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Can time really be slowed?

  1. Mar 6, 2013 #1
    Processes taking place near high gravitation or moving at near light speed are slowed. General relativity tells that it is due to slowing of time in these conditions. Why can’t we say that this is due to slowing of the process itself in these conditions rather than slowing of the time? Is it not possible that in the atomic clock near high gravity or at high speed, the oscillation of cesium atom itself is slowed down rather than slowing of time? Is it not possible that the physiology and cytology of the twin living near ground or moving at near light speed is slowed down, delaying the ageing phenomenon, rather than slowing the time?
  2. jcsd
  3. Mar 6, 2013 #2
    You're speaking of the general theory of relativity and the special theory of relativity. Yes the process appears "slow" relative to another reference frame. The clock is simply another process.
  4. Mar 6, 2013 #3


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    Gold Member

    What mechanism do you propose to cause the processes to slow down while time moves at the same rate as elsewhere?
  5. Mar 6, 2013 #4
    What is the distinction between "slowing all time-dependent processes down" and "slowing time down"?
  6. Mar 7, 2013 #5
    Time is a measurement of the rate of change of processes. You might be assuming that time should be universal and someone should prove to you that it isn't. Why not look at it the other way around? The measurement of time is only consistent locally. Prove to me instead that this is wrong and why it should be universal. You won't be able to. The arguments go back 100 years to when Einstein first postulated relativity.
  7. Mar 7, 2013 #6
    Thanks.slowing of a process is easy to conceive. But the phenomenon was suggetsed by Einstein to do away with concept of absoluteness of time, which is hard to conceptualise.
  8. Mar 7, 2013 #7
    Thanks for reply. Processes are much easier to be slowed than time. When the gravity of a black hole can interfere with the movement of light, why can't the gravity of a massive body interfere with the oscillation of an atom ( a speculation)?
  9. Mar 7, 2013 #8
    Thanks for the reply. When you talk of slowing of a process, it is slowing either in reference to some other process or some reference time. But when you talk of slowing of time, it is slowing in reference to what?
  10. Mar 7, 2013 #9
    Many thanks for the reply. I fully agree with you..
  11. Mar 7, 2013 #10
    Well slowed if you compare it to elsewhere, yes. But you will not notice, seen as time is slowed for you too.
  12. Mar 7, 2013 #11


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    It can, but what about processes that don't involve physical oscillation? It would be very unlikely for all processes to be slowed by the same amount.
  13. Mar 7, 2013 #12
    One thing I think of as a difference between slowing of a "process" and time "slowing down" is the impact on measurement of length.

    The simple process of measuring a length more slowly wouldn't result in a contracted measure. i.e. the measure of length isn't time dependent.

    Time Dilation is time as a dimension comparatively "slowing down", which precedes any "process" that may happen within this dimension. In turn measure of length too is comparably effected.

    Note this is in general with respect to SR, I can't speak for a GR perspective.
    Last edited: Mar 7, 2013
  14. Mar 8, 2013 #13
    I don't agree. Length measurement is a time-dependent process in the relativistic sense, since you must have an associated moving frame for length contraction to occur (in SR). If the frames were moving at different rates, you would detect a change in length. The usual way length would be measured with comoving frames would be to start a clock at the instant you first see one end of a meterstick and stop it immediately once it ends. Since you know the elapsed time and relative velocity of your frame, you can compute its length. In that sense it does depend on how slowly you take the measurement.

    To clarify my original question, I am asserting that anything which explicitly depends on observed time (or its differential) can be viewed in a way that makes it indistinguishable from the process appearing to be slowed by some other means. For example, in a mechanical clock you would find that the lengths and geometry of the gears/servos are contorted such that the observed clock ticks at a slower rate. Does that mean that time has "slowed down"? Yes, but you could equally (and correctly) argue that it was due to a change in geometry. These interpretations are equivalent, so there isn't really a distinction between the two.
    Last edited: Mar 8, 2013
  15. Mar 8, 2013 #14
    So...your calculation is time dependent. is it noted in the result? 3m measured in a time interval of 3s with measured objects velocity of 1m/s. No, it's 3m. And you used proper time to measure proper length. A convoluted method as opposed to using a simple measuring stick, which again is not time dependent in any sense. In fact it's complety exlcuisive of time in a relativistic sense. Orthogonally opposed dimensions, +-.

    Yup kinda what I'm saying. it's a change in geometry that "slows" time and contracts length. Not slowing of processes.

