In sci.physics, Ian Stirling
<root@mauve.demon.co.uk>
 wrote
on 02 Oct 2004 12:58:09 GMT
<415ea5e0$0$42246$ed2e19e4@ptn-nntp-reader04.plus.net>:

In sci.physics Uncle Al <UncleAl0@hate.spam.net> wrote:

Skybuck Flying wrote:

Hi,

Seeing all the bullshit in this newsgroup or maybe sci-fi... or maybe
future technology I thought I add some of mine hehehehe.

My idea is to use the SUN as a way to send a message to aliens ;)

We build a big shield around the sun. And then we can turn it on and off
like a lamp.

Won't work.  Shield reaches equilibrium temp and emits.  Who is going
to launch it, NASA?  Ha ha ha.

Do the numbers before you laugh idiotically.
A shield around the sun at the diameter of the earth would reach 
around 0C.

(there are engineering difficulties.)

For starters -- where would the actual mass come from?  Also, the
shield will have to be in orbit around the Sun, at least during
initial construction.

If we were to generate a Dyson sphere out of pure iron -- I've no
idea what thickness would be required to resolve all of the
stresses and strains -- Uncle Al's observation will come true;
the shield will have to (eventually) throw out as much energy as the
Sun generates, lest things get overwarm inside.  Of course the
actual spectrum may be slightly different.  I'm not sure what
will happen if we leave a single large hole around the pole, either;
it could throw the shield out of alignment if we're not careful,
because of the thrust (not of light quanta, but the solar wind).
We'd need two holes, and careful construction techniques.

If we generate a Ringworld-like construction, the shield will still
have to emit as much energy as it receives, though now in this case
it will be but a fraction of the Sun's total power output.

Either way, I don't know how we'd use it for signaling, though one
rather simple possibility is paired sets of large doors; the Sun
would shine through the doors towards the target star.  (The Sun
would also shine through the doors on the exact opposite side,
to balance out things.)  Another possibility is augmenting the
doors with light-pipes, to redirect the energy in the desired
direction -- and in such a construct one can dispense with the
doors entirely, and simply move all the light-pipes.  Note that
the coordination of the pipes would have to be such so that the
device does not change position or spin.  The shield would still
emit, of course, but one hopes that the directed energy will
emit more brightly, leading to a detectable pattern.

It would be an extremely large undertaking, to say the least.

-- 
#191, ewill3@earthlink.net
It's still legal to go .sigless.