Oy vey

Last Friday City College held a symposium here in Manhattan celebrating physics at City College. I was able to attend just the morning session, which began with a quick rescheduling of Anton Zeilinger for David Gross, who had overslept. Gross finally did make it and gave a talk on “The Frontiers of Particle Physics”. He says he’s taking bets in favor of supersymmetry being seen at the LHC, with 50/50 odds, and expects first evidence for supersymmetry within a year or two. By the time he got to the part of his slides about string theory he was over time, so he bypassed them, flipping ahead several slides at once.

Unfortunately I seem to have missed the real fireworks, which were at a panel discussion that afternoon. There’s a report at Scientific American, entitled Star physicists trade barbs over cosmological model. Alan Guth was there, promoting the multiverse and the anthropic explanation of the CC. Gross was having none of it:

“In reaction to that last talk—oy vey,”…

Gross called Guth’s concept of eternal inflation somewhat speculative, noting that if other universes do exist, they are causally disconnected from ours—”every goddamn one of them.” As such, Gross added, talk of other universes “does bear some resemblance to talking about angels.”

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20 Responses to Oy vey

  1. Nathaniel says:

    Hmm…Gross says that Guth’s multiverse bears some resemblance to talking about angels…huh, what about string theory? Seems like both theories are speculative unless there is some experimental evidence behind either of them. Kind of like the pot calling the kettle black.

  2. Mantis says:

    +20 sanity points for Gross.

    Nathaniel, string theory was supposed to describe our Universe but failed and it’s this failure that prevents it from making testable predictions. Multiverse OTOH is all about things unobservable even in principle and from the very start, so even if it works perfectly it’s still completely worthless untestable speculation.

    Multiverse ideas are a complete waste of time and resources, a pathology, a nonsensical fashionable crap which doesn’t deserve to be associated with physics of natural sciences in general.

    Science is based on empiricism, if something cannot make a connection to experiment even in principle it is not science, it is theology.

    And I don’t mind people studying theology but I do mind theology masquerading as physics especially if it’s consuming funds which society devoted to physics.

  3. Mantis, although I share your point of view regarding landscapism, I was not aware that string theory has failed.

    Perhaps one could say that string theorists have failed so far in delivering what they had promised. In spite of that, I think string theory is too good not to have anything to do with physical reality and it’s just a matter of time that this will be proven to be the case.

    Then one can debate about how much manpower should be devoted to this enterprise
    and other sociological issues but the shear revolutionary potential of string theory is beyond doubt.

  4. Peter Woit says:

    VA,

    It’s not “string theory” that has failed (that term now applies to so much that it is becoming meaningless). What has failed is the speculative idea of starting with string theory in the critical dimension (10) then finding a consistent “string vacuum” that keeps 4 dimensions large and somehow deals with the other six. 25 years of work on this have provided strong evidence that this can’t provide a predictive framework (leading to the multiverse nonsense as a desperate way out). Going to M-theory just makes things worse by providing even less predictivity.

    Anyone who wants to claim that this speculative idea has not failed needs to provide a plausible scenario in which it can be salvaged and turned into a success. I think the only way this can be done is through arguments of the sort “the general idea of string theory is so wonderful that there must be some unknown new insight into it which will come along and save the situation.” These are more wishful thinking than science.

  5. Austin says:

    Peter Woit said,

    “Anyone who wants to claim that this speculative idea has not failed needs to provide a plausible scenario in which it can be salvaged and turned into a success.”

    Correct me if I am missing something, but I see no problem with the following scenario: like any other physical theory, you use observation to constrain the free parameters of the theory, then you can make predictions. Technically difficult, but plausible I think.

  6. Peter Woit says:

    Austin,

    You need to explain why no one has done this so far, and provide a plausible scenario for how this is going to change in the future.

    The state of the art is that in various “string vacua” you can calculate very crude things like number of generations, but find that you can get any number you want. And you don’t even know if you want 3 or 4 (maybe there’s a fourth higher mass generation??).

    For some more detailed numbers, like fermion masses, as far as I’ve ever been able to tell, the state of the art is that you can’t compute these reliably and accurately (say, to better than 1 %). There also seems to be no reason to even try, since the evidence is that even if you could do this for any specific string vacuum, among the 10^500 possibilities you could get whatever number you wanted.

