> assumption that life is rare in the universe
Great filters start with the observation that we have detected no signs of alien technological civilization. The assumption is this means they’re rare.
Great filters start with the observation that we have detected no signs of alien technological civilization. The assumption is this means they’re rare.
In other words, even if the average technological civilisation lasts 1000 years, the odds of those civilisations overlapping are nearly zero if the great filter is ahead of us. Unless civilisations manage to last much, much longer than 1,000 years (millions of years), the chance that two blips overlap in time and space closely enough to detect each other is basically negligible.
That is why the “life on Mars” point feels ominous:
- If abiogenesis is easy, the filter isn’t there.
- If the filter is later (like surviving technological adolescence), then most civilisations blink out quickly.
Which means overlapping, detectable civilisations would be vanishingly rare, explaining the silence, but also suggesting our future may be short.