But an infinite universe wouldn’t have to have an infinity of duplicates. That would assume that the structure of the universe was more or less random. Well, we think this might be so. But suppose the large scale structure of the universe was ordered? Lets say that everything in Alpha quadrant has property x, everything in Beta quadrant has property 2x, everything in Gamma quadrant has property 4x, etc. Since the universe is infinite, we can’t have a beginning, so there is also a 1/Alpha quadrant were everything is 1/x, a 1/Beta quadrant where everything is 1/2x, etc. And each quadrant we will define as finite. So if the earth is in Alpha quadrant, there is no reason to suspect a duplicate earth within Alpha quadrant. But if the duplicate earth isn’t in Alpha quadrant it isn’t anywhere, since everywhere else would have to have an earth with property 2x, 4x, 8x, rather than property x like we have on earth.
Did that make any sense? Obviously, we have no reason to suspect that such a system exists, and we have many reasons to believe that the universe isn’t infinite. But if it was infinite but physical properties changed in an ordered way throughout the universe you wouldn’t neccesary get any duplicates.