by Seth Shostak, Senior Astronomer
Sept. 23, 2009
Despite the accusations of my correspondents, I try to keep an open mind about our search for ET.
That’s not entirely trivial. Scientists, whose job description is to learn something wonderfully new, are just as human as the next haberdashed
hominid. After pursuing an exploratory experiment for years or decades, they inevitably build up both a psychological and monetary investment in their
strategy. They can easily become thoroughly marinated in their current approach, and dismiss other ideas with a sneer and a wave.
I try not to do that, and I credit my colleagues with the same.
It’s a constant battle, as SETI scientists (and string theorists, for that matter) are often accused of falling down the wrong rabbit hole. If only
they’d adopt a completely different research tack, it’s said, they could look forward to stashing a Nobel medal in their desk drawer.
“Why waste time looking for old-style radio signals,” many people have written me, “when the aliens will be shooting neutrinos our way?”
Neutrinos are one of many types of suggestions for “weird SETI” that make sense, but perhaps not overwhelming sense. These ghostly particles have the
advantage of barreling right through such petty obstacles as planets, which means you don’t have to worry much about where to aim your “telescope” –
the signal could even come from behind you. The problem with these particles is that they cost a tremendous amount of energy to produce, and our
neutrino detection efficiency is really low.
Quantum entanglement has become an oft-heard phrase at the low-grade parties I frequent. “The aliens will use entangled particles to signal us,” many
At first blush, this sounds like a nifty idea. QE could offer the gold standard for interstellar chit-chat: inexpensive and instantaneous – a kind of
subspace communication channel a la “Star Trek.”
Well, you can put that thought away for now. A subtle piece of logic known as Bell’s theorem shows that, despite the spooky action at a distance of
entangled particles, they’re not instruments for faster-than-light shout-outs.
Another perennially popular refrain with correspondents is to suggest looking for gravity waves, probably because a lot of people make the unwarranted
assumption that gravity propagates faster than light. As far as we know, it doesn’t, and (like neutrinos) gravity waves are difficult to generate and
painfully hard to detect.
There’s a raft of clever schemes for sending information from one place to the next if you don’t demand a lot of bandwidth (which translates into the
speed of information conveyed). I’ve written before [LINK] about how garrulous aliens might
grab our attention with a flash of laser light beamed our way. This might be a once-a-month or even once-a-century signal, but that would be good
enough. After all, if a periodic, bright flash were to be seen on some random patch of sky, legions of astronomers would relentlessly study that
position – and perhaps turn up a low-power broadcast with gobs of useful information (such as the meaning of life, or how to make a perfect soufflé).
Luc Arnold, a French astronomer, has suggested that aliens might signal us with giant shadow puppets. Possibly inspired by NASA’s Kepler mission, which
uses a space-based telescope to find small planets by the slight dimming they induce when passing in front of their home stars, Arnold opined that the
aliens might produce a simple signal that Kepler – or something like it – could easily find. A signal that’s always “on the air.”
The idea is that the extraterrestrials would construct big, opaque polygonal structures, and sling them into orbit around their sun. Anyone observing
stars using a technique similar to the Kepler telescope could notice one of these light blockers. If the screens were some shape other than round, the
time pattern of the observed dimming would tip off distant astronomers that they hadn’t found a planet – rather, they’d discovered a manufactured
None of these types of “transmissions” is currently the subject of SETI scrutiny, and that might sound as if we’ve got deaf ears to new ideas. Well,
not to worry. These schemes may be pursued by others. Neutrino and gravity wave detectors are being deployed by physicists, and Kepler is collecting
data as we speak. And frankly, there’s ample precedent for serendipity in exploration. Think of the 1967 discovery of pulsars. They were found by a
radio astronomer who wasn’t looking for anything of the kind. Quasars were also found by accident (as was Viagra).
So in some sense, traditional SETI – which after all, involves only a few dozen professional researchers world-wide – has backup; namely physicists,
and just about the entire field of astronomy. That’s a good thing, because SETI funding is still too cramped to permit its practitioners to test a
whole lot of different strategies.
As for me, I try to constantly reassess our work by keeping an open mind about new approaches. So far, none has swayed me from our schemes to hunt for
light or radio signals. But if a slicker idea comes along – even if it’s weird – well, I’m willing to give it an audition.