[extropy-chat] sjbrain calcs

[Spike]

> On Fri, 19 Dec 2003, Spike wrote:
> 
> > ...1 meter class would not have anywhere
> > near the resolution needed to distinguish a Jupiter-like SBrain
> > (SJBrain?) from its star...  {8-[
> 
> Spike, you have lost me.  Is an SJBrain just a cloud of dust-like
> particles in orbit around a star the size of a JBrain?...


The theoretical SJBrain is a roughly spherical Jupiter-mass
cloud of computronium particles about a light-minute in diameter,
with the spherical (or galaxy-style flattened disk orbitting
about a light-hour from the star.  The particles are roughly 
spherical, about a micron diameter, mass of about a picogram,
30 to 50 billion atoms of carbon and silicon, with some other
metals that are sure to be useful to an SJBrain node.

This notion is only a slight variation on the traditional
Bradburian MBrain, except that the nodes bunch together in
a sphere to reduce the distance between them.  

My calculation compared the light-minute sphere against the
5 second diameter G star and estimated the surface temperature
about 130K.  Recall that Jupiter's diameter is a little less
than half a second, so this light minute diameter SJBrain
has a great deal of surface area from which to radiate.  The
total energy coming off the SJBrain in our direction is only
1/25000th as much as is coming off the star, but as you point
out, it is waaaay down there in the spectrum, all the better
for the Lockheeed SIRTF to see it.  Taking the spectral 
argument into account, it is not clear to me that the SIRTF
would not be detectible directly, if it is really close by.

Heres another thought I had last night.  If the SJBrain is
held from gravitational collapse by rotation alone, like a 
galaxy) then of course it cannot be spherical, unless it is
a series of rings like your MBrain.  But the thing could
be held into a spherical shape by having the particles hold
a net electric charge.  Since a Planck mass is about 10^19 GeV, 
that means that gravity is weaker by a factor of roughly 
 1 / (10^19)^2 = 1 / 10^38 than the electromagnetic
force, 38 orders of magnitude.  So if all the particles had
a net positive charge, the cloud could be spherical with no
sidereal rotation, and furthermore if the cloud had a charge 
gradient, with more charge inboard than outboard, it would be 
possible for any given particle to navigate to anyplace it
wanted within the sphere.  COOOL!

Robert see what cool ideas your cool ideas spawn?  {8-]

 
> If so I don't think you should knock SIRTF too soon.  Both the
> Terrestrial Planet Finder and Darwin plan to do most of their
> work in the IR frequency range because the signals from planets
> are much easier to differentiate from stars because more of the
> energy coming off of stars is coming off as visible and UV.

Knock SIRTF?  Im huuuge SIRTF fan.  {8-]  You should see the
LMCNews floating around the plant this week.  It was party
time around there in the astronomy geek crowd, some major
woo-hoo moments for sure.  Our office Newtonmass party was
filled with levity because of the SIRTF images.  On a slightly
more somber note, one of the big SIRTFers and all-around
good-guy who works in my office was carried out on a stretcher 
yesterday.  He was talking and the medics weren't running with 
him like they do on ER, so I suppose he is OK, but we haven't
heard.  He's mid 70s.  {8-|  I sincerely hope the 
life-extention guys score big, and score soon.


> You have to remember that SIRTF has a spectrograph as one of
> the instruments -- it remains an open question whether the
> IR from a planet (or an SJBrain) will produce enough of
> a bump in the IR spectra of the star that it could be noticed...
> 
> Robert