Big Bang - No Single point of Expansion

  1. Cosmologist say that the universe is expanding but from no central point. It seems contradiction to me because the universe also started from a single point and EXPANDED outward. Further, they say if you reverse expansion everything would compress back to a singularity. Seems like expansion is occurred from a single point possibly occurring at one too if you can rewind to a single point!
     
  2. jcsd
  3. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Before the universe there wasn't anything to expand into..
    Don't think of the universe as exploding from a point out into black empty space - think of it as the space itself being created as it expands.

    A common picture is to think of inflating a balloon. ANy two points on the surface of the balloon are expanding away form each other but there is no point on the surface that is the centre that everything is expanding from
     
  4. Space exploded into what?
     
  5. Intuitively it makes no sense that space is expanding into nothing. Is this something I am to accept and look the other way because no one understands it... like gravity?
     
  6. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Intuition is a sense of knowledge from your internal experience.
    Do you have a lot of internal personal experience of the start of the universe?

    In reply to somebody complaining about the confusing terminology of Quantum mechanics - to which one of the founders replied - "yes it's odd that a language invented to tell other apes where the ripe fruit is has difficulty with the notion of a particle as a wave"
     
  7. No, but I know what nothing is, I have lots of experience with nothing. Nothing is a common human concept and perhaps the problem is trying to explain non-classical events terms of the classical event driven human experience. I know that QM makes no sense until you start to view it in terms of hamilitonian space. Maybe the nothingness is something like that?

    I have no problem with expansion but nothing is really abstract and there is actually no true instance of nothing except symbolic. For example, I did nothing to prevent shuttles take off in cold weather. In fact, here nothing means "took no action".

    Also, I did not think that space exploded per se. After all "Big Bang" was met to be a derisive term and only stuck because of media like the term and I guess through constant usage made it acceptable. Explosion implies something blew up and BB came from nothing.
     
  8. russ_watters

    Staff: Mentor

    Intuitively, are you able to visualize a 3 dimensional curved surface (analogous to a two dimensional curved surface of a balloon)? If you can't, then your intuition is failing to help you understand the geometry of the universe and you must learn about a reality that is different from what your intuition tells you. Heck, if our intuition was always right, what would there ever be to learn?!

    Trying to understand the baloon analogy would be a big help here.
    Ok....well think about how the concept of nothing could apply to the expansion of the universe. You're talking about a spherical universe with an edge and a center, expanding out into empty space surrounding it...... so where is this edge? Why don't we see it? Why don't the velocity vectors of galaxies have a preferential direction?
    Actually, the concept of "nothing" really isn't abstract, but people often use imprecise wording that improperly frames the concept. For example, your quote:
    ...is an improper paraphrase of what people are telling you. They didn't say "space is expanding into nothing", they said space is not expanding into anything. These are two very different things because when people hear "nothing", they think "empty space", but the reality is that the universe is not expanding into empty space.....and empty space wouldn't be "nothing" anyway!
     
  9. Is it best to think of this starting point as containing all of this (our universe) mass/energy/space at some instant, or as a point sized 'entry' location for things to follow? Could we ever know the difference?
     
  10. This is what I understand of BB. I will use outside observer to help illustrate. At BB this observer would notice some event, a flash of light and then an infinitely small region, a Point, would plop into existence. (I know photons would NOT be able to actually leave region but i say it anyway for illustration).

    At this point, the infinitely small region, Point, is fixed in size to observer and will never change. However, internally, the region develops space, time and structure further this space starts to inflate.

    So, now I space/time being mysteriously defined inside this region, which is still infinitely small externally. Space time attributes are unique and do not exist outside of region; observer has no concept of space or time only sees a dimensionless point. Now, since space is defined within this region and then the universe itself defines space, it can not expand into space but rather it's space is growing or expanding. At this point I guess I can say that Space/Time is localize to this region and expanding relative to every point within the region.

