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If you had two identical video cameras and started recording synchronized atomic clocks recording at the same speed and you put one on the spaceship and sent it out traveling at 99% of the speed of light for a while and left the other one on earth both recording the whole time, when the spaceship returned and you played back the recordings of the two clocks on monitors next to each other, would you see the recordings of the two clocks going at different speeds with one clock on earth appearing to move faster?

It seems that you wouldn't see the recordings being different or one recording longer than the other if the experience of the observer on the ship experienced reality at the regular speed the world usually unfolds to the observer, not slow motion, but if you looked at the two clocks they would have different times.

How does that work when you're watching the recordings of the same length and frame rate? The cameras are recording the whole thing yet the clocks are different.

I was thinking about time perception. Does the rate the brain is processing information speed up or slow down relative to an outside observer moving at different speeds, but the subjective experience of time passing for both remain the same?

Suppose there was a streaming video from the spaceship. Would they appear to be moving in slow motion in the video stream?

Would the length of the video be shorter for the recording on the ship?

Would the clocks appear to be moving at the same speed?

What would you see when you played back the videos next to each other?

There is something confusing about this.

Qmechanic
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Bryan Aneux
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  • Please see John Rennie's https://physics.stackexchange.com/q/242043/ and the earlier questions he links there. – PM 2Ring Mar 10 '19 at 16:43
  • thanks, but a simple answer about differences in the videos was not clear from the links – Bryan Aneux Mar 10 '19 at 17:12
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    Regarding your questions about streaming video, see my answer here: https://physics.stackexchange.com/a/388549/4993 (My answer talks about what happens if you watch the other clock through a telescope, but exactly the same calculations apply to streaming video.) When you play the videos side by side,they of course look identical. Why wouldn't they? – WillO Mar 10 '19 at 17:17
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    True, but it's definitely worthwhile to invest the time in reading those answers by John Rennie, IMHO. There are a lot of questions on this site connected to the Twin Paradox, with plenty of good answers, and plenty of not so good answers. ;) But John's articles are pretty hard to beat. And although they don't directly answer your questions they do contain all the info you need to figure out the answers to your questions. – PM 2Ring Mar 10 '19 at 17:54
  • if the videos of the two clocks are identical, but the clocks are different when they return? playing back the videos they are the same length but more time has passed. what does that look like if the videos are both recording their own local time. It seems confusing to me. – Bryan Aneux Mar 10 '19 at 18:26
  • I mean if you were watching the streaming video of the local time onbord the ship from home throughout the trip – Bryan Aneux Mar 10 '19 at 18:36
  • Or watching a live news broadcast from Earth onboard the ship throughout the trip. At some point it seems there would seem to need to have some bigger jumps or lags in the playing of the video from Earth like when we are controlling the Mars rover. if they were each recording a streaming video of the local environment of each other, it seems that the recordings of the streams would need to be jumpy or slowed somehow receiving different frame rates to account for the difference in time passing. is that right? – Bryan Aneux Mar 10 '19 at 20:26
  • Just adding this superb resource for tuning your intuitions about special relativity, here too on this SE https://www.lucify.com/inside-einsteins-head/ – CriglCragl Mar 11 '19 at 15:40

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The video playbacks would each proceed ticking away at the same rate, looking identical. The traveling video would end a lot sooner than the at-home video.

JEB
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  • How they can be identical if the traveller video ends earlier? – Alchimista Mar 11 '19 at 09:45
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    @Alchimista He means that the individual ticks look identical. – Conifold Mar 11 '19 at 21:49
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    @Alchimsta l think it's a subjunctive mood continuous future conditional, until it's not? Maybe ask grammar stackexchange. – JEB Mar 12 '19 at 05:28
  • Yes it is probably grammar. I read that the subjects of the sentence are looking identical, not the thicks. Sorry if I don't know English very well. Somehow the answer is "Thicks in the two videos are identical. The video recorded by the traveller is shorter than that recorded on earth.". Got it, but I was suspecting it already. – Alchimista Mar 12 '19 at 08:09
  • @Conifold yes sure. But the sentence means something else. – Alchimista Mar 12 '19 at 14:08
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Each recorder shares proper time with its corresponding clock, so both sets record and show the same amount of time during playback.

The clocks themselves though, after luminal travel, would show different times, because of Time Dilation. Time slows for a moving object relative to an external observer. The Observer would see the moving clock in slow motion. This is a consequence of light traveling at the same speed in all frames of reference. To maintain this constant velocity for all Observers time itself changes between them. The closer you get to light speed relative to another Observer, the more noticeable the Time Dilation.

Inquisitron
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  • Just to be clear: the recordings have the same duration as the time shown on their respective clocks. They do not have the same duration as each other. Everything in the travelling spaceship -- clocks, recording devices, people, etc. -- experiences the same shorter elapsed time. – Eric Smith May 11 '22 at 02:13
  • Agreed, thank you for that clarification. Everything in the moving clock's frame of reference would experience the time dilation. So each recorder and clock pair shows the same time, but both pairs show different times. Dont let me plot your next jump into hyperspace! – Inquisitron May 11 '22 at 11:41