Light clock with spaceship moving vertical at .99c

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Discussion Overview

The discussion revolves around the behavior of a light clock on a spaceship moving vertically at 99% the speed of light. Participants explore the implications of this scenario on the perception of time and the speed of light, considering both the perspective of the observers on Earth and those inside the spaceship.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that as the spaceship moves upwards, the light photon would appear to move very slowly to the top mirror and back, suggesting a near-complete stop of time.
  • Others argue that while the speed of light is constant, the perception of time for the observer on Earth would differ due to relativistic effects, leading to time dilation.
  • A later reply clarifies that from the Earth's viewpoint, the light would take longer to travel upwards than downwards because the mirror is moving away from the light during the upward journey and towards it during the downward journey.
  • One participant mentions that while the light clock's ticking would appear slow to an Earth observer, it would only slow by a factor of about 7, not to a complete stop.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the light clock's behavior and the perception of time. There is no consensus on whether time would come to a complete stop, as some argue it would slow significantly while others provide a specific factor of slowing.

Contextual Notes

Participants do not fully resolve the implications of the light clock's behavior, and assumptions about the orientation of the clock and the effects of relativistic speeds are not explicitly stated.

ebodet18
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So what would happen if there was a spaceship moving at 99% the speed of light straight up. The spaceship has a light clock, so a photon of light moving bouncing between 2 mirrors in such a way that the light moves ALMOST in sync with the spaceship moving up. In theory wouldn't the light photon move very very slowly up to the top mirror and back to the bottom. Would time be almost come to a complete stop?
 
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ebodet18 said:
So what would happen if there was a spaceship moving at 99% the speed of light straight up. The spaceship has a light clock, so a photon of light moving bouncing between 2 mirrors in such a way that the light moves ALMOST in sync with the spaceship moving up. In theory wouldn't the light photon move very very slowly up to the top mirror and back to the bottom. Would time be almost come to a complete stop?

Welcome to PF!
To answer your question:
It seems that way but not really! - Why?
Lights speed is absolute, meaning, it always travels at the speed of light relative to EVERY viewpoint. So...If you were moving at .99 c, and you saw a photon, that photon would STILL be moving 300,000 m away from you every second. THIS is why time and space stretch in relativity. Since C was absolute, Einstein saw that if the speed of light was ALWAYS the speed of light, something else had to give (i.e space and time) In order for it to make sense that a photon would still be traveling away from you at 300,000 m/s if you were traveling .99% of c, Einstein postulated that you the observer would need to experience time much slower in order for this to occur. Hope that helps!
 
Last edited:
Ahh that's interesting! Thanks for the quick answer!
 
ebodet18 said:
Ahh that's interesting! Thanks for the quick answer!
No problem! Relativity is fascinating
 
ebodet18 said:
So what would happen if there was a spaceship moving at 99% the speed of light straight up. The spaceship has a light clock, so a photon of light moving bouncing between 2 mirrors in such a way that the light moves ALMOST in sync with the spaceship moving up. In theory wouldn't the light photon move very very slowly up to the top mirror and back to the bottom.
Assuming the spaceship's light clock is oriented in the usual manner--parallel to the direction of travel--then the light would be moving just slightly faster than the mirror as the light traveled from bottom to top. So as observed by you on Earth (if you could make measurements of the light's travel between mirrors) the light would cover that distance rather slowly. (The speed of light is the same, but the mirror is moving away from the light.) But during the reverse trip (from top back to bottom) the light would be moving towards the oncoming bottom mirror. So from your viewpoint on earth, the travel time going up is greater than the travel time going down.

Of course from the viewpoint of the people in the space ship, everything would work normally.
Would time be almost come to a complete stop?
No. While the "ticking" of that moving light clock would be slow as observed by you, it only slows by a factor of about 7.
 

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