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Is the universe infinite?

  1. Aug 23, 2003 #1

    In terms of the cosmos, which I think is the right word I need to describe 'what's out there', would it be fair to say that infinity exists? I mean, even if the universe was not infinite and was some sort of expanding phenomena, or was circular, it must be expanding against something or, if circular, surrounded by something. So 'somethingness' just goes on and on and on....maybe changing shape or form or just void...but infinity, in this sense, exists?
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  3. Aug 23, 2003 #2

    Contrary to what some might say, infinite does not exist in reality. There is not a single thing known to be at infinite.

    No scalars, and no vectors. No speeds no quantities, no nothing. There is no empirical evidence to suggest anything in existance carries a value of infinity.

    Without this evidence infinity is merely a concept created in the human mind.
  4. Aug 23, 2003 #3
    ...and this directly fits into what you described. If we say for instance that the universe currently fits into finite amounts (which it does) then you say what about beyond the universe?

    That's part of the human experience - that many cannot accept non-existance.

    Beyond our universe - if we are the only one - lies ______.

    I didn't say lies nothing, because it's not nothing. Technically it is not something and it is not nothing. Nothing is a lack of something - but this is so much more than a lack of nothing!

    It breaches existance and pretty the ability to understand. It's like an unspoken non-coordinate. "Nothing" is in fact part of existance. But what is beyond that isn't in existance!
  5. Aug 23, 2003 #4
    That was a speedy reply. Thankyou.

    It is a conceptual problem isn't it? Nothingness and infinity are both creations of the human mind.

    But I still can not help but arrive at the conclusion that there is no end...no finality.

    Being a conceptual problem, it's also a problem of language, I guess. Like the theory of parallel universes...there is only one universe, really, with possible multi-variations.
  6. Aug 23, 2003 #5
    Well I wouldn't say it's necessarily a problem. It's a matter of creative thinking I guess. It's a problem when people fight the truth with it :)

    Well with the entire parallel universe thing, I gather what happened was the meaning of the term universe changed, or adapted I should say!

    Universe meant everything, before.

    Now it's used to mean the entirity of one everything. Because remember between each universe of everything is that ___ nothingness I mentioned earlier.

    So we kind of moved from using it as a term for all that is, was, and will be, to a practical term distinquishes one entire closed system from another.
  7. Aug 23, 2003 #6


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    I believe the root meaning of infinity is "unboundedness"

    If one can specify a bound on something then it is is finite-----goes only this far and no further

    If one cannot specify a bound to the thing then it is unbounded or non-finite.

    Latin noun: finis----boundary, limit
    Latin verb: finire----to set a bound, to limit

    Some people (children, mathematicians) may speak of "infinity" as a number---as if some physical quantity could have "value equal to infinity"---but that is apt to be either a specialized technical use of the word or an innocent misconception. In its commonplace meaning, infinity is not a number but simply the absence of boundaries and limits.

    It would strike me as absurdly pretentious to claim that one can assign bounds to all physical quantities or that all quantities are bounded. I don't know if anyone here is doing that.

    In conventional cosmology there is no upper bound on the distance between two objects in space

    if you choose two specific objects, the distance between them can be some definite quantity, but the set of possible distances is not considered to have an upper limit

    assuming a limit would complicate things----unnecessary conceptual baggage

    carla, I am sure you know the principle of Occam's razor, but please reassure me that you do! The unboundedness of some physical quantities is assumed, I would guess, very largely for reasons of SIMPLICITY (because introducing bounds where we do not know they exist would be to add a lot of clumsy unnecessary paraphernalia---a lot of junk).

    And there are quantities actually known to be bounded, where one can specifically say what the bound is, which is great! But lets not generalize from that and pretend to know an upper limit for everything.
  8. Aug 23, 2003 #7
    I know what Occam's razor is now. Thanks. That's actually useful information.
  9. Aug 23, 2003 #8


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    In general usage I would agree. But that may be changing. In cosmology, the concept of a "finite but boundless" universe is a familiar idea. As cosmological concepts become popularised in mainstream society, the idea is making its way into the public mind.

    It's a bit dogy to describe, though, and can be said to merely move the "boundary" to a higher dimension.
  10. Aug 23, 2003 #9


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    Not sure where this is much about Physics, I'll bump it to math, perhaps should be in General.
  11. Aug 23, 2003 #10
    In the empirical sense, infinity does not exist.

    But what is against the idea that the universe carries onwards in time without a begin or end?

