said: “There are many very good reasons to believe that string theory has something to do with quantum gravity in the real world.”
I don’t doubt it. but what are the real world arguments for quantum gravity? What physical phenomena have we observed that must include both? No one has observed Hawking Radiation, or anything like it, have they?
Why do string theorists seem so certain that this is the only possible answer? (Or am I overestimating their sense of certainty based on message board rhetoric?)
I know next to no one in the field who believes that string theory is the only possible answer. I do know lots of people who believe that it must be some element of the right answer, however.
“… it [string] has proven fruitful in shedding insight on longstanding problems (such as a microscopic understanding of black-hole entropy); and by dualities …” - Sean Carroll
If I can quote a contrary argument:
“The claim to explain black-hole entropy is (as noted in chapter 9) exaggerated, because the string theory results work only for special and aytpical black holes.”
- Lee Smolin, The Trouble with Physics, US ed., p. 277. (In chapter 9, Smolin explains that Andrew Strominger and Cumrun Vafa showed that extremal black holes, i.e., black holes with about maximum possible electric/magnetic charge while remaining stable, have identical thermodynamics to extremal stringy branes.)
Regarding Maldacena’s duality between string theory and gauge theory:
“Even if it is true, the duality conjecture can be useful only if one side of the duality can be defined precisely. So far, it has been possible to define the relevant version of string theory only in special cases.”
- Lee Smolin, The Trouble with Physics, US ed., p. 143.
Aaron:
Thank you. I see. Sorry for being dense.
This reminds me of a conversation I had over ten years ago, with Sir Sam Edwards. He argued that since we were unable to reconcile Quantum Mechanics with General Relativity - that we should toss out General Relativity. After all - the list of experimental confirmations for GR is MUCH shorter than for QM. My teenagers could live without GR, but not without their cell phones, laptops, DVD’s iPods, CD players - none of which are possible without the transistor and/or the laser, neither of which could be invented without QM.
So perhaps there’s a theory of Gravity that can do what GR can, plus be quantized - just as GR could do what Newton could, plus some extra bits. Is this the physical motivation for String Theory? That it intends to replace GR with a new, quantizable theory of gravity? But there are many other alternative models for quantum gravity. I know that some are concerned that these other appraoches are being starved for oxygen , due to all the love garnered by String Theory. Which again raises the timeline question.
Thanks again.
The paper that I referred to is indeed hep-th/0703280 (Chen, Li, Mayes, Nanopoulos) which will be available on the archive tonight. We describe a three-generation model in which the gauge couplings are unified and for which we can calculate all of the Yukawa mass matrices and mixings, as well as the low-energy phenomenology. This is the first model that we are aware of that has all of these properties. It is true that the muon and electron masses are a little off. However, it should be kept in mind that these states are very light and subject to quantum corrections.
Eric
(sorry for the typo: aytpical should be atypical)
You raise two excellent observables. Now, I’m not, by any stretch, an expert on String Theory. Is this what the theorists are trying to explain? I thought that rather than account for our 3 + 1 dimensions, we are to take seriously the existence of higher dimensions, which are hiding in very small or very large length scales.
Yes — in trying to reconcile GR with QM, string theorists (not me, by any means — I’m an experimental particle & astroparticle physicist — if you must know, junior faculty at a major research university) posit an 11-D space, which then is “compactified” at macroscopic length scales. Why one precisely ends up with Minkowski space, though, has _never_ been given a good explanation, to my knowledge.
———–
As an aside, no one has ever answered my question (comment #52). Anyone want to bite?
———–
Anxiously awaiting Mayes’ hep-th/0703280 to see if it explains the universe. I’m sitting down.
“Seventh, evolution predicts a common ancestor for all current forms of life. This prediction has been tested with DNA sequencing, most spectacularly with mitochondrial RNA sequencing, and has been proven true.”
Always knew ‘everything’ was related,
Everything is related, and everyone too.
So which came first the chicken or the egg?
“Like all quanta, the photon has both wave and particle properties, exhibiting wave–particle duality.”
So which came first the ‘particle’ or the ‘wave’?
