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

Expansion of the universe

  1. Apr 28, 2008 #1
    I'm not sure exactly what discipline this falls under, so general it is. If there is a better place to put this, please let me know.

    Anyway, A colleague and I were having a philisophical discussion about the nature of the expansion of the universe from the point of view of big bang theory. I have come to understand that the singularity was contained within space time and that only energy and matter expands from that point. He believes that space time was contained within the singularity and, upon "bang," it propagated and some speed greater than the speed of light and that all matter and energy expands within it.

    We are very curious as to which way is the correct way to interpret the threory, but none of out professors are comfortable answering that question confidently. For the purpose of explanation, we are both about to obtain our undergraduate degrees.

    Thanks for your help in advance!
     
  2. jcsd
  3. Apr 28, 2008 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    I would have said that the best explantion was that the universe - inclduign space and time was created in the big bang.
    Expanding faster than light isn't a problem since no information can travel from one edge of the expanding universe to the other.
     
  4. Apr 28, 2008 #3
    These things aren't universally agreed upon (before i begin). And on top of that, i'm not an expert on the subject, so all that follows is my interpretation/knowledge of the current theories...
    Space itself emerged from the initial singularity (time also, but thats a little more complicated). It did not expand faster than the speed of light, at any time. Spacetime itself, expanded at the speed of light; and matter/energy followed closely behind. All of these things are hard to describe/talk about in standard terms because the universe didn't / isn't expanding like a balloon expands, it would seem to be much more complex (perhaps a good illustration is that every point in the universe is the center).
     
  5. Apr 29, 2008 #4
    So you're saying that space time is propegating like a wavefront, then? Or that it expands in more than four dimensions? Or something else?

    I've looked for a paper on the subject, and I can't seem to find one.
     
  6. Apr 29, 2008 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    By definition a singularity is something that occurs in a man-made theory. It is a place where the mathematical model blows up or fails to compute. there is no scientific reason to believe that a singularity ever existed in nature.

    What scientists have always done when confronted by a singularity is IMPROVE THE THEORY, so that the singularities go away.

    So you need to make a fresh start. The moment you begin talking about a singularity as if it was a real thing existing in nature, you are off on the wrong foot.

    Try reformulating your question so it makes more sense.
    ========================

    Space and time do not PROPAGATE. They are not substances or fields or material. Propagating is something that stuff does THRU space. Space itself does not propagate.

    The term "expansion" is misleading. In cosmology it simply means that distances between widely-separated stationary points increase a certain percentage per year. Motion is not involved. Propagation or transmission of information is not involved.

    At present large-scale distances are increasing at a rate of 1/140 of a percent every million years. Naturally that means that the larger a distance is the faster it increase---because it is a percentage growth----so any distance that is large enough will be increasing faster than the speed of light. But this is no big deal because no motion thru space is involved, so it doesn't contradict any law of physics or anything Einstein said.
    ========================

    Quite a bit of research these days is devoted to getting rid of the singularity in the classic big bang model. It is about time people stopped talking about it as if it were something real.
     
  7. Apr 29, 2008 #6

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

  8. May 1, 2008 #7
    That paper was extremely enlightening. Thanks very much, cristo. The mechanism of the expansion of the universe is much more clear now- but now I'm confused about the existance of energy. Before I read the paper, I thought the theory attempted to partially explain that, but there was no mention of it while I was reading. What are the theories regarding this issue?

    Or, otherwise, how do I find papers on PF? That way I could learn for myself without having to ask question after question. I looked for awhile, but got lost in the chess forums ^_^.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Expansion of the universe
  1. Universe Expansion (Replies: 5)

Loading...