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Hubble UDF and inflation

  1. Apr 1, 2011 #1
    Apologies in advance if this is a stupid question.

    I'm told the Hubble Deep Field shows galaxies as distant as 13 billion light years away.

    13 billion years isn't far off the apparent age of the universe - 13.75 billion years, says Wikipedia, from estimates based on the Hubble constant.

    I'm wondering (and here's the intellectual nose-dive) whether that's long enough ago that those old galaxies should appear "bunched up" - visually closer to each other because we're seeing them at a point in history when the universe had expanded significantly less than it has by now? Or... was most of the expansion in the first billion years (in which case I'll stagger around for a couple of weeks worrying about how it managed to expand at 13 times the speed of light).

    If anyone can shed any light on my confusion, I'd be really grateful.

    Thanks in advance!
  2. jcsd
  3. Apr 1, 2011 #2


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    The redshift of objects in the HUDF (Hubble Ultra Deep Field) are approximately ten at the greatest. This means that when the light from these objects was emitted, the universe was ~10 times smaller (11 to be precise...).

    Inflation ocurred when the universe was very very young, ~ 10^-30 seconds after the big bang or something like that. Way earlier than any structure in the universe had formed, and way earlier than we can hope to (ever) observe directly.
  4. Apr 2, 2011 #3


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    The high redshift deep field galaxies existed in a smaller spacetime region, but, few had yet formed.
  5. Apr 2, 2011 #4


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    Yes, absolutely. And they do! These sorts of tests, looking at the typical separations between galaxies, are our most sensitive tests of the overall spatial curvature of our universe. But you have to realize that to do this test accurately, one of the main things you have to take into account is the fact that when we look really far away, often times we're only seeing the absolute brightest galaxies that far back. So it often turns out not to be feasible to test separations between galaxies as far back as the furthest galaxies we can possibly see (because we're only seeing a small fraction of the galaxies).

    So, for the most part, we look at galaxies that are much closer (though still pretty far away, say a few billion light years), and add in the cosmic microwave background (at a redshift of z=1089, when the universe was over a thousand times smaller) for really far-away data.
  6. Apr 4, 2011 #5
    These are suitably thought-provoking answers - thanks for taking time to post! I'll do some searching for reading about expansion vs. inflation now.

    Have a good week everyone

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