Since high school I was always confused by the concept of energy, in recent years I tried multiple times to understand what it actually is and I failed to grasp it from the common definitions (why does the joule have so many definitions on so many apparently unrelated physical phenomena?).
Recently I stumbled upon this quote from Feynman, addressing exactly what my problem was.
There is a fact, or if you wish, a law governing all natural phenomena that are known to date. There is no known exception to this law – it is exact so far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call “energy,” that does not change in the manifold changes that nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says there is a numerical quantity which does not change when something happens . . . it is a strange fact that when we calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same. It is important to realize that in physics today, we have no knowledge of what energy “is.” We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. It . . . does not tell us the mechanism or the reason for the various formulas. source: The Feynman Lectures on Physics Vol I, p 4-1
So my question is: Feynman died in 1988, do we today, 30 years later, have any better insights on what energy really is? does this quote still hold?
