  We prove the Arad-Herzog conjecture for various families of finite simple
groups- if A and B are nontrivial conjugacy classes, then AB is not a conjugacy
class. We also prove that if G is a finite simple group of Lie type and A and B
are nontrivial conjugacy classes, either both semisimple or both unipotent,
then AB is not a conjugacy class. We also prove a strong version of the
Arad-Herzog conjecture for simple algebraic groups and in particular show that
almost always the product of two conjugacy classes in a simple algebraic group
consists of infinitely many conjugacy classes. As a consequence we obtain a
complete classification of pairs of centralizers in a simple algebraic group
which have dense product. In particular, there are no dense double cosets of
the centralizer of a noncentral element. This result has been used by Prasad in
considering Tits systems for psuedoreductive groups. Our final result is a
generalization of the Baer-Suzuki theorem for p-elements with p a prime at
least 5.
