Quick Links

  • I’ve always thought more philosophers of science should be weighing in on the debate over “falsifiability” and the “demarcation problem” surrounding string theory and the multiverse (i.e. are these really science?). This is a complex and tricky subject that they have a long tradition of exploring, and it would be great to have this inform some of the debate instead of the often very naive arguments that dominate the discussion. Massimo Pigliucci does a nice job here, responding to Sean Carroll’s attack on falsifiability (see here, more discussion here). Pigliucci’s posting is great, giving a concise explanation of the way philosophers of science have found to think about these issues. It does though show that much of what needs to be examined are technical scientific issues (what exactly does “string theory” say or not say? What exactly are the conceivable things one could expect to measure and compare to theoretical predictions? What exactly is the state of efforts by string theorists to make predictions: how deadly are the obstructions they have run into?). In any case, here’s Pigliucci’s conclusion:

    But at some point the fundamental physics community might want to ask itself whether it has crossed into territory that begins to look a lot more like metaphysics than physics. And this comes from someone who doesn’t think metaphysics is a dirty word…

  • This evening at ASU there will be a program on Parallel Realities: Probing Fundamental Physics, you may be able to watch it live here. With David Gross there, at least it won’t be the usual “Isn’t the Multiverse cool?”-fest that this sort of thing recently often has turned into. Yesterday on Science Friday, Krauss, Wilczek and Brian Schmidt discussed Could There be a Crisis in Physics?
  • In case you’re wondering why there’s been no discussion here of Hawking’s recent claims about black holes, the reason is that I’m in agreement with Wilczek’s wise characterization of this on the Science Friday program:

    I think the kind thing to do is to pass this over in silence.

    If you really need some Hawking material, there’s The Top 10 Science Jokes, As Told by Stephen Hawking. Warning: safe for work, but not very funny…

  • Quite a bit funnier (although some might say, also kind of tired and sad..) is this “debate” between Bousso and Rovelli at the latest FQXi conference: String theory vs. loop quantum gravity.

Update: Video of the ASU talks can be found here. Wilczek is still sticking with SUSY, but says “no more excuses… these particles have to materialize [at the full LHC energy]“. According to Twitter, this really was a rock-star event, with the local ladies “getting dolled up” and ready “to throw our panties onstage.”

This entry was posted in Multiverse Mania. Bookmark the permalink.

17 Responses to Quick Links

  1. paddy says:

    Great blog by Massimo Pigliucci. Thank you for the link Peter.

  2. Barack Holder says:

    @ The ASU debate tonight:

    @asuORIGINS David Gross on the multiverse: “It smells of angels.” #1universe

  3. Shantanu says:

    Peter or anyone else. If someone could put a link to the webstream at the ASU meeting that would be great (for those of us who could not watch it live)
    I listed to the public debate. I am surprised Frank is still sanguine about
    proton decay.

  4. tt says:

    why is it crazy to say there might not be black holes?
    the only observational evidence just implies some massive, dense object.
    we dont know what happens in that regime, much like other energy regimes.

  5. Barack Holder says:

    Here it is:


    Unfortunately, the Q&A is missing

  6. Martin says:

    Science does not work only via falsification. The logical positivists referred to verification: a statement is true if you can verify it. Popper retaliated by referring to statements that can be falsified but not verified. This is old ideological stuff from the 1930′s.

    In science we want to estimate the credibility of a statement or hypothesis. Seeing the Higgs boson is a verification. Not seeing SUSY is a falsification. Both, verification and falsification depend on empirical data: from these we can judge whether a theory works well or not. This is in general not possible with metaphysics, which generates statements that could perhaps be true or not without there being any way of judging this on the basis of empirics (seeing, measuring, etc). The problem with string theory is that it is experimentally irrelevant. The problem with mathematical physics is that its afficionados do not care about experiments. Thus they talk about Hawking radiation and multiverses etc. without being bothered about whether there is any experimentally supported reason for taking these subjects seriously. This is a clear symptom of decadence. I do read QFT because it is experimentally relevant, even when it is only an effective theory. I cannot get interested in string theory, though.

  7. Tom says:

    Matt Strassler has a more “nuanced” (I dislike that word!) view of the Hawking/Black Hole Kerfuffle & attributes a lot of it to “Media absurdity”.


  8. Peter Woit says:

    I assume that you’re making fun of Strassler here, whatever he’s up to, it’s not “nuanced” (dramatic accusations against journalists in red type with multiple exclamation points????). I did write a comment there, which it looks like he didn’t really understand. His claim that when Hawking write a paper saying there are no event horizons and explicitly writes “there are no black holes” the media should not quote this doesn’t make any sense to me. The media coverage I’ve seen has been pretty accurate about Hawking’s claims.

