From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Tue Jul 18 2000 - 00:39:47 MDT
On Mon, 17 Jul 2000, Jeff Davis wrote:
> I wrote:
> >1) Nonbaryonic dark matter in our Galaxy seems to be required, and
> >
> >(I freely grant this point, but suspect if my perspective on
> >the activities of intelligent technological civilizations turns out
> >to be true, then this point may need to be reexamined.)
>
> Robert, don't you mean that you *don't* freely grant this point, *except*
> insofar as it is premised on natural cosmic evolutionary processes
> unmodified by purposeful intelligent intervention (ie your perspective)?
No, when I discuss this, I will usually grant this point since the
"conventional wisdom" is that there may be both missing baryonic
and non-baryonic dark matter. I've got an explanation for the missing
baryonic dark matter that seems to involve no magic physics.
To push the non-baryonic dark matter onto the baryonic plate, you may have
to change the big bang theories a lot, and I'm not willing to push
on that rock yet. Conversely SIs may find a way to turn themselves
into non-baryonic dark matter (with what I would call magic physics)
in which case I wouldn't have the foggiest idea how to prove that.
I'm like Niel Armstrong -- one small step at a time.
>
> I also noticed in the paper--which I read but was at some pains to
> decipher--
(don't worry I'm in the same boat...)
> that brown dwarfs were ruled out because of some experimentally
> observed TeraV gamma rays. These TeraV gamma rays would not--so the theory
> goes--be there if brown dwarfs with their accepted IR output populated the
> halo in numbers sufficient to account for the dark matter mass. As I
> understood it, the TeraV gamma rays are consumed in an interaction with the
> IR photons that produces electron/positron pairs.
That is the impression I got, though I think they are using it to
constrain cooling white dwarfs.
[As an aside, I would love it if someone would point me at the theories
that say *when* and *how* photons of different energies interact...].
However, you notice they say IR photons from 0.03-3 eV -- those
are photons with temperatures above that of lN2! While both
white dwarfs and brown dwarfs cannot have cooled down to those
temperatures yet (it takes dozens of billions of years), MBrains
can certainly have constructed shells that radiate at temperatures
below lN2.
Minsky told Dyson at one of the earliest SETI conferences that
they should radiate at slightly above the background temp.
Dyson effectively said maybe.
> This point, plus other bits and pieces of the observed IR radiation
> abundance--the low level of IR, actually--also suggests to me that the dark
> matter is not composed of large numbers of matrioshka brains.
Not so because of the possible failure of the 1-10 TeV gamma rays to interact
with very low temperature IR photons. There is an additional argument
that they are discussing the progenitors to white dwarfs (e.g. the
initial population II stars). I think this is because the gamma rays
at redshift z=0.034 have to travel through a lot of IR photons to get
to us. But if MBrains don't start developing until ~6 Gyr after
the formation of the universe (long after much of the IR radiation
from the white dwarf progenitors has been produced) then the MBrain
IR radiation may not intersect in the time dimension with much of
the gamma radiation.
> If it were matrioska brains *harvesting* the stellar output in an
> orderly fashion, and then radiating away the waste heat, this would
> also result in infrared emissions able to interfere with the TeraV gammas.
If MBrains had existed from the beginning and/or were radiating
at lN2 temperatures or above, I think you would be correct.
But it looks to me like I've got wiggle room.
> The issue of the lack of IR radiation plus the dark matter business leads
> me to a question I've been mulling over. Could advanced civilizations halt
> the unbridled stellar fusion and save the fuel for a more orderly regime of
> consumption? (Is this anything like the *star lifting* business that I've
> heard about?) This seems to me to combine the observed features of
> substantial quantities of dark mass and low IR emissions, while still
> allowing the matter in question to be baryonic rather than something exotic.
I have read Prof. Lorry's (:-)) comment on this and I can only mildly
disagree with what he says. I've seen no peer reviewed paper that
says you cannot disassemble stars or that disassembling them produces
supernovas. Criswell's stellar husbandry (aka star lifting) approach
(which I have online copies of if someone wants it), to my knowledge has
not been disproven. I have seen suggestions (hints?) that as Michael
says, this may age the star prematurely. I think it depends on
whether or not the star has ignited its helium burning cycle
(which is what turns it into a red giant). If all the star is
doing is burning H into He, then, removing the outer mass should
decompress the core and allow the star to shift down the
luminosity curve (G-->K-->M-->L). You may have to do it *very*
slowly to allow the star to adjust. I suspect there may be
some additional complexity depending on the degree to which the
star is losing heat primarily through radiation or convection
(which may depend on its mass and perhaps metalicity).
Perhaps if Amara reads this at some point she could comment.
I'll also state that I'm dubious as to whether there is enough
mass in our solar system to use Criswell's suggested method
for accomplishing the mass removal since it requires some very
powerful, and a potentially large number of, particle accelerators.
It is worth noting that Criswell expected this process would
take hundreds of millions of years.
So I suspect the jury is still out on star lifting and it is likely
to require a fair amount of theoretical work and some large
computer simulations to answer the question.
> Hope I'm not embarrassing myself.
Not any more than I manage to frequently do...
Robert
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