[Atmob-discuss] FW: Silent Sky - A Thought Experiment

[astronut at morlock.net]

This is pondering from one of the engineers that works
for me at foliage.com.  I thought you folks might be
interested in his mental exercise...

Steve

-----Original Message-----
From: Chuck
Sent: Wednesday, May 28, 2008 1:07 PM
Subject: NI: Silent Sky - A Thought Experiment

This is an interesting thought experiment and it involves statistics and
some figuring, so I welcome any of you smart Foliates to comment.

(1) Assume that sentient civilizations with the ability to transmit some
form of radiant communications signals (radio, light, whatever) started
appearing in our galaxy as early as 4.5 billion years ago (when the Earth
was forming), and assume that they continue to appear (each on its own
evolutionary trajectory) for another 4.5 billion years.

(2) Further assume that over this timespan of 9 billion years a total of one
million different intelligent civilizations begin transmitting radiant
communications.

(3) Assume that after a random time period of 100 to 1000 years each
civilization stops transmitting radiant signals, either because they move on
to a better technology that does not require radiant communication (pretty
much necessary for interstellar communications) or the civilization dies
out.

(4) Finally given that our galaxy's diameter is about 100,000 light years,
assume that any of these civilizations when transmitting would be at some
random distance from us which does not exceed 100,000 light years (yes I
know that's a little big since we aren't at the very edge of the galaxy, but
bear with me.)

Now, here we are, smack-dab in the middle of that timescale, halfway between
year 1 and year 9 billion.  We turn an array of radio telescopes to the sky
and listen in all directions simultaneously, constantly, for a period of
1,000 years.

Is our sky silent?  Or is it noisy?  With a million civilizations out there
at some point or another, all sending signals out at different times, what
are the chances we would hear none of them at all even if we listen for 1000
years?

I threw together a crude simulation late last night to try and answer this
question, and I have a result which you might find surprising, but I'm
curious to know what other people think first.  Care to venture a guess?  Or
perhaps create your own sim and see what results you get?  I'll share my
results later if there is any interest.