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[sci.astro] ET Life (Astronomy Frequently Asked Questions) (6/9)
Section - F.07 What's a Dyson spheres?

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Freeman Dyson noted that one of the limiting resources for
civilizations is the amount of energy they can harness.  He proposed
that an advanced civilization could harness a substantial fraction of
its sun's energy by enclosing the star in a shell which would capture
most of the radiation emitted by the star.  That energy could then be
used to do work.

As originally proposed a Dyson sphere consisted of many solar
collectors in independent orbits.  Many science fiction writers have
modified the idea to make a Dyson sphere one complete shell.  In
addition to capturing all of the available energy from the star, such
a shell would have a huge surface area for living space.  While
Dyson's original proposal of a number of solar collectors is stable,
this later idea of a complete shell is not stable.  Without some
stablizing mechanism, even small forces, e.g., a meteor hit, would
cause the shell to drift and eventually hit the star.  Also, the
stresses on a complete shell Dyson sphere are huge and no known
material has enough strength to be used in the construction of such a
shell.

There have been searches for Dyson spheres.  Such searches typically
take place in the infrared.  Because the shell is trapping energy from
the star, it will begin to heat up.  At some point it will radiate as
much energy as it receives from the star.  For a Dyson sphere with a
radius about the radius of Earth's orbit, most of the radiation
emitted by the shell should be in the infrared.  Thus far, no search
has been successful.

Considerably more discussion of Dyson spheres is in the Dyson sphere
FAQ, <URL:http://www.student.nada.kth.se/~nv91-asa/dysonFAQ.html>.

User Contributions:

1
Keith Phemister
Sep 13, 2024 @ 11:23 pm
Copied from above: If the Universe were infinitely old, infinite in extent, and filled
with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP

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Top Document: [sci.astro] ET Life (Astronomy Frequently Asked Questions) (6/9)
Previous Document: F.06 How far away could we detect radio transmissions?
Next Document: F.08 What is happening with SETI now?

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