Communion Of Dreams


A closing window.

The Fermi paradox is at the heart of Communion of Dreams – given what we know, where are the extra-terrestrials?

What do I mean “given what we know”? Well, the Drake equation has been a staple of science fiction (and at least part of the justification for SETI) for decades. Filling in the factors in the equation has always necessitated a lot of guesswork – the Wiki entry goes into that fairly well – but now we have more solid information on at least one of the more important components of the equation: how many terrestrial (Earth-like) planets are there in our galaxy?

Phil Plait has a good rundown on this, coming at the number from two directions, using the latest astronomical observations:

How many habitable planets are there in the galaxy?

By now you may have heard the report that as many as 1/4 of all the sun-like stars in the Milky Way may have Earth-like worlds. Briefly, astronomers studied 166 stars within 80 light years of Earth, and did a survey of the planets they found orbiting them. What they found is that about 1.5% of the stars have Jupiter-mass planets, 6% have Neptune-mass ones, and about 12% have planets from 3 – 10 times the Earth’s mass. This sample isn’t complete, and they cannot detect planets smaller than 3 times the Earth’s mass. But using some statistics, they can estimate from the trend that as many as 25% of sun-like stars have earth-mass planets orbiting them!

And what does that mean? Here’s the closing calculation from Plait:

2 x 1013 / 8000 = 2,500,000,000 planets

Oh my. Yeah, let that sink in for a second. That’s 2.5 billion planets that are potentially habitable!

How many of them would host indigenous life? How many of *those* would develop intelligent, technological civilization? There’s a nice interactive on the PBS site which allows you to play with this. Using that 2.5 billion number, but assuming that only half the planets which could support life will actually develop it, and that only 1% of those will develop intelligent life, and that only 10% of those intelligent lifeforms will develop technological civilizations capable of interstellar communication . . . you wind up with 125,000 such civilizations. You then have to make some assumptions about how long such a civilization would last, and what the likelihood would be that they would be around now (at the same time we are), but still . . .

I’ve complained previously that I worry that solid evidence of extraterrestrial intelligence will be discovered before Communion of Dreams makes it into print. That window is now closing. But you know, I really wouldn’t complain too much now if such evidence beat me to press.

Jim Downey

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[…] previously talked about the Drake Equation, and how new information from a host of sources is changing the calculus of expectation — expectation of what is waiting for us out in the […]

Pingback by Waiting for it. « Communion Of Dreams

[…] last time I played with the numbers, the best guess from Phil Plait was that there were some 2.5 billion […]

Pingback by 30 billion Earths. | Communion Of Dreams




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