KFL@AI.AI.MIT.EDU ("Keith F. Lynch") (03/29/86)
From: ucdavis!ucrmath!hope!corwin@ucbvax.berkeley.edu (John Kempf)
Two questions:
Where would they find the mass to build one?
If there isn't enough mass in their solar system, they can use mass
from other nearby systems. Note that a Dyson sphere is not
necessarily a solid sphere circling a star. It is more likely to be a
very large number of small objects. It needn't be thick enough to
live on everywhere - most rays of light from the central star may be
intercepted by very thin reflectors which focus the light to a point.
There is certainly enough aluminum in the solar system or even here on
Earth to surround the Sun at 1 AU with aluminum foil. If you make the
foil just the right thickness, the Sun's gravity and the light pressure
exactly balance, and the foil will remain stationary.
What would the optical effects look like to an outside observer?
Well, the sphere would be far enough away in relation to its size
that it would appear to be a point in the sky. It would radiate as
much energy that the star inside is radiating, but it would be at
infrared wavelengths corresponding to room temperature (or whatever is
a comfortable temperature for the aliens).
Such stars would be invisble to the eye, and they would be invisible
to any ground based IR telescopes since those wavelengths are absorbed
strongly by the Earth's atmosphere. But they should not be too
difficult to observe from a low Earth orbit observatory.
In fact the IRAS observed what may be a partial Dyson sphere last
year. Fron the vicinity of the star Vega, large amounts of infrared
was observed. This doesn't quite match what is expected for a Dyson
sphere because 1) The IR represented a very cold temperature (of
course the aliens might be methane based, or they might have found
some new laws of thermodynamics allowing them to conserve heat in ways
we think are impossible). 2) The star was not completely blocked. In
fact it was hardly blocked at all (so maybe its only a partial sphere).
3) I seem to recall that Vega is much younger than the Sun, so life
would not have had time to evolve there (so maybe we are wrong and
Vega is older, or maybe the aliens are recent immigrants, or maybe
life evolved much faster there than here for some reason).
More likely, it is just so much uninhabited sand and gravel, perhaps
in the process of forming a solar system, that IRAS observed.
Lets launch more IR satellites and hunt for Dyson spheres and other
IR. Large amounts of IR is quite likely a byproduct of any large
technical civilazation.
...KeithKFL@AI.AI.MIT.EDU ("Keith F. Lynch") (03/30/86)
From: ucdavis!ucrmath!hope!corwin@ucbvax.berkeley.edu (John Kempf)
Interesting idea about the aluminum foil. I had not considered
just a shell, only a fully habitable sphere.
The original idea was that the sphere would be many relatively small
asteroid-like objects.
As far as visuals go, I was picturing things along the lines of a rotating
flashlight from a half built sphere, to a strobe star from a partial sphere
started from several locations.
It would probably be built more or less all around the star at once,
and gradually become denser as more and more colonies, farms, and
factories are built, until finally none of the sunlight escapes into
interstellar space as all of it is intercepted. Much like satellites
around the Earth (except that nobody expects satellites to become so
prevalent that they block all sunlight and moonlight from reaching
Earth).
Of course it is possible that it might be built in the way you
describe, though it sounds pretty unstable to me. And if it is
suspended by light pressure, it would not be rotating. We would
either see the star or not depending on which way the hemisphere
happened to face.
Probably what we should be looking for are room temperature IR
stars, stars that are unusually dim, stars that are getting rapidly
(on an astronomical timescale) dimmer, stars that do vary in
brightness in some hard to explain way, and of course anything else
unusual looking.
Definately agree with launching more satellites and/or observatories,
but why limit it to IR? Wouldn't radio also be a sign of civilization?
Only if the aliens use strong but poorly aimed radio signals for
communications or some other purpose. A more advanced technology
might consider radio obsolete. But unless we seriously misunderstand
thermodynamics, any civilization which uses massive amounts of energy
for anything at all will have to radiate enormous amounts of infrared
into interstellar space.
...Keithhenry@utzoo.UUCP (Henry Spencer) (04/01/86)
> In fact the IRAS observed what may be a partial Dyson sphere last > year. Fron the vicinity of the star Vega, large amounts of infrared > was observed. This doesn't quite match what is expected for a Dyson > sphere... More likely, it is just so much uninhabited sand and gravel, > perhaps in the process of forming a solar system, that IRAS observed. Alas for this theory, IRAS found a number of those dust disks, and one of them (around Beta Pictoris) was photographed in late 1984. Looks much more like a random mass of dust than an artificial construct, although the resolution of the picture is admittedly rather low. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry