There are only two possibilities:
- We’re alone in the Universe.
- We aren’t.
Which to you seems more implausible?
Which frightens you more?
Over the past century, scientists have scanned the heavens with instruments of increasingly exquisite sensitivity, gathering energy from across the electromagnetic spectrum with devices fixed here on the ground, or travelling up in space, peering farther and farther into the distance, and therefore farther and farther back in time, perceiving the most infinitesimal quantities of radio waves, x-rays, and visible light. We’ve discovered that the very space we inhabit is expanding, that the galaxy where our star sits is but one of billions, and that there’s a distant limit to the Universe, we think roughly 46 billion light years away; and in the process we’ve been forced to accept that we are tiny little things of perhaps no significance, tucked away in a corner of a vast cosmos that contains trillions of stars, many, perhaps most of them, orbited by planets of every composition and size imaginable and unimaginable.
All the while, the ultimate question has lingered, posed sometimes with hope and sometimes with dread: is there anybody out there?
There was a time when it seemed we were on the cusp of an answer. Back when radio astronomy was new, it seemed obvious that if we were emitting great gobs of electromagnetic energy skyward at all hours in the form of radio and television broadcasts, other technological civilizations would be doing the same, and we should therefore be able to detect at least some of them. We had just the things for the job, newfangled contraptions called radio telescopes, designed to find distant natural objects, but just as capable of collecting signals of artificial origin, if there were any to be heard. Thus was born the science of SETI.
SETI stands for the Search for Extra-Terrestrial Intelligence. It was promoted early on by astronomers like Carl Sagan and Frank Drake, who in 1961 came up with a famous equation to predict how many intelligent civilizations might be out there. This is the Drake equation:
N = R* • fp • ne • fl • fi • fc • L
N = the number of civilizations in our galaxy with which radio-communication might be possible;
R* = the average rate of star formation in our galaxy;
fp = the fraction of those stars that have planets;
ne = the average number of planets that can support life per star that has planets;
fl = the fraction those potential life-bearing planets that actually do develop life at some point;
fi = the fraction of planets with life that go on to develop intelligent civilizations;
fc = the fraction of those civilizations that develop a technology that releases detectable electromagnetic energy into space; and
L = the length of time for which such civilizations release detectable signals into space (that is, the length of time the civilizations survive before going extinct for one reason or another).
Using conservative estimates to fill in all the variables, they reckoned that there might be as many as thousands of broadcasting civilizations in the Milky Way, and proceeded to listen, favouring bandwidths of the radio energy emitted between the frequencies of hydrogen and hydroxyl, the latter a compound made of hydrogen and oxygen. These two atomic structures combined would form water, so they dubbed this band the “waterhole”, hoping other civilizations would use it as a gathering place for communication, just like animals congregate at a terrestrial waterhole. Why these frequencies? Because amid all the radio noise emitted by the cosmos, these are relatively silent, perfect for getting your message across.
So we listened. And listened. Our computers became more powerful, our telescopes better, our ability to monitor all sorts of frequencies greater, and we listened, and listened, and to this day, nothing. Except – in 1977 a radio telescope called Big Ear at the University of Ohio may have caught something.
Big Ear was just a fixed array, like a big set of bleachers, and couldn’t rotate. The spinning of the Earth permitted it to monitor each portion of the sky for only a short period before any given target rotated out of view – it was impossible to train the telescope so it could keep tracking a fixed point in space while the Earth revolved under it. Big, fancy dish-shaped antennae like the one at Green Bank in England could traverse, but Big Ear was like a mirror hanging on the wall, waiting for something to pass in front of it and make a reflection. Whatever it saw, it wouldn’t see it for very long.
There weren’t any staffers available to keep an eye on it 24/7, so at night it was left running, listening and recording, on a sort of autopilot. One morning, a student arrived to look at the night’s printout, and astonishingly, saw a set of coded numbers and letters indicating that a steady signal of just the kind they’d been looking for had been powerfully emitted right in the waterhole frequencies. It was so compelling that the student wrote “WOW!” in the margin, and it’s been called the “Wow Signal” ever since. Big Ear had been trained on it for barely more than a minute, but radio astronomers all over the world, those with the better antennae that could be pointed, revisited the patch of sky in which Big Ear had detected the signal and found…nothing. Nada. Many times over the years, they’ve tried again, and Zip.
