Why can't we find aliens?

"E.T. is out there," says Slate's Chris Wilson. But "why can't we find him?" It's a question that has long vexed stargazers. If there are more than 200 billion stars in our Milky Way galaxy alone, shouldn't those staggering numbers all but guarantee that there is at least one other Earth-like planet suitable for intelligent life? And shouldn't those intelligent beings contact us? Here, four takeaways from Wilson's examination of these burning questions:

1. The timing could be off

The distance between stars and star systems is enormous, and that creates what's known as the "synchronicity" problem. Even if scientists "were to discover a very Earth-like planet 450 light years away" — not that far in the grand scheme of things — by the time we point our radio telescopes at it, "we’re listening for an activity that might have been going on there in the Earth year 1561." So to detect anything, Wilson says, "the civilization that exists on this planet has to be at least 400 years ahead of ours."

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2. And we may have missed the message

It's "possible that our fantasy civilization would be 500 years ahead of us," Wilson says. But remember, the universe is roughly 13 billion years old. Maybe our "Earth-like planet was at one point dotted with thriving alien cities" — but when these creatures sent us signals, "we humans were working out the kinks in having opposable thumbs." Intelligent species may have been trying to contact us for millions of years — but we hadn't evolved to the point where we were even aware of it.

3. But there are ways we can still find E.T.

First, we need to look for relics of lost societies, a "beacon that would beam out its epitaph for millions or billions of years." Think of it like a "gravestone" or "galactic graffiti." Secondly, we need to preserve our own "collective memory." "If another civilization was so kind as to send a few signals our way, we ought to return the favor. We ought to build our own beacon. It's a simple matter of interstellar courtesy."

4. And the future offers more chances than ever

Between a newly reopened SETI Institute, as in "Search for Extraterrestrial Intelligence," and NASA's Kepler spacecraft, which is beginning to "identify planets elsewhere in the galaxy," the next few years are looking like the dawn of a new "golden age in alien hunting," says Wilson. "The odds of finding an alien civilization out there are about to increase immensely."

Read the entire article at Slate.