[extropy-chat] MBRAIN: Imaging the universe, NOT

[Robert J. Bradbury]

On Mon, 26 Jan 2004, Mike Lorrey wrote:
(in: http://forum.javien.com/XMLmessage.php?id=id::bQ5JCRNB-CUlK-KQlK-W1Eo-a1VrGTkRXiRo)

> An interesting article by Seth Shostak on space.com:
>
> http://www.space.com/searchforlife/seti_shostak_seeing_031120.html
>
> details why the hand waving that Robert made recently about the ability
> of M-Brains to observe the universe should be seriously questioned.
> reach a curve of diminishing returns.  [snip]
>
> Imaging at 1 foot per pixel, small enough to see animals, would reqire
> a telescope 500 million miles in diameter. Interferometry is of
> diminishing usefulness, as one would need a 100,000 mile diameter
> mirror just to catch 1 photon per second at that distance and
> resolution.

Interestingly there has been a fair amount of discussion, in part prompted
by Seth's article, among the non-classical SETI people (SETV, SETIA, probe
supporters), etc. over the advantages of sending probes back and forth
(though they are quite small compared to those we now send).

I would draw your attention to one point -- Seth says "every square foot of
dino skin would reflect about 10 billion billion photons" -- that suggests
that he is talking about visible light.  Astronomers already perform IR
observations and plan to look for planets that way (because planet to star
signal to noise ratio is better in IR frequencies).  They can also measure
atmospheric composition with IR spectral emission lines (for ozone, CO2, etc)
more easily at IR frequencies.  In addition dust is not as big a problem
at IR frequencies as it is at optical frequencies (which is why the SIRTF
can look through the dust clouds in star forming regions and through stellar
nebula for still forming planets).

So I would not view Seth's comments as a complete show-stopper.  There are
a range of capabilities one would like to have -- detection of volcanoes,
detection of forest fires, detection of large buildings, detection of
atmospheric pollutants (e.g. CFCs), detection of the construction of "hot"
MBrains in close stellar orbits, etc.  Seth's points do however lead one
to a conclusion that it may be relatively difficult for ATC to read the
license plates on distant planets.  But I can live with that.

Robert