Re: Fermi's Paradox, again

Anders Sandberg (
Wed, 9 Jul 1997 13:48:06 +0200 (MET DST)

On Tue, 8 Jul 1997, Eric Watt Forste wrote:

> EvMick writes:
> > Doesn't (mumble mumble)'s Law indicate that there has already been time
> > enough for the entire galaxy to have been colonized?
> Well, I've been trying to look into this, although I'm hampered by my lack
> of expertise in astrophysics. The Solar system formed about five billion
> years ago. One of the reasons that life could form here is that the cloud
> from which it formed was already enriched with oxygen and carbon. The Big
> Bang (if that's what happened) produced only hydrogen and helium, and
> happened only some seven to thirteen billion years before the formation of
> the Solar system. It would take a certain amount of time for enough large
> stars to form and go supernova to enrich the interstellar clouds of our
> galaxy with the oxygen and carbon that were available at the time the Solar
> system formed. When I try to answer the question "How much time at a
> minimum would be required to form and disperse the necessary amount of
> heavier elements?" I find I get led into astrophysics textbooks and papers
> that are too hairy for me to understand without devoting a lot of time to
> it, and they don't present "the Answer" to this question in the abstracts
> or conclusions from which a layperson could easily grab it.

I'm not an astrophysicist either (but I do play one on the Net :-),
but here are some rough guesstimates:

Colonizing the galaxy can be done in less than 10 million years using
von Neumann probes (see Tipler & Barrow, the Anthropic Cosmological
Principle for a discussion of this).

The solar system is around 5 billion years old. Life has existed for
(say) 4 billion years. Even if we assume our solar system is one of
the oldest generation I systems in existence, I still have the
feeling that the time from the first bacteria to the cambrian
explosion could have been shorter (the explosion was likely due to
one or more "tricks" like predation and multicellularity which were
slightly unlikely but could have happened much earlier). The same
goes for the emergence of intelligence among the vertebrates: the
oldest vertebrates are around 100 million years old, there is no
strong reason intelligence couldn't have developed much earlier.

If we assume just a 10% variance, then it is quite possible that life
could have turned metazoan and intelligent several hundred million
years ago on some earth-aged planet. Since interstellar expansion is
so quick they should have arrived here a long time ago.

Anders Sandberg Towards Ascension!
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y