AIDS is not caused by HIV. Coal and oil are not fossil fuels. Radiation exposure is good for you. Distributing more guns reduces crime. These ideas make headlines, but most educated people scoff at them. Yet some of science's most important concepts-from gravity to evolution-have surfaced from the pool of crazy ideas. In fact, a good part of science is distinguishing between useful crazy ideas and those that are just plain nutty. In this book, a well-known physicist with an affinity for odd ideas applies his open mind to nine controversial propositions on topical subjects. Some, it turns out, are considerably lower on the cuckoo scale than others. Robert Ehrlich evaluates, for the general reader or student, nine seemingly far-out propositions culled from physics, biology, and social science. In the process, he demonstrates in easy-to-understand terms how to weigh an argument, judge someone's use of statistics, identify underlying assumptions, and ferret out secret agendas. His conclusions are sometimes surprising. For instance, he finds that while HIV does cause AIDS and the universe almost certainly started with a big bang, our solar system could have two suns, faster-than-light particles might exist, and time travel can't be ruled out as mere science fiction. Anyone interested in unorthodox ideas will get a kick out of this book. And, as a fun way of learning how to think like a scientist, it has enormous educational value. Of course, only time will tell whether any of these nine ideas will be the next continental drift—the now orthodox account of the Earth's geology that was for years just a crazy idea.