Other civilisations in the Galaxy - are they really that likely?

Hey, cavediver, I'm a big fan of Fermi's paradox. I tend to be skeptical that advanced civilizations are very common in the galaxy.One nit-pick though:

quote:

---

How long do we need to wait for abiogenesis? (~1Gyr in our case)

---

If the 1 Gyr refers to the time from the very beginning of the solar system to the first signs of life, then this is accurate, I believe.However, it is a little misleading. It seems that this is also about the time of the end of the heavy bombardment, during which life would be impossible. So it seems that life appears immediately (geologically speaking, of course) once conditions allow for it.Unless our solar system is rare in that the heavy bombardment eventually ceased -- then this example does become relevant.On the other hand, I, too, have noticed how long it took for prokaryotic and more advanced life to come about. Perhaps complex multicellular life is pretty rare.Ah, the unknowns! It is very hard to get reliable statistics out of a single data point.

I believe that this is Conway Morris' (of Burgess shale fame) belief. He feels that God created the universe and the laws of physics so that it would be inevitable for intelligent life to come about.However, I agree with you; from our one example (us!), it can be argued that advanced life (much less intelligent life, much much less advanced civilizations) is rare.

quote:

---

2Gyr is 1/7 of the age of the universe!

---

Not to mention that it took half the lifetime of the sun for intelligent life to finally come about.

Perhaps our solar system is inimical to the emergence of intelligent life, yet also unusually conducive, compared to other solar systems, to the emergence of intelligent life.Not too far fetched, seeing how little we know about solar systems in general.Here's a strange thought that just occurred to me. A lot of evolutionary advance occurred after mass extinctions. Maybe life cannot "advance" too quickly if a planet is too stable. Maybe the emergence of intelligent life requires just the right balance of "instability" -- frequent enough mass extinctions to periodically reopen niches and further evolutionary innovation, but not so many that you end up losing what "gains" have already been made.