Active SETI (search for extraterrestrial intelligence) could be courting trouble | Hacker News Reader

Active SETI (search for extraterrestrial intelligence) could be courting trouble

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17 pointsnetcan7 comments

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.

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.

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.)

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.

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")

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".)

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...

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