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I know the explanation involving a clock based on reflected light. But why would every physical/chemical process be slower? Not that the following is a very good idea, but could it be something like, as every particle becomes more massive, inertia increases and so every movement would be slower reflecting this.

Qmechanic
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releseabe
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3 Answers3

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You might consider it a consequence of perspective.

Hold your hand out with the palm toward your face. Now, rotate it so that the thumb faces you. It appears to compress. However, the hand itself doesn't change shape.

It's a bit less intuitive in relativity because we experience time differently from space, and the geometric model of spacetime in SR is Minkowskian, not Euclidean. Acceleration may be modeled as rotation in space-time planes rather than the familiar space-space planes.

John Doty
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    this is far from a "micro" explanation, afaict. – releseabe Feb 24 '23 at 14:38
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    @releseabe Well, of course, physics provides models, not explanations. The phenomena are in charge. SR has proven a productive constraint for model builders, but the details are quite complicated. – John Doty Feb 24 '23 at 14:43
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    This is the best answer. The original question makes the mistake of thinking there is one absolute time that "slows down" for moving objects. But in fact there's no absolute motion ("moving" and "stationary" are relative), there is no absolute space (the notion of "the same place" is different for observers moving relative to one another), and similarly there is no absolute time. There is only relative time, and different observers make different measurements of time. – Eric Smith Feb 24 '23 at 20:27
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The scale doesn't matter. At any scale, as long as the laws of physics are the same in each frame and as long as there is a finite invariant speed then you can derive the Lorentz transform. The derivation of the Lorentz transform does not depend on the scale and does not make any use of the light clock. It is directly based on the two postulates.

Once you have the Lorentz transform, then time dilation immediately follows. The macroscopic light clock is a good easy-to-understand example of time dilation used for teaching purposes, but it is not the way that time dilation was derived.

Dale
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No, there isn't such an explanation. Indeed, if you think properly about your suggested explanation, you should realise it is wrong. Particles 'slowing down' implies that they are taking more time to move from A to B, not less as time dilation requires.

If fact, in a moving reference frame, time does not 'slow down'. Clocks in a moving reference frame tick at one second per second, and all physical processes proceed at their usual rate. The point is that the time interval between two events in the stationary frame is actually longer than the time in a moving frame in which both events occur at the same place. Let me repeat that- it is the time interval that differs between the frames. The interval between two events might be 5s, say, in one frame and 4s in another. A clock ticking at the usual rate in the second frame will tick-off 4s between the two events, not because it is under-reporting time but because the time interval is actually shorter.

Marco Ocram
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