Colonising the galaxy is hard. Why not send bacteria instead?

SCIENCE fiction is filled with visions of galactic empires. How people would spread from star system to star system, and communicate with each other in ways that could hold such empires together once they had done so, is, though, very much where the "fiction" bit comes in. The universal maximum speed of travel represented by the velocity of light is usually circumvented by technological magic in such works. The truth is that, unless there has been some huge misunderstanding of the laws of physic...