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.
Anon: We do not claim that this is THE model or that we are ‘predicting’ the masses of the elementary particles. The point of the model is that string theory CAN correctly describe our universe, and can do so in a elegant, geometrical way. I don’t know of any other theoretical framework which can make this claim or even come close.
Eric,
Did you, or did you not, say that you
“competely derive the MSSM from string theory, including the quark, tau lepton, and neutrino mass matrices and mixings”
Now you say that, actually, those masses and mixings are in fact just pasted in from experimental results right out of the PDG.
I think that’s actually more than disingenuous. I think it helps contribute to the low reputation that “string theory” enjoys today.
Ellipses,
The Yukawa couplings depend crucially on the details of the model and are not just put in by hand. The mass hierachies between the three generations arise naturally.
Eric,
I agree with you and I think your work is very interesting and valuable.
But in your first comment you wrote “We can now completely derive the MSSM from string theory” and to be honest, it seems to me that this would somewhat overstate what you have achieved so far.
As a physics undergraduate, I have to agree with Mike in post #70. While I may not understand the math behind the debate, the way I see it it’s more about the scientific justification and motivation behind string theory and if those justifications are a reflection of the actual merit. This idea is a rather simple one to grasp and understand, and when most laypersons apply their knowledge of the scientific method to string theory they don’t see the point of the argument for it. We’ve spent an awful lot of time telling everyone about the merits of experimental evidence in science and the like, so what’s the motivation?
Plus there are adverse effects to this as well- I run public observing nights with our university telescopes, and one of the comments I often get is “science isn’t really about proving anything or about evidence- just look at string theory!” At this point I howl and cry a little but have a hard time explaining to some why this “doesn’t count,” and it’s frustrating.
(By the way, if someone more knowledgable on the subject than me has a good way to answer the “just look at string theory!” comment, please let me know. It would be much appreciated.)
Eric, you address your comment to “anon.”, but I gather you are replying to someone else? I understand what your paper claims and what it does not claim, and I never meant to suggest I thought you were claiming to have ‘the’ model. Your use of the word “derive” earlier was a bit strong, but anyone who looks at the paper should understand what you really mean.
The reason I ask about the moduli-induced gravitino problem, though, is that in model-building it is not enough to have soft terms that reproduce the SM and get the right dark-matter abundance (though that’s certainly a good start!). One also has to worry about various astrophysical tests, inflation, reheating, BBN, etc…. So I wonder if you or your collaborators have thought these things through.
At any rate, it seems like an interesting direction and I hope to read more details in the future….
Wolfgang,
The model is the MSSM in respect to the fact that it has the following properties:
1. Three generations of quarks and leptons.
2. Gauge coupling unification is realized.
3. Realisitic mass hierachies between the different generations are realized.
4. Realistic SUSY spectrum.
Show me one other example where you can find all of these properties!
Anon:
Sorry, I meant to address the earlier message to Elipses. All of your points are very interesting and the answer is yes, we have thought about them and are presently working on them.
Hello, Sean and everybody. This post is a wonderful addition to the public debate, which I think is valuable. The blogosphere is indeed very repetitious in the absence of fresh news but there is much to be learned by watching it and in the absence of anything better it’s the most recent significant development in human communication. Watching it interact with string theory is fascinating indeed.
But Sean’s principal point is correct; string theorists are losing the public debate because they don’t think it’s worth their time to explain their point of view to others. That would involve explaining at least some string theory, because it is a difficult and technical subject, and requires not just patience but also talent to understand. It will therefore always be a subject which only a privileged minority will be able to understand. The people who don’t become experts in string theory will just have to learn to live with the fact that they aren’t qualified to judge how likely it is to be true because they can’t perceive how richly it interweaves the areas of physics which have already been confirmed by experiment, but not yet unified into a single theory.
That is what I was told before I decided to become a string theorist. I was the brightest in my undergraduate institution and had never had trouble understanding anything mathematical or technical, and from there I went to a Major American University which was one of the centers of string theory, where people talked in hushed whispers in the corridors about how great a genius such-and-such a person was (who I had never heard of). After a while I had heard all the rumors and knew about how so-and-so had done such-and-such by the age of nine (in a certain person’s case it was that he had set c=hbar=G=1 (sometimes belief looks like understanding, you know)).
