csteele,

Yep it's fairly boggling for us lay people : )

But the Earth is responding to the sun's mass warping spacetime, isn't it?

csteele,

Just a little more on the subject....

From "The Fabric of the Cosmos" (once more)

"...Spacetime and, in particular, the way it warps and curves, is an embodiment of the gravitational field. Thus, in general relativity, acceleration relative to spacetime is a far cry from the absolute, staunchly un-relational conception invoked by previous theories. Instead, as Einstein argued eloquently a few years before he died, acceleration relative to general relativity's spacetime is relational. It is not acceleration relative to material objects like stones or stars, but it is acceleration relative to something just as real, tangible, and changeable: a field--the gravitational field.
In this sense, spacetime--by being the incarnation of gravity--is so real in general relativity that the benchmark it provides is one that many relationists can comfortably accept."

"The earth stays in orbit around the sun because it follows curves in the spacetime fabric caused by the sun's presence."

I can only cope with all this stuff by analogy… Which is always inadequate. In this discussion we are all reliant on George with regard to the mathematics.

One of the problems with the infinity of a black hole is that at 'infinity' descriptions, explanations and comprehension all break down and make no sense – at least to human brains.

csteele asks, "shouldn't I be able to substitute light for gravity" to which the answer would be yes. If they were the same thing, or behaved in the same way. But they're not and they don't.

It would be a bit like asking "shouldn't I be able to substitute plankton for the ocean or its currents?"

"This might be a simplistic question but why is gravity able to reach past the event horizon but not light?"

Is probably best coped with by recasting the question as why is the 'effect' of gravity able to reach past the event horizon? The answer being because it has distorted the topology of space itself – a frequent analogy being a 'stretched rubber' billiard table with a black hole like an infinitely deep corner pocket where the billiard ball photons of light can roll into the pocket – can exist inside the pocket – but can't roll up out of it.

The effect of the gravity is on the shape of the table surfaces.

It is an inelegant analogy because it relies on the way we imagine things falling to picture what it is that causes the things to 'fall' in the first place.

For further headaches, imagine a Tesseract – now imagine moving around inside one. Next, look at pictures of the orthogonal projection envelopes of the Tesseract. Lastly, now try to imagine moving around inside one.

To quote Monty Python, "My brain hurts."

I don't believe it is possible for our brains to cope with these sort of tasks – even if we can cope with the mathematics involved, which humans demonstrably can cope with because that's how it was thought of in the first place.

csteele,

>> how on earth you expected me to let you get away with taking my “two gravitoelectrically interacting particle ensembles, such as two planets or stars moving at constant velocity with respect to each other” and downsizing them to “two gravitoelectrically interacting particles” to prove your point.<<

I am not sure whose point was there to be proved. The question you posed was: “If the sun were to suddenly disappear … would the effect be felt instantaneously?”

You offered a quote from http://en.m.wikipedia.org/wiki/Speed_of_gravity#section_5 the part that spoke of “ two … planets or stars moving at constant velocity with respect to each other”, which I juxtaposed with another quote from the same source that spoke of “two gravitoelectrically interacting particles were to SUDDENLY BE DISPLACED (accelerated) from its position”.

Since the sun and earth are neither “moving at constant velocity with respect to each other” nor does the sudden disappearance of the sun seem to be the same as that of an elementary particle, I do not think any of the two quotes provides an answer to your original question.

I do not know the answer for sure; I do not even know how to “model” in e.g. Einstein’s gravitation theory the “sudden disappearance” of something that determines the gravitation field.

In Newton’s theory gravity acted instantaneously. In Eintein’s theory it is more complicated, see e.g. the discussion in http://physics.stackexchange.com/questions/12736/does-gravity-spread-instantly. They seem to know more about physics than do we here.

WmTrevor,

It is not the mathematics that it is hard to “cope with” here, but the physics, more precisely the question of what does our “theory” (a mixture of a theoretically incompatible Einstein and QM) forecast as an outcome of a thought experiment that we are unable to actually carry out.

My brain hurts too.

Cheers,

Tony Gumby

George, of course you are correct in describing the difficulties about our understanding of the physics... but please accept that for me and (I've no doubt) other Gumbies here the mathematics is as difficult, but in a slightly different way, which is why we regard you as the specialist.

P.S. Don't forget the anaesthetic!