avantguardian2020 at yahoo.com
Fri Jan 27 12:29:33 UTC 2012
----- Original Message -----
> From: Anders Sandberg <anders at aleph.se>
> To: ExI chat list <extropy-chat at lists.extropy.org>
> Sent: Friday, January 27, 2012 2:02 AM
> Subject: Re: [ExI] Panbiogenesis
> On 27/01/2012 05:04, The Avantguardian wrote:
>> An unlikely scenario perhaps but it is certainly possible.
> That is the important point. Panspermia depends on very unlikely events, but
> there is so long time and so many planets that it has a chance.
> Consider a biosphere lasting 5 billion years, that manages to seed just one
> other planet out of (say) 10 billion available in the galaxy. That means a
> probability of 1 in 50 billion billion per year. A slightly higher probability
> in this model, and more planets will be seeded and the galaxy will
> "quickly" be colonized.
> One can try to bound probabilities in various ways, but things are very
> uncertain. However, it is not too hard to build a joint model of spontaneous
> biogenesis and panspermia, and then plug in our sole data point of when life
> appeared on Earth. That produces a fairly thin maximum likeliehood ridge in
> parameter space, showing a relationship between the panspermia and biogensis
That sounds like a cool idea for a project. As a fellow Bayesian, I would give the following advice about your priors. Keep in mind that biogenesis (at some space-time coordinate) has a probability of one because life exists. However in almost 250 years of watching and tinkering, biologists have not one documented case of biogenesis being observed either in a laboratory setting or spontaneously "in the wild". That means it has near zero probablity *here and now*.
The biogenesis people say that is because conditions on early earth were different. That is fine. But we can simulate early earth chemically in a lab. We get organics but not life, not yet, *not once*, not after decades of trying.
Panspermia allows you to push the time and place of the probability-one genesis event back as far as you need to until the conditions of the universe itself were different. Perhaps the current value of fine structure constant does not permit biogenesis whereas at some point it did. Let me know what you figure out. :-)
"When the going gets weird, the weird turn pro." - Hunter S. Thompson
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