Is There Intelligent Life Out There In The Universe?

That question is more complicated than you might imagine.

What constitutes intelligent life? How does it come to be? How many totally random happenstances occurred just so we could exist, and could those happenstances occur again elsewhere out there? Why, as Fermi so astutely asked, haven’t intelligent beings communicated with us yet?

Theoretical physicist Brian Greene, author of The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos,a Columbia University professor, and chair...