Background

• The main questions: Are we alone or is there intelligent life elsewhere?
• Need to ask first: How could we find out if it is out and there? How can we communicate?

Where Could Intelligent Life Possibly Develop?

• First conditions: Existence of extrasolar planets (we now know there are lots of those); Environments suitable for life (life in general, we haven't found those yet, but we have found planets with atmospheres, and there are ideas for how to go further).
• Additional conditions: In addition to life existing on a planet, what is the likelihood that it develops into intelligent forms and civilizations?
• How many civilizations might exist in our galaxy? Use the Drake equation to estimate it theoretically; Optimistic result: As many as the average lifetime of a civilization expressed in years; Carl Sagan estimated about 1 million in our galaxy, one every 50 pc!

  What about Communications and Contact?

• Detecting signals – SETI: Some radio telescopes are listening (What was the 1977 "Wow!" signal?); Our best bet is around 18-21 cm waves; Project Phoenix was ended without a signal, but there are other searches; An optical SETI telescope has started operating at Harvard, looking for brief flashes of light.
• How can we reach out? Interstellar travel? Takes far too long. Send out probes? Already done (Pioneer 10, Voyager); Send radio waves? In 1974 we broadcast a radio message to space, and we're waiting; Also, we may be contributing to future life elsewhere by leaking out our own, panspermia-style.
• Contact? No real evidence yet of extraterrestrial presence on Earth (despite some relatively widespread beliefs).

 Summary: SETI could succeed tomorrow, or it may be an endeavor for multiple generations: We are a very young technology in a very old galaxy; Our own leakage radiation outshines the Sun at many frequencies, and we are detectable to others; When our use of the spectrum becomes more efficient, it will be time to consider deliberate transmissions and the really tough questions: Who will speak for Earth? What will they say?

So far, though, the conclusion is: "We live in a quiet neighborhood" (Peter Backus, Seti Institute).