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Old August 27 2013, 01:02 PM   #30
Lindley
Moderator with a Soul
 
Location: Fairfax, VA
Re: Whee are the aliens?

Edit_XYZ wrote: View Post
1. Abiogenesis.
What is the road from a bunch of chemicals to the "simplest" molecules that can replicate themselves halfway reliably?
Let's - VERY optimistically - assume that a specific chain of 100 chemical reactions are enough to create this "simplest" molecule.

Now - Darwinian selection has no part in creating this molecule; for Darwinian selection, you need self-replication, which you do not yet have.
Which leaves probability in charge. For a very rough approximation, calculate factorial 100. It gives a number so close to 0 as the chance of this "simplest" molecule emerging, that the chances are life on Earth is alone in the observable universe (and a huge chunk of the unobservable one).

Conclusion - abiogenesis is rare. VERY rare. Even if my factorial 100 approximation is exceedingly rough and even if there are hundreds of billions of Earth-like worlds in our galaxy, the chances are only ours ever gave birth to life.
Two objections to this argument. First, chemical reactions are highly sensitive to conditions. If the right conditions exist, they can easily drive a particular product from 1% to 99%. We aren't entirely sure what the right conditions are for ambiogenesis, of course.

Second, even an exceptionally unlikely event becomes probable when there are enough chances. Winning the lottery is exceptionally unlikely, yet someone seems to win every few weeks because there are so many players. Similarly, there could be trillions of ambiogenesis precursor molecules out there. Granted, 100! is much larger than one trillion, but the odds are at least improved somewhat.
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