Ask A Scientist© Astronomy Archive

Question:  Assuming the theory that the universe started from a single "point"
(big bang), what caused imperfections during expansion?  The question being "How 
could galaxies form from singularity?" Singularity is by definition one
dimensional and thus inherently homogeneous.
john b smith

Answer:
1. It need not be true that the universe started from a point. There are
solutions exist solutions to the
Einstein's theory which allow a n infinite universe mand the universe is
infinite from the initial instant onwards. This takes care of your objection.

2. There are mechanisms which can generate imperfections
or inhomogeneities without violating any know
principle of Physics.

Once the fluctuations have been generated, gravity
makes sure that large structures can form. However,
gravitation requires large perturbations to begin
with as it is a weak force.
Jasjeet ( jasjeet s bagla )