- #1

garys_2k

- 10

- 0

**A "Simple" Relativity Question...**

I was asked this question on another forum, and it seems easy at first glance but may be more subtle: What would an observer on a very massive star (yeah, a well insulated observer) see about a small body falling in toward the star, from very far away?

Would the apparent mass of the body change? If so, how would you calculate its mass at any point during the fall? Ditto the incoming body's speed -- what would it be as if fell? All the questions from the reference of the observer on the star.

Obviously SR will influence the apparent mass and speed, but what about GR? Does a freefalling body undergo GR changes? Also, does the fact that the observer is sitting in a pretty deep gravity well influence what he measures about that falling body?

I thought I knew how to handle these cases, but when put all together I'm not sure what the net effects are.

Thanks in advance for any help!