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Interesting. my concern would be the extremes of the gedanken. as other have pointed out in similar threads; do the impossibilities of the initial conditions render any insight as invalid? your argument seems, to my untutored eye, to be sound. from quick research the agreement of birkhoffs theorem with newtons shell theorem is a corollary of the main theorem so any challenging of that theorem would have to show the link (between theory and consequence) still holds for a collapsing sphere. this is an area that has great mathematical agreement - and it would seem to me that rigorous mathematical argument is a necessary part of any challenge. Matthew
Imagine an empty universe, where nothing exist and time stands still.
Then add lots of stars
Once the curvature of space-time have propagated, all gravity is instant. When a star moves, the direction of the gravity is immediately reflected for all other observers. Infinitely faster than light. The logic behind this is : once space is curved, everything is affected by the curvature. If one star is defined as stationary, and another star is moving toward it - both stars are affected by the change in curvature - because we can at any time redefine which of the two stars are stationary. This is relativity.
As all stars in the sphere accelerate, so their momentum/energy increase. Increasing momentum/energy propagate at the speed of light. My intuition tell me that the increase in momentum should affect the closest stars inside the sphere first, and as long as the collapse of the sphere is accelerating - all stars inside should experience an outbound gravitational effect. Visually, this should lead to a redshift effect when watching other stars inside the sphere.Where am I wrong in this last conclusion, that a sphere that is collapsing by its own gravity will NOT have zero gravity inside - contrary to Birkhoffs theorem.