Rife machines work because of a principle in physics called sympathetic resonance. It states that if there are two similar objects, and one of them is vibrating, the other will begin to vibrate as well, even if they are not touching. You may recall the commercial where Ella Fitzgerald sings a high note and causes a crystal glass to shatter. This is the same principle at work. Sympathetic resonance, if strong enough, can cause the receiving object to explode.
Dr. Rife used this principle to destroy disease producing organisms. He thought of every little micro-organism as a tiny little tuning fork. He then built his Rife Machine to send out the signal that would cause the little bugs to vibrate. By making the vibrations that came out of his Rife Macine stronger and stronger, he was able to shatter the micro-organisms at a distance. Rife spent years of his life looking into his microscope, learning which frequencies would destroy which micro-organisms.