Seeing 3D in 2D??

How do 3D films work?

After seeing a 3D film, you wonder how the 2D image in front of you somehow becomes translated into a 3D image after putting on a flimsy pair of glasses. 

Our left and right eyes see what is in front of us from slightly different points of view. If you close only your left eye and then close only your right eye you will see the image in front of you shift back and forth. This is the principal used to create 3D films and is called stereoscopic projection. 

Using physics, we can manipulate the images that both our eyes are seeing (for movies this manipulation comes across through the 3D glasses). The filmmakers set two images onto the screen, one meant for our left eye and one meant for our right eye. One of these images is composed of light polarized horizontally and the other is light polarized vertically. Polarized light waves vibrate on a single plane, rather than on all planes. Isolating these two images to these two planes allows us to select which eye sees one image or another. If we allow only horizontal light through the left lens (by making the polarizing filter vertical, and vertical light through the right lens (by making the polarizing filter horizontal) we can create the illusion of two separate points of view in front of us, therefore making a 2D image into a 3D one. Higher tech 3D glasses will polarize circularly, polarizing the light counterclockwise for the left eye and clockwise for the right eye. This allows the viewer to tilt their head without compromising the resulting image.