Blog of Veikko M.O.T. Nyfors, Hybrid Quantum ICT consultant

Quantum Mechanics demystified, a try

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Seeing through glass

Why do we see through a class? And yet we don’t see through it’s frame. Nor the wooden wall besides.

In article What’s light, light is described as being photons traveling in spacetime as bundles of energy. Every now and then hitting an atom of material getting on the way. Atom absorbing the photon, causing one of it’s electrons to be excited on higher energy level. Only to drop down to normal energy level after a short while, with emitting another photon back. It’s like kicking a ball to a wall and it bouncing back. Only that the ball would be different one from that kicked. This is what we call scattering of light.

Then why doesn’t this take place with transparent glass?

When a photon hits the atom, the energy of the photon has to be high enough to cause an electron to excite. Glass is made of atoms whose electrons require more energy than what the photons of visible light (400-700 nm) are able to provide. Thus these photons just travel through the glass. Ultraviolet light (10-400 nm) on the other hand has enough energy to excite electrons in glass. Which is why you don’t get a suntan behind a window :-)

The wooden frame of the window, or the wall, is made of atoms, whose electrons require less energy to get excited. Thus photons of visible light get scattered from them, preventing us from seeing what’s on the other side.

BTW, for the same reason photons are able to travel through air. Air mostly consists of oxygen and nitrogen atoms. These won’t either get excited by photons of visible light.