Quote Originally Posted by christopher leigh View Post
Heisenberg had a discussion with Einstein. He said to Einstein 'A good theory must be based on directly observable magnitudes.'

To which Einstein replied: 'But you don't seriously believe that none but observable magnitudes must go into a physical theory.'

Heisenberg: 'Isn't that precisely what you have done with relativity.'
Einstein: 'Possibly I did use this kind of reasoning, but it's nonsense all the same.'

Nobody knows what gravity is. Certainly not Stephen Hawking who isn't even a physicist. He's belongs to the 'rabbit out of the hat' brigade.
Firstly, you have truncated the quote between Heisenberg and Einstein, and this illuminates more of the discussion than you have quoted. Secondly, this refers to Quantum theory, of which Einstein was a noteable opponent ("God does not play with Dice"). But this is getting away from the point. General Relativity is not a perfect theory by any stretch, but observations (e.g. deviations in Mercury's orbit around the Sun, as to those predicted by Newton, Gravitation Lensing etc) have validated it and it is accepted by nearly every physicst and the general scientific community.

I do not know what you mean by "rabbit out of the hat brigade"