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Where was the big bang singularity?

  1. Aug 22, 2010 #1
    If all galaxies originated from big-bang, and if currently galaxies are still moving away one from the other, shouldn't it be possible to determine also where they are moving away from? i.e.where the big-bang-singularity was?
  2. jcsd
  3. Aug 22, 2010 #2
    No. the nature of an explosion is such that every particle appears to be the centre of expansion.
  4. Aug 22, 2010 #3
    I don't get it.
    In an explosion , all particles come from the same point and each one goes to a different point.
    At least, seen from outside. How does a particle see its own motion? Can "she" see it w.r.t the outside reference system?
  5. Aug 22, 2010 #4


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    Balloon analogy. Think of a bunch of dots marked on a balloon. The balloon expands and every point on the surface of the balloon recedes from every other point. In fact, the rate of recession between any two dots is directly proportional to their distance.

    Note that the surface of the balloon has no centre; no dot can claim to be nearer a centre than any other dot. When the balloon was (ideally) zero-size, all dots were at the centre.
  6. Aug 22, 2010 #5
    The two sentences do not match!

    Indeed, all dots on the surface were previously all in a single point: the centre of balloon VOLUME.

    So, where is this point in the Universe? Can we determine it? How?

    Or maybe the balloon surface (2d) represents our 3d universe?!?

    Could we determine the "centre position" if it was in the 4th (?) dimension?

    Can Flatland inhabitants determine position of objects in the 3d space surrounding them?
  7. Aug 22, 2010 #6


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    As it turns out, the extra dimension is not actually required for the math to work out. The balloon doesn't need a 3rd dimension, the universe doesn't need a 4th, and neither need a place for the centre to be.
  8. Aug 22, 2010 #7
    maybe our math doesn't need the additional dimension, but the Universe has it! The balloon HAS a 3rd dimension!
  9. Aug 22, 2010 #8


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    I'm not saying "just" the math doesn't need the dimension; I'm saying the 3D expansion of the universe works just fine mathematically without the need to resort to a 4th dimension.

    Thing is, it's virtually impossible for the layperson (non-mathematicians) for wrap their head around it, which is why we resort to simpler analogies.

    That's why it's an analogy. Not everything about the balloon analogy is translatable to the universe.
    Last edited: Aug 22, 2010
  10. Aug 22, 2010 #9
    I'm not an expert of this but perhaps I can provide an explanation that will help.

    The first thing you have to understand is that every direction we look, we can see for 13.7 billion light years. This means one of two things. WE are at the center of the universe OR the Universe is much larger than we can see and it is roughly uniform in every direction.

    Every time we say we're at the center of the Universe we are proven wrong. This is why we call what we see, "the observable universe". Base on our observations of the observable universe, there is no edge and since there is no edge, it could be infinite or finite and wrap around itself. If you take the entire earth and you put an ant hill on one small part of it then ask the ant where the center of the earth is, will he be able to tell you an answer or will he just say that the earth goes on forever?

    Basically, you're asking a question which no one can really answer. The data from the CMB seems to show that everything is roughly uniform in all direction. This would imply that there is no center because a center would by definition be where the big bang originated and it would show up as hotter in the survey. Again, if there is a center that is outside of our observable universe, we would expect to see that one direction is cooler (whichever direction is the exact opposite of the center). It is of course possible that the center of the universe is so far away that we can't see the extremely small decrease in temperature with our current equipment.

    In other words, based on current observations, the universe started with everything at a single point in space and everything expanded from there. That's the only way to account for current observation.

    I hope that helped.
  11. Aug 22, 2010 #10
    I think the word "where" is inappropriate to use when describing the Big Bang. When we usually use "where", we are implying some location in 3-D space in our Universe but the Big Bang was the start of our Universe and I suspect just prior to the Big Bang there was no space but rather something qualitatively different and therefore our concept of space, of location, distance, size, volume, area, location, and other similar metrics are not applicable and cannot be used to describe the instant of the Big Bang and therefore "where" it occurred.
  12. Aug 22, 2010 #11
    Q. Where was the big bang singularity.

    A. Everywhere

  13. Aug 22, 2010 #12
    Last edited by a moderator: Apr 25, 2017
  14. Aug 24, 2010 #13


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    A singularity was everywhere ?

    Then everywhere was / is a singularity. Very confusing.
  15. Aug 24, 2010 #14


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    Go back to the balloon analogy. When the balloon was uninflated (ideally, a point), all dots on the balloon were in the same place. None had a preferred location. When the balloon began to expand, all dots that were at the initial point of expansion moved away from that point. Still, no dot has a preferred location. And no one dot is nearer the initial point of expansion than any other.
  16. Aug 24, 2010 #15


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    OK, but when the ballon was uninflated all the dots were at one single point, not everywhere.
  17. Aug 24, 2010 #16
    The single point was equal to everywhere, everywhere was the single point...
  18. Aug 24, 2010 #17


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    What you're missing is that the balloon/point/universe was not a point in space; it was a point that was all space. There was no space outside that point.

    As DLuckyE says, that point is what constitutes "everywhere".
  19. Aug 25, 2010 #18


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    From ..

    I think the agreed consise definition of singularity is;

    Astrophysics; A point in space-time at which gravitational forces cause matter to have infinite density and infinitesimal volume, and space and time to become infinitely distorted.

    It is difficult to believe or to even understand the notion that 'all there is' was contained in zero volume. Very difficult.

    As Chronos said in ..

    Plenty of work is in progress to remove the big bang 'singularity'. It is highly theoretical and speculative - largely because we have little or no clue haw to obtain the necessary observational evidence. We are fairly certain singularities are illogical, but, lack the math/evidence to dismiss them with any confidence. The nature of the universe remains quite mysterious.

    As a layman (or less), I can certainly go no further than this.

    But I sometimes entertain wild notions ..

    "OK, assume it was initially a singularity - could it be that it still is, and that we exist still inside it, and are even smaller than that singularity ? After all, to call the universe 13.7bly wide (for our purposes) or to call us, say, 13.7b times smaller than the initial singularity, might just be the same thing"

    But don't take me seriously - I'm probably being silly, seeing as I can't go in any other direction with it.
  20. Aug 25, 2010 #19
    With respect to the surface of the balloon no location on the surface is the center of expansion

    At time 0, the balloon was a point. As time progresses from then, it expanded into what we see now. The time/space location of point at time 0 only exist in the past and not in the present "balloon surface"
  21. Aug 25, 2010 #20


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    True. Though we have rolled back the film to a very small fraction of a second after the BB, when it was still smaller than an atom.

    I think I'll retroactively loosen the use of the term "point" - whether it is actually a single point or whether it was just a small volume - changes nothing in the scenario being discussed.
    Last edited: Aug 25, 2010
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