Many of you may know that Discover is not only a web site that hosts a diverse collection of entertaining blogs, but also publishes a monthly “magazine” printed on paper. Wild, right? Just ask this baby, who can tell you that a magazine is kind of broken when compared to an iPad.
Nevertheless, people read these things like crazy. I have recently started contributing an occasional column to the print magazine, known as “Out There.” (Our blog neighbor Carl Zimmer has been columnizing about the brain for a while now.) My first column appeared in the October issue (which comes out in September), and is now online — check it out.
The issue I’m tackling, under the draconian word count limit of an actual print magazine, is whether it’s scientific to talk about the multiverse. (Spoiler: it is!) Let me know what you think.
Cliff/observer/whoever you are,
As for your accusations of dishonesty, “every serious scientist that looks at this knows that the experimental difficulties are guaranteed by the Planck scale.” is just complete nonsense. I have no idea who you are, but you clearly don’t spend much time talking to serious scientists in this field, most of whom are well aware that string theory’s problems as a unified theory go far beyond not having data from the Planck scale that would pick out a Calabi-Yau. It’s just not true that the theory is well understood at Planck distances.
The problem with string theory is a problem about unification. It is supposed to not just quantize gravity, but explain the Standard model and particle physics at ALL energies. This simply doesn’t work now, at any energy.
As an addendum, anyone who thinks that there’s a definite prediction about how string theory behaves at the Planck scale might want to consider reading the more recent blog post here from Tom Banks.
Well Mr Woit, Im pretty much just stating my assessment. Im sure your overall attitude on string theory is just what it appears, but over the years I’ve seen way too many instances of you playing fast and loose with facts, which you seem not to know very well. Among other things you seem to like to deliberately create confusion between the assessments of the string community and the media “hype”, which makes for an all-too-easily distorted picture. I have a hard time imagining someone whose primary devotion is to honest education of the public engaging in this sort of behavior. Overall, a person who reads your blog is apt to get the impression that string theory is one giant blob of undetermined nonsense, as if there is no understanding whatsoever. Im not what you’d call an expert on string theory but I know a bit, and I know enough to know that the image that comes out of your blog is a long way from what the experts understand, as seems to become all the more more clear when I see you interacting with them…
I think you must have understood what my sentence meant better than your response would indicate. As long as we agree that the Planck scale is likely to be important for quantum gravity, then it follows that any theory of quantum gravity might be called “unscientific” based on a sufficiently religious definition of what science is. Even though you were answering a different issue, I think your response is silly. Im well aware that a complete definition of string theory is lacking, but we all know that certain sectors and limits are well understood. Your ambitious claim that string theory makes “no predictions” would certainly be interesting if you could prove it. Are you claiming some special knowledge of the complete picture? Or are you just taking the liberty of assuming that a very large number of solutions gives license to do anything?
Anyway, I think you’re setting up an unreasonable standard for what we have the right to expect. There’s no reason why the most ambitious project in science should have an easy answer. There is no reason to think that without very high-energy data we would have anything more than a very broad set of consistency criteria. And since such a set of consistency criteria appears to be extremely rare, maybe even unique, I don’t see any reason why these human-centered demands should be deterring us from investigating these very important questions. I don’t believe what you say can be translated into any *physical* argument against the validity of string theory.
I dont know whats particularly relevant about me. Im a physics student who works damn hard to understand QFT and some string theory. Ive surely made my share of mistakes, but Im not the one presuming to call into question a large part of the mainstream of the high energy physics community (including their honesty, which you don’t seem to much care for yourself).
Cliff,
You make it very clear that you don’t actually know very much about this subject, you’re just for some reason deeply offended that I publicly make arguments that conflict with some of the hype you’ve been exposed to. Before being so sure that this hype represents the mainstream, I suggest you pick a good research university and try knocking on some faculty office doors, asking them what they think of string theory unification and the “multiverse”. You might learn that the mainstream view among professionals who know something is rather different than what you think it is.
