Photo Credit: A. Passwaters/Rice University based on original courtesy of NASA/JPL-Caltech at

The question of whether or not life exists elsewhere in the universe has been examined in countless ways, and much of the discussion depends on knowing how rare an occurrence life is. When it does arise, how likely is it to evolve into an intelligent species? We’re now nearly certain that there are at least hundreds of other planets in our galaxy (based on our best instrumentation and scientific rationale) and assume that the number is actually higher than that by orders of magnitude, but we still don’t know the odds of life arising in any given place, let alone intelligence. And sometimes rather oblique investigations make the issue even murkier.

Although we can imagine forms of life composed of different elements, Earth life is based on the element carbon. Without carbon-based molecules, there would be no life as we know it. So is carbon a common element on extraterrestrial planets? If so, we might have high hopes that carbon-based life would have arisen elsewhere. The problem is that many scientists who investigate planet formation feel that Earth shouldn’t have large amounts of free carbon that isn’t locked into the planet’s core. So some researchers from Rice University have theorized that Earth must have been hit by a Mercury-type planet something like four billion years ago and absorbed the doomed planet’s carbon into Earth’s upper mantle and crust, where it could eventually be used for the evolution of life forms. If that’s true, and if carbon-based life couldn’t arise any other way, then the rarity of that exact type of collision means that the number of planets hospitable for our kind of life would be equally rare.

Another couple of researchers at Cornell University have approached the question of life’s scarcity in a completely different way. They’ve calculated the rate at which genetic material (like DNA) increases in complexity through natural evolution, reasoning that if you work that rate backward you can figure out how long ago the most basic life forms came into being. According to their calculations, it took far longer than we’ve previously thought for life to arise and ultimately evolve into intelligent beings—nearly ten billion years, in fact. Ten billion years ago is before the existence of the solar system, so they propose that life arose elsewhere and travelled to Earth by meteorites. But if it really does take that long for intelligent life to develop, then we shouldn’t be expecting visits from advanced aliens anytime soon. They’ll all be at about the same stage of evolution as we are—we may even be among the first intelligent species to arise.

What would it mean to us if we do turn out to be alone in the galaxy? On the bright side, we won’t go out into space and face a slew of hostile races eager to kill us off, as in Starship Troopers by Heinlein, and the John Scalzi Old Man’s War series. But it would also mean that we’ll never find companionship beyond our own kind, never get fresh perspectives on art, music, love, or the meaning of life. We’d never get a chance to learn from others with very different experiences. Even worse, if the number of planets with carbon-based life turns out to be near zero, then it will also be nearly impossible for us to find new worlds that are hospitable to us and our fellow Earth species, which means we’ll have to terraform every planet we encounter before we can colonize it, a process that could take thousands of years.

Much as I hate the thought that venturing out into galactic space would bring humanity into conflict with other races, I really hope that life isn’t a rare thing in the cosmos, and that we’re not the only intelligent beings. A universe with no inviting planets or potential friends would be hostile indeed.


I’m a supporter of SETI—the Search for Extraterrestrial Intelligence. It’s worth devoting resources to find out if we humans have company in this universe in the form of other intelligent life forms. There are lots of good reasons to want to know, especially if it doesn’t require us to do more than look and listen for signs of other civilizations. But recently some scientists have become impatient that SETI hasn’t detected anything in the past thirty years, and feel that we should be more proactive about the search. That impatience is understandable. SETI methods are painstaking. Space is vast. Even though our ability to search the skies has increased enormously over the decades, SETI astronomer Jill Tarter is quoted in an excellent Washington Post article about the subject, saying, “We’ve explored one eight-ounce glass of water out of the ocean”.

So the impatient scientists believe we’ve been going about things the wrong way. Since the Kepler Space Telescope and other projects have now identified more than a thousand likely planets circling other stars, and a fair number might be the right distance from their star to provide conditions that support life, these folks think we should start beaming strong radio signals toward those star systems, inviting any alien civilizations there to become “part of a conversation”.

Now hang on just a minute. Imagine yourself taking a walk in a strange neighbourhood at night. Would you keep your ears tuned to hear if anyone was around? Sure. Would you jump up and down and yell, “Helloooo! Anybody out there? Anybody feel like getting together for a coffee?

I don’t think so.

For one thing, who do you figure is most likely to respond to your invitation: Mr. and Mrs. Nice-to-know-you, or the neighbourhood muggers?

I’ve always wanted to believe that a species advanced enough to travel between the stars would be peaceful. But there’s no evidence to support that, and plenty of evidence from human history to suggest that I’d do as well to believe in unicorns and leprechauns. Humans advanced enough to travel between continents certainly weren’t peaceful. Ask native North Americans or the Aztecs. In fact, experience on this planet has shown that technological progress is most often for reasons of aggression. Should we compare the research and development budgets of the military around the world to private R & D spending? And of all the reasons for expending resources to get into outer space, population pressures and a desire to exploit what we find rank high. Making new friends probably isn’t even on the list.

Even if extraterrestrial travellers weren’t malevolent, they would surely be so far ahead of us that we’d be curiosities by comparison, or even lab rats worthy of further study but certainly no treatment as equals. The knowledge of their existence alone could destroy all motivation for the human race to make progress of our own.

The point is that we have absolutely no way to know if intelligent aliens would be nice, or very, very bad. But once we let them know we’re here, there’s no putting the cat back in the bag.

Some 28 (so far) notables in the scientific community, including Elon Musk and David Brin, have signed a petition condemning so-called active-SETI. Stephen Hawking thinks it’s a crazy idea. Even the originator of the SETI movement, Frank Drake, believes it’s too soon and a waste of time.

As we venture out into interstellar space on our own we may discover we’re not alone, but by then we’ll be much better equipped to deal with whatever—and whomever—we find. For now, let’s be content with paying attention and not calling for attention.


It’s called the Fermi Paradox: if the universe is so big that intelligent life must have evolved somewhere other than Earth, where is everybody? Why haven’t we seen any signs of them, or at least their TV commercials—those are unavoidable, no matter who you are, right?

Well, first of all, why are we so confident that there must be intelligent life elsewhere? Mainly because the universe is so big: our own galaxy is thought to contain 300 billion stars, and the universe we can see appears to have more than a hundred billion galaxies, so what are the odds this is the one and only planet that produced intelligent life? And that argument was made long before we actually knew that other stars had planets. Scientists working with the Kepler Space Telescope have now found thousands of possible planets orbiting other stars, and feel confident enough to consider more than one thousand of them “confirmed planets” (as of this month). A star system designated Kepler-444 has five rocky-type planets (like Earth) and was formed over eleven billion years ago. By comparison, our own solar system is only five billion years old. So if planets have been around at least that long, mustn’t some have produced life, and probably intelligent life, long before now? After all, here on Earth we’ve found that life can arise under even the most extreme conditions.

But The Great Silence is a fact. The Search for Extraterrestrial Intelligence (SETI) has been going on since the 1960’s, first searching for radio signals, and then many other signs of the by-products or artefacts of civilization. At one point SETI was scanning a billion frequencies of electromagnetic radiation, looking for some kind of signals. Granted, our own planet’s electromagnetic noise has only been spreading outward through space like an expanding bubble since the dawn of radio a hundred years ago, and signals from other galaxies would take millions of years to get here. But why is there such deafening silence within our own galaxy?

Here are some speculations (of my own and others):

- God took one shot at it and was satisfied with the result. (Yes, I’m being facetious, but somebody would’ve said it.)

- Truly intelligent beings recognized television for what it is and banned it forever.

- A lot of species stuck with the landline telephone rather than let cell phone companies gouge them. Or (more seriously) they went straight to line-of-sight communication using light, rather than spraying EM radiation in every direction.

- There are lots of hyper-intelligent races but they recognize that exposure to superior technologies kills a species’ initiative, so they’ve agreed to leave us alone (except for a few slip-ups, but then look how many times Star Trek captains blew the Prime Directive).

- There were lots of intelligent species, but they couldn’t get along and killed each other off.

- Other life forms are so completely different from the kind we know that they also communicate in ways we can’t recognize.

- Maybe the odds of life springing from a soup of organic chemicals and then evolving into a self-aware intelligence really are so low that, out of our whole galaxy we’re the only lottery winners.

There are many, many more serious explanations for The Great Silence. Maybe advanced species build Dyson spheres around their whole suns and have plenty to keep them busy without going anywhere else. Or maybe cosmic ray bursts sterilize huge chunks of galactic real estate on a regular basis. You can read a couple of great articles on the subject by George Dvosrky at io9 here and here.

But we can’t ignore the possibility that aliens have seen our TV shows and decided we’re just not worth talking to. The Kardashians and the House of Commons channel could keep us isolated for years to come.