In the last two months, three rare and dangerous collisions -- in the sea, air and space -- have raised the question: What are the odds?

Two submarines carrying nuclear weaponry of Great Britain and France collided, stirring fears of an imbalance in global nuclear deterrence. Geese crashed into and disabled two engines on the same commercial jet, requiring a gutsy landing on the Hudson River. And most recently, two satellites ran into each other and broke into pieces, more space junk that threatens telecommunications.

Each...