

Active SETI (search for extraterrestrial intelligence) could be courting trouble - netcan
http://www.straight.com/article-320615/vancouver/gwynne-dyer-active-seti-could-be-courting-extraterrestrial-trouble

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stcredzero
The article assumes you need faster than light travel to make aliens
potentially dangerous. You don't need FTL. Relativistic travel is dangerous
enough. The time of danger will approach when we start to develop relativistic
spacecraft. If we can do that, then we could also develop weapons using that
technology. Once we reach that point, we become dangerous enough that aliens
might be interested in wiping us out.

The problem with relativistic weapons, is that there can be no Mutual Assured
Destruction if societies that resemble the current human civilization are
involved. High relativistic velocities can preclude detection with significant
warning time. If the first strike can be coordinated to completely wipe out
the enemy, then there is no chance to launch a retaliatory strike.

If intelligent aliens already uploaded their minds into their starships, then
it would be safe to deal with them. A civilization composed of such sentient
starships would be impossible to wipe out in a preemptive strike, so there
would be nothing we could do to them, and there would be no reason for them to
fear us.

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DrSprout
Unless they're active colonizers, moving from solar system to solar system
consuming all available resources, I don't see why we would want to fear them.
Assuming they are, if anything they would avoid solar systems that might have
active defense.

It's also possible such a civilization might follow much the model many hope
to create for humanity, colonizing worlds then sending out new seed missions
to every available world. If that's the case, there are three possibilities:

A. They respect other life, and avoid inhabited systems. B. They fear other
life, and seek out inhabited systems. C. They don't care about other life, and
attempt to colonize all systems they can.

Because of the assumed exponential growth life is capable of, and the
distances between stars, the limiting factor is travel time, not growth, so it
follows that the difference between B&C is negligible.

Now, if they have some form of FTL travel, then B could be a problem. However,
it seems likely that if FTL aliens were interested in destroying us, they
would have found us by now and begun monitoring anyway.

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mijoro
It seems silly to blame active SETI for giving away our position. (I'm looking
for that image that shows how far some famous radio signals have reached over
time, but I cant find it.)

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stcredzero
A couple of hundred light years isn't that far in galactic terms. Also, the
signals will have attenuated greatly by then. The likelihood that TV and radio
signals will give us away is actually pretty small.

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strebler
I would say the thousands of nuclear detonations we've done (global weapons
tests) have probably sent a fair number of powerful signals. No information
per se (other than "we like 'splosions"), but those are likely unmistakable
indicators.

Of course, there's also these:
<http://en.wikipedia.org/wiki/Active_SETI#Realized_projects>

(but their argument seems to be: "don't keep doing that")

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jerf
Undirectional bursts of noise dampen out in the usual n^2 manner, and at the
distance of light years becomes difficult to sort out from the undirectional
burst of noise that we are pleased to call our Sun. Also, as noise, they don't
yell out "intelligence!" as much as an analog radio signal, which is clearly
from an intelligent source. Nuclear explosions may have some special
characteristics, but frankly there's always something exploding somewhere out
there in the cosmos. It's difficult to characterize the exact detection
radius, but it's probably much smaller than you think.

Interestingly, as we become more efficient with our radio transmissions, which
is to say, use less power, and ever more of it is locked behind at least one
of excellent compression or encryption, it seems that the natural evolution of
a civilization may return it to something that looks pretty natural again at a
distance of light years. Dim, high-entropy signals once again become difficult
to distinguish against background noise.

To be honest, the thing that yells "LIFE!" that is probably detectable out to
a far greater distance than anything we humans have done is our oxygen
atmosphere. We stand on the verge of doing elementary spectroscopy on distant
planets ourselves.

Come to think of it, this is probably the most powerful argument against the
paranoid alien. The paranoid, relativistic-projectile-firing alien isn't even
looking for a sign of intelligence; the logic says they should extinguish _all
other life_ , just in case. But our planet has been broadcasting "I'm alive!"
across the cosmos for between 1.6 to 2.5 _billion_ years. If somebody out
there was looking to preemptively kill everybody around them, they would
already have gotten to Earth.

(Waiting until you can see a trace of intelligence is too late, after all,
without FTL. In cosmological terms that's the striker hitting the alarm bell.
You want to get there _long_ before that. And even if you have FTL you're
still safer preemptively neutralizing planets. Remember, it is _trivial_ to
neutralize a planet and reset its biological clock to zero; if you can wait a
hundred years or two then very gently nudging a very large asteroid will do
the trick, and if you're impatient there's any number of faster ways to do the
same thing with very, very, _very_ modest energy investments. Sterilizing a
planet is _easy_.)

(On that note, no, neither the dinosaur extinction event nor any other impact
would match this profile. An intelligence would _successfully_ sterilize the
planet, not merely "substantially stress the ecosystem".)

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strebler
That's a great post, and yes, I was certainly working under the assumption
that a nuclear explosion would have a distinct spectroscopic signature when
compared to the emissions of our Sun. Is that false?

If we can (eventually) detect the oxygen atmosphere of a planet through
passive spectroscopy, then it does seem to follow that we could easily detect
nuclear explosions from the surface of that same planet. Unless I'm missing
something...

