Tau, and all the other kids on 15, know Uncle Joe. Uncle Joe can be found all over the city. He’s friendly and wise, and he has gray hair, and he’s always smiling. His voice sounds hollow, but Sky tells Tau that it’s because he’s a holocloud. You can’t touch him, she explains, because he’s not there.He’s a series of aerostats that hover in the air and paint themselves different colors at high speed. He doesn’t have a solid body at all, it’s just tiny floating zeppelins the size of a speck of dust. That’s why you can put your hand right through him and he’ll just shimmer and ripple and go back to normal. He can speak, because the aerostats have tiny speakers and they all make a noise at once.
Tau knows better, because he’s read old stories. He knows Uncle Joe is a ghost.
Uncle Joe can quote from the public codex. He always knows where food can be found. He comes out to stop Tau from crossing the street when there’s traffic, even though there isn’t any. Tau knows the traffic control system is a computer. He isn’t sure what it’s telling Uncle Joe, but he’s pretty sure it’s being mean to the nice old ghost.
At night, when Uncle Joe is making his rounds, Tau sometimes comes and finds him. He asks him to come over and tell stories. Uncle Joe loves to tell stories, and Tau loves to listen to them.