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Jan3-08, 08:59 AM
Sci Advisor
P: 7,599
Lost sleep on this question...

Quote Quote by Senlathial View Post
Thanks Dale! I did not understand everything on those pages, but I think I understand a little.

So, in framing my question above, I mistook rest mass for relatavistic mass (which I think is the rest mass plus the energy of its movement). Therefore, if a spaceship flies by a rock at the speed of light, the relativistic mass doesn't really add any more affects to gravity than the invarient mass. Both the outside observer and the astronaut in the ship would see the rock move only due to the invarient mass, and not the near infinite mass I was thinking of.

If this is correct, I will sleep tonight! Thanks again!
No, motion does have an effect on gravity. However, the effect is not as simple as using the Newtonian formula for gravity and replacing "mass" with "relativistic mass".

A close, but imperfect, analogy for what happens to the gravitational field of a moving mass is what happens to the electric field of a moving charge. The case of the moving charge is considerably easier to understand, however. See for example (and also *_14.pdf).

In words: the electric field becomes concentrated in the transverse direction. A similar effect occurs for gravity.

For more discussion see the following old thread: