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nitin singh Grade: 12

I was using a small penlight laser around the floor to have my cat chase the impossible dot. A though came that if I could move the dot fast enough from my porch , and with sufficient power, that at some distance along an arc the dot would move faster than the speed of light.

7 years ago

Answers : (1)

879 Points

Dear nitin,

If you observe the movement of the spot on a distant object (say the surface of the Moon) it will appear to lag behind the 'beam' you are waving around. Imaging projecting a vertical slit of light from a revolving source (lighthouse style) onto a saucer shaped (shallow cone) ground. The shape of the line of light would have a curve to it because of the time taken for the beam to reach the further regions.
Of course, this is a very subtle effect. It was used, in essence, in some of the first attempts to measure the speed of light, using rotating mirrors. You need to rotate the mirror very fast and use a very long 'throw' for the beam to observe the effect.
The spot could, of course, be observed to move between two points on the Moon at faster than c because, as stated before, nothing with mass actually moves..

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Sagar Singh

B.Tech IIT Delhi

7 years ago
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