Light Speed Constancy 

"Light Speed Constancy" is not simply an assertion that light's speed is not variable. In fact it is well know that light speed is affected by the density of objects it passes through such as glass or air. It's not even just a statement that light always travels the same speed in a vacuum. Much more is implied than what one would implicitly - physically conceive.

It is best described by the following commonly used thought experiment. If we know that light travels at 300,000 km/s and we get on a super-fast train that can travel at 299,999 km/s and set it up so that there is a laser beam set up on the ground next to the track and it is set to shine in the direction of our travel on the train. We have a little activation switch that will be tripped by an arm extending from the car at exactly the moment we pass the laser. (we'll also just assume a little fog so we can see the laser beam)

Intuitively, one might assume that the result of this experiment is that we will get to see the beginning of the light beam only passing us at 1 km/s but what is meant by "Light Speed Constancy" is that the light will not be passing us at 1 km/s as would make sense, but instead it is still passing us at 300,000 km/s. Remember that if a person standing on the ground that we are passing at 299,999 km/s measures the light travelling the same direction as us, he will measure it passing him at 300,000 km/s.

Additionally, if we were to mount a laser on the train and observe the light emitted from it while standing still beside the tracks waiting for the oncoming train, we would not measure the light speed as 599,000 km/s. It would be measured as 300,000 km/s from the grounds perspective. (Passing them by at that speed) And at the same time, someone on the train could measure the very same light and say that it is passing him by at 300,000 km/s.

One way that people misunderstand the action comes from understanding Wave Theory. If we were to substitute sound for light in this experiment there would be much more to consider. Sound cannot exist without some medium such as a gas (air) to travel in. Sound is a compression of the medium, completely subject to the properties of the medium. One way to misunderstand the concept is to say that inside a train, the speed of sound is 340 m/s to the occupants of the train even if the train is travelling 339 m/s. And the speed of sound according to people on the ground is also 340 m/s. Do not mistake this as a similarity in concept, it is not even remotely related to light speed constancy. If we were capable of measuring the speed of sound in that train from the ground (let's pretend we can see sound), it would be 679 m/s in the direction of the train's travel. Whereas in the same situation with light it would be the same speed to everyone regardless who fired it and thier perspective.

To give it another context to think about we will instead use a gun instead of a laser to show the vast difference. This is known as Ballistic Theory. (assuming no wind resistance for simplicity) If we fired a bullet that travels at 700 m/s at the precise moment a train was passing by at 699 m/s the occupants would see the bullet riding alongside them and passing them at only 1 m/s. Or if you were on the ground trying to kill a train occupant after they passed. The bulled would thud into their chest at a whopping 1 m/s and laughably fall to the ground. Conversely, if an occupant inside a train were to fire a gun that typically travels at 700 m/s, the other occupants would measure it as 700 m/s but if fired in the direction of travel towards a target fixed next to the track, it would hit at 1399 m/s.

These two concpets of relative travel are what we have to work from intuitively but the effect cannot be conceived in terms of human experience. It is nothing like any process in nature or physics and completely disagrees with every logical person who first encounters it. It makes no sense in common thought processes.

Once the understanding of "Light Speed Constancy" sinks in, it usually sounds ludicrous to people unfamiliar with relativity but this "second postulate" of Special Relativity is the crux of both the special and general theories. If it is not 100% true, these theories and all the science based upon them is utterly worthless. If it is not perfectly 100% true, hundreds of billions of dollars and 100 years of science have been flushed down the toliet.

I need prove nothing else but that this assertion is false to completely disprove all the math and physics that started at that point are utterly useless and meaningless. Proving that fact is what this website is all about.