B Propagation of changes in a gravitational field

[stevendaryl]

Ok, now we're getting somewhere. So presumably these changes propagates at c as well?

It depends on what you mean by "propagate". The gravitational field can change with time. That doesn't imply anything "propagating". Propagation is really applicable to perturbations. If you jiggle a mass, then that will cause a jiggle in the gravitational field, and that will propagate out at the speed of light.

I thought it was the mass inside the black hole that emitted the waves, and that these waves escaped the event horizon.

No, gravitational waves are disturbances in the gravitational field. The "source" of a gravitational wave isn't a mass, it's a little jiggle in a gravitational field. So the waves don't propagate from the center of the black hole; they propagate from the field surrounding the black hole.

 

[Lord Crc]

It depends on what you mean by "propagate". The gravitational field can change with time. That doesn't imply anything "propagating". Propagation is really applicable to perturbations. If you jiggle a mass, then that will cause a jiggle in the gravitational field, and that will propagate out at the speed of light.

Right, and my misunderstanding was equating that jiggle with gravitational waves.

No, gravitational waves are disturbances in the gravitational field. The "source" of a gravitational wave isn't a mass, it's a little jiggle in a gravitational field. So the waves don't propagate from the center of the black hole; they propagate from the field surrounding the black hole.

Gotcha. I'll have to spend some time reprogramming my brain but I think I got the point now.

Thank you all for your input and patience. Clearly I need to work on my question-asking skills.