General relativity is in the old Newtonian framework where you predict what will happen, not the probability of what will happen. And putting together the probabilities of quantum mechanics with the certainty of general relativity, that's been the big challenge and that's why we have been excited about string theory, as it's one of the only approaches that can put it together.
Brian GreeneBefore the discovery of quantum mechanics, the framework of physics was this: If you tell me how things are now, I can then use the laws of physics to calculate, and hence predict, how things will be later.
Brian GreeneEvery moment is as real as every other. Every 'now,' when you say, 'This is the real moment,' is as real as every other 'now' - and therefore all the moments are just out there. Just as every location in space is out there, I think every moment in time is out there, too.
Brian GreeneFor most people, the major hurdle in grasping modern insights into the nature of the universe is that these developments are usually phrased using mathematics.
Brian GreeneThe central idea of string theory is quite straightforward. If you examine any piece of matter ever more finely, at first you'll find molecules, atoms, sub-atomic particles. Probe the smaller particles, you'll find something else, a tiny vibrating filament of energy, a little tiny vibrating string.
Brian Greene