From: Anders Sandberg (nv91-asa@nada.kth.se)
Date: Mon Oct 07 1996 - 05:08:00 MDT
On Fri, 4 Oct 1996, David Musick wrote:
> why not enclose the entire earth, atmosphere included, in one
> big shell, which is grounded in place by several large posts that reach from
> the upper atmosphere, down to the hard surface of the earth.
Nice idea, but remember that the surface of the Earth isn't hard at all -
our whole planet is almost liquid. My guess is that you cannot support
them at all if the forces become too large, and beside the ground is
constantly moving. My suggestion is to use the centrifugal force, and
anchor asteroids in diamondoid beanstalks at the equator to hold up the
shell.
> Now, the first problem with this is that the sun
> would be blocked out and we'd all die. But, this problem can be overcome by
> coating the outside of the shell with solar cells to gather energy and coating
> the inner layer of the shell with lights that emit the same spectrum that the
> sun does (or even a more desirable spectum, if we want). We can also build
> huge fins on the outside of the shell, which are also coated with solar
> collectors, to gather even more energy, to be used however we desire.
My suggestion is that you build a ring of solar collectors orbiting the
Earth instead, which beam down microwave power - less physical strain
(the fins would have to deal with gravity), and they can be extended
indefinitely.
> The shell could be built to be very strong, strong enough to provide us
> adequate protection from very large asteroids (perhaps we could even surround
> the earth with probes that watch out for and explode any large asteroids or
> meteors that are approaching earth, so that the shell gets hit by many small
> fragments, spread out, rather than having all of its momentum concentrated in
> a small area, which could pierce the shell.)
I don't think we can create any material that can withstand the kinetic
energy of even a small asteroid - a few megatons of regolith moving at
several kilometers per second will vaporize diamond just as well as water.
Probes are a better system, and an even safer solution would be to go out
and put ion enginers + solar cells on all dangerous asteroids to put them
in safe orbits.
> The shell could also be very
> insulating, to keep a great deal of our heat energy inside, rather than
> allowing it to be expelled into space so quickly.
Actually, this might be a problem. The heat balance of the Earth is
rather sensitive, and we should be careful not to accidentally push it to
close to a runaway greenhouse effect that would turn it to a new Venus.
> For all these biosphere shells, we need lots of materials. We can get them
> from the earth and from other sources, such as the asteroid belt, the moon. I
> have nothing against taking apart mercury or venus or any of the other planets
> and using them also. Eventually, we could keep taking material from the crust
> of the earth to build new biosphere levels, use the heat energy of the lower
> layers, and as they cool off, use that material to build more shells and
> continue working in until the entire earth is turned into one huge,
> multi-leveled, life-filled starship.
A beautiful idea. But I think it would be much, much easier to build a
Dyson shell instead - many freely orbiting shells instead of one
Earth-onion. The only big advantage I can see with the onion is that you
get gravity for free - but that makes the engineering much harder (not to
mention the risks for a disastrous accident - "Australia crashes, film
at 11").
> I'm still trying to figure out what the gravitational pull would be like in
> the center-most layers, since they would pretty much be surrounded with lots
> of mass. I'm thinking that the gravitational effect would be effectively
> cancelled out down there since any mass in there would be getting pulled
> nearly the same amount in every direction.
Yes, the amount of gravity at a point inside a spherical mass only
depends on the mass inside the point. It might be worth noting that the
overall density of the Earth would become lower as the shells were built,
so 1G fans would have to move outwards.
> There was a thread going where someone was saying the life would transform
> itself into a neutron star and just sit where it was and compute away, not
> sending out any probes because they would be too costly. It may not send out
> probes, but I don't see why it wouldn't propell itself around to various star
> systems and grab up all the matter and energy there. Certainly *that* would
> be cost-effective.
Well, the trouble is that to a neutron-star intelligence, one second would
be a very, very long time. So even if it could get to other places very
quickly from our perspective, it would take forever in the view of the
being. Would you go somewhere if the journey took a few billion years,
even if you were immortal?
Another reason they would not want to rush around is the fact that you
cannot extend a neutron star indefinitely, beyond a certain mass it will
become a black hole (which might be a way to take a short-cut to the Omega
Point if you know what you are doing, or just a very unusual way of
suicide). You can cheat this by using energy to keep the star stable and
extending it (not unlike the onion scenario above, but this time at
nuclear densities and with extremely high energies), but the demands seem
to go up very steeply. My guess is that the really big intelligences have
to guzzle energy so fast that they cannot move, and are surrounded by huge
instalations to support them.
I like this kind of speculation.
-----------------------------------------------------------------------
Anders Sandberg Towards Ascension!
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