String Theory Fails Another Test

Back in 2004, the KITP put out a press release (which I wrote about in an early blog post here) announcing that “Newly Devised Test May Confirm Strings as Fundamental Constituent of Matter, Energy”. The press release announced that Polchinski and collaborators had found “the most viable test to date for determining whether string theory is on the right track”, that this test would be performed by LIGO, which “could provide support for string theory within two years.”

This got a lot of attention and was often quoted as evidence that string theory was testable science. In a 2007 article in Physics World, David Gross answers string theory critics with:

String theory is full of qualitative predictions, such as the production of black holes at the LHC or cosmic strings in the sky, and this level of prediction is perfectly acceptable in almost every other field of science,” he says. “It’s only in particle physics that a theory can be thrown out
if the 10th decimal place of a prediction doesn’t agree with experiment.”

LIGO never found any evidence of cosmic strings within two years after 2004, and now the vastly more sensitive Advanced LIGO experiment has just released results of a search. As expected, the results are negative.

Any guess on the probability of a KITP press release announcing that string theory has failed an experimental test? Or of an acknowledgement by Gross that all the “qualitative predictions” of string theory he was using to justify it ten years ago have now all failed, so, by the standard of “every other field of science”, it should be abandoned?

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10 Responses to String Theory Fails Another Test

  1. Lino D'Ischia says:

    The last sentence of the abstract of the linked paper says: “Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider.”

    How severely constrained are they? That is, is this just a nice way of saying cosmic strings don’t exist?

  2. Peter Woit says:

    Lino D’Ischia,
    It’s always the same story, talking about string theory “tests” or “predictions” is just a way of misusing words to mislead people. If that wasn’t clear back in 2004, it should be clear now, after the “tests” are over and the “predictions” have been falsified. This hasn’t changed the opinions of those making these “predictions” (Polchinski says string theory “over 99.7%” likely to be true, Gross last Friday said he’s still wedded to the idea).

    String theory as a theory of unification predicts (in the usual scientific sense of the word) nothing about anything. You can’t rule out the cosmic strings of superstring theory, because the theory is so unconstrained that you can evade any conceivable negative experimental result, by just saying, “there really are cosmic strings, it’s just that their properties make them unobservable by the current version of LIGO”

  3. Verissimo says:

    Every post like this takes 30 minutes off the life of some random string theorist somewhere around the globe.

  4. Yatima says:

    I don’t understand this at all.

    From the abstract:

    Cosmic strings are topological defects which can be formed in GUT-scale phase transitions in the early universe. They are also predicted to form in the context of string theory.

    Cosmic strings (which I first read about in the 80s in SciAm IIRC) have scant to do with String Theory. And even if they had been detected, this would STILL say nothing about String Theory as the implication works the wrong way.

    And maybe it would say nothing about GUTs either.

    Is elementary logic still on the program nowadays?

  5. David Appell says:

    I have the same question as Yatima — are cosmic strings the same as string theory strings?

  6. Anon says:

    A concise description of cosmic strings generated during inflation independent of string theory:

  7. Peter Woit says:

    The history is that such things were first considered (late 70s) in the context of GUTs, where you can have string-like gauge/higgs-field configurations that may be stable for topological reasons, depending on the ingredients of your GUT (this doesn’t happen for the ingredients of the Standard Model).

    In 2003, in arXiv:hep-th/0312067 the authors came up with some string theory models with metastable fundamental strings (using complicated configurations, along the lines of the “string vacua” that supposedly stabilize moduli). Remember, in this game of Rube Goldberg models, you can get pretty much anything you want, why not large metastable fundamental superstrings?

    String theory proponents then went to work claiming that, if you found cosmic strings, and you could study them in enough detail to see whether they were GUT strings or these fundamental ones, then you would have “evidence” for string theory. The KITP press release was part of this publicity campaign, timed to coincide with publication of the 2003 paper. From then on, this regularly appeared as a “test” or “prediction” of string theory. The “could you even tell if your cosmic string was a GUT one or a superstring one?” question rarely got mentioned.

    I don’t see any point in wasting any time going over the details of this particular hype campaign and the supposed science behind it (probably it appears in a dozen or so of the posts on this blog). The fact that falsification of these “predictions” hasn’t changed one iota the faith in string theory of the people promoting them is good reason not to take this supposed science seriously. If the people behind these ideas don’t, why should you?

  8. Lino D'Ischia says:

    “The fact that falsification of these “predictions” hasn’t changed one iota the faith in string theory of the people promoting them is good reason not to take this supposed science seriously.”

    It stops looking like science, doesn’t it?

  9. Shantanu says:

    Peter: maybe you (or someone else) should forward this or ask this question to KITP PR folks and whether string theory has been falsified?

  10. Kea says:

    The only thing that will bring down string theory is a full theory of quantum gravity that shows precisely how string theory fits into the theory as a physically-not-very-relevant piece of structure, say like bubble graphs for scattering amplitudes.

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