Does the Null speed exist ?

[julz]

Hello everyone ;)

When we talk about speed, it's known that motion is relative.
I can say my speed is 0 relatively to my chair.

Is there any possible notion of "absolute speed", as there is no center of the universe ?

I believe that the answer will be no, as motion is relative, however I don't get the reason (and it might be because I don't really understand the concept of speed/motion).

But, when we say that a galaxy is moving at x speed, but what is it relative to ?

Once again, the question is difficult for me to express, but it's still worth trying ;)

[bapowell]

When we say that a galaxy is moving with speed x, we mean relative to the earth -- since that is where the measurement is made. The speed of light is the only absolute speed in the universe -- it moves at the same speed (in vacuum) for all observers. If you are not familiar with Einstein's special theory of relativity, you should investigate it. I think it will be just what you are looking for.

[julz]

Actually, I "knew" about the speed of light and special relativity. Or should I say, I read about it, as I don't think I have the necessary background to fully understand it. Maybe I have missed something about it though :)