It's been 46 years since Frank Drake aimed an antenna at the stars in the first modern SETI experiment. His hope was to hear a deliberate signal - guided into space by intelligent beings - rather than the natural, noisy dance of hot electrons.
Since then, SETI has expanded its search space, bettered its equipment, and refined its strategies. But the bottom line hasn't budged: still no confirmed chitter from the cosmos.
Some people mistakenly confuse a long search with a thorough one, and figure that the lack of a SETI detection indicates that we're alone in the Galaxy. This, however, is nonsense.
The number of star systems we've carefully examined is only about a thousand. That's a trifling sample compared with the several hundred billion suns that stud the Milky Way, and of little statistical significance. It's comparable to initiating a quest for Americans who play the oboe, but considering the search meaningful after interrogating only two people. In addition, and of great consequence to those who actually do SETI, the speed of the experiments is growing geometrically. Every two years, the breadth of the search approximately doubles.
In my opinion, the reason that SETI hasn't yet succeeded is simple: we've just begun to look. Nonetheless, every day I get e-mails from folks who suggest other reasons for our failure to pick up an alien thrum. It probably doesn't surprise you, but many of these proffered explanations are similar. Indeed, there are four conjectures that are so popular, so prevalent in e-mail after e-mail, that I list them below for your edification and assessment. I also append my own take on each.
Top four reasons people suggest for why SETI hasn't found a signal
1. "You're counting on the aliens using communication technology (radio, light) that's oh-so-last century. They will be far beyond this."
In other words, SETI's technical approach is wrong. Variations on this theme are to suggest that we should instead be looking for gamma rays (more bits per second), gravity waves (unclear benefit, except that some people think they move faster than light), or taking advantage of what is somberly and imposingly described as "hyperdimensional physics."
Well, gamma rays are wasteful, requiring an enormous amount of energy per bit. Gravity waves are hard to produce (you need to shake planets or something similar) and hard to detect (consider the complexity of LIGO or any of the other gravity wave experiments). In addition, and as far as we know, gravity waves move no faster than the speed of light.
As for invoking hyperdimensional physics - well that might be dandy if we knew what it was.
True enough, there may be some important, undiscovered laws of the universe that will show us how to send bits from one place to another either more cheaply than light and radio, or faster (and no... quantum entanglement doesn't seem to do it). If and when we discover these new laws, we'll adjust our experiment accordingly. In the meantime I can only point out that, without the physics, it's hard to wire up the equipment!
2. "If hi-tech societies or thinking machines were out there, they'd have colonized the Galaxy by now. Clearly, we're alone... lone... lone."
This is, of course, an appeal to the Fermi Paradox, which assumes that if sophisticated societies are common, they should also be ubiquitous. Well, I just checked the parking lot outside the Institute, and I see no large animals with long, prehensile noses. The conclusion a la Fermi is that elephants don't exist on this Earth, right? After all, any putative pachyderms have had plenty of time to get to my office, even if only a few of them are so inclined.
To use the Fermi Paradox as a reason for the lack of a SETI signal is to make a very big extrapolation from a very local observation. Seems chancy to me.
3. "The aliens don't want to communicate with us. Look at what we're doing to the planet!"
Even aside from the fact that our television signals haven't yet oozed far enough into space to tip off any aliens about our proclivities for deadly conflict, our enthusiasm for environmental degradation, or our addiction to sports, it's self-centered in the extreme to think that any of this would matter to them! Did E.O. Wilson refuse to study ants because they routinely war with other ants?
4. "You SETI types are just looking in the wrong places. We know where the extraterrestrials are: on a planet in the Zeta Reticuli system."
I like this explanation the best, even though it's the worst. At least it offers a recipe for remedy: simply turn our antennas at the nearby (39 light-years) double-star Zeta Reticuli, and the signals will thunder in. (For those readers who are scratching their crania at this, I note that Zeta Reticuli is the star system that was the supposed origin of the short, brazen aliens who, in 1961, reportedly abducted social worker Betty Hill and her postal worker husband, Barney. The system's identification is based on a "star map" Betty drew with a dozen points on it.) But allow me to note that we did look at both of Z. Reticuli's stellar components during our SETI observing run in Australia, a decade ago. The aliens, for their part, remained coy.
There's one thing you can definitely say about SETI: there's no dearth of ideas on how to do the experiment better. I offer this listing to alert readers to the fact that not all ideas are new.
- Just the Facts: Three SETI Myths
- Mars Analog on Earth: Taking a Trek in the Outback
- VIDEO: Figuring Out the Odds of ET Existing
- VIDEO: Reflections of Fermi's Paradox
- VIDEO: Listening for Life
- GALLERY: Scenes from SETI at Arecibo