How Can We See Light?

Light is tricky. You probably know that we experience "light" by seeing it bounce off something before being absorbed into our eyes. But what about light itself? That's much tougher, since in order to see the light, it has to be absorbed. Solving for this little Catch 22 won Serge Haroche the 2012 Nobel Prize in physics.

Basically, you need to build a super dark, super cold box, where sometimes there's an atom, and sometimes there isn't. The inside of the box is coated with super-reflective mirrors. Then you send through an atom in a "super position" of two atomic states. That sounds complicated (and it is!), but just means that when it comes out on the other side it will look one way if there's a photon of light in the box, and another way if there isn't. And then, once you know if there's a photon of light in there, you can do all kinds of experiments on it, before picking up your Nobel Prize. [MinutePhysics]

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