How do we know that the speed of light is uniform ( the same) throughout the universe?

Question

How do we know that other physical constants (such the gravitational constant and electrical charge) are constant thoughout the unverse and time? Are there any physical "constants" that are not constant in time or throughout the universe (i.e spatially)? Thanks for your response

Answer 1

Einstein once said of his theories (including those about the speed of light) that no number of experiments would ever prove him right, yet only one experiment could prove him wrong.

The honest answer to your question is that no one knows for sure. We can only measure relatively close to Earth or by what we can observe from Earth (which is surprisingly much), so we assume that what we have observed is true everywhere. It's just the best we have to go on.

Answer 2

We know that the speed of light is uniform throughout the universe because the futon, as the only materialistic component of light, is constantly moving at 186,000 miles per second, without becoming pure energy itself. If, at any instance, the futon changes its speed, light becomes invisible. Therefore, as long as light is visible, its speed is constant, and we can accurately measure the distance between earth and any object in the outer space, such as a galaxy or a star, by calculating the time light needs to reach earth. This is an application based on Einstein's famous equation: E=MC square.

Answer 3

The big hint that motivated Einstein and others to figure that the speed of light is constant has to do with an interesting result from Maxwell's equations of Electromagnetism. The equation:

c=1\sqrt{mu epsilon}

falls out, where mu is the magnetic permeability of free space constant and epsilon is the electric field permittivity of free space constant. Wiki has a nice write up about it.

Answer 4

Well, the speed of light has been measured several times here on Earth, and it always came out the same speed. We don't actually know the speed is the same everywhere, but we assume it is. I think there are several observations of stars, galaxies and such that exibit the effects of relativity, so that's kind of indirect evidence that light has the same speed everywhere.

Answer 5

well, think about it. both of the constants you have mentioned have to do with the movement of the earth. and think about the word constant itself. constant means it goes on and on. if there was a "physical constant" that aren't constant they wouldn't be called a constant!

Answer 6

i would imagine that the speed of light is NOT constant. as the waves that make up light are pulled into a black hole, they should be pulled faster than normal (hence why light cannot escape a black hole).

but that's just a theory :)