    In other cases (vacuum energy), people working in this area have explicitly given up. Generically computations give something wrong by absurdly large numbers of orders of magnitude, leaving the only way out the one Gross describes by “Oy vey!”.

  7. Austin says:

    I don’t know why no one has done this, but it’s a plausible scenario, I think.

    “…among the 10^500 possibilities you could get whatever number you wanted.”

    Yes, but most or all of those 10^500 are at odds with observation. Thereby observation can cut the 10^500 possibilities down to fewer (perhaps zero).

    Regarding vacuum energy: I thought (admittedly I’m not familiar with this technically) that various string vacua allowed different values of the vacuum energy, (just like fermion mass and number of generations) some of which are negative, some of which are positive but too large (“by absurdly large numbers of orders of magnitude”), and some of which may be in the experimentally allowed range.

    Still it’s just a plausibility argument, I assume that actually making this work technically would be beyond difficult.

  8. Mantis said : “Multiverse ideas are a complete waste of time and resources, a pathology, a nonsensical fashionable crap which doesn’t deserve to be associated with physics of natural sciences in general.”

    This is a rather dogmatic point of view. MWI interpretation of QM is in some sense “saner” than wave function collapse. More generally, science is full of entities that can’t be observed but are theoretically useful, so one must keep an open mind.

    As I see things, the problem is more with anthropic explanation than with multiverse theories. Saying that something is anthropically explained amounts to saying that it happened merely by luck, so it is equivalent to say that there are no reason for it. It is fine if there really is no reason, but this means we gave up explaining that thing, it does not mean that we explained it.

    So adopting a multiverse theory for the sake of anthropic reasoning is not a good deal. But if you have other, compelling reasons, to adopt a multiverse theory, and that theory says something (like the cosmological constant) is environmental, then it is ok for me.

  9. Peter Woit says:

    Austin,

    You should think carefully about the significance of numbers like 10^500. Say you are wildly successful, and you manage to calculate the 20 or so parameters of the standard model each to 1 % accuracy. You’d expect each such achievement to cut out 99% of the possible vacua. Doing all 20 calculations successfully and imposing the results, you expect to have 10^460 viable possibilities left.

    There are very good reasons most particle theorists have given up on this, whether or not they’re willing to use the word “failure” to describe the situation.

  10. Peter Woit says:

    Fabien,

    The kind of cosmological multiverse motivated by the string theory landscape that Guth is promoting and Gross is “Oy vey”ing about is something different than the multiverse of the MWI interpretation. They’re two quite different things.

  11. Austin says:

    Peter Woit said,

    “Say you are wildly successful, and you manage to calculate the 20 or so parameters of the standard model each to 1 % accuracy. You’d expect each such achievement to cut out 99% of the possible vacua.”

    I don’t follow this reasong. “1% accuracy” is not the same as “1% of all possibly allowed values” and therefore is not the same as cutting out 99% of them.

    I’ll try a simple counterexample to clarify what I’m saying. Take some free parameter of the standard model, say unit charge e, that theoretically can have any real positive value. Measuring the value of e even to 50% uncertainty eliminates a fraction of the previously allowed values that is arbitrarily close to 100%. See what I mean?

    10^500 is a huge number, but (as far as I know) before observational constraints, the standard model allows uncountably infinite possible values for its free parameters. In light of this, calling 10^500 big is a bit like a black hole calling the kettle black, isn’t it? At least 10^500 is finite.

  12. Peter Woit says:

    Austin,

    One can make pointless arguments about things like finiteness of the number of string theory vacua all day, but the bottom line is that the LHC is starting up and despite more than a quarter century of intense effort by thousands of smart people, string theory has led to no predictions at all about what it will see. If you actually spend time understanding string vacuum constructions and how they work (or don’t), the reasons for this become apparent. If you want to claim that this situation is not a failure, you need to come up a plausible explanation for why things have not worked out so far, but will work out in the forseeable future.

  13. Peter said :
    “The kind of cosmological multiverse motivated by the string theory landscape that Guth is promoting and Gross is “Oy vey”ing about is something different than the multiverse of the MWI interpretation. They’re two quite different things.”