    It can't be obviously measured, it can only be infered from:
    - causality
    - conservation of energy/mass

    And a logic argument pro no-begin of time and no-end of time is this:

    If the world (all that exists) is said to have had a begin in time, then all it can have begun from is from nothing.

    But nothing is not a begin. Nothing is only nothing.
  12. Aug 23, 2003 #11
    Heusdens - the second half of your post is nonsensical. This is an argument too many people attempt to use, this "nothing can come from nothing" thing which doesn't work in the real world.

    The first half is fine.

    Let's recall that the big bang is the energy source of the universe expanding.

    The big bang expanding created the spacial dimensions - thus the universe is finite. It's that simple.

    In short - the Big Bang could not have occured if the universe is infinite - and the Big Bang has mounds of evidence.

  13. Aug 23, 2003 #12


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    The "Big Bang" is merely an event where the entirety of the observable universe was compressed into a highly dense volume, it is not the "creation" of the universe, as it is often misinterpreted. The big bang is consistent with, but does not require, an infinite universe.
  14. Aug 23, 2003 #13

    This just sounds nonsensical with anything I have ever heard.

    The Big Bang has never had anything to do with compression, but just the opposite. I've read plenty of Big Bang explanations including Hawking - never heard him mention anything but the opposite of what you just said.

    And also that indeed the big bang does NOT coincide with an infinite universe.
  15. Aug 23, 2003 #14


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    It seems my use of the word "compression" was misleading; I meant by that sentence that the observable universe was once in a highly dense region of space-time.

    "A highly dense region of space-time" (which, of course, promptly expands) is certainly not prohibited from existing in an infinite universe.
  16. Aug 23, 2003 #15
    Well then if it was once more concentrated - and now it is less concentrated, and continueing to expand - how could it be infinite?

    It can't be expanding if it's infinite, and it could never have been compressed if it isi infinite.
  17. Aug 24, 2003 #16
    Endless nothing. Endlessness. Nothing ad infinitum. Foreverness. Or just..endless. It's not a useful idea but something that has always fascinated me nevertheless. I know science requires concepts it can work with, which are useful to the human mind; empiricism, need to be able to be quantified in some way in order to fulfill scientific enquiry. It's a conceptual problem. It is impossible to even find words to adequately describe what is in my head. It almost slips into mysticism. Simply beyond reach.
  18. Aug 24, 2003 #17


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    Infinite space can most certainly expand; expansion of space is defined locally, not globally. (A region of) Space is expanding iff nearby parallel geodesics tend to start diverging after a short period of time. Heuristically, it means that tiny dust clouds tend to grow in volume over time.

    Anyways, BBT says nothing about the entire universe, just the observable universe. It asserts that some time in the distant past, our past light-cone enclosed a tiny volume.

    BBT does not require that tiny volume to have been the entirety of the universe, nor does it require that the entire universe to "simultaneously" be similarly dense.
  19. Aug 24, 2003 #18
    You it is "our" light-cone, meaning we are lying in a region of space which comes from the expansion of this light-cone.

    If our light-cone was enclosed in a tiny volume, and is now NOT in that tiny volume - it has expanded. Locally.

    And if our local space-section is expanding, it cannot be infinite.

    Thus if the universe were to be infinite, it could not ONLY be the results of our own expanding light-cone.

    But because our expanding light defines the spacial properties and thus the universe of our expansion (because there were no spacial dimensions in this location before the existance of the matter - this comes from Greene) could not possibly be infinite.

    Even if it collided with zillions of other universes, none of them could be infinite, thus the total could not be infinite.

  20. Aug 24, 2003 #19


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    I will agree that the observable universe must be finite...

    But I'm troubled by "because there were no spacial dimensions in this location before the existance of the matter - this comes from Greene"; I presume this is a statement of some sort of relativity that you can't make measurements without a reference to compare them against, but the gravitational field itself can serve to be a reference, even in the absense of matter.

    It's also curious why you would bring this up anyways; BBT does not claim matter did not exist before the BB, yet you seem to imply that you think otherwise.

    I'm not sure what you mean by colliding...

    And while it is true that a finite collection of finite objects is finite, why would you think that the collection is finite?
  21. Aug 24, 2003 #20
    Hi Carla,

    I think that Quantum Mechanics gave us a very important insight about ourselves.

    We are no longer observers but full participators in our world, and there is a complementary relation between our internal end external sides.

    To every thinkable concept there is an opposite and among any system of opposites there is a potential balance.

    And beyond any balance the unthinkable.

    And beyond the unthinkable

    And beyond


    Last edited by a moderator: Aug 24, 2003
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