    I thought that position was made clear with the statement

    Time Dilation is time as a dimension comparatively "slowing down", which precedes any "process" that may happen within this dimension. In turn measure of length too is comparably effected.

    Does that mean time slowed down? Yes it does, does it mean the processes merely slowed down? No, they haven't the spacetime interval is the same. The geometry is comparatively "different".
  16. Mar 8, 2013 #15
    Can time be slowed

    Dear Cwilkins and nitsuj
    Many thanks for for participating in this discussion.
  17. Mar 8, 2013 #16
    This does not work. If it worked this way, then Observer A would see observer B's clock has slowed, but observer B would not see that observer A's clock has slowed. Special relativity has it right: A sees B's clock is slowed, and also, B sees A's clock has slowed.
  18. Mar 8, 2013 #17
    If all of the slowing/speed of clocks and contracting of matter continues to seem "just wrong," I think it's important to remember that in the case of SR there are a number of assumptions one makes that lead one to conclude that a traveler is slowed and contracted. But the result of measuring / deciding the slowing and contracting can just as easily lead you to question these assumptions - basically the assumption of what events appear to be simultaneous in your own frame. It is very practical in a day-to-day sense to operate with our notion of an extended frame with its simultaneity, and this leads us to have a practical understanding of the longevity of the incoming muon for instance. But in each traveling frame, it is the other fellow's clock/rod which appears slowed, and this cannot logically be literally true. If you hold on to the version of simultaneity that seems normal and practical in your rest frame, you have to let go of the intuitive view that clocks and rods operate without contraction if they are moving. It is just as physically "true" though normally less practical to let go of the intuitive view of simultaneity in our rest frame. Then rods and clocks are free to be uncontracted. I get the impression that in GR there is a similar alternative - an intuitive idea we could "let go of" and keep the clocks all running at the same rate... something related to uncurved spacetime. Something like this: ? "To determine that someone else's clock is running at a different rate at a different altitude, the information from that clock to get to you has to travel through a region of spacetime in which the curvature is constantly changing and this brings about the *seeming* change in clock rates." Again, for practicality's sake I understand it makes more sense to simply think of the clock rates changing, to calibrate GPS satellites and so on.
  19. Mar 8, 2013 #18
    It is literally true and because of logic. The situation is symmetrical.

    What "cannot logically be literally true" is one frame of reference claiming to be at rest & the other to be moving.
  20. Mar 8, 2013 #19
    I just mean in the sense of A>B and B>A not both being literally true logically. It is logical that each "appears" to run slower to the other (similar perhaps to receding travelers viewing each other as shrinking). However, often beginners are scratching their heads and looking for alternate "physical" explanations for slowed time and timepieces. Not only does A not directly perceive his own timepiece to run slower, B does not "perceive" A's timepiece to run slower either... at least not "perceive" without the baggage that the beginner may not be keeping in mind when "perceive" is being casually used by the more experienced.
  21. Mar 8, 2013 #20
    Ah I see the perspective, "appears" is kinda misleading imo. it is not merely an appearance but a comparative difference in the geometry of the FoR's. Each literally true, as in relativity of motion - all physics the same in inertial frames.
  22. Mar 8, 2013 #21
    Many thanks for the reply.
  23. Mar 8, 2013 #22
    Thanks for the reply. I am encouraged by your last sentence.
  24. Mar 8, 2013 #23


    Staff: Mentor

    Nobody claims that. What is claimed is that A>B and A'<B' are both literally true. Length is frame variant so A' is not equal to A. That is the important take-home message.
  25. Mar 8, 2013 #24
    It is literally true that each clock *appears* slow to the other. It cannot be true of course that each clock is in some objective sense "slower" than the other. As for what someone might claim... I was thinking more in terms of what someone might believe before they understand the subtleties - I wasn't attempting to imply there was any ambiguity in the science.
  26. Mar 8, 2013 #25


    Staff: Mentor

    Just to be clear, this is not an optical effect. It is not a mater of visual appearances, all of the relativistic effects (except relativistic Doppler) are what remain after correcting for the finite speed of light.

    Suppose A is the time between two ticks of clock 1 in the unprimed frame and B is the time between two ticks of clock 2 in the unprimed frame, and suppose A' and B' are the corresponding quantities in the primed frame. Then A>B and A'<B' can both be objectively true, and neither is a statement of appearances or any other optical effect. There is no contradiction in the two statements since the two statements are comparisons of frame variant quantites in two different frames.
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