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Is string theory worthwhile?

  1. Jul 3, 2013 #1
    There is still, to this day, absolutely no empirical proof that string theory is correct, or even that it can predict anything , but I know it's mathematically elegent ,here's feynman view on it:''I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with a n experiment, they cook up an explanation—a fix-up to say, “Well, it might be true.” For example, the theory requires ten dimensions. Well, maybe there’s a way of wrapping up six of the dimensions. Yes, that’s all possible mathematically, but why not seven? When they write their equation, the equation should decide how many of these things get wrapped up, not the desire to agree with experiment. In other words, there’s no reason whatsoever in superstring theory that it isn’t eight out of the ten dimensions that get wrapped up and that the result is only two dimensions, which would be completely in disagreement with experience. So the fact that it might disagree with experience is very tenuous, it doesn’t produce anything; it has to be excused most of the time. It doesn’t look right.'' –Richard Feynman
    I know this was before M-theory but I still think it's a little half-assed ....I really like it though and would be a string theorist If I had the chance to become a physicist ...but what do you people think?
     
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  3. Jul 3, 2013 #2
    I'm far from an expert on string theory, but the rationalizations I've heard from string theorists after the failure to find evidence of SUSY at the LHC (on par with anything I've ever heard from homeopaths or creationists) lead me to believe that it is steadily losing credibility as a scientific discipline.

    Peter Woit details some of the news on his blog: http://www.math.columbia.edu/~woit/wordpress/. From what I've heard, academic jobs in string theory are steadily drying up.
     
  4. Jul 3, 2013 #3

    QuantumCurt

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    I keep reading about how string theory research is steadily drying up too. That's disappointing, because I would ultimately like to go on and research string theory in some kind of capacity, but after seeing how the research has been drying up, I'm starting to rethink that path. As of right now though, I think I'm going to continue with that goal in mind though. I'm still an undergrad with a few years left before I get my bachelors though, so I still have a lot of time to really figure out what direction I want to go.
     
  5. Jul 4, 2013 #4
    I think a lot of the research in string theory is shifting from trying to use it as a GUT to using it as a framework for working out new mathematical methods. For example, some methods originally developed in string theory have been used in condensed matter contexts.
     
  6. Jul 5, 2013 #5

    ZombieFeynman

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    To all who say they wish to become a String Theorist (but may not have even graduated from college yet), I ask a serious question:

    Why would you want to do such a thing?
     
  7. Jul 5, 2013 #6
    Because it has 26 dimensions.
     
  8. Jul 5, 2013 #7
    Because Michio Kaku.
     
  9. Jul 5, 2013 #8
    This is, unfortunately, completely true.
     
  10. Jul 5, 2013 #9

    ZombieFeynman

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    I'm not joking or trying to poke fun at anyone.

    I am completely interested.
     
  11. Jul 5, 2013 #10

    QuantumCurt

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    I see a lot of comments like this around this forum. It almost seems like String Theory is met with a sense of contempt by a lot of people. Is this really the case? I'm still very early in my undergrad, but the concepts in string theory are incredibly fascinating to me. I've always been incredibly intrigued by the Standard Model, and the idea of getting down to even more elementary constituents of nature seems like an awesome field to be involved in. I do realize that actual String Theory research is not quite like a Brian Greene book or something like that, but it seems like an incredibly engaging field to be involved in.

    My interest in String Theory has nothing to do with Michio Kaku. I've never read any of his books, nor have I ever watched any of his documentaries or anything. Beyond seeing a few of his appearances on The Universe a long time ago, I know relatively little about Kaku. Honestly, some of his ideas strike me as a bit sensational. I don't know that I really buy into the "many worlds interpretation" of QM. It's an amusing idea, but it seems a bit much to me. I obviously don't have the real knowledge of physics or mathematics to back up that feeling, but I've seen other interpretations and propositions that seem a lot more plausible to me.

    Also, I thought String Theory was down to only 10 dimensions now. Is it back up to 26?...lol

    I don't know if String Theory is really the path that I'll end up going down. I've been reading up on other elementary particle ideas, such as the hypothesized existence of Preons, lately...and many of the other ideas seem quite fascinating too.

    Is String Theory really losing support?
     
  12. Jul 5, 2013 #11
    Yes.

    They painted themselves into a corner suggesting that SUSY could be detected at LHC. And, the idea that the multiverse precludes prediction of standard model parameters is circular reason and turns string theory into pseudo science.

