How do you find an alien?
We can't just go and look for them, even if they do exist. There are probably billions of planets in the Milky Way alone, and to send a spaceship even to the closest ones outside our own solar system would take tens of thousands of years.
Maybe, though, we don't have to go all the way there. Maybe we could just send a signal. Come to think of it, maybe they're doing that already!
This is one line of thinking behind the work done at the SETI Institute in California. SETI stands for Search for ExtraTerrestrial Intelligence, and for a number of years SETI researchers have been scanning the skies for radio signals. Now the SETI project has dedicated its first full time visible light receiving telescope at the Oak Ridge Observatory in Massachusetts.
Why a visible-light-receiving scope?
It's just a guess, but laser pulses, for example, would make for a natural interstellar communication device. An intense pulse of laser light could be far brighter than the sun, and would stand out against the galactic background.
Who knows? Such a laser might carry information encoded in its frequency, or maybe just act as a kind of homing beacon. Once you spot it, you know where to look to find other civilizations like your own.
So far, no one has found any conclusive evidence of alien life at all, much less intelligent life. However, the Milky Way is a big, big place. If there is an alien lighthouse shining out there somewhere, finding it would change everything on Earth.