Can infinity fit in the palm of your hand

  1. I'm currently trying to reassess my image of the BB and the universe in general.

    I've been led to believe/understand that at the moment after the creation event the universe would fit millions of times within the space occupied by a single subatomic particle.

    However there's something wrong here because the universe is infinite yet without a boundary (so I'm told) therefore it was still infinite when it was smaller and I can't see how it suddenly stops becoming infinite, I mean it's either infinite or it is not.

    Therefore at the moment of creation when the universe was the planck length in size it still must have been infinite.

    My question is this... how do I visualise this infinite yet tiny object.
    Last edited: Sep 14, 2011
  2. jcsd
  3. DaveC426913

    DaveC426913 16,534
    Gold Member

    No, the universe is finite yet without boundary.

    Your fears are unfounded.
  4. Dave, I thought that was still an open question. Not so?
  5. Drakkith

    Staff: Mentor

    Is there a difference between distance WITHIN the universe, and the size OF the universe? Not sure if that makes any sense though.
  6. If the universe is finite, then immediately after the BB it would have been very small. If the universe is infinite then it has always been infinite. Immediately after the BB it would have been infinite in volume, yet extremely dense.

    When people say things like "X time after the big bang the universe was the size of a grapefruit" what they usually mean is that all the matter in the current observable universe was in a volume the size of a grapefruit. What exists outside our observable universe still existed then, just outside the grapefruit sized sphere. Don't take it to mean all of existence was wrapped up in a grapefruit.
  7. Is there a better way then of visualising the nascent universe than as point like object as say one would visualise a proton.

    If the above is true (a proton like universe), I'd like to then know if it is valid to picture the universe at the earliest possible time in it's evolution as occupying the smallest possible quantum of spacetime. In which case all that would ever exist (in the Universe) was already existent albeit in a dormant form.
    Last edited: Sep 14, 2011
  8. Drakkith

    Staff: Mentor

    Mrspeedybob's post seems good to me. Instead of trying to imagine ALLLLL of the universe, even that beyond the observable universe, just imagine the observable universe as that size.
  9. What would be your reaction to the suggestion that at the instant of the creation of time and space and stuff that everything that is within the current universe, whether observable or not, would have occupied the smallest possible quantum of spacetime. Is this a valid point of view.
  10. Drakkith

    Staff: Mentor

    Claiming that the universe could fit within X volume implies that there is a definite size of the universe itself. I'm not sure I agree with that, as it conflicts with my limited understanding of the way it works.
  11. This is precisely what I'm trying to understand. How to visualise this nascent object. How do you picture it in a way that is consistent with what you understand?
  12. My own impression had been that the whole concept is a difficult one (for me anyway) in that the universe was smaller at the time of the big bang than it is now but that it still occupied all of space and was therefor infinite. To say that implies that "all of space" would therefore have had to have been a size that we would consider finite is wrong and this is both the essence of what I believe to be the case and also the thing I can't really get my head around.

    Dave, I'm still waiting to hear from you from post #3
  13. Drakkith

    Staff: Mentor

    I don't try to picture the universe as being "inside" of something, such as another dimension. If you could go back to 1 billion years after the big bang, everything would be much much closer together in space, however there would still be no boundary to the universe, no edge. It would be without limits. Whether this is because the universe is actually infinite in size or because it is closed and going past a certain point just means you come back around to your starting point, I don't know.
  14. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    The 'true' size of the universe is unknown [and possibly unknowable]. The little patch within which we reside, aka the observable universe, is and always was finite.
  15. DaveC426913

    DaveC426913 16,534
    Gold Member

    Please note that there was no matter - no "object" - anywhere near the beginning of the universe. Matter did not even come into existence until tens of thousands of years after the BB had expanded and cooled.

    The post-BB universe during that time was comprised entirely of energy. How much light can you fit in a room? As much as you want. Photons (bosons), unlike fermions, do not take up space.

    That's how it is possible to have it fit in a small space.
  16. @Chronos, but what about at the instant of creation, is it possible to speak of the size of the entire universe then?
  17. marcus

    marcus 24,218
    Science Advisor
    Gold Member
    2014 Award

    Yummy, since we do not KNOW whether time and space began at the start of expansion (BB) there is not one unique correct mental image. The BB may have been a bounce, our U could have been contracting till it reached a density high enough that quantum effects make gravity repel---and then the contraction rebounded. Quite a lot of the research effort is on that kind of model these days. So far there is no scientific reason to think that time and space began at the BB.

    So there is no one correct way to picture the BB. The BB is simply the start of expansion. It may or may not be a "creation" of anything. Could simply be a bounce at very high density.

    Also we don't know if the U had a FINITE SIZE OR NOT at the moment of the BB.
    Cosmologists work simultaneously with two different versions of the standard model cosmos---finite and infinite. In the same technical paper you may see two tables, one with numbers for the finite volume case and one for the infinite volume case. Or you may have just one table with separate columns of numbers.
    IT IS PREMATURE TO COMMIT to one mental picture or the other.

    AFAICS everything in these two posts by SpeedyBob and Drakith is correct. One cannot say that the U had some definite size. It is unscientific to claim this because we do not have evidence of that. It COULD have, but we do not know that yet. (So Drakith is right.)

    And like SpeedyBob says, there is the currently observable chunk, just a limited region of the U that we have gotten light from so far. We are sure there is more out there. The model must include the rest or it wouldn't work. It is not like we have evidence of an "edge".
    Even if the total U is finite, the evidence suggests it is many times bigger than our observable chunk. And it may be infinite. I would suggest keeping both images in mind.

    Have a look at the first link in my signature, immediately below this sentence where it says "einstein-online".
    Last edited: Sep 14, 2011
  18. That's just my bad terminology, by 'object' I did not necessarily mean 'matter' specifically, for my purposes I consider 'energy' to be an object.

    So redefining 'object' to mean 'anything that exists' would you be happy to accept that at the smallest possible increment of spacetime after the creation event, that all that currently exists was existent at that first moment, albeit in an undifferentiated or unmanifest form
  19. DaveC426913

    DaveC426913 16,534
    Gold Member

    Hrm. I was rather hoping that, with the realization that object versus energy was a critical shift in mental models, you'd say 'Ohhh! Ah! I see now.'
    Well... yes. That's the general understanding.
  20. So IF the universe was a bounce then that makes our universe special insofar as it's not going to bounce again. Isn't that a little strange? If it originated from a bounce then then how many bounces would there have been before the BB seeing as it ain't gonna bounce no more. It can't be between one and infinity because infinity can neither begin nor end and since our universe is the final bounce (if there was a bounce) there cannot have been an infinite amount of bounces. All in all it seems to me that a bouncing universe does not make sense if we accept that the expansion of the universe is accelerating.
  21. Drakkith

    Staff: Mentor

    Just because we see accelerating expansion currently, does not mean that it will continue. We don't even know the reason for the expansion, only that it is occuring. (Although I'm almost certain there are several theories) In the view of inflation after the BB, something had to cause it and something had to cause it to end. Remember that all of the theories on the BB and on the end of the universe are VERY tenuous and only represent our current knowledge on the subject, which is improving as time goes on. If there is something that will cause the universe to stop expanding 10 billion years from now, well there's pretty much no way for us to even know about it yet!

    The short version of this is pretty much take the views on the beginning and end of the universe with a grain of salt and stick to the middle!
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