    The one criticism I have is that it would be better if the media provided some context, that this was just one of a lot of rather incoherent stabs at the black hole information paradox, in the backwash of the “firewall” realization that just invoking holography doesn’t solve the problem. I think the media is accurately portraying the claims of a small group of prominent physicists. If other prominent physicists were willing to go on the record (kudos to Wilczek) saying that this, and Hawking in particular, is best ignored, we’d be much better off. This is a (minor) physics community problem, not a media problem.

    Personally I don’t see any reason to waste time on this. The media is doing a reasonable job. A celebrity physicist is getting too much attention, some physicists are hyping their work, while most of the physics community is ignoring them. All is normal. It’s not like the multiverse or string theory story….

  9. Thomas says:

    The exact quote is:

    “The absence of event horizons mean that there are no black holes – in the sense of regimes from which light can’t escape to in finity. There are however apparent horizons which persist for a period of time. This suggests that black holes should be rede fined as metastable bound states of the gravitational field.”


    For decades, physicists and their huge egos have been roaming the earth claiming to whoever would listen that black holes are places where the density of matter produces such extreme spacetime curvatures that, to cite what has to be the most tired cliché ever, “nothing, not even light, can escape.”

    Hawking’s quote above is a direct repudiation of this definition, period. Both him and the press have recognized it and there is nothing wrong with that. It remains to be seen whether the new definition has content or not. Let’s not hope too much, but if via Hawking’s paper the firewall craziness could actually help physicists to retire their nauseatingly obligatory “nothing, not even light, can escape” phrase, and to try and seek words of their own when they talk to the public, then it will have been worth something.

  10. DrDave says:

    Fave quote from Pigliucci on the fine tuning problem: “I actually think that people who seriously maintain that this universe is friendly to life haven’t gotten around much in our galactic neighborhood.”

  11. Art says:

    Actually, I much prefer your one-sentence assessment above (“just one of a lot …”) to the smug, snide (and disrespectful) put-down by Wilczek that you applaud. People are interested in this stuff, and are looking to experts for informed guidance, but not to just be told “ignore it” with no back-up. Kudos to Motl for engaging with the argument.

  12. Peter Woit says:

    You’re right that people are interested, and looking to experts for informed guidance. I think Wilczek is providing exactly that: telling you that this is getting much more attention than it deserves and your time is better spent elsewhere. I actually think he’s trying to be polite by not giving more detail about why he thinks this (as well as trying to avoid wasting his own time). If you really want to ignore wise counsel from a Nobel Prize winner and join Lubos and others in studying this, go right ahead, but I don’t think you should be criticizing Wilczek for providing something the field sorely needs. Far too few like him are doing what should be part of their job: giving an expert opinion about what is overhyped and best ignored.

  13. Sesh says:

    I don’t agree with one aspect of Pigliucci’s argument: the cosmological constant problem is not simply one of “fine-tuning”, and certainly if the minimalist version of the anthropic argument proposed by Weinberg actually correctly predicted the value of the cosmological constant, this would be a very good reason to take the multiverse seriously.

    However, in light of modern observational data Weinberg’s argument does not give the right value of the cosmological constant. It is off by about three orders of magnitude, which is pretty much the limit at which Weinberg’s original paper stated we should conclude the anthropic argument did not work. Which is not a fact that is often mentioned.

    What’s worse is that, as Lee Smolin was pointing out in the comments on a previous post here, the stringy multiverse actually does not satisfy one of the key assumptions necessary for Weinberg’s argument (namely that the bubble universes differ only in the values of Lambda). Once you allow other variables to vary there is no longer any model-independent prediction for Lambda and therefore no way that the multiverse hypothesis can be tested by any observed value of the cosmological constant.

    So ultimately I agree with Pigliucci’s conclusion, though not with the reasoning. The details of this argument are of course pretty well known, but for completeness I have also written them up explicitly here.

  14. Art says:

    Fair enuf, but these days “proof by reputation” doesn’t cut it. (Did it ever?). The thing is, it wouldn’t have required much more effort to make the contextual eval you did above, and then reputation can legitimately come into play, since it’s clear that there’s some basis for the opinion. Love your blog …

  15. Peter Woit says:

    I commented on your blog also about this, but for here also, could you provide a reference to the best current numbers for this kind of “prediction of Lambda”?


  16. Sesh says:


    I’m afraid I’m not enough of an expert on this to give you the “best current numbers”. However, I think the point is somewhat moot in any case. Weinberg’s original argument was attractive because it didn’t depend on the details of the measure problem. But that argument gives the wrong value.

    To get the right value (even assuming that only Lambda varies) one must tackle the measure problem, and since there is consensus on the correct way to do this, it becomes a question of retro-fitting the measure to get the correct Lambda. Note that even the Martel et al paper you linked to on my blog does this, because it was already clear by 1997 that Lambda was too small for the original argument to work.

  17. Sesh says:

    Sorry, I meant *no* consensus in the comment above.