Meanwhile I studied Green, Schwartz and Witten and Polchinsky and interacted with the string theorists who were supposed to be geniuses and found that I needed to brush up on some mathematics (although the mathematics department from which I had come had given me an undergraduate education second to none). I did so. I learned my Calabi-Yau’s, and my Yang-Mills; I geometrically quantized this and harmonically formed that. But I couldn’t understand why everybody about me was behaving in such a bizarre way when it came to REPUTATIONS. Why was I being asked to respect these people’s intelligences so much? They had not earned it. Their request was illegitimate (yes, I probably have Asperger’s, and so do a lot of these people). No. Earn it first. Do something intelligent.
I did not actually say this, of course (I’m high-functioning). I engaged diplomacy and patience. When I asked them questions about technical matters, they told me I was probably too stupid to understand. The mathematics was fine; nothing difficult really, except that the language they used was rather flowery, and occasionally turned into some kind of hand-on-heart saluting the beauty of string theory and the universe, like the way that American children are trained to behave when they ritualistically worship their flag every day. This kind of behavior always irritated me. The stupid savages were using peer pressure to enforce conformity. All of this “We have to be reverent in front of this holy thing” crap is illegitimate. Against the law of my understanding.
And these people didn’t seem at all to be able to answer any of my questions about string theory. What does it mean for a mathematical structure to be “true”? How can you claim to have explained everything when you have said nothing about quantum mechanics, which is quite clearly the thing most in need of explanation? The connection to experiment was not what I was concerned about at all (at the time, I disrespected experiment). I wanted to see if these people had their LOGIC correct.
I was told that, if you want to make progress, you have to abandon the hope of understanding every tiny little bit. You have to build a conjecture here on top of an opinion there. We don’t have to worry ourselves about it; there are very clever people in string theory and the consensus of many geniuses is that this or that thing is true. Occasionally people had told me things like that throughout my life, and I had always thought to myself “Oh, you’re one of those subhumans with no respect for his own intelligence, who is led around like a slave by other minds because you yield to others the ability to think for yourself.” Was I supposed to think that about EVERY string theorist? The mathematicians had never told me that; neither had the physicists, except when they quoted the mathematicians.
It seemed that the physicists and mathematicians were working within a structure where they knew they had to earn my respect, and they did so. The string theorists did not seem to understand this; they expected my respect (for their intelligence and the idea that they knew what they were doing) as though they were entitled to it without proving anything to me, and they insulted me if I asked for any proof, despite the fact that my mathematical skills and intelligence could clearly equal theirs.
I have to say that I think it is very unwise to demand of somebody that they should feel despicable compared to you. Yet that is the one message that the string theorists constantly produced: Feel despicable compared to us because of our Big Brains and our Big Theory, which is too complicated for Stupid You to understand.
So in the end they lost me, and I think I was very fair to give some number of years of my life to hear what they had to say.
Now of course here I am not saying that I think string theory is false. Rather, the two-dimensional conformal field theory which they are studying is a part of pure mathematics, and therefore the assertions they make about it are true. But the string theorists as a community have some problems, and a great many of them place too high a value on this reputation for being a genius, and they have become disdainful of others, and this is leading to their downfall.
Eric,
Is it possible to have m_{3/2}~O(TeV) in Type IIA with fluxes???
I thought that the flux superpotential in Type IIA can’t be tuned to be small, unlike in the Type IIB case.
Since m_{3/2}~e^(K/2)*|W_{flux}| and W_{flux} is is of order one in Planck units, the gravitino mass should be of GUT scale, unless the compactification volume is exponentially large (a la Conlon & Quevedo constructionin in Type IIB).
Kostya
Aaron Bergman wrote:
“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.”
OK, but that still leaves the *why* unanswered. To reiterate my comment from above, the fact that competing theories may have worse problems explains why people work on string theory, but not why they believe it’s right. Most of the pro-string arguments seem to be that it passes consistency checks, although each of these come with their own caveats:
– anomalies cancel in 10 dimensions (and perhaps we live in a 10-dimensional world)
– the different versions of string theory seem to be limiting cases of a single theory (but we don’t know what it is)
– black hole entropy has the right form for “extremal black holes” (and maybe this will prove true for other black holes)
etc.
