The whole question in science is often misunderstood by people in other
disciplines. ... They overlook the fact that whatever we are allowed to
imagine in science must be consistent with everything else we know.
... We can not allow ourselves to seriously imagine things which are
obviously in contraction to the know laws of nature. And so our kind
of imagination is quite a difficult game. One has to have the imagination
to think of something that has never been seen before, never been heard
of before. At the same time the thoughts are restricted in a straitjacket,
so to speak, limited by the conditions that come from our knowledge of
the way nature really is. The problem of creating something which is
new, but is consistent with everything which as been seen before, is one
of extreme difficulty.

The Feynman Lectures on Physics, Vol 2, 1963

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