Mr Woit, you’ll surely be surprised to learn that Im constantly seeking out viewpoints from all kinds of physicists, most especially those who disagree with me in their assessment, but I always found that quantitative arguments to be much more meaningful than slogans. In fact Im quite grateful whenever someone can provide me with any substantive logic leading me to revise my assessment. I noticed you’ve declined to provide any. Its not news to me that there are many researchers who differ.
Some physicists whom I respect can, and have, caused me to adjust my views somewhat based on less concrete explanations of how they see things differently, however this only happens if he or she has a unmistakable record of valuing the truth above all else. A person with an agenda has very little chance to influence me without solid arguments. Sorry but my assessment is that your main project in life seems to be to influence popular perceptions of physics in the PR arena, and Ive yet to see any convincing evidence that you’re capable of deviating from that pattern.
Anyway my assessment is based in large part on a few textbooks and countless papers. Maybe its all still what you consider hype. But Im fairly certain that if there ever exists any rigorous arguments why all of this work must be thrown out the window, I will notice it.
Peter and Cliff,
No accusations of dishonesty out of me towards either of you, for the record. I’m just trying to have a conversation 🙂
Peter, I don’t disagree with you that there has been a lot of string hype and that it has been overstated and huge promises have been made that should not have been made. But you still didn’t really deal with the nuances of my statements, instead you just changed to a statement about hype and then made statements about field theory that showed you missed my point.
As you well know, quantum field theory is a framework for physics that is very good, due to the notion of effective field theory, at describing a wide variety of systems at low energies. For each system it might describe, there is a different quantum field theory. My point is that “a quantum field theory” (e.g., the standard model) is a theory, but “quantum field theory” is a framework. (I know you know all this, I’m just trying to make my point clear, I really don’t mean to sound pedestrian!)
Similarly, note that I tried to be very careful to denote the difference between a string vacuum and “string theory” as a whole, though many vacua could exist as local minima on a connected moduli space. One of my points was that, in a given string vacuum, the gauge theory and matter content of the theory are completely unambiguous, (at least in all parts of the landscape I know), assuming you know how to do the relevant computations. Most vacua give some sort of gauge symmetry and particle content, and this is one of the great successes of string theory as a framework (and a specific prediction, accessible at low energies, of each individual string vacuum) where quantum field theory fails: gauge symmetry is output in string theory, it is input in quantum field theory.
What I mean is that you can write down a gauge invariant Lagrangian if you want to, and in particular you should because experiment tells us there is gauge symmetry in the world. But ultimately it’s dependent on the fact that you wrote down your Lagrangian in a particular way. On the other hand, simple considerations of the quantization of a fundamental object – a string – naturally leads to gauge theory, as output of the theory. If you know of a similar argument for why gauge theory is output, rather than input, in quantum field theory, please enlighten me 🙂
Let me emphasize that I completely agree with you that the landscape is an ENORMOUS problem. The honest statement, though, is that string theory as a framework predicts the existence of gauge theory, and in particular any particular string vacuum tells you the gauge symmetry and matter content of the theory.
That’s all I meant. The landscape is a huge, huge problem, I agree. Just because string theory as a framework predicts gauge theory, which we do see in our world and which is input in quantum field theory, doesn’t mean that it predicts our world, or that there is any string vacuum that contains the standard model complete with Yukawa couplings.
There, hopefully my point is a bit clearer 🙂 I’m agreeing with you that there is a lot of hype, and the landscape is a problem. If you’d like me to elucidate more on gauge symmetry and matter content in string vacua, I’d be happy to, but I think you probably know all this.
J
Peter and Cliff,
Here’s a thought. The QFT formalism makes no definite predictions about what causes electroweak symmetry breaking. There are many possibilities: a single Higgs boson, many supersymmetric Higgs particles (because SUSY is part of QFT), technicolor, extra dimensions (because the QFT formalism does not depend on the dimensionality of spacetime), etc.
