Re: Dyson spheres are not dark

Carl Feynman (
Thu, 26 Jun 1997 10:47:19 -0400

At 11:41 AM 6/25/97 -0500, Dejan Vucinic wrote:

> o What is the minimal distance from Sun at which a (diamondoid?)
> statite can preserve its crystalline structure?

The minumum distance is around 136 kilometers [not a typo!]. Allow me to
quote from a not-yet-complete essay I have cluttering my hard disk:

<p>The surface of the Sun is hotter than the boiling point of any known
material. Indeed, it is hot enough to rip any known molecule into atoms.
One might think this would preclude the direct exploration and
exploitation of the Sun. However, this is not the case. It
is possible to build a device that can operate for long periods of time in
the atmosphere of the Sun. This can be done with plausible near-term
technology, operating with known materials and entirely within the
well-established laws of physics.

<p>I call my design for such a device a <i>heliopter</i> (from the Greek
<i>helios</i>, Sun, and <i>pter</i>, wing). It is essentialy a helicopter
that can hover indefinitely in the Solar atmosphere, using solar energy as
a power source.

<p>First I will discuss the environment of the solar atmosphere. This is
well-established science. Then I will discuss how one might keep an
object immersed in that atmosphere cold enough to remain solid. This is
an application of well-established engineering thermodynamics. Finally, I
will describe the heliopter as a whole. This is an excercise in wild-ass
system engineering. There's nothing in the design that I know to be
infeasible, but I certainly haven't worked out every stress and heat flux
and confirmed that it will work.

[end excerpt]

You'll get to see the rest of this essay once I calculate some more, and
maybe draw a picture or two. Provided I don't decide to first finish my
essays on re-engineering the human body or burning down the Sun...

> o Outgoing radiation doesn't have to have a blackbody spectrum.
> Lasing comes to mind, or one could heat up relatively small
> radiators to a very high temperature.

Blackbody radiation over the largest possible area is the most efficient way
of getting rid of heat. All other methods of heat disposal will leave less
energy available for useful purposes.

Lasing in particular is very bad. You wouldn't know it to look at one, but
laser beams are very cold, i.e. have very low entropy. Thermodynamically
speaking, they're like a perfect crystal at very low temperature, and the
process of producing one requires extracting lots of entropy from a lasing
medium and dumping it in the environment. Trying to cool something by
emitting a laser beam is like trying to cool your house by installing a
powerful freezer, making lots of ice cubes, and throwing them out the
window. (Hmmm... that has a certain surreal delight to it. Imagine a house
with ice cubes flying out all the windows...)

>--d(isn't physics fun when you don't have to give answers)v

That's OK, I love giving answers.