    Now, if I run the process backwards, the space-time within this region would collapse into super dense stuff; but the outside observer not notice anything different until the space inside the point, or region to us, becomes so dense that it collapses and plops out of existence. At this point observer would think he was seeing things because it would have vanish as quickly as it appeared, if it did at all.

    But I guess the stuff our universe, region or point, to observer, persists in is of no consequence since we or any law of classical or QM physics could exist there anyway. Our world and laws are inside this infinitely small but vast point. But still I wish I could somehow how see it anyway.

    In second to last paragraph I said space-time collapses because, purely intuitively, I think that Time and Gravity were once unified but somehow broke apart.
     
    Last edited: Sep 29, 2009
  11. The Big Bang didn't come into existence since nothing existed. Also this observer which I assume is made of nothing but can still interpret things(...some how...i feel kind of bad saying that last sentence) wouldn't see the actual big bang unless he could see pure energy then Gamma rays, X-rays and ultraviolet then finally light which we can see.
     
  12. he is a pseudo hypothetical being I made up for illustrative purposes. Hmm, i would have met the region of space came into plopped into existence. But citing those few discrepencies I guess my understanding must be nearly correct since you had simple quibbles about post.
     
  13. If (which is very likely) our universe is infinite now, then it ALWAYS was infinite, and the initial singularity was still INFINITELY BIG in size. Singulary is not (always) a point!

    Singularity IS NOT a region. ALL places of the universe were in the same conditions. There were never "in" and "out" of the expanding region. All regions were the same. It is important.
     
  14. I totally agree with this. Who says "WE" originated in a dimensionless point? A "dimensionless point" (ie singularity) is usually indicative of a flaw in our mathematics & logic.

    Either we started with an infinite Big Bang (?), or we are "bouncing" back from a previous (finite) >4D-collapse...(is what I say).

    Infinity (like singularities) does not make much cerebral sense. After all, we (our "minds") are part of the universe, and we don't see "infinities" nor "infinitesimal dimensionless points".

    I think it's likely that the universe is "bouncing" (breathing) and is an organic entity. We are the neurons/synapses in this Universe's brain. We are the Universe's self-awareness.

    The closest I come to this idea theoreticized is Smolin's theories.

    Or maybe I'm stoned, who knows.
     
  15. Those aren't just discrepancies, those are HUGE parts of understanding the Big Bang based on current theory.
     
  16. So there must be some kind of boundary between created space, and not yet created space?
     
  17. sylas

    sylas 1,745
    Science Advisor

    No. "created space" in this context just means that there's more space between things.

    On sufficiently small scales (a couple of hundred million light years, perhaps) it is no different to things moving apart from each other in the way we are used to. On larger scales, you have to describe space and movements and expansion with general relativity, which doesn't always fit nicely with initial expectations or intuitions; but in general, it's still just everything moving apart from everything else, with no center, and no boundary apparent or implied.

    Cheers -- sylas
     
  18. So it is expanding into its future self. There must be some propagation front that we can describe. Does GR strictly implies that it does not exist?
     
  19. sylas

    sylas 1,745
    Science Advisor

    The term "propagation front" is not well defined. In the normal sense of the word, no there does not have to be a propagation front.

    But I guess you might be able to think of "time" as a "propagation front". There is no location of a front in space; but all of space is expanding as time passes. This just means there is more space in between things; subject of course to the fact that objects are also moving with their own peculiar motions and gravitationally bound conglomerations like a galaxy don't expand.

    I suspect you are still holding on to misleading metaphors and analogies with an explosion of material out from a point. You have to drop that idea; it's wrong. And you're probably best to forget about trying to shoehorn the idea of a propagation front into cosmological expansion. It's terminology that is bound to mislead.

    Felicitations -- sylas
     
  20. Thanks sylas. If I understand this correctly galaxies are not moving apart because expanding space is exerting force on them which overcomes gravity, but simply because more space is being "stuffed" in between them?
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?