These things are good signs, but how do we know an incorrect theory couldn’t pass these checks? It seems like we’d need to know every *possible* theory of quantum gravity to make that assessment.
Then again, I suppose you could say the same about empirically tested theories: How do we know an incorrect theory couldn’t have predicted such-and-such experimental result? But the history of science seems to show that at least provisionally trusting your theory when it passes experimental tests is an OK thing to do. Whereas I don’t have a clue whether trusting a theory based on “anomaly cancellation” or what have you is a good idea.
Despite all of the above, I’m really not at all anti-string theory. I freely admit that I don’t know enough about string theory to form an educated opinion pro or con. But I’d love to see an explanation (intelligible to non-high energy physicists) of why so many people are convinced it’s right — something that goes beyond the laundry list of string theory achievements, to address the underlying question how much weight these achievements should carry as evidence in the theory’s favor.
Hi Kostya,
We haven’t turned on any fluxes in doing the phenomenological analysis we present in the paper.
Hi Eric,
But how do you then stabilize the moduli?
Are you just assuming that the moduli are somehow stabilized and pick some values? Do you know of any mechanism other than the fluxes to fix the complex structure moduli in Type IIA?
Kostya
Hi Kostya,
The moduli can be stablized with fluxes, which in this case do not contribute to the Ramond-Ramond tadpoles (see Chen, Li, and Nanopoulos ’06). However, the phenomenological analysis becomes very complicated if we include fluxes, so for the present analysis we turn them off. You are correct that the fluxes should be taken into account, and we plan to do this in later work.
Hi Eric,
I was not concerned about the tadpoles, this should not be a problem.
My concern was the order one (in 4D Plack units) flux superpotential
W_{flux}~sum_i{q_iU_i} which results in the gravitino mass being of order GUT scale since m_{3/2}=e^{K/2}|W_{flux}| and the only suppression is from the inverse volume^{3/2}. Presumably, since you claim to have the standard gauge coupling unification at ~10^16 GeV, the volume can’t be exponentially large to give you the TeV scale superpartners.
Hence, if you say that the complex structure moduli can be stabilized by fluxes you automatically get a huge m_{3/2} in this case. So, unless someone comes up with a new way to fix the CC moduli in Type IIA, getting low scale superpartners from Type IIA is problematic.
You say that you turn off the fluxes but in this case you can’t claim that the moduli are stabilized can you?
Kostya
Sean: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.
You leave lots of information which to discern what is going on. I don’t think anyone is being fooled here. The public either. It’s been explained time and time again and the recurrent conversations attest to this.
I call it the “Pink Elephant.” We get this wonderful view of people holding different parts of the elephant, and they are the product of research in terms of quantum gravity models.
Why Pink elephant?
Well Susskinds provides for a thought experiment, and information given from entanglement from inside the blackhole? Now this elephant takes on all kinds of attributes, maybe as Babar looking through a window? Or, it being, just a plain Dumbo elephant. 🙂
So “string theory” is about the Pink elephant?
Yvette’s and Mike’s comment also suggests that string theory is losing the debate precisely because it is too much debated in public. When science is discussed in the popular literature, newspapers etc. then it usually become hyped too much and that then backfires.
My personal opinion is that string theory is not the solution because it is not really new physics. It is the same old known physics (quantum mechanics) applied to new postulated degrees of freedom. A good analogy would be if 19-th centrury physics were applying ordinary Classical Mechanics to imagined degrees of freedom to find a theory of everything that would explain the unsolved problems they were dealing with.
Except for ‘t Hooft’s deterministic models, no new physical theories have been proposed since the invention of quantum mechanics and general relativity.
Firstly, there are no public debates on evolution. There are pseudo-debates caused by religious nuts, but no real debates. Your sarcastic analogy (I assume you were being sarcastic) would work if there really was an actual debate going on about whether or not evolution was a scientific theory. But there isn’t.
