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  • Writer's pictureNick Cook

Beam Splitters and Vampires

(Original Article Published 23/1/2016)

“The window of life is mirrored. And tinted. And shattered. And borrowed.”

― Jarod Kintz

At night in a room with the light on, if you gaze out of the window, you will see your own reflection gazing back at you…unless maybe you are a vampire!

You have probably never given this a second thought. After all the window is a partly reflective surface, bouncing the light back at you. Simple. This works fine in principle if one intuitively thinks of light as rays…some get through the glass, some bounce back. And it was this exactly this idea that gave Sir Isaac Newton, who thought light was made of particles, a severe headache.

Newton grappled with this concept, trying to explain why a particular particle was reflected or travelled on through the glass. His best explanation was that it was to do with flaws in the glass itself. And in this he was wrong. The actual explanation has everything to do with the far weirder world of quantum mechanics…

It turns out that the glass is in fact a sophisticated quantum device called a beam splitter. And of course at the quantum level, the world as we know it, behaves very, very strangely.

Photons of light are in a superposition state (waves). As each photon of light interacts with the atoms of the glass, there is a probability of it passing through…or not. For those photons that are detected, they become entangled with the cloud of atoms that make up the glass. Also, as the glass thickness increases, the greater the chance of entanglement, the greater the probability, i.e. creating a reflection being created as its not just happening on the surface of the glass.

So the next time you gaze out of a window and see you own reflection, remember the glass is actually a sophisticated quantum device called a beam splitter, capturing some of the photons like so many flies in its web of sticky atoms. Unfortunately, I’m not quite sure what the quantum explanation is for a vampire’s lack of a reflection, although would be an interesting discussion in its own right!

Photo credit: heddaselder via Visual Hunt / CC BY-NC-SA

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