Question: What is the "Great Filter Theory" and is it important?

Claire Greenwell answered on 8 Mar 2019:

It’s an interesting thought experiment! What it says is: we haven’t observed any advanced extraterrestrial civilisations colonising the universe – therefore there must be a step in the evolution of a species into a star-faring civilisation that is really unlikely. Given that the human race has passed most of those steps (e.g. evolved into complex organisms, learned to use tools), then the difficult/impossible step must be in our future.

The argument is basically: we don’t see aliens colonising all the planets, because there is some development on the way to that point that is very unlikely to happen. Whatever that step is, that’s the Filter.

There are arguments against this too. For example, perhaps we’ve just happened to be on the opposite side of the galaxy from where the aliens are. Or perhaps the aliens are just too alien for us to understand we’ve found them – many of the assumptions depend on them being at least a bit similar to us (e.g. from a planet!).

If you’re interested in this sort of intersection between physics and philosophy there are a lot of really cool thinking points out there! Even some joint degrees!