For many years, we have been experimentally unable to determine which of these possibilities is correct (if any).
Therefore, QFT is not predictive. 🙂
J,
I just don’t see a meaningful argument here. You’re just playing games with words like “prediction” “string theory” and “gauge symmetry”. And you’re doing this with the goal of making an obviously absurd point (that a theory that cannot, even in principle, be confronted with experiment in any way is as good or better than the one that has done this more successfully than any other scientific theory in human history). What’s the point of trying to argue with someone about an absurdity? It’s an obvious waste of time.
Cliff,
OK, you should ignore what I have to say because I’m a dishonest, publicity-hungry, money-grubbing guy whose views are far out of the mainstream, and is completely delusionally unaware that he is so, so wrong and his betters the agenda-free string theory experts are right. You’re quite right to stick to the mainstream point of view presented at this blog on the multiverse and string theory.
One piece of career advice though: for some mysterious reason, no US physics department is willing any more to offer permanent positions to anyone working in this mainstream. Something to keep in mind…
“A person with an agenda has very little chance to influence me without solid arguments. Sorry but my assessment is that your main project in life seems to be to influence popular perceptions of physics in the PR arena…”
I agree. If one follows Peter’s blog, he will get the impression that Peter has it in for SUSY and finds enjoyment in reporting on the LHC’s failure to see any evidence of SUSY. It seems to me like he wants SUSY and String Theory to fail, to not have any evidence in its favor. But why? What difference does it make how nature works one way or another?
Peter,
“I just don’t see a meaningful argument here. You’re just playing games with words like ‘prediction’ ‘string theory’ and ‘gauge symmetry’. And you’re doing this with the goal of making an obviously absurd point (that a theory that cannot, even in principle, be confronted with experiment in any way is as good or better than the one that has done this more successfully than any other scientific theory in human history). What’s the point of trying to argue with someone about an absurdity? It’s an obvious waste of time.”
It seems like arguing with you is a waste of time. I understood J’s argument pretty well. For example, J said, “Most vacua give some sort of gauge symmetry and particle content, and this is one of the great successes of string theory as a framework (and a specific prediction, accessible at low energies, of each individual string vacuum)”
Now, what’s so hard to understand about that? You specify a vacuum, and out comes a specific gauge symmetry and particle content as a prediction of that particular string vacuum. The trouble, in my opinion, is how to construct promising string vacua? And that because string theory is not that well understood, theorists don’t have a good handle on constructing string vacua. But given a vacuum, out pops the gauge symmetry and particle content. Is what J said incorrect? Do you have any references that shows J’s error in this statement of his?
Peter, you said that the theory cannot in principle be tested? Intelligent design cannot, in principle, be tested. But if you smash particles together near the Planck scale, and if string theory is true, you surely will see evidence of this at those experiments.
If QFT is so predictive, how come it doesn’t unambiguously predict the source of electroweak symmetry breaking? There are many possibilities from the QFT framework.
Peter, you said, “One piece of career advice though: for some mysterious reason, no US physics department is willing any more to offer permanent positions to anyone working in this mainstream. Something to keep in mind…”
How do you know this? Do you receive reports from every research university and liberal arts college in the US?
Peter,
I’m surprised to be treated with any level of animosity (absurdity? really?) after I tried myself to write so respectfully.
I’m not playing any games with the words string theory and gauge symmetry. I made a very clear point that you either do not understand or choose not to address. Rather than just calling it absurd, why don’t you address it? Do you disagree that each individual string vacuum predicts the gauge symmetry and matter content one would see at low energies? Just curious . . .
Happy to keep chatting about this, but I need to ask one question at a time since you’ve now avoided (twice) good arguments from a trained physicist.
And, just to be clear once more – I DO agree that you make some good points: the landscape is an enormous problem. I’m just criticizing other points and am asking you to address my criticism or back away from the aggressive statements you’ve made in this thread.
