B Where Does Momentum Go Near Merging Black Holes?

[Filmo]

Let's say you start 2 rockets in the opposite direction from a platform that's close to two soon to be merging black holes, the first rocket starts way before the second, but the second will ultimately fly a bit further, before they stop and fly back to towards the black hole(s). When black holes merge, they create new gravity and this gravity is supposed to attract the rockets. The second rocket who is closer to the merged black hole and has more momentum than the first rocket will not make it as far as the first one. This means that the second rocket that had more momentum, is losing some momentum and the first rocket will actually fly back faster. Where has the momentum of the second rocket gone?

But what if gravity doesn't really attract, but it actually increases the momentum and this effect is only visible when new gravity is created?

 

[jbriggs444]

When black holes merge, they create new gravity

The merger of black holes does not create new gravity. Heuristically, the gravitation of one merged hole is the same as the combined gravitational effects of two separate holes.

In general relativity, momentum is conserved locally. I am not expert enough to know how this translates into global momentum conservation. Or the extent to which a law of global momentum conservation can even be stated in the context of curved space-time.

 

[PeroK]

Let's say you start 2 rockets in the opposite direction from a platform that's close to two soon to be merging black holes, the first rocket starts way before the second, but the second will ultimately fly a bit further, before they stop and fly back to towards the black hole(s). When black holes merge, they create new gravity and this gravity is supposed to attract the rockets. The second rocket who is closer to the merged black hole and has more momentum than the first rocket will not make it as far as the first one. This means that the second rocket that had more momentum, is losing some momentum and the first rocket will actually fly back faster. Where has the momentum of the second rocket gone?

This post is too much a confusion of ideas to be answerable. There are no black holes in classical physics - so, as an absolute minimum you would need to upgrade your ideas of time, space, momentum and motion from classical to relativistic thinking.

 

[Dale]

When black holes merge, they create new gravity

What does this mean? Are you taking about non-linear parts of the Einstein field equations? If so, can you point a reference to exactly what effects you mean by this?

Momentum is locally conserved, so if any momentum disappears from the matter then it must go into local gravitational waves.

 

[PeroK]

Are you taking about non-linear parts of the Einstein field equations?

Not in a B-level thread, I would imagine!

 

[Dale]

Not in a B-level thread, I would imagine!

Definitely not! But I cannot think of any other legitimate meaning for the phrase about creating new gravity.