Electrons, when they were first discovered, behaved
exactly like particles or bullets, very simply. Further research
showed, from electron diffraction experiments for example, that
they behaved like waves. As time went on there was a growing
confusion about how these things really behaved ---- waves or
particles, particles or waves? Everything looked like both.
This growing confusion was resolved in 1925 or 1926
with the advent of the correct equations for quantum mechanics.
Now we know how the electrons and light behave. But what can
I call it? If I say they behave like particles I give the wrong
impression; also if I say they behave like waves. They behave
in their own inimitable way, which technically could be called
a quantum mechanical way. They behave in a way that is like nothing
that you have seen before. Your experience with things that you
have seen before is incomplete. The behavior of things on a very
tiny scale is simply different. An atom does not behave like
a weight hanging on a spring and oscillating. Nor does it behave
like a miniature representation of the solar system with little
planets going around in orbits. Nor does it appear to be somewhat
like a cloud or fog of some sort surrounding the nucleus. It
behaves like nothing you have seen before.
There is one simplication at least. Electrons behave
in this respect in exactly the same way as photons; they are both
screwy, but in exactly in the same way….
The difficulty really is psychological and exists
in the perpetual torment that results from your saying to yourself,
"But how can it be like that?" which is a reflection
of uncontrolled but utterly vain desire to see it in terms of
something familiar. I will not describe it in terms of an analogy
with something familiar; I will simply describe it. There was
a time when the newspapers said that only twelve men understood
the theory of relativity. I do not believe there ever was such
a time. There might have been a time when only one man did, because
he was the only guy who caught on, before he wrote his paper.
But after people read the paper a lot of people understood the
theory of relativity in some way or other, certainly more than
twelve. On the other hand, I think I can safely say that nobody
understands quantum mechanics. So do not take the lecture too
seriously, feeling that you really have to understand in terms
of some model what I am going to describe, but just relax and
enjoy it. I am going to tell you what nature behaves like. If
you will simply admit that maybe she does behave like this, you
will find her a delightful, entrancing thing. Do not keep saying
to yourself, if you can possible avoid it, "But how can it
be like that?" because you will get 'down the drain', into
a blind alley from which nobody has escaped. Nobody knows how
it can be like that.
Richard P. Feynman, The Messenger Lectures, 1964, MIT