> Anxiously awaiting Mayes’ hep-th/0703280 to see if it explains the universe.
You can read it here.
Arxiv bug making papers available early? Hmm.
So, Eric Mayes, since this apparently is not an April Fool’s joke: does your model have a cosmological moduli problem?
If by cosmological moduli problem you mean the problem of moduli stablization, it has already been shown that all moduli can be stabilized in the model by turning on fluxes (Chen, Li, Nanopoulos ‘06). If you’re referring to the the problem of obtaining a cosmological constant, then that is a story we’ll have more on later which will likely involve noncritical string theory.
Eric,
I don’t want to be too harsh on your paper, because I think models like these have some value, but I’d like you to explain:
1) Why did you choose: \epsilon^{D1} = 0.061 and \kappa^{(1)} = 39.6i. To match the data, right? _That’s not a prediction, my friend_. That is a post-diction to match what experimentalists have already told you.
2) Same for v^1_u, v^2_u, v^3_u, etc. etc. etc.
3) Where are the CP phases in either the CKM or PMNS matrices? The latter would be especially nice to know because it would be a _prediction_ (you haven’t forgotten what that means, have you?)
I have my physics diploma from 10 years ago. Now I earn my money with software and physics is kind of a hobby. So at least I have no personal stake in the subject.
My 50 cent are, that string theory is loosing the public debate, because Woit and especially Smolin have the better arguments. To me it looks just that simple. You can say I am too dumb because I am not able to follow the complicated mathematics of string theory (still struggeling with ordinary field theory) (@Sean: I was however able to follow your three hours introduction to general relativity, which is available online, very nice). But so far I have not read a reply to Smolin’s book from a string theorist that really convinced me. The ideas presented by Lee (Loop quantum gravity, deformed special relativity) just seem more exciting and really falsifiable.
“Ockham’s razor tells you that LQG is closer to reality.”
Ockham’s razor is a load of crap. The “aether” was seemingly simple and straightforward, yet it was wrong. a^4 + b^4 + c^4 = d^4 was long thought to have no integer solutions. That was wrong too. Goethe (or somebody) said that once you scratch the surface of something “simple”, you find it’s complex and deep.
Eric, sorry — what I actually meant to ask was, do you have a moduli-induced gravitino problem? (Moduli decaying to the gravitino, which is long-lived, and can screw up BBN etc…)
Sean,
The proposed title “Why String Theory Must Be Right” falls into the rhetorical trap-hole that both string theorists and their detractors have collaborated in digging. I know you don’t actually believe that it is necessarily right and therefore experimental verification is merely a filigree on its mathematical edifice, but that is the impression such a title gives.
In my limited understanding a more accurate, but less catchy title would be “Why String Theory Must Be Useful [in constructing a theory of quantum gravity, whatever that theory turns out to be in the long run].” Sometimes, a theory that is useful is even more worthwhile than one that might in the long run be right. I didn’t watch any of the Horgan/Johnson exchange because I’m not interested in the rhetoric surrounding this subject. One thing that string theorists have not always succeeded in getting across is that (so far as I know) constructing a mathematically consistent and elegant theory that reduces to our current low-energy understanding of the universe is difficult. So working out such a theory would be a major mathematical-physics success even if it made no new experimental predictions.
Part of the problem is that string theory is legitimately difficult to explain, and the culture of superiority that has existed among high-energy theorists (We are the most fundamental, etc) has meant that they haven’t always bothered to try. This has alienated even many fellow scientists, let alone the public. (I am not a theorist, but I did go to physics grad school at Rutgers, so I am quite familiar with this phenomenon.) I’ve seen Ed Witten give a brilliant talk in which he made us feel for half an hour like we sort of understood string theory. An hour later, I realized I still didn’t understand it at all. But, he was talking to the audience, rather than engaging in triumphalist rhetoric. I do think one reason string theory is getting this flak is that people, including PhD physicists, are threatened by things they don’t understand, especially when the proponents are overbearing.
Sean,
Don’t you think there’s something funny going on here when you and others assume that a string phenomenolog