J
P.S. Phil, just saw your post after I posted this and am posting this edit. I’m glad to hear that you understood my point.
One thing to correct – string theorists do understand more than you’re giving them credit for, though, including how to construct vacua with promising gauge symmetry and matter content. Doing it uniquely and dealing with all the other issues is the problem. I’m happy to elaborate, if you’d like!
Also, it seems that a small fraction of vacua look anything like our world wrt gauge theory. But people are clever and can get things a whole lot like the MSSM in terms of gauge symmetry and matter content. These are both scientific facts. One is a con, and one is a pro, in my mind. The important question is why would we be in a string vacuum with our gauge theory (as opposed to many other possibilities), rather than whether there are vacua with similar gauge theory to what we see in the world. The latter is settled, similar vacua exist.
P.P.S. Phil, I agree completely with the Planck scale argument. That’s predictive at high energies. (More specifically the string scale, but that’s likely close to the Planck scale if we live in a string vacuum).
Phil,
http://particle.physics.ucdavis.edu/rumor/doku.php?id=archive:2011
No, the statement “string theory is true” makes no predictions about what you will see at the Planck scale. Try reading the discussion between Tom Banks and Sean above to get some idea of how little understood such a question is. Huge questions about the very nature of such a theory are completely open, it’s extremely far from “just look at the string vacua and calculate what they predict”. Generically, you don’t know how to characterize a “string vacuum” (string theorists admit they don’t know what the theory fundamentally is, why do you think they understand its ground states and how to do reliable calculations in them?).
J,
Sorry if my response came off as animosity. But the bottom line remains: I understand exactly what you wrote but I’m not getting any younger, life is short, and I’ve wasted enough of mine already on this kind of thing the past few years. The situation of string theory “predictions” vs. SM predictions speaks for itself.
A wise and very prominent HEP theorist told me long ago that he felt there was no point in wasting his time arguing with string theorists, since as time went on and it became more and more clear that string theory unification predicted nothing, the field would move on and abandon the idea. I think he was right and I should have listened more carefully to him….
Peter,
Thanks for the links. I’ll take a look.
Hi Peter,
It’s okay, we all care a lot about these things (fundamental physics) and it sometimes gets charged up.
I hear you that you’re sick of arguing about such things. But again, you’re comparing one particular quantum field theory (the SM) to a framework for physics, not a string compactification. But alas, it seems this is not a distinction that you and I are going to reconcile here. Well, perhaps not the importance of it, at least 🙂 We can disagree.
Regarding what you said to Phil: I agree that there are very fundamental open questions, and that the nature of M-theory is still not understood. But this doesn’t mean that nothing can be said, and in particular weakly coupled corners of string theory definitely are quite well understood, and it IS known what the gauge symmetry and matter content are. Would you like examples? I’m reasonably familiar with most of the semi-realistic corners of the landscape, and can both cite papers and explain examples in a few sentences. Type II and heterotic are probably the best understood. F-theory has some of the most beautiful mathematics. (Kodaira classifications of singular fibers –> ADE –> gauge symmetry from 7-branes)
J
P.S. And, yes, I’ll vouch that jobs (as will the rumor mill) are going to phenomenologists more and more. Part of this is string theory PR, but most of it (and the right reason) is that the LHC is cranking up and phenomenologists really should be hired with more frequency.
Alright, it seems like conversation has waned, but I’ll check back here periodically for updates.
The fact of the matter is that the gauge symmetry and matter content at a particular point in the moduli space of a string compactification is very often explicitly known. I’m still happy to provide examples, both in terms of papers and explanation.
But the fact is that very often the gauge symmetry and matter content at a point in the landscape is known, even if not all aspects of the theory are understood. Just string theory isn’t fully understood doesn’t mean that it’s not understood at all!
Thanks for the lively discussion,
J
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