[ExI] Fermi question, was is a FTL drive a dream . . .

[Anders Sandberg]

On 2011-12-20 22:43, Eugen Leitl wrote:
> On Tue, Dec 20, 2011 at 08:26:08PM +0100, Stefano Vaj wrote:
>
>> Could we ourselves really make us blatantly visible to a civilisation the
>> other side of Andromeda even if we considered it a top civilisational
>> priority?
>
> Best bang for the buck would be lasers. You can easily outshine
> the Sun in narrow enough spectral bands.

And you can arrange the bands in weird changing patterns that might 
signal a non-natural origin (there are a few natural maser and laser 
sources). But it is not glaringly obvious. Now, if we can outshine the 
sun using planet-sized power through a laser, we might be able to 
outshine the galaxy by using a Dyson sphere to power a laser.


> Dimming a galaxy would not be any more difficult than dimming a
> single star. And it's pretty easy to dim a single star, provided
> you have enough orbiting material in the system. You do it with
> an ISRU with self-rep closure over unity. The shorter the self-rep
> times the sooner you blanket it out.

Yup. However, something we have been thinking about recently is whether 
we would actually see a dimming front. The classic technosphere scenario 
has lots of colonization probes making short jumps, leading to a front. 
But you can send probes much further ahead than a few lightyears: while 
it is likely a bit harder, it doesn't seem that difficulty scales 
proportional to distance. That means you can have a very high branching 
factor at early stages, using early resources to send probes to every 
other galaxy (or at least very far away), and then do local filling in 
once the probes have germinated. This might produce a much less clear 
front, and maybe even a universal dimming. It also interacts with 
Robin's cosmic commons scenario.

The key factors are probe survival as a function of travelled distance 
(my BOTE calculations of interstellar dust suggested that the mean free 
path is pretty long) the cost of launching and slowing probes from high 
speeds, and whether you want to do really long range colonization on the 
off chance that some other civ might get there first.



-- 
Anders Sandberg
Future of Humanity Institute
Oxford University