The Great Filter (1998) | Hacker News Reader

The Great Filter (1998)

hanson.gmu.edu

23 pointsstavrianos10 comments

There's good reason to believe that the Great Filter is not only behind us, it's way behind us.

A Great Filter in the future would have to apply to the vast space of possible intelligent lifeforms. This means that no matter what the psychology of the intelligences that evolve--no matter what they value or attempt to create--they all get themselves killed somehow. Every intelligence would need its own unique story of how it died so quickly, and these are burdensome details on our theory.

In contrast, the pre-biological past is simple and homogenized. Any Great Filter would be a regularity of physics and chemistry, which we know apply universally. If physics dictates that it's really hard for anything self-replicating to form (excluding trivial things like crystals and fire) then we've explained the lack of life everywhere. The theory is simpler, and Occam's razor tells us the simpler theory wins.

The future answers don't need to be unique and convoluted. Offhand, there's Baxter's suggestion in "Manifold: Space" that epic-scale collapses of multi-star systems might happen more often than we think, with sterilizing effects on big chunks of space. Egan used a variation of this in "Diaspora".

the scenarios Baxter and Egan write about only push the Great Filter up to the moment of being able to create self-replicating probes (the most basic form of explosive colonization).

i think that's actually the point after which filters have to contend with a diversity of "the psychology of the intelligences that evolve" (rather than at the emergence of biology, since biology is localized and subject to regularities in astrophysics such as supernovae).

how far are we from being able to produce such probes, and could our psychology become so idiosyncratic between now and then that we wouldn't deploy them?

I guess if we'd throw all our resources at it, the probes would not be far off.

Hey, if we transported enough garbage up to Mars, now, some Microbes would probably survive, adapt and flourish.

It's an interesting topic, but talking about probability when you're extrapolating the extremely limited information we have is dubious. There could be so many other explanations for why we haven't detected alien lifeforms, and we don't know how to assign probabilities.

i don't follow what you're suggesting between 'other explanations' and 'assigning probabilities' - are you saying there are filters we haven't thought of, which we (obviously) aren't assigning probability to?

"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"

I think that statement is completely unfounded. We don't know how dead the space is, except that we haven't detected anything so far. The author goes on about us a single data point like that makes us incredibly rare, all it makes us is incredibly ill informed.

I think that quotation by itself refers just to the Great Silence, and there seem to be two essential possibilities concerning this silence, both of which the author addresses:

Either there is a sterilizing filter which lies ahead of planet bound species such as ours, preventing explosive colonization;

Or, there is a psychological filter which "prevents" higher civilizations from making their existence visible - the author addresses this when discussing the Common Zoo hypothesis.

Within a single galaxy you might entertain the possibility that we are just the first occurrence of intelligence to emerge. However:

"Consider, for example, that the energy of a single star might power an intermittent very narrow-band signal detectable to pre-explosive life like ours across the entire universe [Gott 82]."

So we would have to be a cosmically nascent intelligence. That makes the absence of both a biological and psychological filter exceedingly improbable.

I think it's possible (although not a foregone conclusion) that in fact much of the filter is from what he terms 'discrete' events. That is, having the right sort of sun, the right-sized planet at the ideal distance from this sun, with a substantial moon to act as a gyroscope, active tectonics to recycle elements that would otherwise get locked up, etc.

I've not, for example, seen any conclusive estimates on how likely it is that an otherwise earth-like planet would get a moon to act as a stabilizer for axial tilt (which itself is probably important for complex life).

Also, his assumption that life could spread at nearly the speed of light may be overly optimistic. If, by contrast, one assumes that light can spread at only 1/10th the speed of light, and that the earliest star-faring life could have arisen was a billion years ago (due to as the time needed for a second-generation yellow star to brighten enough to keep an earth-like planet warm after its conversion to an oxygen/nitrogen atmosphere), then one only needs to explain why star-faring life has not yet arisen in relatively nearby galaxies, rather than why it has not yet arisen anywhere in the visible universe. This is a much less daunting hurdle.

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