How alien would aliens be? Would they look like us or perhaps more like an octopus? How would they communicate? Could we even hear their voices, assuming they have them? Like us, aliens would be constrained by the physical world. Understanding how those physical constraints apply both to us and to aliens is the theme of this book. The constraints imply that they will not be all that different from us, perhaps half to twice as big as we are. They will depend on vision and hearing as we do and they will live on a planet much like ours. But where will they be? Do they even exist? The odds are not good. We may be the only intelligent life in the universe.
