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Is this too broad a statement?

  1. Sep 15, 2005 #1
    Since expanding space is not limited to the speed of light, there is no limit to how fast space itself can travel. This can be described as the relative speed between space and nothingness. Anyone think it's too broad a statement to say that infinity is the relationship between space and nothingness?
  2. jcsd
  3. Sep 15, 2005 #2
    I don't think its too broad. Of course, I don't think it makes any sense, either.
  4. Sep 15, 2005 #3


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    Space is not travelling it is expanding, and it isn't expanding into nothingness or into anything else, This is all happening within spacetime; things are getting farther apart, without themselves moving.
  5. Sep 16, 2005 #4
  6. Sep 16, 2005 #5
    There are no compelling reasons to think that our
    universe is infinite, in any sense.

    Suppose that the speed of light is a consequence of,
    and directly proportional to, the the rate of expansion
    in any arbitrarily circumscribed region of our universe.
    (That rate might increase as you get closer to the edge
    of our universe.) The edge of our universe (in a big bang
    scenario) might be viewed as the wave front of the shock
    wave that is still moving isotropically away from the source
    (the explosion that marks the beginning of our universe).
    There's no way to know the exact volume or shape of the
    original big bang -- just that it was appreciably smaller than
    the visible universe. And, there's no way to know the
    exact volume or shape of our universe -- just that it's
    appreciably larger than the visible universe. (There are
    some good reasons to think that, if it's finite, then it's
    more or less spherical -- and if it's rotating, then the
    sphere will tend to flatten out and become eliptical
    in the plane perpendicular to the primary rotational axis.)

    Assuming that a finite amount of kinetic energy was
    imparted via the big bang, and assuming that the
    'fundamental' medium in which the universal wave front
    produced by the the big bang is moving has some physical
    properties (even though they might remain forever
    undetectable as far as we're concerned), then it's
    reasonable to assume that the universe will eventually

    Accepting a big bang scenario means that our universe
    is a disturbance in some encompassing medium -- a
    medium which is more fundamental than the interacting
    particulate media (the flotsam and jetsam that is the
    wake of the expanding universal wave) that we call our
    physical reality.

    However, since infinity might be taken to refer to an
    unmeasurable extension of some physical process or
    parameter, then your statement that,
    space/nothingness = infinity is about as 'meaningful' as
    anything else I've read on the origins and fates, or
    nature, of our universe -- including, even though there
    is a certain logical chain of reasoning associated with it,
    what I wrote here. :-)
    Last edited: Sep 16, 2005
  7. Sep 16, 2005 #6
    That's true. However, I checked out the link you provided.
    I didn't like the example of the ant on the surface of a balloon
    as an analogy to there being no edge or boundary to our
    universe. We're not travelling on the edge of our universe.
    We're inside it. It could very well have an edge -- a sort of
    gradual interface with the medium that it's expanding in.
    But, we can never reach the edge, because the propagational
    speed of disturbances in our universe is limited by the rate
    of expansion which is more or less equivalent to the speed
    of light in a vacuum. That's an assumption of course, but I
    think it's a good one. Think of it as the fundamental physical
    law. The expansion is what inertia *is*. It's why there's *any*
    motion at all.
  8. Sep 16, 2005 #7
    What I am having trouble wrapping my head around is that if the speed of expantion of the universe is not limited to the speed of light and my statement is true, then wouldn't space expand to everywhere that it possibly could instantaniously (with infinite speed)? If the universe is in fact still expanding then this doesn't hold true for some reason.
    When I picture the expansion of the universe it's just like you say, Sherlock. A shock wave at the edge moving away from it's source (the BB) into some medium which I am calling nothingness for convenience. Perhaps I have answered my own question in that the we can describe the speed of this shockwave as infinite only because of it's speed relative to nothingness. It's like saying at what speed may the entire universe move? Move compared to what? Although it is nonsensical I think it is useful as a tool to visualize speed 'relative to nothingness' as infinite.
    Is the rate of expansion in fact infinite or only some speed faster than light?
    If it is infinite then how can space still be expanding?
  9. Sep 16, 2005 #8
    Well, there are some good reasons to think that our
    universe is expanding, and at a finite rate. And, afaik, the
    rate of expansion is pretty close to the speed of light.
    (But, I don't know for sure, so that's a question we can ask
    in the cosmology forum. I'll bet it's already been asked and
    answered somewhere in the archives. If I get time tonight
    I'll do a search.)

    Anyway, your conjecture about infinite, instantaneous expansion
    would seem to be contradicted by observations.

    Assuming that our universe is roughly spherical and finite, the
    universal rate of expansion would be the increase in the
    radius of the universal wave front per unit of time.

    You wouldn't necessarily have to know the radius of the
    entire universe to calculate the rate of expansion for some
    region smaller than that. You'd just need some way to
    measure the distance between objects on a scale
    encompassing, say, groups of galaxies.

    "Nothingness" is as good a word as any for whatever
    our universe is expanding into. We can't measure
    anything relative to that. But, we can compare some
    measurement of objects in our universe at a time, t, to
    another measurement of objects in our universe
    at a time, delta t, to get some idea of the velocity
    of the expansion.

    As I mentioned, afaik, the rate of expansion is, apparently,
    finite and possibly closely linked to the speed of light in a vacuum.
    As for the extent and lifetime of the expansion, who knows.
    It doesn't seem likely that mankind will have any good
    answers to these questions during our existence.

    And, apparently, the expansion is accelerating, which is a puzzle.

    So, we've got some good questions to ask the astronomers
    and cosmologists. :-)
  10. Sep 16, 2005 #9
    Statements such as this are never backed up with any degree of certainty. Frankly I'm getting tired of it, because it's repeated so often. You could spit out a few references that fall a buck short of definitive, as if to say this is enough to state the expansion of space as a categorical fact.

    I beg to differ.
  11. Sep 17, 2005 #10
    How can things get farther apart without moving?
    Isn't things getting farther apart or getting closer
    together how we define/detect motion?
    Would it be better to say that the motion (or some
    portion thereof) of some objects is assumed to be
    due to the expansion of space? If so, which objects,
    and why?
  12. Oct 2, 2005 #11
    Thats a very classical physics way of thinking.

    Please stop doing that lol
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