What are the difficuties and accuracy of measurement of the speed of light?

Answer 1

The difficulty is that the speed is so great, compared to human senses and

everything we can experience with them. This, plus the fact that we are

prisoners, with our movements restricted to the space on or near the surface

of the Earth, and the fact that we can't communicate from one place to another

any faster than the speed of light. All of this imposes tough limits on the kind

of experiments or measurements we're able to set up.

When something is moving fast and you want to measure its speed, you need

to somehow compare a distance it covers with the time it takes to cover that

distance. For experimental precision, you want to be able to observe it over a

long distance and a long time, but for accuracy, you need to be able to measure

both the distance and the time accurately.

With something that moves VERY fast ... and light moves faster than anything else ...

-- If you mark out a distance that you can measure conveniently and accurately,

then it covers that distance in a tiny sliver of time that you can't measure.

(Light covers 10 miles in 0.000053682 second.)

-- If you track it for a length of time that you can measure conveniently and

accurately, then it has covered a distance that you have no way to measure.

(In 10 seconds, light is 1,862,824 miles away from your flashlight ... almost

8 times the distance to the moon !)