    There is contempt out there because many string theorists acted a bit like fascist dictators, shutting down all opposition once they took control of so many academic departments. Quite a few experimentalists feel we've wasted a lot of time.
     
  13. Jul 5, 2013 #12
    I think a large part of it has to do with their rationalizations after the LHC failed to detect SUSY. A good many of them are going to great lengths to explain away its predictive failure; I've heard some go so far as to claim that "empirical science" is outdated, and is not a valid means of testing string theory. More and more it has the trappings of a pseudoscience.
     
  14. Jul 5, 2013 #13
    "Shutting down all opposition"? What are you talking about? What opposition was "shut down" by string theorists who "took control" of "academic departments"?
     
  15. Jul 5, 2013 #14
    I would advise that you read Not Even Wrong or The Trouble with Physics to see that string theory research isn't quite the glamorous sparkling wonderland Brian Greene, Michio Kaku, et al make it out to be. I never really understood the fascination with string theory; even when I was just learning about it from the Discovery Channel it seemed like a bunch BS to me (same goes for dark matter, but that's a different story for another time).

    One of the reasons that string theory research is drying up/changing focus away from GUT-type stuff is that it is a failure. String theory has failed to be the theory physicists thought it would be. Time and time again string theorists have made claims saying the [insert biggest detector of the day*] will soon find all the supersymmetric particles, extra dimensions, etc. thereby confirming all of string theory. But as detectors reach higher and higher energy levels, surpassing the predicted levels of string theorists, no sign whatsoever of SUSY, extra dimensions, etc. have been found. However, the string theory mythos persists since the underlying mathematics are so complicated that a string theorist can just cook up a new version of the theory and say ``the last version was wrong; SUSY will actually be detected at [highest experimentally available energy level]+[itex]\epsilon[/itex].'' I've heard decent technical arguments against string theory, but most of the arguments supporting string theory I've heard consist of ``it conforms to my sense of aesthetic beauty, so it must be true (makes things more symmetric, unifies everything, etc.).'' Who said Nature needs to conform to that aesthetic?

    That being said, string theory isn't a completely worthless field. See this article for an example. As I alluded to in my last post, the merits of string theory lie not in its potential for a GUT, but rather as something of a testbed apparatus.

    Do you want to study what Nature really looks like, or do you want to study what you want Nature to look like?

    *claims that SUSY would be found experimentally have not been limited to the LHC. String theorists said over a decade ago that SUSY would be confirmed by the Tevatron and the LEP at energies below 1TeV.
     
  16. Jul 5, 2013 #15
    It became very difficult for a theorist who wasn't aligned with string theory to get an academic appointment in the 1990s and 2000s at least in the United States. I was being dramatic, certainly, but theoretical physics in the United States has lots in common with an echo chamber.
     
  17. Jul 5, 2013 #16
    I am not capable of really understanding the math behind string theory, but what little I can understand is quite beautiful. I can see why it's adherents are so dedicated to it... it's incredible to have such an otherwordly frame work and have general relativity pop out of it. If I'm not mistaken Witten has said at some point that that is equivalent to empirical verification.

    As for dark matter, if you define it as "there is something going on we don't understand, and we will label it dark matter while we investigate" then I would disagree that dark matter hypotheses are BS. I'm tangentially involved with a high-pressure liquid Xenon detector project that will be able to detect WIMPs (one of the proposed dark matter particles). So, at least dark matter physics so far makes falsify-able predictions, right? ;)
     
  18. Jul 5, 2013 #17
    It would be interesting to know what these were.
     
  19. Jul 5, 2013 #18
    You know, I haven't heard a good technical refutation of string theory and I follow it as best I can. If there is one I'd like to hear it again. For me, the best argument "against" string theory is that in some forms it appears to be unfalsifiable, and if so then maybe it's not going to end up terribly useful (except for the math it generates).

    String theory could be true, certainly. It's a gorgeous theory. But the opportunity cost of putting all our theoretical eggs in one basket has been nagging at me since I first learned the basics of string theory in the late 90s.
     
  20. Jul 5, 2013 #19
    As Mark Twain once said: "The news of my death have been greatly exaggerated". The same goes for the way string theory is often treated in this forum.

