> But it would almost definitely have to be species that never got to the "expand rapidly into other solar systems" phase.
It's certainly not a given that our species will ever do that or that we'll last long enough to do that.
> This doesn't preclude us knowing about that 1.
Let's say we're the 1 currently in the milky way galaxy. There could be another in the closest galaxy the Canis Major Dwarf Galaxy which is 25,000 light years away. But being able to detect a signal from 25,000 light years away... well, that's the problem. And what if they're just getting to the point where they could transmit a signal now? So maybe in 25,000 years we'd notice something... maybe? (if we're still around) As far as physically traveling 25,000 ly, well we know that even trying to go 1 ly is going to be super difficult technically. Similar problems even if there's an intelligent species on the other side of our own galaxy since it's 52K ly across.
It's certainly not a given that our species will ever do that or that we'll last long enough to do that.
> This doesn't preclude us knowing about that 1.
Let's say we're the 1 currently in the milky way galaxy. There could be another in the closest galaxy the Canis Major Dwarf Galaxy which is 25,000 light years away. But being able to detect a signal from 25,000 light years away... well, that's the problem. And what if they're just getting to the point where they could transmit a signal now? So maybe in 25,000 years we'd notice something... maybe? (if we're still around) As far as physically traveling 25,000 ly, well we know that even trying to go 1 ly is going to be super difficult technically. Similar problems even if there's an intelligent species on the other side of our own galaxy since it's 52K ly across.