A new Drake Equation calculation suggests ghost signals haunt parts of the Milky Way
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 savvy civilizations are born and die at a constant rate. When a civilization dies out and stops broadcasting, the signals it had sent continue traveling like concentric ripples on a pond. Part of the Milky Way should be filled with these ghost signals.
If the civilization lasted less than 100,000 years