Okay, I'm confused.
We are always shown the picture of the Einstein space/time continuum: a marble (representing a planet) rolling around on a cross-hatched sheet, circling a steep central drop-off (representing a black hole). The momentum of the marble keeps it from falling inward.
Gravity, in this model, is the curvature of the sheet (the space/time continuum).
Isn't the curvature "felt" instantaneously by the marble because gravity is embedded in the very "fabric" of the space/time continuum?
Damnit Jim, I'm a biologist, not a physicist!
I saw a model of this in the Los Angeles County Museum of Science and Industry, many years ago. At the time, I thought that showing a model that used gravity to demonstrate the concept of gravity was cheating. ;)
Gravity and magnetism are two of my favorite puzzles. They embody "spooky action at a distance" for me...
Yes. And if you pull the sheet down a little farther in that spot, the curvature won't readjust itself instantaneously across the whole sheet... instead, the increased curvature propagates as a wave outward from the place you pull on, at some measurable rate.
If the gravitational attractor (say, the Sun) is just sitting there minding its own business, then yes, the gravitational field ("dent" in the space-time rubber sheet) is constant and any other object (e.g. a comet) which wanders by will "feel" the effect of the gravitational curvature "immediately".
But what this discovery describes is how quickly the "rubber sheet" responds to *changes*. For example, if you just plunked the Sun down into a spot of space where it didn't previously reside, the question is how long it would take the resulting "curvature" of the "rubber sheet" to propagate outward. Or alternately, if you start rolling the ball (Sun) north across the sheet, does the rubber sheet instantly adjust as the ball rolls, or does it take a little time for it to "catch up" (i.e., will a spot of curvature 50 yards away instantly feel the change, or will the changing curvature have to "ripple" out there like a crowd doing The Wave?
This is hard to describe will in words, an animation would be ideal, but I don't know of any on the web which show this.