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Why does time slow down the faster you go?

  1. Dec 8, 2011 #1
    Or is this only true when I am viewing someone else's clock?

    Why does time slow down the faster something travels?

    How could this apply to the Earth? How would our time on Earth slow down? Would the Earth have to be rotating faster and revolving faster around the Sun?
     
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  3. Dec 8, 2011 #2
    It's just like politics. Your own clock is always right. It's always the other guy's clock that is wrong.

    The other guy's time slows down in order to preserve the laws of physics. If it didn't slow down, the laws of physic would not be preserved and things would be messier than they are.

    Time is almost exactly the same at sea level, everywhere on the surface of the Earth. Gravity is more at the poles, though.
     
    Last edited: Dec 8, 2011
  4. Dec 8, 2011 #3

    PAllen

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    You are in good company - Einstein was initially confused about this (though his confusion was the revers of yours - he thought time would run slower at the equator, due to rotation speed).

    The reality is that the geoid (surface) conforms to be an equipotential surface (this will be true for any body that is shaped by its self gravity - part of the definition of a planet). The oblateness (leading to less gravitational time dilation) at the equator cancels rotational time dilation, so there is no difference (on average) between time flow at the poles versus the equator.

    [EDIT: I see this is what you meant. So we are in agreement.]
     
    Last edited: Dec 8, 2011
  5. Dec 8, 2011 #4

    ghwellsjr

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    He wasn't confused and he was right in what he said concerning Special Relativity in 1905, long before anyone had yet thought of General Relativity:
    He was predicting for the first time what became known as the Twin Paradox and for you to say he was confused makes as much sense as someone complaining about the Earth twin being stationary when we all know that the Earth revolves around the Sun.
     
  6. Dec 8, 2011 #5

    PAllen

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    Ok, you are right. There are many accounts of this around as a mistake by Einstein, but in historical context it was not. It was a mistaken prediction, but not a misunderstanding of what was then known.
     
  7. Dec 8, 2011 #6

    ghwellsjr

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    It wasn't a mistaken prediction. He said, "under otherwise identical conditions", which means, all other things being equal. It's no different than everyone else ignoring gravity or the earth not being in the same place when they talk about the Twin Paradox.
     
  8. Dec 8, 2011 #7

    PAllen

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    Now you're quibbling. If cesium clocks existed in 1906, and the experiment were performed to validate SR, it would have been recorded by history as a mistaken prediction (later explained by the development of GR). Scientific history is filled with such incidents - predictions correct based on what was known that turn out wrong due to phenomena not yet known. We don't have to deify Einstein and not use the same language we do for similar historical cases.
     
  9. Dec 8, 2011 #8
    In SR time is only slowing down for the other frame of reference and vice versa?

    But isn't it true that time is actually slower in some places than in others? For instance clocks tick slower at sea level than they do at higher altitudes although not by much.
     
  10. Dec 8, 2011 #9

    PAllen

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    In SR, if you start with clocks together, separate them, and bring them together, they will generally differ (the path with greater deviation form an inertial path will accumulate less time). The exact same thing is true in GR.

    In SR, mutual observation of inertial clocks is symmetric - each sees the other slower. In GR, this is still true for 'nearby clocks' with different inertial motion. Quite generally, SR global behavior becomes GR local behavior.

    Finally, for comparing inertial and non-inertial clocks (or two non-inertial clocks) without bringing them together, you have asymmetric effects in both SR and GR. For example, in SR, clocks will run slower at the front of a long uniformly accelerating rocket[edit: compared to the rear of the rocket], and this effect is not symmetric.
     
    Last edited: Dec 9, 2011
  11. Dec 8, 2011 #10
    Right. But that's gravity/general relativity, and special is about no-gravity.
     
  12. Dec 9, 2011 #11
    So where would I actually age slower?
     
  13. Dec 9, 2011 #12

    ghwellsjr

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    The lower your elevation, the more time dilation you experience.
     
