Rich Kulawiec on 3 Mar 2017 02:42:01 -0800

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Re: [PLUG] "Nearby"

On Thu, Mar 02, 2017 at 06:01:15PM -0500, JP Vossen wrote:
> But there may be lots of other things emitting EMR I'm not
> thinking about.  So--how much longer are we going to be emitting at
> detectable levels?

Your line of reasoning (including the next part that I've elided)
is sound.   EMR leaving the planet represents wasted power, in some
form or another, so it's reasonable to assume that as a civilization
progresses, it will seek to minimize that waste just as it would
seek to minimize any other.  So there's probably a time window
of a century or two that marks the boundary between when a civilization
starts emitting EMR into space and when it effectively stops -- unless
it's being broadcast deliberately.  Thus (more or less) there's an
expanding spherical shell of detectable EMR perhaps a few hundred
light years in thickness that you need to detect during the time period
that you have the technology to pick it up.

And then it gets even harder.  It's not possible to monitor the entire
spectrum, nor is it desirable: radio frequencies aren't as attenuated
as visible light, for example, so they're preferable.  But some parts of
the radio spectrum are full of background noise from space; other are
full of background noise from the atmosphere.  Also, as you might guess,
the budget for this is tiny, so even within the ranges left over
there's not enough money to keep an eye on everything.

Enter "the water hole", which is roughly 1.5Ghz.  The emission frequency
of atomic hydrogen (H) is somewhere around there, I don't recall the number
offhand.  So is the frequency for hydroxyl (HO).  So there are a lot
of people already looking at this range because they're very interested
in H and HO and of course the combination of the two.

And thus our efforts to listen are constrained by physics, noise, budgets,
and the need to shoehorn this research into someone else's grant money.

My guess is that there are lots of others out there, but we're never going
to meet them.  We're not alone, but we are.

See, this is why those bar arguments go on to closing time and are then
continued in the hotel lobby, fueled by whatever can be found in the
room minibars and/or delivered by local carryout restaurants.  How would
you like to be the overnight clerk, looking forward to a quiet night,
only to find the place overrun by drunk people scribbling equations
on napkins and thrusting them in each others' faces?  Why couldn't
it just be something simple like a couple breaking up loudly?

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