2

Possible Duplicate:
The speed of gravity
Does gravity travel at the speed of light?

Imagine there is a large mass $m_1$ (e.g. a star) 1 light-year away from us. It is stable, stationary relative to us and has been in place for a long time, much more than a year. A small mass $m_2$ (e.g. a proton) has just been created locally, 1 light-year away from $m_1$.

How much time does it take for $m_2$ to feel the gravitational pull of $m_1$, and how can this be explained with the virtual-graviton theory of gravity?

Some possible answers I can imagine:

a) Immediately $m_2$ interacts with virtual-gravitons sent by $m_1$, a year ago.

b) 1 year. It takes this long for freshly launched virtual-gravitons from $m_1$ to reach $m_2$ and vice-versa before any effect is felt on either mass

c) 2 years. There needs to be an exchange of information / virtual-gravitons between $m_1$ and $m_2$ and this is the minimum time it could take.

d) None of the above

Community
  • 1
roblev
  • 701

1 Answers1

2

This isn't really an answer, since Chris White's comment links a couple of questions that cover the same ground as your question. However you specifically ask about virtual gravitons, so I thought it might be worth a note on this.

Even if virtual gravitons are a good way to describe quantum gravity (and to be fair at such low energies they probably are) the energy of a graviton is so low that the interaction of even something a small as a proton is well described by classical gravity and there is no need to involve gravitons. The proton will feel the spacetime curvature created by the distant star immediately i.e. the answer is (a). However the star won't feel the (very small!) change in the spacetime curvature created by the proton for a year.

John Rennie
  • 367,598