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I realize the situation where a laser beam moves vertically in a moving vehicletime dilation proof

but what if the laser beam was a normal ball If we do the same steps of the proof considering that the velocity of the ball is not absolute and will have different velocities in different reference frames there will be no time dilation what is wrong in my understanding because according to special relativity there should be time dilation whether the event is a laser beam bouncing or a ball.

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The speed of light is $c$ in every reference frame. The speed of a ball depends on the reference frame. – pfnuesel Jun 28 '14 at 12:20
ok and that is what the question is all about if we used a laser beam we can prove the time dilation but when we use a ball we can't as the ball's velocity is not absolute – Abdo Saeed Anwar Jun 28 '14 at 12:25
@pfnuesel i think you are absolutely right – agha rehan abbas Jun 28 '14 at 13:12
how can I be right! according to my understanding time dilation is always there whether the event is a laser beam bouncing or a ball – Abdo Saeed Anwar Jun 28 '14 at 13:30
Time dilation is always there, you just can't use the ball experiment to give you a neat expression for it in a few lines of work the way the light experiment does. Physicists are lazy and the light version of the problem is clear and easy, so why would we spend time on the hard and muddled version? – dmckee Jun 28 '14 at 18:41

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