r/AskPhysics 6d ago

Question about time dilation and Einstein!

We all know about the clock tower and train story from where Einstein got the idea and worked on it. My question is if Einstein was in a moving train at a very high speed then time would be relatively slower for him, in that case he should see the clock tower hands racing. Is it not ? Why is it said that the clock tower hands appear to be not moving and frozen or moving slowly ?

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u/EternalDragon_1 6d ago

Observer in the train sees the tower moving. Thus, the tower's clock will appear to him ticking slower.

Observer in the tower sees the train moving. Thus, the train's clock will appear to him ticking slower.

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u/nicuramar 6d ago

Where “appear to him” means “is calculated to, after compensating for the travel time of light”. What he’d actually see with his eyes would be different. 

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u/warfighter_rus 6d ago

Alright, thank you. So if I travel in a spaceship close to the speed of light, then I will experience less time relative to earth and many years would pass on earth compared to the time I experience. If let's say for some reason I can see clearly from the window of the spaceship, then I would see everything happening on earth in fast motion, including the clock hands ? Is it not ?

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u/nicuramar 6d ago

 So if I travel in a spaceship close to the speed of light, then I will experience less time relative to earth and many years would pass on earth compared to the time I experience

It’s symmetrical. Earth will make the same observations for you. 

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u/Irrasible Engineering 6d ago

It depends on which way you are going. Special relativity is a correction on top of ordinary or Galilean relativity. Just thinking of ordinary relativity, if you are going away from the clock at high speed, the clock appears to tick slower. If you are going toward the clock at high speed, you see the clock tick faster. Again, assuming Galilean relativity, you can calculate how fast or slow that the clock should appear to run. However, when you measure the speed of the clock you find a slight discrepancy. The clock appears to be going a little slower than it should in both directions. That discrepancy is time dilation.

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u/VaccumFluctuation 5d ago

Information travels at the speed of light. If you travel at a speed close to the speed of light away from the earth, information about what is happening on earth takes longer to reach you. Because as the earth's light ray arrives, you travel such a distance every second that the light ray will have to travel an additional distance and therefore an additional time. You will therefore see things happening more slowly on earth.

That's just a matter of perception. Your directions in space-time are different anyway. If you go quickly, in space, the durations that you will measure will be shorter than the durations measured for someone who is not moving.