  14. Dec 9, 2011 #13

    ghwellsjr

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    This is the wrong way to express the issue in SR. Time is not going slower for different Frames of Reference. You need to think about a Frame of Reference as extending out to infinity in all directions and including everything and everybody. Observers/objects/clocks at rest as defined by the coordinates of your selected FoR will not experience any time dilation. That is true for all FoRs. The faster an observer/object/clock moves as defined by the coordinates of your selected FoR, the greater their time dilation. So in the FoR in which one Twin remains at rest, he never experiences any time dilation but the other Twin does experience time dilation while he is traveling and ages at a lower rate. You can analyze the situation with any FoR but unless the twins re-unite, different FoR will assign different amounts of time dilation to the two twins with no agreement between them.
    Yes but that is a GR effect which we usually ignore when talking about SR.
     
  15. Dec 9, 2011 #14
    It doesn't seem like your question was satisfactorily answered. Which is ok because, afaik, it's an open question in physics in the sense that there's no physical, mechanistic explanation for relativistic differential aging.

    If you start with two identical clocks side by side and accelerate one clock to, say, .5 c and then decelerate it and bring it back alongside the stationary clock, then the moving clock will have recorded less time than the stationary clock.

    If the clock engines are, say, vibrating quartz crystals, then that means that the period of oscillation of the crystal in the moving clock was, during the round trip, on average greater than that of the stationary clock.

    How does this happen? What's the mechanics of it? Nobody knows. It's one of the outstanding mysteries of physics.
     
  16. Dec 9, 2011 #15
    PAllen's post # 9 gives as precise an explanation as is currently known.

    One could also answer "nobody knows" or "because space and time are not fixed (meaning
    it's the speed of light that is) for all observers....but our models and mathematics show what happens not really why things happen.
     
  17. Dec 9, 2011 #16
    I agree with what you say, but would like to add that it's precisely because the speed of light is an observationally well verified constant (and an assumed boundary of propagational speed) that it can be inferred that there's an objective/universal meaning wrt distance and time.

    Relativistic differential aging is a fascinating phenomenon. It suggests that what's been historically thought of as empty space isn't empty, and that there are currently unknown/unmapped interactions occuring which are the root cause of the phenomenon. The geometrical explanation of relativistic differential aging is, as you note, a certain depiction/description of what happens. As you also indicated, it isn't, however, a physical explanation of how/why it happens in terms of wave mechanical interactions. This is the mystery that remains for physicists to sort out and solve.
     
  18. Dec 9, 2011 #17
    Well for me personally the best way to "visualise" the answer to your question is to visualise a moving photon clock. Cheers.
     
  19. Dec 11, 2011 #18

    ghwellsjr

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    Let me repeat the quote of Einstein's:
    Aren't you using the fact that at sea level, the equator experiences a different GR effect than the poles experience at sea level, correct? But isn't this primarily because the diameter of the earth is greater at the equator than at the poles? And wouldn't it make more sense in order to apply Einstein's stipulation of "under otherwise identical conditions" that we put the clocks at the same distance from the center of the earth and not at different distances? But to be more precise, we should put the clocks at elevations where the effects from General Relativity are the same in order to have "identical conditions". So if we put one clock at the South Pole at the top of whatever mountain is there and found a lower elevation somewhere along the equator that had exactly the same GR effect, then the clock at the equator would run slower than the one at the pole, exactly like Einstein predicted, don't you agree?
     
  20. Dec 11, 2011 #19
    I was watching a documentary one of these days and it said that we could travel to the future by orbiting a massive black hole and then returning to Earth.

    The concept was clear to me: time passes slower near strong gravitational field, for instance let's say an astronaut spends 1 hour orbiting the black hole and when he returns 50 years have passed at Earth. However I have always read that for the man in the spaceship time would pass slower at Earth because he sees Earth at a high speed and the Earth would see time pass slower for him.
    For example, in the reference of the Earth he would have been 50 years near the black hole while he would been only 1 hour.
    In the man's reference he would have been 50 years near the black hole and only 1 hour would have passed at Earth.

    The implications of each scenario are very different. Which one would happen?

    I know this question has been asked many times here but I still cannot comprehend its explanation.
     
  21. Dec 11, 2011 #20

    ghwellsjr

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    The symmetrical relationship you're talking about occurs when two observers are traveling in more or less a straight line with respect to each other. When one travels in a high-speed circle, it is no longer symmetrical.
     
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