Sean's Challenge

Sean Carroll of the incomparable Cosmic Variance blog has asked his readers to give their best guesses about the probability of some current speculations/theories in fundamental physics. I can't resist:


1.  Inflation - 75%

     This should be some number between 50% and 100%. Since I have no idea what it should be, I'm going with Sean's value because he's much smarter than I am. There are plenty of reasons to like inflation: it explains why the universe is so flat, homogeneous, and isotropic: no mean feat. But the requirements on the inflaton (the particle that provides the phase transformation that drives inflation) seem oddly narrow. Back when Guth introduced the inflationary model, it seemed that the Higgs field could play the role of the inflaton. But now we know that's not possible, so the model is not as economical as one would like.

2. Supersymmetry - 10%

    Since I did my Ph.D. thesis on supersymmetry, I'm sorry to give this such a low value. But I don't see any really compelling reason to think SUSY is out there, and, of course, there's no experimental confirmation so far.

3. String theory - 0.01%

    String theorists have had three decades to some up with some definitive predictions, and so far, nada. I don't expect this to change within my lifetime. String theory is, possibly, interesting math. But it doesn't seem to be anything more.

4. Some form of Higgs boson - 99.9%

   I'm surprised at the low values given this in Sean's poll. Something has to play the role of the Higgs in the Standard Model. I'm allowing 0.1% for the possibility that some mechanism I can't imagine would give us the Standard Model without incorporating anything (particle or condensate) that could reasonably be interpreted as playing the role of the Higgs. Modest of me, I know.

5. Large extra dimensions - 0.0001%

    They require string theory. But string theory doesn't require them. Nuff said.

6. WIMP dark matter - 80%

    As pointed out in the comments on Sean's post, this is oddly specific, given the "Some sort..." and "Any..." of the other options. Some sort of particulate dark matter I put at 99%. I mean, we've SEEN it. But what form that dark matter should take is still very much up in the air. WIMPs (for the uninitiated: weakly interacting massive particles) are the most likely possibility.

7. Any non-cosmological-constant explanation for cosmic acceleration - ??

    I don't understand the question. The evidence to date indicates that dark energy, whatever that is, behaves just like a cosmological constant. Sean seems to be asking if the value of that constant has an explanation, other than "it just is."  Or is he asking if the value doesn't behave like a cosmological constant; for example, does it change over cosmological time? If it is the former, I expect that, some day, we will have a deeper explanation for whatever the value turns out to be. If it is the latter, I have no clue.