William,

I'm not sure about the first two, but the third seems extraordinarily sensible to me and renders the first two unimportant.

If you conclude that serious interstellar travel is such a technological stretch that no species can reasonably accomplish it, then it answers Fermi's paradox in a way that is solid enough that the "millions of other inhabited planets" angle becomes a moot point.

My conclusion, after learning about the heliopause, was that whatever exists beyond the narrow bounds of our solar system is probably so difficult to traverse that material means of crossing it in any meaningful way just aren't realistic.

It doesn't even have to be impossible. Just very unlikely. Imagine that there are ten billion species as smart as us, speckled around our immediate vicinity. If there's only a one-in-a-thousand chance for a species to break out of their system, that means each species that breaks out has a thousand other neighbors it could bump into besides us.

We'll probably try getting past the heliopause, anyway. It's just how our species is.

J