A) I am intrigued by the multiverse theory as mentioned in Stephen Hawking's new book, "The Grand Design". According to his theory, one can have different 'universes' in one ultimate existence, a 'multiverse'. But what exactly differs between one universe and the other? Is it that:
- There are different universes; the existence of each of which cannot be measured from any other universe; but all universes have identical laws of physics, and all the physical constants such as the gravitational constant and the speed of light are the same across all 'universes'?
- There are different universes, all of which are governed by the same laws of physics, like general relativity and quantum mechanics ( eg: the Einstein gravitational equations and Dirac equations are of the same form across all universes), but where physical constants are different? For example, in another universe, the speed of light may be only a half of what it is here.
- There are different universes, but all these universes have different physical laws. For example, the Einstein gravitational equations are only applicable in a subset of these universes, there can be a universe where the gravitational equations take a different form of mathematical expression; and in a weak gravitational field limit, the gravitational force follows a 'proportional square law' instead of newton's 'inverse square law'.
Which of the above is the real multiverse theory?
B) In any of these cases, I fail to see how does the string-theory/M-theory gives rise to the multiverse concept, any layman explanation for this?