[ExI] Silence in the sky—but why?

[Rafal Smigrodzki]

On Mon, Aug 26, 2013 at 10:53 AM, Eugen Leitl <eugen at leitl.org> wrote:
>
> We're not talking about just single galaxies, but patches of
> real estate GLYrs across. Stellar systems would go dark very
> quickly, so by the time you see half of the sky going dark
> (FIR) your own system is already toast. Not a damn thing
> you can do about it, unless you're already expansive.
> So time interval from observer to expander is very short
> (few centuries in our case), and hence you need to be arbitarily
> unlucky in order to see half of the sky go dark.

### It would be interesting to model the likelihood of observing a
spreading civ, assuming various fractions of c. Probably we can assume
the delay from probe arrival to sun darkening to be negligible, so the
extent of a sphere of darkening would be a good approximation of
extent of probe spread. Depending on distance from point of origin and
the speed of probe dispersion there would be very different pictures,
persisting for various amounts of time. The way the sky looks now, we
can probably exclude close to mid-distance (1000 to 100 million
lightyears), moderately old, slow spreaders. What remains is: very far
spreaders (far origin), very recent spreaders (any distance), very
fast (near lightspeed, almost any distance), or no spreaders. The two
latter possibilities are most disconcerting, for different reasons.

I would guess that our warning from seeing the darkening sky to
meeting the vanguard could still mostly range from thousands of years
to hundreds of millions of years, depending on point of origin and
speed, but I don't have the math to prove it.

Rafal