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

Why does time expand?

  1. Jul 9, 2008 #1
    Why are we constantly traveling into the future? Doesn't this suggest that not only space is expanding, but spacetime is expanding as a whole?
  2. jcsd
  3. Jul 9, 2008 #2
    No it does not. A given spacetime does not change under GR.
  4. Jul 9, 2008 #3
    That wasn't my question. Why are we constantly traveling into the future?
  5. Jul 9, 2008 #4
    Perhaps such a "why" question is better asked in the philosophy section of the forum.

    At any rate this has nothing to do with "expansion" of time.
  6. Jul 9, 2008 #5
    I used the word expansion to describe the motion of time moving into the future; There has to be some accepted theory of why time continues to expand, isn't there?
  7. Jul 9, 2008 #6


    User Avatar

    Staff: Mentor

    Just choosing to use the word doesn't make it right - it isn't an arbitrary choice. You suggested a comparison to the expansion of space. That's not a valid comparison. Time doesn't expand. A better word is flow. Time flows. Why? Dunno. As said, that may just be a matter of philosophy.
  8. Jul 9, 2008 #7
    Flow sounds right because its been used in the context of describing time before. You could just as well describe the movement of time as expanding. (You're not thinking of it in the right way anyways, but that's not the point)

    It's hard to believe that there are no theories on this, considering all of the other theories out there; In reality it's not a matter of philosophy.
  9. Jul 10, 2008 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    I'm moving this to philosophy, since the topic is not related to Cosmology. You might want to have a read of, say, The River of Time by Igor Novikov: it's quite a good book on the nature of time.
  10. Jul 10, 2008 #9
    Time is a mental representation of change; some say that time is a "measurement" of change. The complete absence of any change anywhere in the universe would mean no time, so a more fundamental question is: why does change happen?

    The question "why" asks for a cause. But if a cause for change ever existed then it would be the cause for a change from the universe going from a state of "no change" into a state of "some change". Of course, this would already be a change, so the cause would not really be a cause of change since such a change is already assumed in the question. This circular assumption invalidates the question. A cause of change cannot be stated, so a cause for time cannot be given either. The question simply does not apply to change (and time).

    See a similar discussion about https://www.physicsforums.com/showthread.php?t=171193" Asking for the cause of existence asumes that such a cause could exist already, which makes this question meaningless as well. Existence and change are both undeniable and "why-proof" realities.
    Last edited by a moderator: Apr 23, 2017
  11. Jul 10, 2008 #10
    What you are referring to is the "arrow of time".

    Acc. to some physicists this is caused by the breakdown of a symmetrie which happened at the big bang.
  12. Jul 10, 2008 #11
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook