[ExI] Drake Equation Musings

BillK pharos at gmail.com
Tue May 17 18:02:33 UTC 2016

On 17 May 2016 at 11:59, Anders Sandberg wrote:
> Remember the Carter argument: the probability of life emerging may be very
> low, and there could be secondary low-probability steps between it and
> intelligence. So most planets never get it, and among those that get it the
> secondary steps never happen. The planets with observers on them will be the
> ones that have the unlikely combination of getting all the steps, and if the
> natural rate of them happening is slow, we should expect them to be about
> equidistant across the time interval the planet is habitable. So early life
> is not evidence of easy life unless there is no reason to think there are
> any hard steps. However, we do have some evidence for hard steps (e.g. at
> least one transition in genetic coding, which is something we know tends to
> be stable over 10^80 cell divisions).
> In short, observer selection bias makes data from Earth suspect in updating
> our probabilities.
> Note that your idea is nicely testable: if we do find life on Mars, Europa
> or Ceres, then we have reason to think life is indeed common and not a great
> filter. That is bad news for our future, though: while the probability of
> intelligence evolving factor decreases the most given this, the expected
> lifespan of civilization decreases second most.

You seem to be depending on the 'Rare Earth' claim to validate
ignoring the evidence of life everywhere on Earth, even extremophiles
which live in environments that would destroy most earth life. I doubt
whether it is valid to use observer selection bias to ignore evidence
unless you first refute the arguments against the 'Rare Earth'
the really big numbers in the universe (quantity of planets, stars,
galaxies and 13.8 billion years),
the way the laws of physics are suited to life. This is a universe
where life happens. To claim it only happened on Earth and will never
happen anywhere else seems unlikely.
Amino acids are built wherever the components are available and have
been detected on meteorites, comets, etc. Organic chemistry happens in
George Dvorsky has a good summary of the arguments (also discussed in comments).

Finding life elsewhere will certainly be another argument against the
Rare Earth hypothesis. But as we find Martian meteorites on Earth,
cross-pollination between Solar System planets could explain life on
other planets. To be definitive it would have to be very different
from terrestrial life forms.

> Isn't this a rather backward way of reasoning?

No, it's just a fancy way of saying we don't know what
post-Singularity civilisations will decide to do.
It almost certainly won't be more of the same stuff we do.
And to explain the Great Silence, it seems that they all decide on (or
are forced into) a supremely attractive path that causes them to be
undetectable by more primitive civilisations.


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