Why I Hope the Search for Extraterrestrial Life Finds Nothing

Save your summaries for techcrunch. They are not for refereed writing on subject X (i.e. 'existential risk') by the foremost authority on subject X. If you're not reading the whole thing (perhaps 2 or 3 times), you may as well not read it.

True, but that a form of reasoning inevitably gives a wrong conclusion under rare circumstances is only a weak argument against it.

-Based on our experience, it takes ~4bn years for life to evolve in a planetary system.

I don't think we have a strong reason to believe that there's something special about that length of time. Not much change happened on Earth for most of that time, suggesting dependence either on stochastic evolution of a few things like photosynthesis (so 4bn probably isn't much more likely than 3bn) or on something like increasing solar output crossing a threshold (it's doubtful such a threshold would be crossed at ≥ 4bn years at every location). That aside, even a few tens of millions of years is plenty of time for life to cover a galaxy.

Even if we can't intercept their communications, we should be able to see their works. The universe looks far too natural to contain much technologically advanced intelligence.

All our current technology says that all future civilizations may have radically greater resources than us, but still finite. Finite resources means there will still be some sort of internal competition. Competition implies that one solution to the local competition is to pack up and head for the next star system to exploit. This logic then applies again from that system once it has been tapped out. It borders on the inconceivable that it is physically possible to colonize the stars, that intelligent life is common, and it is easy to get to "post-human-equivalent", but absolutely nobody has ever chosen to colonize the galaxy. One of those axioms is wrong (including, potentially, the finiteness of future civilization's resources).

This argument is mentioned in the paper, I'm just re-drawing your attention to it. It's a big one that is very important when talking or arguing about this; the answer must not cover 10% or even 99.9% of the cases because if intelligent life is that easy the galaxy still ends up colonized long before humans are sentient. It must cover 100% of the cases across an unknowably wide variety of intelligent life forms in an unknowably wide variety of initial conditions.

It's a tall order and most, if not all, of the self-loathing answers like "intelligent life like humans just suck so hard that they all die" really don't hold up under scrutiny very well; all life forms pollute themselves to death? Any problem we can see, some other life form somewhere will have solved. All life forms develop weapons technology and war themselves to death? Even hyperintelligent bees who early in their human-class civilization's history figured out how to share one mind such that war is impossible? All life forms ever decide to just stay home because they learn to live in harmony? Even on Earth you can see that while some humans may make that choice, other humans quite rationally never will.

And the whole "harmony with nature" thing isn't even a very rational idea if you get down to it, it is a very human form of romanticism that I seriously doubt will be a universal among the stars. Not destroying that which you need to live is rational, but posthuman technology generally implies that you no longer need your original natural environment to survive; I seriously doubt that all civilizations and individuals will fetishize their ecosystems the way some humans do, an ecosystem now distinctly more primitive and choatic than their own technology.

(One reason why it matters if a species has infinite resources is that it may mean that it is possible for a species to create it's own universe and migrate there, which would make sense for a lot of reasons, especially if they can guarantee that no other species can ever find it and muck with it. Be it a real universe or an advanced simulation, doesn't matter. "All civilizations, before advancing to the point they can colonize the stars, discover a method of creating a new sub-universe or performing infinite computation in finite time, and instead colonize that new infinite realm since it is so much safer" is an appealing answer since it solves the Fermi paradox in a way that implies a happy future possibility for humanity, but we're running out of physics that might contain such a possibility. It gets to the point where even if we figure out how to trick a string into performing infinite computation it wouldn't matter anyhow since there may be no way to manipulate a string anyhow, for example. This also falls afoul of my own argument above... every member of the species must choose this, no member should have doubts about it and decide to just safely colonize space anyhow and perhaps choose that answer in the indefinite future.)

More sustainable civilization in the universe is still better than less. (cf. Bostrom's "Astronomical Waste": http://www.nickbostrom.com/astronomical/waste.html)

"Attempts to model interstellar colonization may seem hopelessly compromised by uncertainties regarding the technologies and preferences of advanced civilizations. If light speed limits travel speeds, however, then a selection effect may eventually determine frontier behavior. Making weak assumptions about colonization technology, we use this selection effect to predict colonists' behavior, including which oases they colonize, how long they stay there, how many seeds they then launch, how fast and far those seeds fly, and how behavior changes with increasing congestion. This colonization model explains several astrophysical puzzles, predicting lone oases like ours, amid large quiet regions with vast unused resources."

The point of the submitted article seems to be already mentioned in:

"The Great Filter - Are We Almost Past It?" (first version August 1996) (http://hanson.gmu.edu/greatfilter.html)

"Humanity seems to have a bright future, i.e., a non-trivial chance of expanding to fill the universe with lasting life. But the fact that space near us seems dead now tells us that any given piece of dead matter faces an astronomically low chance of begating such a future. There thus exists a great filter between death and expanding lasting life, and humanity faces the ominous question: how far along this filter are we?

Combining standard stories of biologists, astronomers, physicists, and social scientists would lead us to expect a much smaller filter than we observe. Thus one of these stories must be wrong. To find out who is wrong, and to inform our choices, we should study and reconsider all these areas. In particular we should seek evidence of extraterrestrials, such as via radio signals, Mars fossils, or dark matter astronomy. But contrary to common expectations, evidence of extraterrestrials is likely bad (though valuable) news. The easier it was for life to evolve to our stage, the bleaker our future chances probably are."

Both links are from the collection `The Economics of Science Fiction' (http://hanson.gmu.edu/econofsf.html)

So a sufficiently advanced civilization could construct a self-replicating probe that heads to each solar system, replicates and recharges itself, then heads on to the next stars until the whole galaxy is populated.

From the perspective of the civilization sending the probes, this is relatively cheap; just the price of the materials necessary to build a single ship capable of carrying itself outside the solar system, even if it takes hundreds of years to get anywhere.

would be? Why on earth would they inevitably - every single one of them - develop such a civilization? We most certainly haven't; we'll set aside a few areas as parks, but even those are heavily contaminated by our civilization.

Why wouldn't they make Dyson spheres around all their stars - spheres which ought to have shown up on our infrared surveys - and use that energy? Think of all the computations and matter they'd be wasting by just letting the star blaze away. A few parks, sure, but an entire universe of them?

That point sounds like wishful thinking. 'They'll be, like, cosmic hippies man - they won't want to go around harshing Mother Nature's groove.'

> 3. In terms of the author's "Great Filter" idea, maybe some fraction of the supernovas observed by astronomers are really interstellar industrial accidents.

Then why aren't the astronomers & astrophysicists in a tizzy about how all these supernovas simply don't mesh with the well-thought-out models? Supernovas are the outcomes of processes which take millions upon millions (or billions) of years to finish. I doubt their models of include a random fudge factor to explain away alien Homers.