Anonymous asked in Science & MathematicsAstronomy & Space · 3 months ago

Horizontal light clock?

What is ct2 in the round trip as shown in the lower figure of the picture? The upper figure in the following figure seems wrong to me if the velocity of light is constant in all inertial frames. It's just because a pulse doesn’t move forward with “v” but bounces back forthwith with “c” when it strikes the front mirror of the horizontal light clock. This can be seen in the lower figure. The t1 of the first second ends at B' while its t2 (from B' to A") ends at A". Next second starts at A". Is this overlap of t1 with t2 or vice versa possible in a clock of the subject?

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3 Answers

  • 3 months ago

    With all SR questions the difficulty invariably comes down to correctly identifying which observer's frame of reference ,one is looking at -- the one in the "moving" frame or the one in the "stationary" frame 

    In your pictures the first series is the view of the observer moving with the clock --and in the second , it's the view of the "stationary" observer .  

  • 3 months ago

    I can't understand your question. But I am reasonably certain that it is an illustration of the Special Relativity time dilation that occurs with increasing velocity. The classic explanation is described as a light pulse that is jumping vertically up and down between two horizontal mirrors, while the whole thing is moving laterally. Since the speed of light is constant in all reference frames, therefore the time to travel from the top mirror to the bottom mirror must be the same no matter what lateral velocity is happening. One can imagine a right triangle where the distance between the top mirror and the bottom mirror is vertical at rest, but it is the hypotenuse of the triangle when the mirrors are traveling laterally at a velocity. The time to travel the vertical distance has to be equal to the time to travel the hypotenuse. Thus, the hypotenuse rate of passage of time must be slowed down by a factor to make this happen. The time dilation effect can thus be derived mathematically based on the Pythagorean theorem. 

  • 3 months ago


     The speed of light depends on the medium. You have to be specific if you mean in a vacuum or near vacuum. Do a Google or Bing search on Snell's law or take a mineralogy course. 

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