    Yes the unification program in string theory has slowed down. That's not because noone believes its true, if SUSY exists, which is by no means given, then string theory is most likely correct. In order to make SUSY consistent with gravity you need supergravity, and supergravity is just the low energy approximation to the 10d superstring theories, which are in turn low energy approximations of the 11d M-theory.

    Also to OP, i have the utmost respect for Richard Feynman, but you shouldn't really be citing him in the context of string theory. He passed away in 1988 before the second superstring revolution and when the first one was just started. A useful comparison is with renormalization. Feynman also was distrustworthy of QFT because in order to make sense of calculations you had to sweep infinities under the rug through a process of regularization and renormalization. You can find textbooks where the authors (maybe it was bjorken) say to be wary of any calculations that use renormalization because it was such a strange tool. This was of course before Kenneth Wilson revolutionized the study of QFT and the renormalization group through is his physical insights. So here too you have giants who are simply a little behind the times.

    But suppose SUSY does not exist or is not detectable within any detectors humans can build. Is string theory still useless? I would argue once again the answer is no. The reason is the celebrated gauge/gravity duality, which should really be called the gauge/string duality. The AdS/CFT duality says something very profound, that a certain subset of quantum field theories and string theories are exactly dual. I don't think all quantum field theories have gravity duals, but string theory has become a greatly simplifying tool in studying strongly coupled quantum field theories, which previously were inaccessible. On a conceptual level it means if you think the study of QFTs is important, which since they describe all phenomena we can observe with the exception of gravity to incredible accuracy, then string theory is unavoidable.

    I could go on and on, but I'll stick to two other applications I'd like to bring up. One is that string theory has had an incredible impact on mathematics and the study of geometry and topology in particular. The other is to phenomenology: string theory can be used to simplify calculations of physical processes at the LHC. A string theory that lives in a very strange universe, the so called twistor string, is dual to a gauge theory and has been used by the blackhat group (http://profmattstrassler.com/2012/08/15/from-string-theory-to-the-large-hadron-collider/)

    As for job hirings, yes the number of job hires for string theory has gone down in the United States. I wouldn't recommend anyone go into ST if they want to stay in academia. Basically the markets saturated, regardless of the impression given off by Kaku and Greene, String Theorists have always made up a very small subset of all theoretical physicists. Most particle theorists work on QFT and pheno work. After the second superstring revolution there was a surge in string theory hires, but with the LHC up and running and experiments like Planck being launched the trend has swung the other way. Some departments truly are lopsided, like Princeton's, but its the exception.

    TL;DR String theory is far from dead, its inextricable from QFT through dualities but the unification program is on hold, and the job market for theoretical particle physics has never been a large one.
     
  21. Jul 5, 2013 #20
    Oh also about technical refutations of string theory, there aren't any. And whenever people do caluclations and compare them to the gauge theory results through holographic dualities it always works. That and in string theory you can derive that the area of black holes scales with the area as predicted by Hawking (who used semiclassical methods).

    So string theory is internally self consistent and gives the results expected in GR and QFT in curved spacetime when he semiclassical limit is taken.

    Finally for anyone who thinks string theorists shut out any other particle theorists, it helps to actually look at the statistics:
    http://www.physics.utoronto.ca/~poppitz/Jobs94-08

    You can see that string theory hiring peaked ~1999 which makes sense given that the original AdS/CFT paper was published in late 1997. This was near the end of the second superstring revolution so departments were hiring more string theorists to keep up with all the developments in the field. After that surge hiring has waned, but all job markets go through cycles. But needless to say, even at its peak, people working on other areas were still getting hired.

    Of course if you want to see really the state of ST, you have to check the arxiv. And for anyone interested in making a judgement call on the state of theoretical particle physics for themselves (excluding pheno work), and not basing their opinion on some random internet person (like myself!) check hep-th frequently for several weeks. It's better (and in my opinion much more enjoyable) see what particle theorists are actually working on instead of having someone explain it to you.
     
  22. Jul 5, 2013 #21

    QuantumCurt

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    So, as an undergrad, would aiming for research in String Theory be a bad idea? It's sounding more and more like it would be nearly impossible to find work in which I was actually researching String Theory, so I'm starting to think that I need to broaden my horizons more. Yes, I realize that "researching String Theory" is already quite a broad topic, but as far as general direction, that's where my interests have mainly been.

    If String Theory is no longer being regarded as the most viable theory for sub-standard model physics, where is the majority of the research going these days? I've been reading about hypothesized Preon's lately, and from what I've read, it seems like a very interesting field of research. I've been reading about some of the research that's being done at CERN and Fermilab, and it sounds like a fairly promising field.

    I've got a lot of time to really figure out a definite direction at this point, but it's never too early to get some ideas going. My main interests really lie within particle physics, but that's obviously a broad field. If anyone could link me to some good papers/articles about the more popular research in current particle physics, I'd surely appreciate it.
     
  23. Jul 5, 2013 #22

    WannabeNewton

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    If you don't understand the technical details of string theory, then why are you on here bashing it? Seriously, use some common sense before trashing a theory that you do not know the mathematics nor the physics of because it is at best a comical display.
     
  24. Jul 6, 2013 #23
    I think that's the point, though, wbn. The point is that all the so-called mathematical elegance of the model is not only not making directly testable predictions, but is even failing at derivative predictions such as finding supersymmetric particles at the LHC. So perhaps not understanding the math gives one more of an objective view, or at least an alternative view, of the state of the science. It appears to me that the math is so seductive that many people lose their objectivity, get sucked into alternate dimensions, and can't seem to find their way back out. So what is it worth? Well, if it can make some predictions that are testable, then there you go. Otherwise I don't think it fits the definition of "science," does it? Of course it will have some utility in the development of mathematical methods and some derivative applications perhaps. Didn't some other poster say something about condensed matter physics? What troubles me about it, is that, granted the level of study is down to the planck length, but isn't the science to the state where the construction of some of its elemental constituents can build to a level that is detectable at least to 10^-19 meters. I mean, really...

    I started a string theory rant thread on here a little over a year ago that got shut down immediately. I think the fact that this thread is still going might be reflective of a changing zeitgeist in this area. Probably most of you have already seen this, but I think Lee Smolin sums up the issue quite nicely here..

    https://www.youtube.com/watch?v=I_FG8kRVWkQ
     
  25. Jul 6, 2013 #24
    Diracpool: Lee Smolin is not exactly an objective observer, he criticizes string theory and in the same breath promotes Loop Quantum Gravity, a theory which by all means should be studied, but is also currently untestable simply because the effects of QG are so small.

    Also about going from the planck scale to the observable scale, the issue is with pinning down the right vacuum. Getting vector bosons, i.e. the mediators of Yang Mills theory, isn't hard, its getting the full structure of the standard model with all the right numbers. As for condensed matter systems, the route from string theory to CMT is completely different.

    Theres also a quote by Richard Feynman that goes: "every theoretical physicist who is any good knows six or seven different theoretical representations for exactly the same physics."

    Thats what the description of QFT through gravity and string theory amounts to, not just a useless mathematical derivation, but a new representation which offers new insights and ways to make progress. This attitude that gauge/gravity duality is no more than a trick is like the attitude people have when they first learn Lagrangian and Hamiltonian mechanics. Yes it looks at first like just a mathematical trick until you learn about how in fact these formulations are much deeper, they reveal the importance of symmetries which are obscured in the Newtonian formulation, and more importantly, they are conceptually more closely connected to quantum mechanics and QFT.
     
  26. Jul 6, 2013 #25
    In some of these comments, supersymmetry is discussed as if string theory is the reason why so many people expected it at the LHC. But supersymmetry was expected primarily because the effective mass of the Higgs boson should be massively increased unless lots of Feynman diagrams cancel, and supersymmetry is a way for this to happen, but only if the "superparticles" themselves aren't too heavy. Supersymmetry added to the standard model also strikingly improves the convergence of the forces at high energies, so it dovetails with grand unification theories, which offer neat explanations for the assortment of charges seen in elementary particles.

    The fact that string theory also contains supersymmetry and grand unification just reinforces the confidence in this general picture. But the vast majority of the models saying that supersymmetry is just around the corner are supersymmetric field theories.

    Even the talk of extra dimensions that are large enough to be detectable, came much more from particle physicists than from string theory, and was largely motivated by the challenge of explaining why all the known particles are so light, relatively speaking. The fact that string theory has extra dimensions was undoubtedly an inspiration, but the idea (edit: the idea of large extra dimensions that would be seen at the LHC) was driven by concerns that are internal to particle physics and independent of string theory. When it comes to explaining the observed particles and forces, the string theorists are mostly just following paradigms already established by particle physicists.
     
    Last edited: Jul 6, 2013
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