E.T. was one of the first movies I remember seeing in a theater (I was terrified.) 34 years later, if I am counting correctly, we are still waiting for extraterrestrials to return our calls. The New York Times has a review of four new books on the subject, including one (partially) by Neil deGrasse Tyson.

The astrophysicist Neil deGrasse Tyson, in WELCOME TO THE UNIVERSE: An Astrophysical Tour (Princeton University, $39.95), revisits the Drake equation using contemporary data. The equation holds that the number of communicating alien civilizations is a function of seven variables, starting with the rate at which new stars are born in our galaxy, the fraction of these stars that host planets and the number of planets per star that are habitable. In 1961, scientists could fill in only one variable; the other six were sheer guesswork. With our advanced understanding of the cosmos, Tyson — whose book is written with the astrophysicists Michael A. Strauss and J. Richard Gott — is able to work out, in some technical detail, a more sophisticated estimate. The verdict? According to his calculations, we might expect to find as many as 100 alien civilizations in our galaxy communicating with radio waves right now. “So,” he concludes, “we have a chance.”

The unambiguous discovery of an alien signal, if it ever happens, would instantly be the biggest event in human history. It could happen tomorrow, or decades from now, or never. Then again, since we’ve had a few false alarms, we might not recognize or believe a real signal at first, only confirming it after some period of time has passed. I wonder, would we just shrug it off and continue with our lives, or would it really change the way we think about ourselves and our place in the universe.