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

Birth Home of our Universe?

  1. Jan 22, 2004 #1

    Not sure if this has been asked before. Feel free to refer to any previous post.

    My question is this: Since we know that our universe is expanding, has an extrapolation been done to approximate the actual origin in space of the Big Bang?
  2. jcsd
  3. Jan 22, 2004 #2
    I think since space itself is expanding, the origin of the big with respect to space is meaningless. The big bang happened everywhere, although that everywhere at the time of the BB was pretty small.

    If I'm correct, not exactly sure, the farthest we can look back (directly) is approximately 500,000 years after the BB, during the time of photon decoupling. This happened when the universe was cool enough to become transparent to electromagnetic radiation. This is the source of the microwave background radiation. Today, you can look in any direction and see this radiation. In essence, the origin of the universe surrounds us.


    Edit: When I said meaningless, I wasn't critisizing your question. Just that there is no origin of the universe with reference to space. Where the BB happened in relation to what may lie outside what we call the universe would be an interesting discussion. Are there other 'big bangs' and 'big crunches' happening, etc.
    Last edited: Jan 22, 2004
  4. Jan 22, 2004 #3
    Small? Is no "locality" suggested? Surely it MUST be within our current frame of referance... somewhere.??
  5. Jan 22, 2004 #4
    I suppose small might be a meaningless word as well in reference to the big bang. I'm not really sure. I'm also not aware of any frame in which you can reference the origin of the BB. That doesn't mean a frame doesn't exist. I just don't think anyone really knows. As far as space goes, you definitely can't pick one point and say that the origin of the BB was there...
  6. Jan 22, 2004 #5
  7. Jan 22, 2004 #6
    Do we not, in fact, exist in that very frame?
  8. Jan 22, 2004 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Where did the BB originate, in terms of today's locations? Well, it was inside my PC, in your big left toe, at Jimmy's mother's old home, on marcus' primary school desk, at the centre of the Sun, in a dust mote in the outer reaches of 3C273, ... in other words, everywhere in the universe today is exactly where the universe started expanding from.

    According to the WMAP results, the earliest we can see (so far) is the 'surface of last scattering', which according to the best fitting models was 379,000 years after t = 0.

    If we ever succeed in detecting relict neutrinos, we will be able to see an earlier surface of last scattering (sorry to say I don't have an estimate to hand of how soon after the BB that would likely be).

    Of course, the great 'let out' clause is that we can't know anything about the first ~10-43 seconds (Planck time), because we know that our best physics (GR and QFT) cannot both work in this period. If we convince ourselves that String Theory/M Theory/LQG/Monty Python is how the universe 'really' is, then we may be able to say for sure that it all began in your living room.
  9. Jan 22, 2004 #8
    Here's a good analogy. Consider a loaf of raisin bread, with soem evenly spaced raisins. When you put it in the oven, it expands and all the raisins move away from each other. There is no "center" of expansion.

    Now, if you imagine that before being baked the dough and raisins were all concentrated into a single point, you see that the Big Bang really did happen EVERYWHERE in the universe, since all matter that exists was originally concentrated in one point.
  10. Jan 22, 2004 #9
  11. Jan 22, 2004 #10
    You talkin' about my mamma?? :wink:
  12. Jan 22, 2004 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Ain't she the centre of the universe? :smile:
  13. Jan 22, 2004 #12
    May I suggest that if the universe "started expanding" that it must have a local origin? An origin of expansion. If there is no origin of expansion, expansion itself is not possible ????
  14. Jan 22, 2004 #13
    Of course. But she isn't in an 'old home'. lol!
    Last edited: Jan 22, 2004
  15. Jan 22, 2004 #14
    There isn't a center of expansion. Any location in the universe appears to be at the center of expansion. From any point, the farther you look out into space, the faster space will appear to be expanding. That's why more distant galaxies are receding faster than galaxies that are closer.

  16. Jan 22, 2004 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    oops, please excuse my poor choice of words; I meant 'the home she lived in when she was a little girl' {insert Smilie of Nereid with a red face}
  17. Jan 22, 2004 #16
    Haha! Don't sweat it. I was never offended. I thought you were just kidding around anyway. I understand now though. It's my mistake really. I just jumped to the wrong conclusion. An 'old home' isn't necessarily a on 'old folks home'.

    Thanks, Nereid.
    Last edited: Jan 23, 2004
  18. Jan 22, 2004 #17
    OK. Please offer corrections on the following assumptions:

    1) Expansion is a function. It is a function of separation. Without separation, the function of expansion is impossible.

    2) Separation directly implies and demands origin.

    3) Complex expansion functions are characterized by a net internal "pseudo origin"

    4) Regardless of whether or not the expansion function is simple or complex, the potential of expansion must be initially constrained/contained to some degree, else expansion is not possible, as there would be no relative frame to ascribe the event of expansion.
  19. Jan 22, 2004 #18
    So, basically are we saying this:

    If I am on earth, viewing Alpha Centauri, then Alpha Centauri is receeding. And if I am on Alpha Centauri viewing earth, then the earth is receeding.

    Hello!! What's wrong with this picture? If everything is expanding relative to one another, then it follows that everything at a previous time was in the same place.
  20. Jan 22, 2004 #19
    Yes. That's how Edwin Hubble's findings were interpreted which evolved into the Big Bang theory. The universe itself is expanding; space-time included. The question is, where was the universe when the expansion started? is it in the same place now as it was then?
  21. Jan 23, 2004 #20


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The origin is at Time = 0. (Space and Time are intimately linked...which is why we speak of "spacetime".) This is a point that is inaccessable to us (since time is a one-way street) except through ancient images that approach that origin as captured by our telescopes. Space alone has no such origin. It is the entirety of existence that matter and energy reside in. The expansion is what we see as the behavior of space to drive galaxies apart as time marches on. Or am I mixing up cause and effect and it's the expansion of space that drives time forward? Guess I'm back to the linking of spacetime - the very fabric of the universe.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook