How does light travel through glass?

14 February 2010

Question

I believe that light is considered to be both waves and particles.  My understanding is that particles are physical objects.  If that is true, how is light able to travel through glass?  Is it just the light waves that travel through glass or can the particles also penetrate glass?

Answer

The first thing is that any solid object that looks solid to us is actually has huge amount of space in it. Even in an atom, the nucleus of the atom is about a hundred thousandth of the size of the actual atom. So there's immense amounts of empty space only containing electrons which are even smaller than the nuclei, so there's lots and lots of space for things to travel through as long as it doesn't interact with the nuclei or electrons. A lightwave is actually quite big compared to the size of an atom. It's a quantum mechanical object - it's kind of a particle, but it's kind of a wave. You can think of it as wave which only arrives in particles - not really something with which we have a handle on. It's a lot easier to think of it as a wave in the circumstance. The only way to stop a wave is with something which will actually absorb it or scatter it and in something like glass there's just nothing there which will absorb or to scatter it. So it just carries on going in a straight line.

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