Microwaves are shorter than radio waves but longer than infrared radiation. The microwave used for cooking is about 12 centimeters from crest to crest, says Louis Bloomfield, a professor of physics at the University of Virginia. At this wavelength, microwaves are readily absorbed by most foods. But the particles in a microwave, known as photons, don't have enough energy to damage molecules and cause cancer like ultraviolet rays or X-rays.