[ExI] Fermi Paradox and Transcension

spike spike66 at att.net
Tue Sep 11 20:29:11 UTC 2012


>... On Behalf Of BillK
Subject: Re: [ExI] Fermi Paradox and Transcension

On Tue, Sep 11, 2012 at 6:11 PM, spike wrote:
<snip>
>> ...Parting shot: if an MBrain is mostly transparent and relies on a 
> mostly unobstructed view of cold space for heat rejection...

>...Why not go to the source? The much-missed Robert Bradbury invented
MBrains.
In 'Year Million', edited by Damien Broderick, Robert has a chapter "Under
Construction: Redesigning the Solar System."
I don't have a copy...

I do have a copy, however... read on please.


>... but a review quotes:
MBrains, comprised of swarm-like, concentric, orbiting computronium shells
that use solar sail-type materials to funnel and reflect the largest
possible quantity of stellar energy.
-----------------

Of course, however...

>... The standard M-Brain architecture I designed, radiates heat only in one
direction (outward, away from the star). Each layer's waste heat becomes the
power source for each subsequent (further out) layer...Robert J. Bradbury
Thu, 2 Dec 1999>   

Hmmm, Robert and I did not agree on this.  He and I spent many hours at my
home debating and deriving thermal models after this was written, most of
the activity happening between 2001 and 2004.  After that he became
distracted by another project, but my own feeling at the time and today is
that his design does not close.  His contribution is valuable: the inner
nodes have a different construct than the outer nodes, and must be able to
operate at higher temperatures.

>... To satisfy the laws of thermodynamics and physics, you have to get
cooler and cooler but require more and more radiator material. At the final
layer you would radiate at the cosmic microwave background (or somewhat
above that if you live in a "hot" region of space due to lots of stars or
hot gas)...  Robert J. Bradbury Thu, 2 Dec 1999

Robert did not have, never did have, a detailed thermal model.  He had good
ideas.  But there is a lot of blood, sweat and tears yet to be shed over a
detailed thermal model, as well as some actual tests of hardware in space to
measure their control parameters before I will trust my own models.

>...However it is important to keep in mind that the mass of the computers
in a node is probably very small compared to the mass of the radiators and
cooling fluid (this is the part that needs to be worked out in detail).
Robert J. Bradbury Thu, 2 Dec 1999 (?)
-------------------

BillK
_______________________________________________

BillK, I can't tell if this last sentence is part of Robert's commentary or
yours, but Robert and I never did agree on the use of cooling fluid.  My
MBrain nodes always relied on passive cooling only, for I did some calcs a
long time ago which convinced me that cooling fluid doesn't help at all in
the long run.  It can only help if you have available a low entropy cold
space into which you dump waste heat.  But in Robert's vision, the inner
nodes have only a view to a high entropy warm space, and the outer nodes
which have a view to cold space do not need fluid of any kind.

There is a lot of work to do on this.  I worked out the orbit mechanics
first, because orbit mechanics are easier and cleaner than the thermal
models, and I know how to do those.  Now the hard work begins.

Final shot: microprocessor technology moved a long ways since Robert wrote
the above passages.  He didn't live to see a cell phone win a chess
tournament against several masters and two grandmasters, without a charger
and without phoning a friend.

spike




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