Secondly, Peter Woit may agree with John Horgan and George Johnson that “things are not looking good for a physical theory when there start being public debates on the subject” but in the link you provided (i.e. the blog article) he did not actually say that he agreed with them. So you must have misread that.
Thanks Sean, I am more or less in agreement with you, except for matters of packaging. Strangely enough there is a large number of people (including professional physicists, some of them even blog…) who are very interested in forming and expressing strong opinions on the merits of string theory (and theorists), but show no interest whatsoever in the physics. I personally have no problem with losing the debate among that crowd.
However, there are some very beautiful aspects of string theory that may appeal to non experts, would be a shame to keep them to ourselves, only one has to think carefully on how to talk about the subject. I have no good ideas, but at the very least it seems to me that framing the discussion in terms of motivation or justification (e.g. explaining why the approach seems promising) is counter-productive, it invites the kind of uninformed commentary we are all too familiar with. Perhaps one can simply describe all kinds of things we find kind of neat, or even pretty, other people might enjoy those as well, and we can leave the debates and judgments to those who enjoy them.
Quantum Tunnelling and the Landscape?
For a quantum particle moving against a potential energy “hill”, the wave function describing the particle can extend to the other side of the hill. This wave represents the probability of finding the particle in a certain location, meaning that the particle has the possibility of being detected on the other side of the hill. This behavior is called tunnelling; it is as if the particle has ‘dug’ through the potential hill.
For layman “the question about the String Landscape” may still exist?
I’m an interested layman, which is why I read this blog. It is my feeling that when the general public reads the popular literature in physics, they do not expect to come away ‘understanding’ what string theory is really all about. Frankly, it is such a complex subject I suspect there are only a very few people in the world who understand it. I think what captivates the public interest, is the idea of what appears to be very esoteric thought, being applied in a quest for an understanding of our universe, the world around us. For me this type of thinking is beautiful, it represents a pinnacle in mans ability to formulate abstract concepts, concepts which may or may not describe the physical world, but which already have succeeded in extending our understanding of the mathematical world.
Count Iblis said, When science is discussed in the popular literature, newspapers etc. then it usually become hyped too much and that then backfires.
I would respectfully disagree. As far as the public is concerned, I believe it is a good thing for us to see the debate, to see the mechanism of disagreement, the quibbling among scientists, that it follows a complex process not unlike other areas of human endeavor. Ultimately, string theory will be a valid solution, a partial solution or no solution at all. For the interested public it won’t matter because the current research will eventually lead to some further evolution of our understanding of the universe, and it is the process as well as the progress of knowledge which is interesting.
I can’t wait until they fix that little part that broke on the LHC and plug it back in 🙂
Yvette quoted members of the public saying:
…and requested suggested replies.
I would tell them that science is exactly about proving things and evidence, which is why many scientists do not consider string theory true science…because it can’t yet be tested with experiments or prove it’s validity with predictions.
I would also tell them that to take the current debate over string theory and use it to draw conclusions that discount all scientific advances suggests they don’t believe in the existence of the telescope they just looked through, and that they should throw away their cell phone and walk home, because neither could exist without the advances of science.
But then, I’m not long on tact.
Personally, although a quantum theory of gravity that can predict the value of something that hasn’t been measured yet, and might be within this century, would be lovely, all I’d really like is to get a response to my comment #52.
Rob said: “I would also tell them that to take the current debate over string theory and use it to draw conclusions that discount all scientific advances …”
There was a time when people would drop dead at age 30. In many developed nations, the life expectancy is beyond 70. It wouldn’t surprise me if the life span (for all nations) was up to 100 years, by 2100 or 2200. Science is extending / enriching lives, so that we have the time and energy to debate how many angels on the head of a pin.
Hi Ellipsis,
In regards to your comment #52, this is basically what string theory does. For example, in the bosonic string there are 26 bosonic fields which ‘live’ on the string worldsheet which are interpreted as dimensions. These bosonic fields are needed to cancel the conformal anomaly, however one can trade bosonic degrees of freedom for fermionic degress of freedom (two fermions for each boson) and reduce the number of required dimensions. This is why the superstring requires 10 dimensions instead of the 26 for the bosonic string.