Holograms

When you see an object what you are actually seeing is the light scattered 
off of it and to your eye. 

Both photography and holography are techniques for storing information 
about the light scattered by an object. 

Two forms of information are needed to specify a wave of light.  One is the 
amplitude of the wave and the other is the phase.  Simply put, the amplitude 
relates to how bright the wave is, and the phase is a measure of the 
difference between the starting points of different waves.

When we take a photograph, only the information about the light's amplitude 
scattered from each point of the object is stored.  So when we look at a 
photograph we can only see two dimensions and we have no sense of depth. 

When we take a hologram, we store the information about both the phase 
and the amplitude of the wave.  So we can reconstruct the image entirely. 
When we look at a hologram the image is indistinguishable from the object 
itself. 

Applications

Museums sometimes use holograms to present rare or fragile objects. The 
clones are of such high quality that everyone believes they are real!
 
Biomedical applications are actively pursued in the U.S. Holograms are made 
inside live organs giving far more details than ever before.

They are also used for high density information storage. So one could store 
all the information in the libraries of the world in a relatively small piece of 
film. Makes you think.......