"Sparks are drawn to each other. It's not obvious when you're already surrounded by life, but if there are only two sparks in an otherwise empty universe and they are given free mobility, they will move towards each other. Sparks also do not exist in isolation, they connect to the sparks of people close to their owner. Individual humans randomly selected from different universes can tell who is from their world. Also, if you put someone in a random world, they can tell if they are in their own even without other sensory input. I can give you copies of the studies?"