Hyperpat\’s HyperDay

SF, science, and daily living

Seen a UFO Lately?

Posted by hyperpat on February 15, 2007

The aliens are coming! The aliens are coming! Where? I don’t see them. Nor does anyone else, at least not yet, even though quite a few people have been assiduously looking for some real evidence of them, using the latest and greatest technology we have.

Now the current theories on how life came to be on this planet indicate that the proper combination of elements, molecules, and energy sources should be fairly common in any normal solar system. And the number of bodies we have found orbiting other stars indicates that most stars will have something circling around them that could serve as bedrock for developing life forms. Given the number of stars in just our own galaxy (somewhere between 200 and 400 billion), even if the odds of having a solar system with an orbiting planet in the region where liquid water would be present is one in 1,000, and the odds that all the rest of the requirements for life to form are met is one in 10,000, that would still give us some 20,000 worlds with life of some sort. But perhaps the real kicker is if that life would ever develop intelligence and technology good enough to send a message (or a space ship) to us. This may just be a matter of time; eventually all worlds with life may be driven to this development level because of evolutionary survival pressures. But if these assumptions have any validity, where are the aliens? This is generally known as the Fermi paradox, as so far the only intelligent race we’ve heard from is ourselves.

The above factors, along with a few more, are encapsulated in something called the Drake equation:

N = R * Fp * Ne * Fl * Fi *Fc * L

R = rate of star formation in our galaxy
Fp = fraction of those stars that have planets
Ne = the average number of planets that can potentially support life per star that has planets
Fl = the fraction of Ne that actually develop life
Fi = the fraction of Fl that go on to develop intelligent life
Fc = the fraction of Fi that are willing and able to communicate
L = the expected lifetime of such a civilization

Determining proper values for these parameters is difficult and subject to a lot of assumptions and guesswork. When this equation was first developed in 1961, the values used for a first guess were: R = 10/year, Fp = .5, Ne = 2, Fl = 1, Fi = .01, Fc = .01, and L was 10,000 years, leading to an estimate for N, the number of alien civilizations we should be able to talk to, of 100. Other estimates using the results of data obtained since this equation was first developed give results for N ranging from considerably less than 1 to 5000.

But the value for L, or just ‘time’, in this case, could be the killer. Humans have been around for a distressingly short 20,000 years or so, and had the technology to think about talking to the stars for only about 100 of them; this is out of a planetary lifetime of four billion years. Clearly if these alien civilizations came to be a million or so years ago (a relative eye-blink in terms of the astrophysical time) and then died out before we came down from the trees, we’d never hear from them.

Of course, our own development may be atypical; life has had to start over almost from scratch at least a couple times on this planet. And how long we can last as a species with good enough technology to communicate to other stars is very much a pure guesswork figure – after all, we have only one example, and we haven’t ‘died’ – yet. Though the way we’re going, perhaps a figure of only 200-300 years should be used, as that may be all the time we have before we blow ourselves up or poison everything. Which may be the real answer to the Fermi paradox.

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