> Spike Jones <spike66@ibm.net> wrote:
>
> I did have an idea tho. Consider all the dark matter out there.
That was what got me thinking about this a couple of years ago when I first realized how significantly our astroengineering capacites change at the time of the singularity.
> We think we could detect a Dyson Sphere by the low frequency radiation
> that would need to be emitted by reason of conservation of energy.
Depends on the temperature. A "young" M-brain probably doesn't have enough matter to fill its outer shells, so it might be "warm" (perhaps 50-1000K). An "old" M-brain could have collected enough matter to fill the outer shells and therefore be "cold" (slightly above the microwave background. Cold is good for both the preservation of long term memories (for data you don't really need access to for the next 10 million years) and it gives you the greatest thermodynamic efficiency. I've considered that the anisotropy in the microwave background radiation could be due to greater or lesser concentrations of M-brains in various regions of space. [But I would suggest that this idea will not make the astronomers happy. :-)]
However, one well informed person I've talked to thinks that if star dismantlement is feasible, that the optimal architecture would be diamondoid based shells that could operate @ ~1500-1700K.
I'm not sure it matters much since our observing capabilities at this point in the mid-to-far IR region are very poor. We have a difficult time finding warm brown dwarf's (which are hotter than M-Brains) beyond ~400 ly.
> But what if... the universe is a dangerous place?
I assume you mean dangerous from the perspective of other aggressive intelligences.
> Then any ETI that has any brains knows to hide.
No, I thought about this after I read "The Killing Star" by Pellegrino & Zebrowski. For an SI to want to make war (unless it is suicidal), it has to be able to guarantee that it can wipe out *all* traces of its enemy. That would require incinerating, irradiating, or black-hole-izing *all* possible nanobots in a very large volume of space. I strongly question if that is possible. This might be a worthy effort as "revenge", but seems questionable as an evolutionary strategy in general.
Since the MAD (mutually assured destruction) scenario would seem to prevail (because all SIs would have berserker-nanobots hidden somewhere) it would never seem to make sense to do anything that would trigger the response.
> Could not a really advanced ETI build a Dyson sphere, then
> somehow collect the waste energy, collimate the radiation
> into a narrow beam and focus it out in some harmless (starless)
> direction?
This seems quite feasible. Enough highly reflective layers (a large multi-layer solar-sail) on one side would cut the radiation signature significantly. It could also be an intereresting form of propulsion/navigation.
> Are there SF stories based on this explanation of dark matter?
Not that I know of, but "The Killing Star" (already mentioned), and "The Wanderer" by Fritz Leiber discuss some aspects of super-astro-engineering.
>
> Given enough raw material, it seems that a really out-there nanotech
> civilization could make a sphere and keep its surface at 3 kelvin, so
> that it would be undetectable by us less advanced (and therefore more
> dangerous) intelligences. Do we have any thermodynamics experts
> out there who can confirm that such a scheme does not violate the
> third law? Seems to me it doesnt. spike
>
My impression is that it doesn't violate the the laws and does in fact give you the best computing structure. The problem is that power in has to equal power out. If you surround the star, to radiate at ~3K you need a *really* big sphere. This is because heat radiation scales with T^4 (i.e. hot radiators are much more efficient (smaller) than cold radiators). Think about Neptune and perhaps Pluto - the He/H2/Ne/O2 if retained by the gravity isn't "frozen" solid. They are heated by the sun. [This is true to some degree with Jupiter & Saturn, but you have to factor in the heating due to ongoing gravitational collapse as well.]
In our solar system, my calculations show that you don't have enough mass to get a 3K radiator (at least if you want to circulate the cooling fluid from the computers and use all of the power the sun produces). If your only goal is to "hide" I'm unsure. Given the solar sail idea, I suspect "hiding" is relatively easy.
Robert