What did Big Ear hear?
We still don’t know, not really. A couple of years ago an astronomer pored over reams of old data and reckoned he had figured out a disappointingly prosaic answer: it was nothing but a pair of comets that had been passing through, which comets were surrounded by great clouds of hydrogen gas emitting radio waves in just the frequencies that Big Ear detected. This was widely reported as the solution:
Upon reflection, though, many astronomers were inclined to doubt it:
There it sits. Maybe it was just a couple of overgrown snowballs on the way by. Maybe it was the most momentous signal we’ve ever detected. We’ll probably never know. If the Wow Signal was some sort of alien transmission, it wasn’t meant for us, and we’ll almost certainly never hear it again.
That was over 40 years ago. All the while, we’ve continued to spew huge quantities of electromagnetic energy into space in all directions, forming a detectable bubble of transmissions that now measures about 100 light years in diameter. Some day, then, somebody somewhere might be wondering what the Hell was up on Gilligan’s Island, but unless they’re close they’ll need excellent equipment, since all of our transmissions have been thrown into the void in an indiscriminate fashion that allows them to spread out and dissipate, growing fainter and fainter over time as the bubble expands.
There was a better way, if we actually wanted to be heard. Decades ago, Frank Drake proposed that we should send a focused burst of radio energy at a likely-looking cluster of about 300,000 stars known as M13, 25,000 light years distant, bearing a message that was designed to be received and decoded by scientists. This was done in 1974, almost just for the Hell of it, using the mammoth radio telescope at Arecibo, Puerto Rico:
Given the available technology, the message was, per force, rudimentary. If properly decoded, it would present the alien astronomer with a picture reminiscent of the imagery generated by contemporary video games – it was the interstellar communications equivalent of Pong:
It contains, among other things, representations of the integers from 1-10, a graphic of the solar system indicating the planet of origin, a graphic of the DNA double helix, a crude representation of a person, and another image of the transmitting telescope.
There isn’t much chance it will ever be received by anybody, of course, and even if it is, a return message wouldn’t get here for another 50,000 years.
Perhaps that’s all to the good. There are those, the recently departed Stephen Hawking among them, who counselled strenuously against trying to reach out to other civilizations. Drawing upon the examples presented by our own history, which has repeatedly seen civilizations destroyed by coming into contact with others that were more advanced, Hawking and others like him argue that actively trying to get anybody out there to notice us is just shy of insane. Sure, they might be real sweethearts and email us a copy of the Encyclopedia Galactica, gifting us with knowledge and wisdom we’d struggle for many millennia to obtain on our own. Sure. Or, they might be the same sort of vicious bastards we are, and think to themselves “Oh look! A nice little planet orbiting a nice little star, with plenty of land, water, and tasty bipeds to eat!”.
In the terrific 1953 movie version of War of the Worlds, one of the fellows contemplating the strange, hollow rock that has fallen from the sky, which seems to have some sort of alien periscope sticking out at the top, urges caution to the others in his group when they decide to approach it more closely. “Don’t fool around with something when you don’t know what it is“, he tells them. That’s never bad advice.
Of course, there’s nothing we can do to prevent anybody with the right receivers from tuning into Survivor some day. But maybe we should just leave it at that, and not actually try to grab their attention with any more powerful signals beamed right at them. Safety first. There’s still no harm in listening, though, is there?
So we listen. So far, but for the Wow Signal and a few other anomalies, it’s still nothing but the same spooky silence, but it’s a big universe, and the distances between stars are very great. We could listen to the ambient hiss for ten thousand years and still know nothing conclusive. I can’t think of a more hopeful, romantic, and potentially life-altering use for our time, can you?
You can join in, if you want – really! Click here for SETI@home:
Wouldn’t it be wonderful to get another Wow signal?
Or would it?