It's something science fiction readers and writers love to talk about all the time. Making first contact with another civilization would of course revolutionize everything about the way we live. Of course the typical science fiction book will lead you to believe that first contact is in the form of direct contact with alien races, as in meeting them in person, but it's much more likely that our first form of contact will be through signals sent to one another, and chances are that's going to take a long time, which brings me to the topic this post is on.
While we've only sent out signals to distant worlds for the last decade or two. Just traveling at the speed of light, not taking into account the decrease in signal strength over distance, we've only reached a few hundred stars, most of which are red or brown dwarfs. However, we've unintentionally been sending out signals for much longer, going back into the early 20th century, however most early signals were only intended for short-distance communication and likely wouldn't get beyond the orbit of the Moon, much less interstellar space. However more intense radio signals have been used over time, to a point where our planet is essentially a beacon of radio waves in space. Of course any civilization within 50 light years, with sufficient signal sensitivity, would have already noticed us and possibly recognized us as a civilization. But how long would it be before we made contact?
Well assume we send out a signal in 2000 AD, and it reaches an alien civilization 50 light years away. By the time it reaches them, it's 2050. It would be 2100 before we receive any signal whatsoever from them, and much longer for them to reach us. Even if they traveled at 1/10th at the speed of light, or ~1,086 miles per second it would take them 500 years. In other words, if a civilization recognized we exist recently, we won't know for quite some time, and if decide not to send any signals before arriving, it could take until at least 2500 AD before we know.
Then its also possible we've already found alien signals long ago. On August 15, 1977, Jerry Ehman, working for SETI using the Big Ear radio telescope, detected a radio signal coming from the constellation Sagittarius. The location is fairly uncertain, and is limited to between two narrow bands in the area, neither of which contains any remarkable stars. Chances are that whatever the signal came from is very distant, leaving one to wonder how strong the signal sender would have to be. According to one source, it would have to be approximately 2,200,000 watts of power. For comparison the strongest signal transmitter on Earth is only 2,500 watts, roughly 1/1000th of the required amount. Whether or not it came from an intelligent civilization is likely something we won't know for quite a long time.
