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Relativity Questions on Motion Limits

  1. Nov 26, 2009 #1
    If I could move at c (yeah yeah, I know I can't), the universe would see my watch at a standstill. I can attribute this to placing all my energy into going forward in space leaving no room for moving forward in time.

    But does relativity tell me that the opposite end has a "limit" as well? Can a particle be at a perfect point of rest so that it could be moving only in time? Is it possible for an object to be at a perfect point of rest?

    A different question looking for the same type of answer; What is, or is there, a limit to how fast observable time can be moving?

    I tried to think of a thought experiment to play this out, but could not figure out how to get an object to be at complete rest except for an atom, at absolute zero, in a vacuum, in a static universe, with no gravitational force to act upon it.
  2. jcsd
  3. Nov 26, 2009 #2


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    Science Advisor

    Velocities v are only defined between two observers. So then you could ask why this is not the case for the speed of light? That's because the speed of light is basically the norm of the 4-velocity and is a fundamental constant of nature. So every observer moves "with the speed of light through spacetime". How the components of this 4-velocity decompose into a temporal and spatial part depends on the relative motion of the observer and the object of interest.
  4. Nov 26, 2009 #3


    Staff: Mentor

    Yes. The limit is 1 second of proper time per second of coordinate time, a clock cannot tick faster than that in SR. In that case you are at rest and therefore "moving" completely through time and not through space.
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