This is such a cute book. The main character, Mr. Thompkins, dreams he's in various universes where such physical values as the speed of light and Planck's Constant are different than here. For example, in the universe where the speed of light is about 25 mph, the cars can't go a whole lot faster than the bicycles, no matter what country manufactured them. Conveniently, a professor is there to explain why the things are happening the way they're happening. Thompkins later marries the daughter of the professor, which I think is blatantly nepotistic, but then, it's science -- I'm sure they've had their DNA checked against mutation. If your kids are interested in physics or you want to see if they are, this is a good book to start them out with.