Questions for Cosmologists

I was pleased to get a comment from cosmologist Sean Carroll frighteningly soon after starting this thing up. Here’s some questions about cosmology that have been on my mind recently, maybe he or someone else will be able to answer them:

Witten has argued to me that “results about CMB fluctuations which are suggestive of inflation at the GUT scale” provide evidence that “grand unification is on the right track”. What exactly does the CMB data say about inflation? Can one extract the GUT scale from either the current CMB data or any conceivable better future CMB data?

More generally, while I’ve heard a lot about attempts to extract information about Planck-scale physics from CMB data, what about all the scales in between where accelerators stop (hundreds of Gev) and the Planck scale? Can one find out anything about electroweak symmetry breaking? Could this have anything to do with inflation?

There’s another question that often bothers me: “How can you have a field called ‘String Cosmology’ when string theory isn’t really a theory and can’t be used to predict anything?”, but I’ll be good for now and leave that rant for another time.

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3 Responses to Questions for Cosmologists

  1. Gary says:

    Who can really know for a certainty where future CMB research will lead (if but to answer the aforementioned question regarding the extraction of the GUT scale from CMB data.) We will just have to wait and see. But I will tell you this much, that when we do hopefully we’ll be smart enough to recognize a designer involved in the greater scheme of creation, and not the theories themselves.

  2. Alexander Crawford says:

    However interesting the statistical/mathematical models may or may not be, the actual difficulties aren’t addressed very seriously in terms of experimental problems or circuit design methods (errrr… the standard deviation measure of step rise times from step response to impulse response doesn’t suggest “extra-dimensionality” in a physical sense).

    It’d probably be very interesting for most theoretical physicists to look into the wire spring relay developed by Western Electric and current in the mid-1960’s, especially for those interested in String Theory. It might be as interesting as the M-M interferometer design as that relates to other somewhat older cosmological models. The magnetic field model is available at MIT and a couple of other sites (view source option-read comments) for a curious take on m-m data.

    Regarding the questions specifics…

    Here’s a link to the NIST page for phase noise and metrology:

    http://www.boulder.nist.gov/timefreq/phase/

    Here’s the optical frequency measurement group links

    http://www.boulder.nist.gov/timefreq/ofm/index.html

    useful glossary:

    http://www.boulder.nist.gov/timefreq/general/glossary.htm

    (The USNO has a very comprehensive library of technical papers for the serious.)

  3. Sean says:

    These are very good questions, so much so that I started a multi-part answer over at my blog. Basically, the energy scale of inflation is roughly equal to the Planck scale times the square root of the perturbation amplitude; this works out to be the GUT scale. It’s nicely consistent, but by no means direct evidence; Witten was right to say that it’s “suggestive,” but not more than that. If we were able to measure gravitational-wave modes, that would give a direct measurement of the energy scale.

    This is only in the simplest models, of course. If you get more baroque you can do whatever you like, including inflation at the electroweak scale. But you have to work at it. Likewise with getting information about Planck-scale effects; it’s unlikely, but worth thinking about.

    We should talk about string cosmology another time. String theory is not a completely well understood theory, but it’s not vacuous, either. But string cosmology is in its infancy, to say the least.

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