4 ms·
A black hole is a region that light cannot gravitationally escape. It has nothing to do with singularities which often but not always exist inside of a black ho
by garmaine 9y ago
A black hole is a region that light cannot gravitationally escape. It has nothing to do with singularities which often but not always exist inside of a black hole. Small black holes often have singularities just to have enough mass density to capture light. It is not required though — imagine a binary system of two neutron stars that are each just below the mass threshold to collapse into a singularity. It would be a black hole to external observers. Oddly larger black holes require less mass density. More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang, meaning we exist inside of a black hole as big as the observable universe.
I’m not sure why I’m being so heavily down voted for stating this fact you can find in any cosmology textbook.
- yaks_hairbrush 9y ago> More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang This is true... > meaning we exist inside of a black hole as big as the observable universe. This is an unwarranted jump. I'd recommend looking at the reference [0] from Sean Carroll. [0] http://www.preposterousuniverse.com/blog/2010/04/28/the-universe-is-not-a-black-hole/ http://www.preposterousuniverse.com/blog/2010/04/28/the-univ...
- garmaine 9y agoThere is nothing to be learned in that article. He says that the question is nonsense because we don’t know what is outside the observable universe. That’s not a very interesting thought restriction.