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The Sciences

Do You Think Inflation Probably Happened?

Cosmic VarianceBy Sean CarrollFebruary 7, 2011 7:40 PM


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I was at a meeting in Princeton a short while ago, a small and focused workshop for people who are working on fundamental questions in inflationary cosmology. I hope to talk more about the meeting once the website is up (talks were not recorded), but here's a simple question: what is the likelihood you would attach to the idea that some form of cosmic inflation occurred in the early universe? My answer was 75%, which I thought was generous. It's very hard to give a high probability to a speculative theory about what happened at energy scales to which we currently have no experimental access. But I found myself on the low end of opinions at the meeting, where the median was about 90% confidence. Of course, these are people who work on inflation professionally, and have chosen to do so. When I came home to ask the same question of my lunch crowd at Caltech, the answers were more like 25%. An interesting glimpse into the non-unanimity of scientific opinion when it comes to untested theories. So, just for fun, let's ask what your personal likelihoods are for the following theoretical ideas.

  1. Inflation

  2. Supersymmetry

  3. String theory

  4. Some form of Higgs boson

  5. Large extra dimensions

  6. WIMP dark matter

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

I'm not defining these very carefully, and let's posit that we're not interested in weaseling about what the definitions mean. We're asking what you think the probability is that, if you were to ask an omniscient being who knew everything about the workings of Nature whether these ideas were part of how the world works, would they answer in the affirmative. What do you think? (It's helpful if you say a bit about what kind of perspective you are coming from.)

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