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Homework Help: Questions about relativity

  1. Sep 30, 2013 #1
    1. Is there any body on earth which can move with constant or uniform velocity?

    2. According to Special Theory of Relativity, speed of light is same for all inertial frames. Then can it be different for non-inertial frames?

    3. What is General Relativity and what is the difference between Special and General Relativity?

    Thank You
  2. jcsd
  3. Sep 30, 2013 #2


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    (1) If you mean bodies fixed to the surface of the Earth then no; the Earth is not an inertial reference frame. For starters, it rotates about an axis.

    (2) Yes. Even in the simple case of a uniformly accelerating frame (the so called Rindler frame) light can move at speeds other than ##c## and even stop (at what is called the Rindler Horizon).

    (3) To put it in very simple words, in SR the geometry of space-time is just a backdrop on which fields and particles interact with one another but it itself never interacts at all with the fields or particles. It just sits there in the background as an innocuous stage. In GR, the geometry of space-time interacts with fields and particles (any kind of mass-energy in fact) so as to not only be affected by the propagation of fields and particles in space-time but also to affect the very propagation of these particles and fields. On top of that, gravity becomes nothing more than a manifestation of this "dynamical" space-time geometry.
  4. Oct 2, 2013 #3
    Thanks a lot @WannabeNewton

    I have a question that If we travel in an airplane, it is not fixed with the earth, but it is in air. Can it move with constant/uniform velocity? Will gravity affect it?
  5. Oct 3, 2013 #4
    Is there anyone to help me?
  6. Oct 3, 2013 #5


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    I hope not. The Earth is not travelling with uniform velocity, so if a plane did it would leave Earth's atmosphere quite quickly.

    Why are you asking? Perhaps with some context we can be more helpful.
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