Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Does the Null speed exist ?

  1. May 11, 2010 #1
    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 ;)
  2. jcsd
  3. May 11, 2010 #2


    User Avatar
    Science Advisor

    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.
  4. May 11, 2010 #3
    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 :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook