Winning the E.T. Lottery

Consul writes "Space.com has a cute story about the statistical probabilities that we have been visited by an alien civilzation. He seems to make a convincing argument."

Comments

Bit unimaginative.

[Fweeky]

All it takes is for someone, somewhere to build an intelligent(ish) self-replicating machine programmed to spread throughout the galaxy - one per interesting star system.

Such a system could cover the entire galaxy in a couple of million years easily (and cheaply after initial design/construction cost). They can do whatever you like; sit and watch, make contact, try to destroy any competitors (The Forge of God style; soon to become a set of movies, yay), and call home (since you end up with a network of them; sure, it'll take a while to get back home, but it's one hell of a cheap way to learn an awful lot about the galaxy).

Given that it only takes one civilization to have done this, and given that our solar system is probably quite interesting given it's layout, I wouldn't put too high odds on there NOT being such a device hanging around near here.

Re:Vanishingly small probabilities

[TwP]

You have a quarter in your pocket and decide to flip it in the air. It lands with the heads side facing up. You repeat this procedure, and without fail the heads side is always facing up after the quarter lands. You do this ... oh ... 10,000,000 times and every time the heads side is facing up. What is the probability that on the next throw the heads side will be facing up?

Are you ready for the answer? ... 50%

The existence of intelligent life on this planet does not necessarily imply the existence of intelligent life on other plantes. Just because a quarter lands heads up 10 million times does not imply that the next toss will produce the same result.

The existence of life on any planet must be taken as an individual probability just as each individual quarter toss must be taken as an individual probability.

QED

So how common is life in the universe?

[Lars T.]

This tries to give the answer - almost. For those to lazy to read the whole paper, these Australien scientists conclude that:

It is sometimes assumed that the rapidity of biogenesis on Earth suggests that life is common in the Universe. Here we critically examine the assumptions inherent in this if-life-evolved-rapidly-life-must-be-common argument. We use the observational constraints on the rapidity of biogenesis on Earth to infer the probability of biogenesis on terrestrial planets with the same unknown probability of biogenesis as the Earth. We find that on such planets, older than ~ 1 Gyr, the probability of biogenesis is > 33% at the 95% confidence level. This quantifies an important term in the Drake Equation but does not necessarily mean that life is common in the Universe.

Warning: uses math heavily, and thus can be derided as simply theoretic. Hah-hah.