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I understand that the larger the mass the greater gravity is and the slower time is, as well the faster an object is traveling the slower time passes. My question is that since the faster an object travels the more mass it has, is the increase in mass the reason for the change in time, or is it the velocity?

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I think the question uses a piece of the General Theory of Relativity and a piece of the Special Theory of Relativity.

Perhaps this article about the Global Positioning System ( which uses both the Special and General Theory to keep time) will be helpful. I've talked to Astronomers that get the answer wrong! (They're amateur astronomers).

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

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  • $\begingroup$ Thank you for the article. It describes the difference between general and special theory well. I was more specifically wondering if general theory comes in to play as an object approaches the speed of light. As I understand it ( and I could easily be wrong) as an object the speed of light it gains in mass. Is it possible that this gain in mass is responsible for time slowing down for the object? Or is special relativity the only thing at play in this situation? Sorry that I was not more clear on my first post. $\endgroup$ – Warren Oct 29 '13 at 3:18
  • $\begingroup$ I'd say special relativity is in play here. I'd think in terms of an accelerator, you pump energy into it , the entire power supply of a small city, and particles are accelerated to 99.99 % of the speed of light so collisions occur at high energy. They have become heavier, say 10-100GeV. Energy is equivalent to mass according to e = mc^2 . But again the particles experience time dilation , particles that would ordinarily decay to Muons in a laboratory remain Pions in the particle beam for a longer time . (I know you want to bring in GR to explain the mass increase). $\endgroup$ – Quitting this forum Oct 29 '13 at 4:18
  • $\begingroup$ Thank you for your answer and your patience. As you can probably tell I only study physics as a hobby, not professionally. $\endgroup$ – Warren Oct 29 '13 at 13:53
  • $\begingroup$ So just to be clear, the effect that gravity has on time is related to an objects 'resting mass' not the relative mass an object gains as it approaches the speed of light? And this is why when we consider time dilation due to velocity we use SR instead of GR. $\endgroup$ – Warren Oct 30 '13 at 14:00
  • $\begingroup$ @Warren you might like to read through this: math.ucr.edu/home/baez/physics/Relativity/SR/mass.html . $\endgroup$ – anna v Nov 7 '13 at 5:19

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