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Comment by stupidcar | Hacker News Reader

The idea that the "great filter", if there really is one, remains in our future seems to me to be extremely improbable. The fact is, we already have the ability, just about, to colonise space. That we haven't yet has more to do with economic reasons than technological ones, and it's entirely conceivable that we'll see substantial non-Earth settlements in our lifetime.

Now, that isn't to say we won't nuke ourselves get turn into grey goo or something before that happens, but the point is, but we're close enough to it that, even being pessimistic, there's got to be a reasonable chance we'll make it (over 0.01, say). And that's not good enough for a great filter. Any catastrophe that happens so close to the point of becoming a multi-planetary civilisation simply wouldn't catch enough species. There'd be too many who would make it through.

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> Any catastrophe that happens so close to the point of becoming a multi-planetary civilisation simply wouldn't catch enough species.

Unless you're missing some sort of fundamental serialization of events, like technology A that enables colonization is also so destructive that it wipes them out. Nuclear power could have been an example.

Perhaps we would need to master genetic engineering in order to survive the ravages of long-term space exposure, and that might inevitably lead to an outbreak that wipes out most of the species.

Or perhaps sufficient automation is needed because biological brains are too slow and imprecise, but sufficient intelligence and automation inevitably yields an AI that supplants them.

As I said, we already have technology to colonise space. Not to spread throughout the galaxy, no, but at least to get to multiple places in our solar system. At that point the feasibility of a single event like a genetic accident always occurring and always wiping out the entirety of every species seems unlikely.

Not impossible, of course, but my argument wasn't about possibility vs impossibility, but probability.

> Not to spread throughout the galaxy, no, but at least to get to multiple places in our solar system.

To get there, yes. Not necessarily to live there. I was saying that we might need to actually engineer ourselves to live in these other environments, and the path to that might itself lead to the great filter.

The idea that the "great filter", if there really is one, remains in our future seems to me to be extremely improbable. The fact is, we already have the ability, just about, to colonise space.

Semi-plausible plans exist to colonize the asteroid belt and there's a plan to send a microscopic probe to the nearest star. Those plans are a far, far cry from any colonization of the stars, any really impact on solar systems other than earth.

It's worth that if an earth society existed on every star in the galaxy, none would be able to detect the others - all communication fades to quantum noise before it gets to the nearest star.

If you're arguing it may not be possible to colonise space at all, that may be true but isn't germane to this discussion. The idea of Fermi paradox and the "great filter" presupposes that it is possible, and that there is some other, civilisation-ending event that stops it.

My argument is that, within the context of a debate that accepts the precepts of the Fermi paradox and great filter, the likelihood of where the great filter can be placed is constrained by probability. Within that context, even a limited colonisation of our own solar system would be sufficient to drastically reduce the likelihood of a single event to wipe out humanity entirely.

Sure, this is the presupposition of the Fermi paradox but it is generally presented as an obvious things. Obviously, an advanced civilization can and will colonize not just it's own solar system but some larger area, even a galaxy. I don't that's either obviously possible or obviously what an advanced society would do.

The "filter" could be that a society based on quick growth either wipes itself out or reaches a situation of stability such that "colonizing the galaxy" doesn't hold any great appeal.

And human beings so far are extraordinarily depend on earth. It be easier to survive on even earth degraded by global warming or nuclear war than it would be to live in space. Space colonies, if they ever exist, will extraordinarily fragile and their ability to survive a disaster rendering the uninhabitable seems minute.

There's nothing which says that the Great Filter needs to be caused by endogenous factors. Let's say that these are all relatively "easy" to achieve: planets, life, complex life, technological civilisation. Even if they're "easy" now, there will have been a time, billions of years ago, when they weren't. Let's say that all of this has only been achievable since the emergence of the first high-metallicity stars, maybe 5 or 6 billion years ago.

At that time, There will have been a number of "first" civilisations. Imagine that one of those civilisations grew up to be even more paranoid than us. "Nature, red in tooth and claw" shaped their psychology profoundly. For them, to meet any strange species is to utterly fear it. They know, to the core of their being, that if they do not annihilate the stranger, the stranger will annihilate them. Let's call this species "the Fearers".

So when The Fearers become aware of the potential for species elsewhere in the galaxy to exist, they decide that the best defence is a good offence. They throw all of their civilisational resources into developing technology which ensures that no alien species will ever bother them.

