# Concequences of the speed of light beeing absolute? [duplicate]

If photons have a speed limit (speed of light), what happens when you shoot photons through a flashlight but you yourself already have some speed? Do the photons from the flashlight only travel at [speed of light]-[your speed]?

Example: if solar system, galaxy and earth rotation movements were nonexistent and only earth orbital speed existed (30000 m/s), and you were to shoot photons in the approximate same direction the orbital movement is pointing at one time, would the speed of those photons be 299792458 - 30000 = 299762458 m/s ?

If that's the case isn't it possible to determine all movements the earth is suffering in relation to whatever object by measuring the speed of light in various directions over some amount of time?

## marked as duplicate by John Rennie, user36790, garyp, Martin, David HammenJun 1 '16 at 18:14

The speed of light is the same in all frames. If you are moving relative to Earth at 99% the speed of light and you measure the speed of light you find that the speed of light is the same. Assume you shine light in the direction of your motion. From the perspective of an observer on Earth the photons creep forwards at 1% c relative to your frame. However using Lorentz factor this observer witnesses clocks slowed by $7.1$ and the light travels an apparent distance contracted by $1/7.1 = .14$ Putting all of this together, recognizing the special relativistic effects, the Earth observer finds that indeed you would observe the speed of light to be the same as on Earth.

The speed of light is always 299,792,458 meters per second, regardless of the speed of the source and the speed of the receiver.

According to Newton's corpuscular theory, both speeds of the source and the receivers were being added or subtracted from $c$. According to an aether theory of the electromagnetic field, the speed only depended on the speed of the receiver because the "fixed medium" was oscillating.

However, the Michelson-Morley experiment measured exactly the effect you referred to – the change of $c$ to $c\pm v$ because of the motion of the Earth in space (and Earth's surface, a smaller effect) and found a negative result: the speed was indistinguishable from $c$, much closer to $c$ than to $c\pm v$, to say the least.

This is not explainable using the independent space and time. Albert Einstein found the theory of relativity that explains all the motion and agrees with the postulate that the speed of light is always $c$. Einstein actually wasn't too aware of the Michelson-Morley experiments – he convinced himself that the speed should be constant by theoretical considerations.

Einstein's theory of relativity.

Seriously. That's the answer to your question. The purpose of Einstein's theory was to describe what the universe would be like if the speed of light was an absolute constant.