The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.

https://en.wikipedia.org/wiki/Great_Filter

The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, “If life is so easy, someone from somewhere must have come calling by now.”

https://en.wikipedia.org/wiki/Fermi_paradox

Personally I think it’s photosynthesis. Life itself developed and spread but photosynthesis started an inevitable chain of ever-greater and more-efficient life. I think a random chain of mutations that turns carbon-based proto-life into something that can harvest light energy is wildly unlikely, even after the wildly unlikely event of life beginning in the first place.

I have no data to back that up, just a guess.

  • Allero
    2·
    5 months ago

    I don’t think there is a single universal Great filter, and living and then potentially sentient beings with various traits will face various obstacles.

    First, life needs suitable materials for polymers and a lot of energy. Most places don’t have both.

    Next, basic blocks of life that would be self-replicating and adaptive should be randomly generated, which is extremely unlikely and literally took over a billion years on Earth, a planet with generally great conditions for such process.

    Then, those blocks should be able to get together to form complex structures - ideally, many separate ones, so that one event wouldn’t destroy the entire effort. Earth had it easy, with billions of super simple life forms.

    Next, assuming life survived up to this point in a potentially unfriendly and ever-changing environment, bombarded by UV light and exposed to myriad of sources of damage, it should not destroy itself or environment too badly to never recover. Earth had periods when life generated too much carbon dioxide or too much oxygen (yes, that too was a thing), and those were critical points at which our story could very much end.

    Then, life has to evolutionize and get into complex forms, either by forming multicellular organisms or by making a cell a powerhouse of everything.

    Then, life has to get sentient, and some kind of response system should be available and get highly complex.

    Then, most of the sentient creatures just won’t be tribal, and civilization requires society and a common effort.

    Then, many more won’t be expansionist, and will die out in some small region.

    Many also won’t be competitive, which would slow down evolution.

    For those species who are competitive, they shouldn’t destroy each other while they’re at it, and this is currently one of the risks of our own.

    And after all that, they should develop space travel and either get as developed and decisive and resource-rich as to send a generational ship to some random planet named Earth populated by genocidal monkeys, or to somehow hyperdrive here. They can very much decide it’s not worth it, and they may be so far away we couldn’t see signs of their civilization.