
“It is important to realize that in physics today, we have no knowledge what energy is.”
volume I; lecture 4, "Conservation of Energy"; section 4-1, "What is energy?"; p. 4-2
The Feynman Lectures on Physics (1964)
Context: It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way.