The laws of physics provide clear-cut principles defining what is possible - and not possible - in the physical world. This book examines and critiques many widely held pseudoscientific beliefs in light of these laws. Rather than treating supernatural claims on a case-by-case basis, Milton Rothman uses the general principles supplied by physics to show why they are, in fact, impossible.

Rothman divides the laws of physics into two classes: laws of permission and laws of denial. Laws of permission, such as Newton's laws of motion, generally do not allow precise predictions except in the simplest cases. Laws of denial, such as conservation of energy, permit very accurate conclusions about what cannot possibly occur.

He uses these concepts to examine and critique the possible existence of various paranormal phenomena, such as UFOs, telepathy, perpetual motion machines, poltergeists, etc. He also discusses a number of concepts traditional to science fiction: anti-gravity, faster-than-light travel, time travel, etc., which are shown to be impossible when subject to rigorous examination.

Written in a technically accurate yet entertaining style, this book will appeal to the non-specialist yet still present concepts of interest to both professional scientists and philosophers of science.