[extropy-chat] FW: The Drake Equation and Spatial Proximity

The Avantguardian avantguardian2020 at yahoo.com
Mon Oct 23 01:16:19 UTC 2006

--- spike <spike66 at comcast.net> wrote:

> Forwarded for Amara Angelica:
> have
> interesting discussions. I don't understand why it's
> a paradox if we've only
> explored a miniscule portion of the search space
> (number of stars,
> percentage of time they are observed, EIRP range,
> frequency range, signal
> modulation schemes, etc.), based on an unpublished
> study of search space I
> did a few years ago. Comments?

I don't consider it a paradox either, Amara. To
summarize my thoughts on the matter:

1. SETI has been in formal operation for approximately
50 years.

2. The disk of the milky way is about 45,000 light
years (ly) in radius and 1000 ly thick. 

3. The central bulge of the milky way is approximately
6520 ly in radius.

4. Subtracting the volume of the central bulge from
the total volume of the galaxy leaves us with a
cylinder with a hollow center sort of like a
flattended torus or a washer. (I do this because the
the stars of the central bulge are too densely packed
to allow life to develop without being fried with
radiation.) This shape has a spatial volume of
approximately 6.23 trillion cubic ly.

5. The maximum volume of SETI's light cone (assuming
that every steradian of the sky has been scanned) is
4*pi*(50ly)^3/3 or a mere 523,299 cubic ly. 

Dividing 523,299 cubic ly by 6.23 trillion cubic ly
gives me a figure of 8.41 E -8 or 1/841 millionth of
the light cone of our galaxy for the fraction of
space-time that we have thus far scanned for
intelligent life.

To draw conclusions of being alone in the galaxy based
on such a miniscule sample size is mathematically
irresponsible. It would be the equivalent of drawing
sweeping conclusions about all of mankind based on a
quick survey of the nearest 500 people to you. (All
six billion people are well-nourished malaria-free

Unfortunately that is not to say that such poor
statistical extrapolations aren't rather common in
other fields as well.

Stuart LaForge
alt email: stuart"AT"ucla.edu

"More persons, on the whole, are humbugged by believing in nothing, than by believing too much."

- P. T. Barnum

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