why is the speed of light constant no matter the frame of reference... please explain in layman's terms...

Question

any good reference with animations would be of great help.
Thanks.

Answer 1

If you are in an inertial frame (i.e. moving at a constant speed), you cannot tell that you are moving. Thus it looks like you are at rest, just as you would be at rest on the surface of the earth. Einstein's postulate was that you could not tell that you were not at rest by finding some change in the basic laws of physics that would apply just to your inertial frame. Thus Maxwell's equations, which determine the propagation of electromagnetic fields, such as light, would be valid in every inertial frame.
Maxwell's equations specify the speed of an electromagnetic wave in vacuum. It is c, what we call the "speed of light". Einstein's postulate then leads to the conclusion that the speed of light is constant in every inertial frame, and from there to the physical theory called the Special Theory of Relativity.
Many experiments have been done to test Einstein's postulate, and so far have validated it. If you are accelerating in some way (for example in an orbit around the sun), you are not in an inertial frame, and thus Special Relativity does not apply. Einstein and others have attempted to fix this in the General Theory of Relativity, which allows for acceleration, for example by gravity.

Answer 2

Actually there is no "explanation" as to why it is so. It just is. It's just one of those fundamental truths of the universe. But I think it's got a lot to do with the fact that photons (the particles that carry light energy) are massless. (Credit goes to yoohoowee who told me this. And who should be answering this, really.)

Anyway, just want to make something clear to you. It's not "no matter the frame of reference." The frame of reference is actually an "inertial frame of reference" meaning it is not accelerating. It must be either stationary (relative to an observer) or moving with constant velocity (again, relative to an observer). Once that frame of reference accelerates (meaning changes speed or direction or both), then things happen a little differently.

Answer 3

This site explains it rather well:
http://www.pitt.edu/~jdnorton/Goodies/Chasing_the_light/index.html

It is a violation of Maxwell's equations for light to appear stationary. So, it's is impossible to catch up to light, no matter how fast you go, because if you caught up with it, it would appear stationary, relative to you.

Let's say we have two spaceships. Spaceship A is chasing a beam of light. Spaceship B is sitting "motionless" and watching A chase the light, from the side.

Spaceship A gets up to 99% the speed of light. From B's perspective, the beam of light (which is magically visible to everyone) is just barely getting away from spaceship A.

However, time has slowed down drastically onboard spaceship A, and spaceship A has also been drastically squashed along the direction of travel. Spaceship A perceives none of these things, but spaceship B sees the clock onboard spaceship A running very slowly, and also sees that the entire ship appears squashed along the direction of travel.

Onboard spaceship A, time has slowed down and the ship has contracted just enough that the beam of light they're chasing, while really only getting away from them at 1% the speed of light (to an outside observer) appears from their perspective to be getting away at 100% the speed of light.

Strange, but true.

Answer 4

I believe that is a fundamental postulate of General Relativity. Einstein simply thought it should be so, and all sorts of wondrous and amazing things came as a consequence of that.

Answer 5

There is no "why" about it. It's an observed fact, and GR is our attempt to live with that fact. For the answer to "why," please walk across campus to the philosophy department.