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Our 'Background' Speed and How it Fits with Time Dilation

  1. Jul 29, 2011 #1
    me: layman's understanding of physics and mathmatics

    My (very basic) understanding for this question is that: a higher rate of (objective) motion = lower rate of time for anything with mass.

    Is there a working figure for how much motion we experience per a specific time period from such sources as the motion of the local galatic cluster, the rotation of the galaxy, the motion of our star, the spin of the earth, etc.?

    Whatever that figure might be, are we experiencing any time dilation effect in relation to the universe at-large?

    Lastly, for the purposes of figuring your speed as a percentage of the speed of light, at what point do you begin counting? For example: If my star is moving at 100,000 miles per hour and I launch my spaceship in the same direction going 20,000 mph and shoot myself out the tip of my craft at 100 mph, at what speed am I going in relation to achieving the speed of light? 120,100? 100? Or do I need to start at rest and develope my own motion?

    Thank you.
  2. jcsd
  3. Jul 29, 2011 #2

    Doc Al

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    What do you mean by 'objective' motion? All speed is relative.

    As far as time dilation goes: If something is moving with respect to you, you will measure all processes in that moving system (such as clocks) to run slowly compared to your own clocks. Your clocks run normally.
  4. Jul 29, 2011 #3
    By 'objective motion' I meant motion measured against an absolute stillness in spacetime. I'm sorry if that was incorrectly worded or an absurd notion, but my thought was that a single object's motion against a fixed point in spacetime would be objective and would only become relative with the addition of a second object in motion?
  5. Jul 29, 2011 #4

    Doc Al

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    There's no such thing as absolute stillness. If you are moving at some speed with respect to something, you'll be moving at other speeds with respect to other things. Nothing 'objective' about it.
  6. Jul 29, 2011 #5
    That's good intuition imo. Not an absurd notion at all.

    There is a recent thread in here regarding the use of the EM radiation from the big bang used as a point of reference.

    Think of how a fixed point in absolute stillness in spacetime could be determind so "objective motion" could be measured. Should conclude it can't be done.
  7. Jul 29, 2011 #6


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    To chime in on nitsuj's post, I will say that choosing the background radiation as a frame of reference in no way invalidates relativity or anything to do with it. You are simply choosing to measure all other frames in regards to that one frame. Choose another frame to compare with and everything is exactly the same. The same thing would happen if we chose the Earth, Sun, or Moon as a reference point to measure against.
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