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Is the edge of the universe the begging of time

  1. Mar 15, 2009 #1
    I know this question sounds far to naive but anyway,

    "Is the edge of the universe the begging of time"

    My rational is simple. The further you look out in space the faster things are moving away from us. Therefor I would suspect at the edge of the universe time would hardly move at all (relative to our reference frame) given special relativity.
  2. jcsd
  3. Mar 15, 2009 #2


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    Re: Is the edge of the universe the beginning of time

    Special relativity does not apply at cosmic scale because spacetime is curved.
    SpecialRel only applies in a small local neighborhood which is close enough to flat so that it is a good approximation.

    The geometry modeled by SR has no curvature and has no expansion----another reason that SR is a bad fit for the universe as a whole.

    Maybe it would help you to read some of the first part of the Balloon Model sticky thread.

    You should realize that most of the galaxies we observe are receding faster than the speed of light, often several times the speed of light.

    If the recession speed were real motion, rather than just a rate of increase of distance, it would seem to be prevented by SR. But SR does not apply, as I said.
    And distances increasing is just the dynamic geometry of General Relativity.

    SR was published in 1905 and GR was published in 1915, and it overturns some of what you might expect from SR, and it trumps it. In GR distances can change actively without anything corresponding to conventional ideas of movement. That's what spacetime curvature is about.

    In standard cosmo there is no edge to space. And space is approximately uniformly filled with matter. Like the balloon speckled with dots representing clusters or individual galaxies.

    There is a limit to the region of it that we currently see because out beyond that we didn't get light yet. But that is a shifting imaginary boundary because more light is on its way always coming in from more distant stuff. There is no physical edge or boundary.

    Currently we are seeing microwave (CMB) from stuff that is currently 46 billion lightyears from us and that stuff, which used to be hot hydrogen when it emitted the light, is doubtless condensed into galaxies and stars and planets so it looks very much like us and our local neighborhood.

    And if there are people on those galaxies 46 billion LY away they will be receiving CMB microwaves some of which come from our direction and are from the glowing gas that later on condensed into us. We are getting their CMB radiation and they are getting ours. It goes both ways. It started out as kind of reddish orange light and it got stretched to microwave by the expansion while it was traveling.

    So what we see when we look at the most ancient light from the most distant stuff is that the beginning of time? Well, maybe...
    Not in any simple way though.
    I don't think of it as that.

    There is too much chance that the bang was a bounce---a contraction expansion event---papers being written about that, books coming out about it. Increasing research effort. If so then time extends well back before the bounce. So when we look at the most ancient light we see stuff happening near the bounce, within a few hundred thousand years of it. But that is just an episode. We have no reason to call it the "beginning of time". That's sort of poetic/romantic sounding. Just my personal view. Nice question though.:smile:

    Carid, thank you for the approving comment. It's a real boost!
    Last edited: Mar 16, 2009
  4. Mar 16, 2009 #3

    That was a very clear answer. Maybe it should be tacked up on a notice board at the beginning of the Cosmology thread as a "read me first"!
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