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Comment by simonh | Hacker News Reader

There are multiple explanations for why the sky isnt lit up with radio and laser signals from advanced civilisation. The great filter is one explanation, that there are existential crises or threats that wipe out most civilisations or cause them to collapse to subsistence level. Nuclear war, biological weapons, ecological collapse, paper clip maximising AI, etc.

I once ran a Traveller RPG exploration campaign where one of the systems they visited looked really odd on sensors. Just fuzzy clouds and clumps and ring formations of diffuse metallic debris. It turned out it was all paper clips.

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For context, the examples you mentioned are cases of the great filter lying ahead of us. The more optimistic hope is that the great filter is behind us - things like abiogenesis or multicellular life being extremely unlikely to happen. "Great filter" is just the name for "a barrier that stops life from becoming a spacefaring civilization".

This explanation is also the reason why finding basic life (say, bacteria) in the Solar System would be a cause for worry - if life evolved independently twice in the same star system, it would imply abiogenesis isn't that unlikely - thus strongly suggesting the great filter is still ahead of us.

Could the great filter be something like developing language? That's something that seems quite rare (only one species on Earth has it). If so, then discovering bacteria in the Solar System wouldn't be such a cause for worry.

> Could the great filter be something like developing language?

Perhaps it's a combination of factors? Dolphins are social animals that appear to be capable of complex communications among themselves, but don't have hands to manipulate their environment the way we can.

Apes have hands, but don't have complex language.

Another interesting one I've heard is getting into space, period. It's possible that there are other technological civilizations out there, but all stuck under a few hundred km of ice or on a 2-earth-mass monster where it's impractical to reach orbit.

Earth may only be special in being in a sweet spot between Mars (too small to hold an atmosphere or protect from cosmic radiation, hence no life) and Gliese 832c (with its low-orbit velocity of something like 15km/s, hence much less practical to put stuff in space).

> protect from cosmic radiation

That raises another issue of the planet having a magnetic core...

You can also get shielding with a thick enough atmosphere, or being under a solid ice/rock crust. But both of those also make it much harder to reach space.

Speak for yourself.

I hope you snuffed them out before they took over the universe.

The surprisingly addictive game is below.

https://www.decisionproblem.com/paperclips/

I hate you

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