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From: KFL@AI.AI.MIT.EDU ("Keith F. Lynch")
Newsgroups: net.space
Subject: Observing Dyson spheres
Message-ID: <[AI.AI.MIT.EDU].22222.860328.KFL>
Date: Fri, 28-Mar-86 21:43:30 EST
Article-I.D.: <[AI.AI.MIT.EDU].22222.860328.KFL>
Posted: Fri Mar 28 21:43:30 1986
Date-Received: Sun, 30-Mar-86 02:27:54 EST
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    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.
								...Keith