Empty Space of Atoms
If atoms are mostly empty space, why can't we see through walls?
The reason is that light interacts strongly with many materials. Even
though a photon is small, it can still be absorbed by the electrons in,
say, a wall. Think of atoms as a bunch of frogs (electrons) bouncing
around on bungee cords attached to central points (nuclei); if a fly
(electron) tries to go through a thick enough assembly like this, it's just
about certain to be eaten by a frog. Even if there's a lot of space
between the frogs, sooner or later, a frog will get the fly.
Now, obviously there are some problems with this analogy (it doesn't
explain how light can pass through glass, for example), but I think you can
see what is going on. If you make the wall very thin, some light will pass
Richard Barrans Jr., Ph.D.
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Update: June 2012