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I What is time?

  1. Apr 2, 2016 #1
    I'm wondering if time is just a way we have to "measure" how things change its characteristics in space. Is that correct?
     
  2. jcsd
  3. Apr 2, 2016 #2

    andrewkirk

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    'What is time' is a philosophical question, not a scientific one. Science concerns itself simply with the performance of time and its relationship with other observables.

    If you are interested in questions of what time 'is', you might like to look into the history of the competing views of Henri Bergson and Albert Einstein in the early 20th century. There's a temptation to say that Einstein must have been correct, because he was such a great physicist. But that does not necessarily follow, as the controversy was not about physics but rather the interpretation of physics.

    I am closer to Einstein's view than Bergson's, but that's just an aesthetic preference. In the final analysis, I think the question 'what is time?' dissolves into meaninglessness.

    There's a book about the controversy here and a podcast that discusses it here.
     
  4. Apr 2, 2016 #3
    (sorry for my poor english) I'm not trying to analyze it from a philosophical point of view but instead I'm trying to understand what is the physical meaning of time. I think it could be explained in terms of self change of things through space. If you have, say, a body wich never changes itself, then the time is not running for that body. But, yet, that body could be moving freely through space. What I'm doing here is trying to analyze the time from this point of view. Why would this reasoning be wrong?
     
  5. Apr 2, 2016 #4

    Drakkith

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    Time is always running for all objects, regardless of whether they are "changing themselves" or not.
     
  6. Apr 2, 2016 #5

    andrewkirk

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    What does that mean?
    There is no physical meaning of time (or of anything else), because meaning is not physical. When you inquire into meaning, you are doing philosophy not science, regardless of whether that was your intent.
     
  7. Apr 2, 2016 #6
    What about photons?
     
  8. Apr 2, 2016 #7
    I'm just going to give the complicated answer:
    Time is defined in relativity in an odd way. Technically, time actually doesn't exist on its own, it is part of spacetime. In fact, space and time work very similarly. Both can be stretched or contracted (in a sense) by high velocities, both can be curved by gravity, and both can be measured in meters (technically time is measured in lightseconds, but if you just call it about 3*10^8 meters, they are both measured in meters). That last one is a little confusing, but it makes sense if you think about it. How can you have one combined spacetime if space and time are measured in different units? If you multiply the time axis by the speed of light c, you will get the ct axis. By doing dimensional analysis, you will get the dimensions of length. And now to focus on my other points, time is not fixed, it is relative. Gravity makes time feel slower for you (I'm pretty sure, mentors please correct me if I'm wrong), and high velocities make you feel like time is slower for people not going as fast as you (and if you are traveling with a high velocity relative to someone else, you will think that person is experiencing time slower while he/she will think time is running slower for you). So that's time (probably a little more complicated than you expected :wink:).
     
  9. Apr 3, 2016 #8
    Time is the ongoing sequence of events taking place.
     
  10. Apr 3, 2016 #9

    Drakkith

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    I'm going to close this thread before it attracts crackpots and misinformation (as threads on time usually do).
    I think the wikipedia article on time provides a pretty nice explanation of what we consider time to be and the difficulties associated with trying to precisely define it. Give it a read if you haven't already.

    Thread locked.
     
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