Re: Fermi Paradox in the news

From: Nick Bostrom (
Date: Wed Oct 25 2000 - 21:01:42 MDT

Jason wrote:

>Hi Nick.
>Alright, let's play a hypothetical game. Let us suppose that there was
>intelligent life on Mars. ... explain how this
>second data point defeats the observational selection effect inherent in the
>anthropic principle.

I think Curt and Eugene have already answered this.

>... Remember: no matter how small a fraction of all solar systems in our
>infinite universe develop life, we would by neccessity find that we
>(Earthlings and Martians) originate from one of the exceptional ones that

Yes, but it would not be necessary that we would have found ourselves
originating from a solar system where two civilizations had evolved
independently. That is the extra finding that would make all the
difference. If the evolution of intelligent life is very improbable then it
would have been extremely unlikely that it would have happened on another
planet in our own solar system. That would have been a remarkable
coincidence. By contrast, it is no coincidence that we find intelligent
life evolved "here", because the "here" is not a random position in the
universe: it is a random sample only from the set of positions where there
are observers.

I hope that we will not find any signs of advanced life forms in our solar
system or elsewhere. The deader Mars is, the better. Advanced life would
show that the Great Filter is probably not in our past, so we'd have to
fear it in our future.

The Fermi paradox is not really a paradox. I know of no arguments why
anybody should expect intelligent life to have been common in the universe.
The only thing that our own existence shows is that the improbability of
intelligent life evolving on a given planet is not so great that the total
probability of at least some life evolving somewhere in the universe is
small. But if the universe is very big (especially if it's infinite) then
this does not place any constraint at all on the probability of a given
planet evolving intelligent life: even if it's extremely small, it was
still probable that intelligent life would evolve somewhere.

Nick Bostrom
Department of Philosophy
Yale University

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