Attempt at the briefest content-full Less Wrong post:
Once AI is developed, it could "easily" colonise the universe. So the Great Filter (preventing the emergence of star-spanning civilizations) must strike before AI could be developed. If AI is easy, we could conceivably have built it already, or we could be on the cusp of building it. So the Great Filter must predate us, unless AI is hard.
Going off of this, what if life is somewhat common, but we're just one of the first life in the universe? That doesn't seem like an "early filter", so even if this possibility is really unlikely, it still would break your dichotomy.
The problem with that is that life on Earth appeared about 4 billion years ago, while the Milky Way is more than 13 billion years old. If life were somewhat common, we wouldn’t expect to be the first, because there was time for it to evolve several times in succession, and it had lots of solar systems where it could have done it.
A possible answer could be that there was a very strong early filter during the first part of the Milky Way’s existence, and that filter lessened in intensity in the last few billion years.
The only examples I can think of are elem... (read more)