[ExI] Silence in the sky-but why?

[Rafal Smigrodzki]

On Wed, Aug 28, 2013 at 4:38 AM, Eugen Leitl <eugen at leitl.org> wrote:
> On Tue, Aug 27, 2013 at 11:18:20PM +0200, Anders Sandberg wrote:
>
>> Well, we might be lucky and life is amazingly unlikely. A more
>
> This appears the default scenario. I don't see why people see it
> as problematic. Just because it looks like anthropocentrism/geocentrism
> in new guise? That's not a sufficient reason.

### Absolutely. Plus, we have to remember that our information about
the far reaches of the universe is very outdated. It takes time for
light cones to intersect.

There is a metallicity constraint on the formation of life-friendly
planets, and there must be a sharp threshold effect, with intelligent
life only possible after some number of billions of years passed. If
that number is close to 13 (.... some special significance....), then
not seeing signs of expansions in galaxies farther than 0.7 billion
years is to be expected. This means we don't have to be the firstborn
in the whole universe, only the firstborn in a much smaller sphere, to
explain the still-empty skies.

Scenarios where multiple civs develop per galaxy are highly unlikely,
otherwise we would have seen millions of them or we would have to be
on the extreme far left part of the distribution in time. This leaves
scenarios with one civ per galaxy cluster on a sharp time-threshold,
with us being relatively but not ridiculously early in our
few-hundred-million-lightyear neck of the woods. Quite plausible, if
you ask me.

If you wait another billion years, you might see multiple independent
expansion spheres rapidly extinguishing all stars.

Rafal