I'm a big proponent of "alone in the galaxy, one of many in the universe" not because of plugging numbers into the Drake equation but rather the principle that the galaxy isn't all that large viewed through the lens of geometric growth over geologic time scales. There isn't anything fundamentally difficult about constructing Von Neumann probes, so assuming that there are other advanced civilization in the galaxy the question isn't "why haven't they contacted us yet?" but rather "why wasn't Earth colonized by aliens eons ago?",(reply>), @Casper Ablij I don't think that's a valid comparison. We can agree to disagree on that point though.,(reply>), @Casper Ablij In terms of game theory, there's no reason not to colonize with Von Neuman probes. If another civilization emerges and is expansionist, they could end up posing an enormous threat.<br><br>It's still possible that you have another alien civilization that is either not colonizing or has some sort of prime directive, but the odds are against it and quickly become infinitesimal as you add additional civilizations into the mix. Again, if you don't do it you're disadvantaged versus the next guy who does.<br><br>If there are plenty of Earth like planets, then that makes our apparent isolation in the galaxy more puzzling, not less.