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

What is time?

  1. Oct 8, 2011 #1
    What is time??
  2. jcsd
  3. Oct 8, 2011 #2


    Staff: Mentor

    It is the thing referred to by the "t" in many physics formulas.
  4. Oct 8, 2011 #3


    User Avatar
    Science Advisor
    Gold Member

  5. Oct 8, 2011 #4
  6. Oct 8, 2011 #5
    An evolution parameter.
  7. Oct 8, 2011 #6
    Time is a value we use to chronicle changes in matter.
  8. Oct 9, 2011 #7
    It's the same stuff as space, but different.
  9. Oct 9, 2011 #8
    Time is the rate at which things change. Some perceive it as fast others slow. It is said that if we were capable of travelling at the speed of light time would stop.
  10. Oct 9, 2011 #9
    So you think time has a relative velocity. Care to clarify this-- you know, as the ratio of one thing compared to another. What are you comparing?
  11. Oct 9, 2011 #10
    time is another dimension of space in which all particles in the universe move in one direction only .but because all particles around us move in time with approximately the same velocity we find it hard to visualize time as a dimension of our universe.
  12. Oct 9, 2011 #11
    The time as we perceive is relative to the observer. The biological time is constant, which is the rate at which we live. If we where to go outer space and travel at speed near the speed of light we would age less compared to people on earth, thus "travelling into the future". When we came back everyone would of aged much more.

    Gravity also influences time, it is well known that due to the gravity force or field that satelites "time" is slower than earth time. That is why the GPS (Global Positioning System) time has to be adjusted.
  13. Oct 9, 2011 #12
    Whao, all of this are new information. thanks they help alot=D
    But one more question, if time is (space ,other dimensions that things travel to one direction.), What is before time? If time is what is mention, anything that happen before that should not even happen. Hence if that did not happen how does time even start?
  14. Oct 9, 2011 #13
    Nobody knows, if anyone states anything it is only a theory. In my opinion we will never know, but we will eventually get closer...

    I believe everything has always existed, we are just newcomers to this reality.
  15. Oct 9, 2011 #14


    Staff: Mentor

    The question is nonsensical. Time defines before and after, so it doesn't make sense to ask what is before time. That is like asking "what is north of lattitude".
  16. Oct 10, 2011 #15
    I think that what he means is what happened before the big bang which is our time reference (13.7 billion years ago).
  17. Oct 10, 2011 #16
    You didn't get my point. Time, as you use the word, is not a rate, nor is there something like a "biological time constant" that measures elasped time.

    Anyway, sure: elapsed time differs for different observers.
  18. Oct 10, 2011 #17
    Time is separation in space-like points in spacetime. The more separation the space-like points (i.e. the less dense the spacetime), the faster the relative rate of time. (This is seen with gravitational time dilation.) If there is no separation between space-like points--like at a singularity of a black hole--time does not pass.

    Thus, before the Big Bang came out of singularity, there was no separation in space-like points, so time was not passing.

    Only if there was an event preceding the big bang, in which there was separation (i.e. a contracting cycle, or 'big crunch') time didn't ever pass prior to the instant the big bang came out of singularity.
  19. Oct 10, 2011 #18


    Staff: Mentor

    To our current understanding that is like asking "what is north of the north pole."
  20. Oct 10, 2011 #19
    Easy, south pole.

    Maybe the question "what was before time?" implied a frame of reference different from the one without time. i.e. looking at a black hole from Earth. (your statement regarding north of north pole implies same thing, otherwise south pole is right)
    Last edited: Oct 10, 2011
  21. Oct 10, 2011 #20


    Staff: Mentor

    In what way is the south pole north of the north pole? The south pole is, by definition, not north of anything.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: What is time?
  1. What is Time? (Replies: 4)

  2. What is time? (Replies: 8)

  3. What is space-time? (Replies: 12)

  4. Time dilation. Um, what? (Replies: 57)

  5. What time is it? (Replies: 5)