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.