Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Infinite, or finite universe

  1. Jun 20, 2004 #1
    Is there any proof whatsoever leading to our universe being infinite? If there was, is it even possible for finite beings (us) to exist in something infinite? The universe must be either infinite, expanding, unchanging, or contracting, because anything that is infinite cannot expand any more, for there is no end to it. Also, does the word infinite mean to expand forever, and if it does, then what rate is it expanding? Or does it mean to exist as something with no end. I shouldn't expect an answer to this question because finite beings cannot understand the infinite. Some say that are universe is 1 dimensional to the 3rd power. How could this be so? 1 to the third is still 1, and what is 1 dimensional? how could something only have 1 side? PLEASE try to explain some of these things, any explanation would be appreciated.

  2. jcsd
  3. Jun 20, 2004 #2


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    It's not true that something infinite can't expand, in the meaning of expand that cosmologists use. Take an infinite line with tick marks every inch. Now multiply all the distances on the line by two ("expanding" in the sense of cosmology). The tick marks are now two inches apart, and the line is still infinite.

    Now think of 4 dimensional spacetime instead of the line, and galaxies instead of tick marks.

    Your difficulty is thinking that expand means the same thing for an infinite continuum as for a finite one.

    But no, there is no hard evidence that the universe is infinite. Still that possibility cannot be ruled out.
  4. Jun 20, 2004 #3
    Thank you for your response. The way that you mentioned looking at expanding is different in the way that I look at it as "stretching the ends" of a number line, with the tick marks neither decreasing or increasing, and you look at it as merely increasing the intervals. That is interesting. I haven't thought of it that way before. But back to another one of my questions-Is it possible for something finite to exist in something infinite? If no, then the possibility of an infinite universe is impossible. How would you set intervals on something such as the universe? Or are you saying that the distance between objects such as planets would increase? Also, could you explain 4 dimensional? And what do you think about the 1 to the 3rd theory.
  5. Jun 20, 2004 #4
    finite has an end;infinite has no end.at this time im thinking what 'thing' is infinite;maybe life is. :redface:
  6. Jun 20, 2004 #5


    User Avatar
    Science Advisor

    You might be interested in reading up on Olbers' paradox, if you have not done so already. Olbers thought that the fact that the night sky is dark implies that space is finite in size. I think there are several modern objections to that reasoning. One is that space could be infinite in size but finite in its current age. Another is that space could be infinite and expanding, as I recall. Selfadjoint has pointed out that expanding infinite space is not oxymoronic. There may be other objections too, having to do with interstellar dust or something.
  7. Jun 20, 2004 #6


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    I believe the standard explanation for the dark sky is that most of the light has not reached us. Olbers' argument sort of tacitly assumed the speed of light was infinite.
  8. Jun 20, 2004 #7


    User Avatar
    Science Advisor

    Right, finite (low) in age plus finite speed of light leaves the night sky dark, even if space were infinite in volume.
  9. Jun 21, 2004 #8
    If space/time came into existence with BB, how could the cosmos be of infinite volume? Does this imply that the term "infinite" has a meaning other than the obvious implications? I also had a problem with the term "singulatarity" until I became more familiar with the physics definition.
  10. Jun 21, 2004 #9
    well i have one thing to say thats semi-relavent and may spark interest

    the universe is only finite in its infinite capacities
  11. Jun 21, 2004 #10
    I like to think that all infinity is is an infinite collection of finite systems. One could also ask, I suggest, that if there is no infinity, how can we imagine it to be so? what refrence could we ever have? Our minds can be infinite, yes, but how can a finite system contain the infinite?

    it appears that universe is either infinite, containing an infinite number of finite systems, or, it is finite, containing a finite number of infinite systems...which seems much more difficult to grasp than infinity itself.

    Also, our 'universe' which sprang from the big bang may only have been a portion of universe that expanded out. are there super universes?

    If universe is infinite, as opposed to finite, i dont think many also realises what that may suggest about us as a species, for anything that can happen in an infinite set DOES happen an infinite number of times.....

