Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Opinions of ideas in Not Even Wrong

  1. Sep 21, 2006 #1
    Opinions of ideas in "Not Even Wrong"

    The new book by Peter Woit, Not Even Wrong, gives a lengthy discussion as to why we should abandon string theory and move to more promising fields of study. He claims, and as far as I know correctly, that superstring theory has not made one single testable prediction, but has simply stated what is already known in terms of superstrings.

    He cites the fact that superstrings need more dimensions than have been empirically observed to exist in order to make any sense at all as one indication of a problem. And the necessary "hiding" of seven of the required dimensions in abstract "calabi-yau" spaces as going against the Occam's Razor principle. In other words, superstring theorists have begun clutching at straws, so to speak, to make the theory true, when they should be trying to find ways to make it false, and thus testable.

    What are others opinions on this topic? Are superstrings, while mathematically rich, only a fanciful want of today's theorists? Or can real testable science be coaxed out it?
  2. jcsd
  3. Sep 22, 2006 #2

    Perhaps it is more fair to ask yourself whether there exists ONE research line in quantum gravity which satifies the above mentioned criteria.

  4. Sep 22, 2006 #3
    I fall somewhere between the two extreme views. I definitely think American physics has been concentrating its resources too much on string theory. But I don't think string theory is a waste of time. I would like to see continued funding of string theory research, but I would like to see a greater emphasis on particle physics phenomenology, by for example contributing to the ILC.
  5. Sep 23, 2006 #4
    The author does not offer any constructive advice about what to do for research. I suspect if he would be able to contribute something positive to science, he would have already done so in the form of real publications. Instead he chooses to gain his 15 minutes of fame by discrediting the work of others.

    There are definitely a number of true statements and deserved criticism in the book, but also a lot of quite misleading claims. First of all, there aren't really "more promising" fields of study other than string theory, as of today.

    Means: while there are other approaches, they have even more problems and thus are much less promising. That's why so many people work on string theory. It is wrong to claim that ppl want to stick there because they don't want to switch - almost every physicist dreams of making a surprise breaktrough and to impress his peers, so wherever he sees a minute opportunity in a particular direction, he will go there. That ppl do not switch en masse towards LQG has very good scientific, and not sociological reasons, in contrast to what self-proclaimed experts try to convey.

    Again misleading. String theory makes an enormous amount of predictions, but we humans of today unfortunately cannot measure them experimentally (and the same tends to apply to any theory of quantum gravity). This is a huge difference to a theory that makes no prediction _in principle_, and this issue is confused by purpose all the time. String theory is very much the opposite of a completely arbitrary and floppy theory.

    I usually like to make the comparison with ants who have, by sheer smartness, discovered Maxwell's equations. However, they are accused that they cannot make a prediction concerning their little world - indeed while practically all what they see (or rather smell) around them is governed by these equations, they cannot pin down how to test them. They may even have found electromagnetic waves as a solution, but lack the technological means to detect them.

    In the real world, what people have been doing instead was to make theoretical experiments, like computing the entropy of toy black holes. There have been countless tests of this sort, and they all have passed. This is extremely non-trivial. Other "alternative" theories did not pass such tests. So already at this level, string theory stands out without credible competitors.

    Don't be brainwashed by wannabee theories presented here in this forum and otherplace, like what is discussed under "Lee Smolin's LQG may reproduce the standard model". There is no indication whatsoever that this makes any sense. These "may reproduce" speculations are much worse than in the worst speculative string papers (and indeed, there are plenty of those).

    (Here I recycle something I was writing before:)
    String theory requires for consistency extra degrees of freedom beyond gravity;
    this is a richness and not a disease. In 4d string models, this is what leads to elementary particles such as the electron. Often these extra degrees of freedom can be given a geometric interpretation, namely in terms of extra "hidden" dimensions. This viewpoint is however valid only at weak string coupling, in a particular corner of the parameter space. Generically, such an extra dimensional interpretation does not exist (because quantum corrections blur the classical geometrical picture), and therefore debates whether one likes or does not like extra dimensions are moot - whatever, the matter fields must originate from somehwere, and whether one uses the language of extra dimensions or rather avoids it, does not matter; the point being that string consistency forces one to have certain extra matter degrees of freedom. However, unfortunately, this has turned out too much of a good, in that in four dimensions there are too many possibilities for matter theories that pass all consistency conditions.

    In a purely gravitational theory such as LQG, I don't know of any consistency constraint that forces you to have a matter sector in the theory in the first place. The recent discussions (eg at Distler's blog) about matter couplings in LQG just show how poorly understood this point is even to the experts in that field. In particular, they don't see anything wrong even when coupling inconsistent (anomalous) matter theories, and this tells me and my collegues that they are far far away of any understanding of what consistency means in their theories to begin with. Perhaps matter coupling and thus the unification of the interactions is simply outside of the scope of LQG, and predictions pertaining to this sector may not be even there _in principle_.

    So if you don't like string thery and extra dimensions (which is the stringy way of parametrizing extra "matter" degrees of freedom that are needed for consistency), you have to come to grips with "another" mechanism to provide those matter fields like the electron in the first place. But you will find that almost inevitably, internal (matter) degrees of freedom are intimately tied to extra dimensions, simple because charge behaves like momentum in other dimensions. For example in the recent work of Connes he rewrites the standard model in terms of non-commutative extra dimensions; I think this may well be most minimalistic way to do this, and shows how extra dimensions almost invariably pop out if one wants to see them. However, this framework is not restrictive (because the outcome is put in by hand) and it is not yet clear what can be learned from it. The situation for strings is better: internal degrees of freedom must be there, but in the present stage the theory is not restrictive enough in order to make a prediction at low energies. Whether an important ingredient is missing, or whether things really are undetermined at a fundamental level and our Universe is anthropic, is IMHO an open question too early to decide given the limited knowledge we have.

    As for falsifying string theory: this is certainly possible in principle, while not in practice (at least as of today). Just fire up your favorite Planck energy accelerator and look for the excited string modes - either you see them or not. So Popper cannot be invoked to claim string theory isn't science.
  6. Sep 24, 2006 #5


    User Avatar

    Here is a link to the thread that R.X. is criticising, for the benefit of anyone who would like to appreciate what R.X. is saying:

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook