In a valley eight miles southeast of the Norwegian city of Tromsø, a radar antenna has just transmitted a short bit of radio programming to potential alien listeners: some specially composed electronic music and a tutorial about geometry and the use of binary numbers.
This isn’t the usual approach to the search for extraterrestrial intelligence (SETI). Ordinarily, scientists engaged in SETI use such antennas with the hope of hearing a signal that would have been broadcast tens, hundreds, or even thousands of years ago. So far, no dice. But at least SETI offers the chance of short-term success. It’s like a slot machine that’s been stubbornly ungenerous despite having been fed a ton of quarters. There’s always a chance the next coin will trigger a jackpot. SETI could succeed before tomorrow.
That’s not true with the Tromsø transmission. It’s an example of active SETI, or what some scientists call METI (for messaging to extraterrestrial intelligence). The idea is simple: Send a signal that would alert aliens we’re here, and listen for a reply.