Unless every single civilization out there is made up of inert sand particles, that's not a solution for why we don't see anyone. You're right of course that we

Unless every single civilization out there is made up of inert sand particles, that's not a solution for why we don't see anyone. You're right of course that we tend to assume somewhat similar properties to ourselves, because that's what we know, and we tend to assume that we're at least in some ways "normal" - or at least not unique. > with no physical artifacts of "civilisation" I would not be surprised if there are quite a few intelligent organisms out there that are not tool users. Earth itself has a few, as well. These would potentially make great candidates for a visit, if we could detect their biome from afar. > just not at the pace and scale we are accustomed to I don't disagree that these are probably out there. But that's not the same as asserting that every single culture besides our own is on a completely different and imperceptible scale than us. We'd expect at least some organisms to build tools that we can detect, that is unless we're one of the first civilizations in the universe. Another solution would be that FTL travel is possible and/or thermodynamics can be at least partially circumvented, but even if such techology existed, it would have to be ubiquitous in order to explain why we don't see anyone.