[nine_k]

I suppose nothing but gravitational waves can escape the even horizon — or, rather, gravitational waves are born near / around it, because the black holes bend the space enormously.

OTOH whatever else may be outside the black holes near the merger and count towards their mass for astronomical purposes, such as accretion discs, should be much lighter weight than what's inside the event horizon.

[ars]

Gravitational waves also can not escape. Those waves carry energy, and it's actually energy that can't escape.

The waves are actually made just to the outside of the event horizon.

[berkes]

I always understood that the waves are "made" everywhere, but that only the waves outside the even horizon will escape.

Was my understanding wrong all along?

[ars]

Sort of correct?

Time is halted inside the black hole, so the waves made inside it never show up. Static gravity does show up though, but changes do not.

[thaumasiotes]

> The waves are actually made just to the outside of the event horizon.

How do we feel about this vis-a-vis action-at-a-distance?

[ars]

Gravity does action at a distance. That's its thing.

The reason these waves are not generated from inside the black hole is that, to us, time stops there. For example these black hole mergers aren't actually merging, they are getting closer, and then they time dilate out of existence.

[thaumasiotes]

> Gravity does action at a distance. That's its thing.

Why does it need to travel in waves at the speed of light? If one mass moves, a distant mass is unaffected until the information reaches it. That's the opposite of action at a distance.

[ars]

Your question is confusing. Action at a distance does not imply going faster than light, it means there is some sort of field connecting the two things.

[thaumasiotes]

Action at a distance means there is nothing connecting the two things. That's the "distance" part of action at a distance. Modern physics rejects the concept, saying instead that forces are carried by particles from a source to a destination, and the effect of the force is the result of local [opposite of "distant"] interaction with the particles carrying the force.

Compare wikipedia:

> Under our modern understanding, the four fundamental interactions (gravity, electromagnetism, the strong interaction and the weak interaction) in all of physics are not described by action at a distance.

( https://en.wikipedia.org/wiki/Action_at_a_distance )

Or: https://en.wikipedia.org/wiki/Principle_of_locality

> This is an alternative to the concept of instantaneous, or "non-local" action at a distance.

> The idea is that for a cause at one point to have an effect at another point, something in the space between those points must mediate the action. To exert an influence, something, such as a wave or particle, must travel through the space between the two points, carrying the influence.

You'll note that "action at a distance" does in fact specifically mean that information travels faster than light!

But this understanding would seem to be incompatible with the idea that the mass inside a black hole can interact gravitationally with anything outside the black hole.