Assembler probes are dispatched to a large metal asteroid. They pull it apart, re-assembling it into an autonomous listening post attached to a 10-million-kilometer-long solar-powered mass driver. If the listening post detects signals from any species other than the Fearers, then the mass driver will spend a few years tweaking its orbit, take careful aim, and dispatch a stream of projectiles towards the source of the signal. Each projectile only weighs a few hundred kg, but travels at 99.9% the speed of light, making it a gigaton-class impactor. Not quite a planet-killer, but the mass driver can take several shots per hour, and has trillions of tons worth of ammunition at its disposal. It spends a few years shelling the source of the signals, plus any other planetary body in the target system, just in case the emerging technological civilisation was able to develop interplanetary capabilities before the first impactor arrived.

The Fearers realise that although this first mass driver is sufficient to clear their local neighbourhood of potential adversaries, they are still, in the long term, vulnerable. What if some species on the far side of the galaxy was able to develop interstellar travel, making them potential resilient to such an attack? The Fearers then conceive of a next-generation defense grid: self-reproducing probes which spread out through the galaxy, establishing listening posts and mass drivers every 100 light-years or so. It only takes a few hundred thousand years to saturate the galaxy with the these defence stations. There, they lurk indefinitely, completely radio-silent, waiting to snuff out signals as soon as they arrive.

Unfortunately for the Fearers, their early foray into self-replication causes them to succumb to a Grey Goo catastrophe, shortly after launching the first interstellar defence probes. But the damage was done. The Fearers have now been gone for billions of years, but their defence grid remains active. In that time, hundreds of thousands of technological civilisations have emerged, but within a century of their first long-range radio broadcasts, all of them have been snuffed out by a fusillade of near-lightspeed projectiles. That is too short of a window for any species to develop the class of interstellar capabilities needed to survive such an event.

Maybe this story seems implausible. But these kind of capabilities will probably be within humanity's grasp within a couple hundred years -- and the galaxy has been around for billions of years, during which it only takes a single species being that much of an asshole to construct a Great Filter like this.

It's scenarios like this which really make me hope that the Great Filter is behind us.

The least plausible thing about it rationally is that the fearers would have anything to be afraid of with billion years head starts and relatively assymptoic accelerating technological capabilities.

It is of course possible that they could be bug nuts paranoid - although they would have more to fear from their own rivals amongst themselves than any life which just started radio communication. MAD could keep the peace amongst themselves. Of course xenophobes also tend to go fractal with more arbitrary divisions of "the other" so they could have just wiped themselves out.

I'm assuming that they are pre-Filter, but not the first. From the moment they develop radio technology, they immediately start receiving signals from dozens of existing alien civilisations. This causes them to think "shit, we really have to do something about this."

Some of those civilisations may already be far more advanced, and have taken to the stars tens of thousands of years previously. No matter. The interstellar mass driver is a weapon against which no defense can be erected. No level of technology can track a 1-meter-wide iron sphere as it moves through interstellar space at near-lightspeed. If you're on the receiving end of a volley, the insanely blueshifted, tiny spec of light from the projectile won't arrive until shortly before the projectile itself. To an observer, it would appear as if all the planets in the system suddenly started exploding. Few systems would even be able to get a warning cry out, and those who did would be unable to provide actionable intelligence on where the attack came from. Even if they could provide actionable intelligence, their warning would spread out at light-speed. If there were listeners to receive it, then those listeners would also presumably have attracted the attention of the Fearers -- and a fusillade of projectiles would already be inbound towards them, almost immediately behind the warning itself.

Imagining such a scenario, the Fearers say to themselves: "If we don't do something like this, then surely it's only a matter of time before somebody else does. And we'll have no way to see it coming. So the first species to build interstellar mass drivers will, inevitably, be the last species left standing. Therefore, we have no choice but build and use them ourselves."

In other words, they do unto others not because they're bugnuts paranoid, but because they have a not-altogether-unrealistic apprehension that if they don't, others will do unto them.

This isn't Mutual Assured Destruction as we know it. What made MAD work was the fact that enemies could observe each other in realtime, and that retaliatory strikes would be possible. Neither is the case here. The Fearers are convinced that the only rational course of action is to assume others will attack someday -- if they haven't already -- and therefore their attack needs to be launched immediately.

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