How does a hologram work?

A true hologram is a three-dimensional image created by recording how light waves interfere with one another. To make one, a laser beam is split in two: one beam illuminates the object, and the other, the reference beam, shines directly onto the recording surface. Where the light reflected from the object meets the reference beam, they create an interference pattern that is captured on the film. When light later shines through this pattern, it reconstructs the original light waves, so the eye sees a 3D image that shifts perspective as you move around it. Many so-called holograms in shows and museums are actually clever optical illusions using reflections rather than true holography.