Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What if expansion rate of a universe is the speed of light?

  1. May 8, 2015 #1
    What If we accept starting point of the big bang as the central point and what If the equatorial expansion rate of a spinning universe was the speed of light, how would it impact universe?
    ( In this question, you may think yourself as an observer from out of universe. I try to mean with "the central point", the coordinates. Starting point coordinates are according to an outer observer.)
     
  2. jcsd
  3. May 8, 2015 #2

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    There is no such point. The big bang did not start from one point in a pre-existing space and spread out from there. It happened everywhere in the universe at the same time.
     
  4. May 9, 2015 #3
    Thank you. :-) Then, You think,our universe is absolutely "the only one" ? There is no multiverses... At first, I thought like that. But a friend confused me...
     
  5. May 9, 2015 #4

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    What I said has nothing to do with whether or not a "multiverse" theory is true. Multiverse theories are highly speculative, but regardless of whether they're true or not, what I said still applies to the Big Bang that happened in the universe we can see.
     
  6. May 9, 2015 #5
    I like this question, but maybe in a different form...

    I think the present expansion is described as an increase in velocity per some distance of observed object, like 73.8km/s per Mpc (megaparsec or 3.26 million ly).

    This makes comparing the expansion to c kind of apples and oranges... but I'm wondering if cosmologists have come up with some kind of derived attribute of expansion, back near the beginning, that does have some relationship to c... some aspect of the expansion or maybe inflation that had some perameter that might be correctly comparable to c. I wonder what that might be and what physical significance it might have for the point in time when the magnitudes (of whatever they are?) were precisely equal, and when that was.

    Anyone know of such a parameter as this?
     
  7. May 9, 2015 #6

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    No. As you note, the expansion rate of the universe can't be described as a speed; the closest you can get is a ratio of speed to distance. (This is often better thought of as a fractional rate of expansion, i.e., the universe expands by some percentage per unit time.) This is true at any point in the universe's history, early as well as late.
     
  8. May 9, 2015 #7

    OCR

    User Avatar

    (...My bolding...)

    The words, "happened in the universe" ... seems to imply that the universe already existed...?
     
  9. May 9, 2015 #8

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    No, it just means that the event we refer to as the "Big Bang" (which, strictly speaking, is not the "initial singularity" that appears in idealized FRW models, but the initial hot, dense, rapidly expanding state of the universe which we know existed, even if we don't yet know what came before it) is part of the spacetime that we call the "universe".
     
  10. May 9, 2015 #9

    OCR

    User Avatar

    That sounds fine by me... :oldcool:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What if expansion rate of a universe is the speed of light?
Loading...