SETI

Given the sheer vastness of the universe, the growing number of Earth-like planets that have been discovered, and the logical conclusion of the Drake Equation, it's extremely unlikely that humans are the only sentient, sapient, intelligent, technologically developed form of life in the universe. That's why organizations such as SETI (short for the Search for ExtraTerrestrial Intelligence) have radio telescopes pointed to the sky whose sole purpose is to listen out for any messages those intelligent life forms might have sent out our way.

(If you're wondering how this all works, consider this: We currently have the technology to find extraterrestrial planets orbiting other stars, and are perfecting the technology to analyze their atmospheres for water, which is considered the universal requirement for life. Any alien races with the same technology might have sussed out that Earth is a life-sustaining planet and sent a concentrated message our way. The problem with these messages are many. There are so many different frequencies that we're not sure which to listen in on (think of it like this: your friend is going to send you a radio message today, but you're not sure when, and you only have ten radios. However, there are one thousand possible radio stations your friend could be sending this message on.) and some scientists believe that an alien civilization might scatter their message across every frequency to increase the probability of it arriving here at least mostly intact. There's also the problem that there are so many planets, and so much universe out there, and until fairly recently, we weren't sure where to point our telescopes. (Your friend could send you a sky-written message, but if your back is turned, you're still not going to see it.) There's also the problem that messages decay over long distances, such as those between planets, and that the extraterrestrial races might have already given up contacting us and/or are simply not interested in making contact because they have enough friends/problems of their own.

If we ever did get a message, there would also be the problem of interpreting it (it would be a lot simpler if those dang aliens would just speak English, right?) and replying. If we got a message for 80 lightyears away, that would mean that it was sent 80 years ago, and our reply would take an additional 80 years to reach them. Unless these ET's were extraordinarily long-lived, it's likely that we'd be sending a message back to their children or grandchildren. Also, we'd never get to hear how that particular conversation ended, and that'd just be maddening.

You can learn more about the work SETI is doing and read about new developments in their search here. And if you think that this is super-cool/awesome/a worthy cause/kinda a good idea, check out SETI@home to see how you can help for free.