  12. Jun 22, 2004 #11
    as I see it, the universe is finite. Someone once defined the universe as the collection of all possible trajectories. SInce there is a universal limiting speed, c, the universe has a volume given by (4/3)*pie*(cT)^3. Of course, if there was only an instant in the history of the universe when the limiting speed was infinite, the universe would also be infinite. But in this construction, space is being built as time passes.
  13. Jun 22, 2004 #12


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    The speed limit c does not apply to the rate of spacetime expansion, since that is not a speed. Speed is the rate of crossing space. But space in expanding doesn't cross itself, so its rate of expansion isn't a speed. And cosmologists are convinced that
    1. At time in the past space expanded a lot faster than c (inflation).
    2. Galaxies we see today are receding from us (not actually travelling but the space between is expanding) faster than c.
  14. Jun 22, 2004 #13
    What I meant is that nothing will be "outside" the light cone with its vertice at the big bang. Thus, if we define the universe as everything, since nothing can be at the other side of the cone, the universe is finite in 4-volume.
  15. Jun 22, 2004 #14


    User Avatar

    I vaguelly remember reading that E.A. Poe (writer) gave the first logicaly valid treatment about sky darkness paradox .In his time it was known that speed of light was finite.
  16. Jun 22, 2004 #15
    The best place to look is Stephen Hawkings book 'A Brief History Thourgh Time'. He goes through 4 different state and proves each wrong one at a tmie leaeving it open. Makes you think though and will help you to formulate your own ideas.

    The Bob (2004 ©)
  17. Jun 26, 2004 #16
    btw moonrat, i believe our minds or finite, just that there capacity is so large itd be very difficult to fill - also if the universe is expanding TECHNICALLY its finite because it is possible (not at this time meybe) to calculate its volume or what-not

    because to expand is to grow in a sense and that means day 1 cude has 1 foot volume day 2 cube has 1.5 ft volume

    or maybe im perceiving this wrong?
  18. Jun 27, 2004 #17
    percieving is a good choice of words. the mind can most certainly experiance and expand out into infinity. If it cant, then it is only because there is a finite concept or belief that it has prevented it from doing so.

    infinity is just continuous. there is a state of mind that matches that, how else could there even be a concept of infinity if it did not? (such is my suggestion)

    infinity is difficult perhaps to percieve because it has no end point, and the beginning can be anywhere from a personal point of view, but nowhere from an objective point of view.

    a 'finite' is only a container. the mind does not contain the objects of universal reality, but it definatly creates them for the subject's point of view. the mind can continue on in doing this......

    once you have experianced an infinite mind state, then it will be more difficult and impossible to percieve how their could NOT be infinity.

    Now, I do not say that this proves universal enviroment is infinite, my only suggestion is how could it not be if the mind CAN be continuous?

    would that not be the same things as a infinite set existing inside of a finite? (which is impossible, no?)

    I also suggest that an infinite universal enviroment creates a completly different model of what universe is up to than a finite model. For example, if universe is infinite, then that raises many questions about the nature of intellgence itself, questions that are not raised in a finite set....

    when their is infinitity, at least percieved to be, then the mind has complete open space to expand perspectives.....
  19. Jun 27, 2004 #18
    couldnt we measure the universe if we found out how fast its expanding (we may know this i dunno tho)

    like sommit in programming terms like you have an equation like this -

    x=size of universe at 6/27/2004 9:25:37.45.67(etc etc)
    y=rate of expantion per second
    z=current universe size


    or am i going insane?
  20. Jun 27, 2004 #19
    Well, right now, as far as I know, we do have measurments for the expansion and extension, but also these measurements are just reading as far as they can currently percieve, and then again, that is just measuring that which is expanding, not anything else. For example, at the moment of big bang, did the universe expand, or just a portion of universe?

    hehe, I dont think we can code that yet! I mean, just recently we discovered the the universe is expanding more than we thought, and the collapse seem less likely, even though our current understanding says it should collapse..

    We dont know...it is mystery still.

    and mystery is infinite, so here we arrive at it again.

    if you feel like your going nuts, go nuts! it is a perfect way to escape the linear finite artistolian universe. It is not infinity that is driving you nuts, it is finity that is driving you nuts....

    The mind knows what to do with mystery and the infinite naturally. The finite restricts it and creates irrational boundries and all sorts of things...

    chaos man, you know, have fun with the chaos (infinite) and create the order (finite)

    imagine an infinite number of finite systems, and you get both...

  21. Jun 28, 2004 #20
    also this has a little connection with a post i made in the proof of god forum but it has relavence to this also

    what if the universe has a sort of mind type ability and expands at a rate to comprably equip each organism, course this may be wrong, but isnt the universe rapidly expanding at huge intervals? which would coincide with just the human population skyrocket,

    but this is just an idea, no idea if it has applicability or not
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook