We probably won’t hear from aliens. But by the time we do, they’ll be dead.

animation of signals from alien civilizations
CAN YOU HEAR ME NOW? Electromagnetic signals (blue circles) from alien civilizations will continue traveling through the Milky Way even after the aliens are gone. The appearance of a doughnut hole represents when a civilization dies out.

If signals from an alien civilization ever reach Earth, odds are the aliens will already be dead.

In an effort to update the 1961 Drake Equation, which estimates the number of detectable, intelligent civilizations in the Milky Way, physicist Claudio Grimaldi and colleagues calculated the area of the galaxy that should be filled with alien signals at a given time (SN Online: 11/1/09).

The team, which includes Frank Drake (now a professor emeritus at the SETI Institute in Mountain View, Calif., and the University of California, Santa Cruz), assumed technologically…

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