    I know, but Mantis was saying that any multiverse theory was junk, on the ground that other universes are unobservable. I replied because it’s a rather common point of view, which I think is completely misguided.

  14. Peter said :
    “Anyone who wants to claim that this speculative idea has not failed needs to provide a plausible scenario in which it can be salvaged and turned into a success.”

    I’m not a string theorist myself and there are people better qualified than me to defend string theory. But as far as I know string theory is by far the only serious game in town when it comes to quantizing gravity, which is a notoriously difficult and non trivial task.

    It also seems clear that much much more work will be needed to make definitive progress in proving that this theory has something to do with the real world.

    At this point, what do you propose to do? To abandon the most serious candidate we have to solve this problem, simply because you’re not patient to wait longer? I don’t think your position on this is very serious. Some dose of criticism on the string community might even be healthy but you shouldn’t throw the baby out with the bath water.

  15. Bill K says:

    At this point, what do you propose to do? To abandon the most serious candidate we have to solve this problem, simply because you’re not patient to wait longer? I don’t think your position on this is very serious. Some dose of criticism on the string community might even be healthy but you shouldn’t throw the baby out with the bath water.

    String theory has been looking for a baby for 25 years, but it is all bath water.

    Neither “abandon” or “wait” has anything to do with the way research is conducted. When a theory runs into a dead end, as string theory has, you don’t abandon it, but you do put it aside temporarily. And you don’t wait, you just try to find something that’s more productive.

    Witten has been quoted as saying that string theory was ahead of its time, and maybe that’s the problem. Maybe we just need to take things in the proper order, and after understanding what comes after the Standard Model we’ll be better able to appreciate what, if anything, string theory is good for.

  16. Pawl says:

    VA,

    At the risk of repeating old arguments (but yours are old too):

    (a) “String theory is by far the only serious game in town when it comes to quantizing gravity” is inaccurate.

    (b) The sense in which string theory was a hopeful approach to quantizing gravity was that it seemed to be an approach along the lines that quantum field theorists were familiar with which looked like it might tackle the problems which seemed most bothersome to quantum field theorists. It was far less convincing to relativists even in its heyday — something which is only fair to take into account in assessing its strengths.

    (c) If we’re going to make progress on quantum gravity we need to have a hard-headed assessment of when to give up on poor approaches. At some point the argument that one approach is “the best thing going” becomes a weaker one than the judgment that that approach seems to have little going for it and quite a lot against it: it becomes an error not to cut one’s losses and reconsider the question and the entire approach.

    (d) We are likely to make little progress on quantum gravity until the right breakthrough occurs. It is very hard to figure out what sort of steps the field as a whole could take to try to hasten this. But the first thing would be to set a standard of examining carefully and fairly the strengths and weaknesses of different ideas.

  17. Bill K, make up your mind. Either string theory is bath water or ahead of its time. Let me trust Ed on this one.

    “Neither “abandon” or “wait” has anything to do with the way research is conducted.”

    Exactly. And when you stumble on a theory ahead of its time you don’t wait to be ready to deal with it. You jump on it and devote all your effort to understand it. Taking things in its proper order is for bureaucrats, not for curious scientists eager to find the right theory behind Nature.

    Pawl, it’s fine for arguments to be old as long as they are right. Your (a) is not even an argument but simply an statement. Without further qualifications it’s useless.

    (b) hahaha

    (c & d) The breakthrough will come from more work, not from your clear definition of when to give up or how to precisely weight the worth of different ideas.

  18. jpd says:

    a)
    arxiv search for “quantum gravity” AND NOT “string”
    returns:
    Your query resulted in too many hits, only 1000 hits are being displayed. These are not necessarily the 1000 most recent papers. We recommend that you try a more specific search.

    b) “hahaha” isn’t even a statement

  19. jpd

    a) Oh, you convinced me! Now it’s clear to me that there are much better ideas out there on how to consistently quantize gravity. Just with one click! I’ll use your insightful method in the future!

    b) Sure it is.

  20. Peter Woit says:

    VA,

    Excellent job of driving the intelligence level of a discussion down to zero. Enough.

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