Quote:
Originally Posted by sjastro
Apart for violating isotropy, there is no reason why local geometry should be any different. The Hubble radius for any observer in the Universe is 13 billion light years. Space-time within this radius is spread out to obey a flat Euclidean geometry.
The use of non Euclidean geometry for space-time is very much a localized phenomena for high gravitational potential objects such as neutron stars and black holes.
For anything else flat space is a good approximation.
I'm afraid I can't see how sitting in a void actually increases the velocity of space time expansion. Low density or no density will retain the inertia effect of the BB, in which space-time expansion proceeds at a constant velocity.
Regards
Steven
|
Being in a void confuses the local versus universal seperation rate and local expansion (recession velocities) in their models. Frankly I think its a strech (pun not quite intended). Recession velocities due to an expansion of space time can only occur in non gravitationally bound regions. I think their thinking is a lower mass volume would have a different (higher) expansion rate as it would have a lower gravitational well to slow expansion. At under $7 its worth a read.
Personally I think all space time being the same in all directions at a large enough scale is a bit arbitary. But I have no thoughts on how much variation could exist nor what gradations would be needed in a model to compensate. But if large difference did occur this might possibly re-shape the topology of space time (in a way that necessiates more than a flat Euclidian model). Its doubtful in my mind that this last part would be true - but should be detectable so it could be tested simply to be ruled out.
.
