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

[Keith Henson]

On Wed, Dec 21, 2011 at 2:50 PM,  Eugen Leitl <eugen at leitl.org> wrote:
>
> On Wed, Dec 21, 2011 at 12:30:43PM +0100, Anders Sandberg wrote:
>> On 2011-12-21 10:44, Eugen Leitl wrote:
>>> On Wed, Dec 21, 2011 at 09:57:36AM +0100, Anders Sandberg wrote:

None of the discussion to date really addresses the (modified) Fermi
question.  Fermi's original question was "Where are the aliens?" when
he realized that nuclear energy was enough to get from one start to
the next.  The modified question is "Why don't we see any aliens?"

Either we are the first in our light cone, or if technophilic life is
common, then something keeps *every single one of them* from making a
visible mark on the universe.  (Or, negating the whole question, we
are in simulation.)

If we are the first, then our future is really unknown.  If
technophilic life is common, then something will keep us from growing
to the point of being observable from a distance.

> The probability that we'd observe a front while we would recognize
> it for what it is is probably just 2-3 centuries in our case. Unless
> we collapse, we'll start expanding in about a century.

I would say less.  Singularity (AI/nanotech) plus a few years--if
anyone wants to go at all.  The problem is that effectively unlimited
virtual worlds can be constructed and inhabited for a *tiny* fraction
of the time and energy needed for the hop to another star system.

> I think the
> expansion will be close to relativistic (at least 0.1 c) right from
> the first hop.

Laser/light sails will go substantially faster.  How much before dust
abrasion becomes a problem I don't know.

Drexler proposed using lasers on both ends, sending vehicles that
don't slow down to target star system.  As a sent ahead pilot vehicle
approach the system they fire bacteria sized seeds backward to near
rest for the target system.  The seeds are small enough to enter an
atmosphere without damage, drift to the ground and grow up to a Niven
type stage tree to get back into space.  There they grow a microwave
antenna for information they could not pack inside and construct a
braking laser for the incoming star ship.  Not saying such a thing
will ever be done, but it's an obvious way to get from one star to the
next.

Incidentally the amount of mass you can accelerate up to substantial
fraction of c given the amount of energy a star churns out is
substantial.  Even considering efficiency of converting light to
electricity and from there to laser light it's around 500,000 tons per
second.  In a year the sun could launch a 150 ton vehicle to all of
the 100 billion stars in the galaxy.

Keith