[billytetrud]

> enough of them

How much is enough? A von neumann machine shouldn't need to be that big. You can send a single one to a solar system and let it replicate itself indefinitely. A single seed can sprout an entire civilization.

> If an intelligent species directed such an object to our galaxy, how close would is need to be for us to detect it?

We could probably detect it for many hundreds of lightyears if not orders of magnitude further. Why? Because an intelligent species capable of sending a von neumann machine to another solar system would probably be intelligent enough to make large scale infrastructure projects like dyson swarms. Such structures would basically be visible from any distance we could see the individual star from, which we can do from at least 50 million light years.

And not only that, but we could see evidence of a von neumann machine coming through in the distant past as well, even if for some reason its no longer active, because it would have left an enormous amount of artifacts behind.

> When it is part of the question, how is it irrelevant?

Fair enough. But what I mean is that if life isn't "rare" (for any definition of rare really), one would expect to see a massive amount of evidence of life and civilizations etc. Since we don't see that evidence, we should assume either that life is rare, or we're not the "average" planet that the copernican principle assumes.

> If it was on the other side of the galaxy, how would they know to send someone to our solar system

They wouldn't have to know. They would simply send spaceships everywhere and would happen across us by random chance within a million years.