The search for intelligent life in the universe took a hit earlier this year when SETI had to put the Allen Telescope Array on hiatus due to lack of funding. (It now appears that SETI may soon raise enough money to get the ATA up and running again.) But then, there’s a good chance that this approach, based on the idea that somewhere in the universe alien civilizations are sending radio messages directed at Earth, may be completely misguided. “In my opinion,” Arizona State University astronomer Paul Davies writes in his book The Eerie Silence, “this ‘central dogma’ simply isn’t credible.” He points out that if even a fairly close civilization, say 1,000 light years away, were to look through a telescope and find Earth, it would see the planet 1,000 years in our past. Why would they bother to send a message to a planet that hadn’t even discovered electricity, let alone built a receiver for such a message?
If listening for radio messages is a bit of a long shot, how else could we go about it? Here are 10 ideas that have been put forth, and even put into practice, by various sources (and if you want more detail, I recommend Chapter 5, “New SETI: Widening the Search,” of The Eerie Silence):
1 ) Optical SETI: Russian and American scientists have been searching the skies periodically for the last couple of decades looking for laser light, which is not only distinguishable from other natural types of light, such as starlight, but could only be produced by an intelligent source.
2 ) Look for huge alien structures: When people bring this one up, the best example is always the Dyson sphere, a hypothetical structure that a civilization would build around an entire star to capture all of its energy.
3 ) Find evidence of asteroid mining: Humans are already looking at the asteroids in our solar system and considering their potential for mining, so why wouldn’t an alien civilization do the same? Evidence could include changes in the chemical composition of the asteroid, the size distribution of debris surrounding it, or other thermal changes that could be detected from Earth.
4 ) Check planetary atmospheres for pollutants: If there are non-natural chemicals, such as chlorofluorocarbons, in a planet’s atmosphere, it’s a sign that there might be someone with technology on the ground.
5 ) Look for signs of stellar engineering: For now, this is the stuff of science fiction, but a civilization capable of tinkering with a star would surely be of interest to us Earthlings.
6 ) Look for an alien artifact here on Earth: Earth has been around for billions of years—who says that aliens haven’t been here before? If they visited long ago, perhaps they left behind something in a difficult-to-reach spot, such as at the bottom of the ocean.
7 ) Find a pattern in neutrinos: Davies points out in his book that neutrinos, those ghostly subatomic particles, are probably better suited for bringing a message over a long distance than either radio or optical signals. A message would have to be simple—transmitted in a sort of alien Morse code—but we could detect it here on Earth.
8 ) Check for a message in DNA: DNA is just another way to encode information. Aliens, or even just an alien probe, could have visited Earth long ago and inserted a message into some ancestral creature. Of course, there are several hurdles to such an idea, as Davies notes—getting the message here, getting it into a critter, keeping it from getting destroyed by mutations over perhaps millions of years—but it certainly an intriguing possibility.
10 ) Invite ET to log on: A group of scientists have set up a web site asking for an extra-terrestrial intelligence to send them an e-mail. So far all the responses have been hoaxes, but asking for a shout-out never really hurts.