Although there is strong reason to believe that any star more
massive than the Chandrashekar limit will turn into a black hole, that
does not mean that any collection of things whose total mass is that
big will do so. Consider two stars, each with 2/3 the Chandrashekar
mass, very far apart and departing rapidly from each other (faster than
the classical escape velocity). They will never get together and form a
So whether objects collapse depends not only on their total mass but also on the initial distribution of relative velocities.
There is no way within the known laws of physics that any object
can travel past any other object with relative speed greater than the
speed of light. However, in general coordinate systems designed to
include all objects in our universe, the rate of growth of the spatial
coordinate of some object, as a function of its time coordinate, can
exceed c. That object would be outside our horizon.
As for the question of what set the initial conditions for the Big
Bang, we just don't know. People are trying to work out a consistent
combination of quantum mechanics and gravity, which may lead to
pictures of how the spacetime of our universe is included in some
larger manifold. If that works, we may have some more definite reasons
for thinking of other universes.
Some theorists speculate that we live in one of a large multitude
of possible universes, each with its own unique physical laws. This is
a fun idea to entertain, although I have yet to see anyone make an
acutal prediction using this idea which can be tested in the laboratory
or in anywhere else in the accessible universe. Maybe someone will come
up with something good (but given that signals travel only as fast as
light, I'm afraid we're stuck in the corner of just this one universe
we can see. Fortunatley this includes a vast amount of past history of
things far away, but still not enough for this idea).
(republished on 07/19/06)