Re: SETI/ASTRO: MBrains/JBrains & Globular Clusters

From: Robert J. Bradbury (
Date: Tue Jul 17 2001 - 13:03:01 MDT

Robin has posed a series of comments/questions:

> ...might be worth following the argument through to see
> what velocity it suggests.

Hal did a rough cut on that (Thanks Hal). The 6 small
objects would appear to be going ~40x faster than the
larger object. The orbital speeds in our solar system
range from 4.7 km/sec for pluto to 47 km/sec for Mercury.

While 10x range vs. 40x range isn't too much of a difference
I can't think of any really good XBrain bound to orbiting
star scenarios that would make much sense. So as the
article suggests these would have to be "free-floating"
objects. (Or else the article is mis-interpreting one
set of observations.)

Its useful to keep in mind that within globular clusters the
available "starlight" is much greater, so Jupiter Brains
don't have to orbit stars, they can use the light energy
from the cluster as a whole.

One other reason has occured to me for fast transit times.
If JBrains are star-lifting by direct encounter, e.g.
fast transit through the star's upper atmosphere sucking
up material as you go, then I suspect you are going to
want those orbits to be made at fairly high velocity.

> So does this imply a correlation between object mass & attachment?

Civilizations derived from low-mass stars or constructed from
nearby brown dwarfs probably only have enough material for JBrains.
They could migrate to the globular clusters because of the
greater material resources there.

Civilizations derived from larger-mass stars probably construct
MBrains and have to do a lot of star-lifting of said star
to lengthen its lifespan. They are less likely to migrate
due to the larger mass they have to cart around.

> OK, might be worth estimating this velocity (drift velocity) too.

"Natural" star velocities are going to vary with distance from
the galactic center. Stars very near the center are orbiting
very fast, stars out beyond the sun are moving more slowly.
The sun is orbiting the galaxy at 220 km/sec. There is a
velocity dispersion of +/-40 km/sec in various regions (older
stars have had more close encounters and are going faster).
So that is what a civilization would start with. How fast you
can crank up the speed depends how long you have been accelerating,
how much matter & energy you were willing to sacrifice and what
you had nearby for gravity assists.

Spike is better at these types of calculations that I am, perhaps
he could set some constraints on what various strategies and
costs associated with accelerating a 0.25 M_J (5x10^26 kg) object
from say 15 km/sec around a star traveling at 300 km/sec (closer
to M22) up to say 600 (15*40) km/sec. I'm reasonably sure that it
depends on how much energy you can pump out on really close flybys of
massive objects.

> I realize that it would be more work to make these estimates,
> but this does seem the key datum that you have to predict soon.

Given the fact that stellar velocities span at least an order
of magnitude (so J/MBrains could potentially start with
a range of velocities almost as large), it isn't clear how much
value such a velocity prediction would have. A much better
"predictor" (IMO) is setting constraints on the rate at which stars
"go dark" (that I am working on). I would predict that
JBrains should have significantly higher interstellar velocities
than MBrains, but how much higher would require a complete
a galactic model of stellar evolution, rates of development
of ATC, and some simulations of the various gravity assist
acceleration strategies and an economic analysis of what
the civilization can afford to sacrifice if it can recover
some or all of it when it arrives at the destination. I think
thats a PhD thesis or two of work.

> As you know I'd estimate a pretty low chance that these things
> are MB/JB, but I am interested in thinking about how to check this.

Yep, I know you are in Eugene's camp (or perhaps he is in yours),
but thats ok, the questioning and provoking of study in the
nooks and crannies of these ideas is what makes them interesting.
Even if it isn't about the way the Galaxy "is", it is about the
way the galaxy might someday be.

> How solid is the spectra prediction, btw?

I'm pretty confident in that. I forgot to mention it in
my OSETI III presentation and Charles Townes suggested it
during the Q&A period. The problem is you need big telescopes
so odd ratios of those gases might give a hint of what lay beneath.
to get good spectra. For comparison, we can get spectra from brown
dwarfs out to a few hundred light years at this point. So we
have a way to go before we can get spectra for JBrains at ~7000+ l.y.

Any ATC evolving around a G or F class stars, with a metallicity
after the first few billion years of galactic history "should"
have enough metal available to enshroud the star. Not doing
so would seem to be a waste. If its an MBrain architecture
the spectral argument is good. If its a JBrain architecture
(particularly if they decide to store the "fuel" as an "atmosphere")
then the spectral argument may work less well. I'd suspect
though that that engineers whould choose to save the H
and throw away the He and use the carbon in any methane,
so its not entirely useless.


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