—The Feynman Lectures on Physics
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 manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.
“Energy,” you might say, is the most boring of all things, in physics at least: it is the name of a quantity, and what's more, the name of a quantity that doesn't even change. There is nothing qualitative or concrete about it: it is, as Feynman says, inexorably mathematical and abstract.
It's a made-up word of pseudo-Greek origin, and I should admit that I have a prejudice against such words. There was a respectable reason for importing Latin scientific terminology into English. Latin was, for many centuries, the common learned language of the Western world. If you were going to learn just one foreign language, Latin was what you learned, and if you were going to write about something of international significance, you wrote in Latin and used Latin terms. The Polish Copernicus, The Italian Galileo, and the English Newton all wrote their books in Latin – and could all have read each other's writing with ease. The loss of this common language is one of the great intellectual disasters of our time. But that's all by the way. My point is, there was a good reason to use Latin terms: everybody who was interested in science knew what they meant, and they meant the same thing from Cracow to Pisa to Cambridge. But there's only ever been one reason to import Greek terms in the post-classical West, and that's to show off. You use Latin if you want to be understood: you use Greek if you want to impress. And often to people who actually know Greek, it's not very impressive: the Greek words get hauled into ludicrously wrong contexts, get fitted up with Latin plurals, and generally look, to someone with linguistic sensitivities, like wizards trying to dress as muggles.
One of them was a very old wizard who was wearing a long flowery nightgown. The other was clearly a Ministry wizard; he was holding out a pair of pinstriped trousers and almost crying with exasperation.-- J.K. Rowling, Harry Potter and the Goblet of Fire
"Just put them on, Archie, there's a good chap. You can't walk around like that, the Muggle at the gate's already getting suspicious-"
"I bought this in a Muggle shop," said the old wizard stubbornly. "Muggles wear them."
"Muggle women wear them, Archie, not the men, they wear these," said the Ministry wizard, and he brandished the pinstriped trousers.
"I'm not putting them on," said old Archie in indignation. "I like a healthy breeze 'round my privates, thanks."
Well, somebody around the beginning of the 19th Century dug ἐνέργεια out of a Greek dictionary, much as Archie dug his nightgown out of a muggle shop, and we all need to pretend that it's a real word now: not because anyone is very sure what it means, but precisely because they're not. It's all very highfalutin and authoritative, but as Feynman, with his gift for isolating essentials, pointed out – it's a name for the strange fact that you can run certain calculations over at the conclusion of a change and get the same answer you got before it. It's not a description of change, or of the operations of cause and effect, or of force: in fact it's very nearly the opposite, and its co-option into English to mean things such as “vigor” or “transfer of force” is particularly inept.
Of course, that's just the way language goes: there's no use in objecting to the process, and I wouldn't even if there was. I'm just explaining my visceral response to the word: it strikes me, before we even get to bodywork, as bogus and posturing.
Don't get me wrong. It is a real word, thought not a common one, in classical Greek: it means something like "action" or "operation." But in the New Testament, where our English borrower no doubt found it, it is, as Strong says, "used only of superhuman power, whether of God or of the Devil." In other words, the English word "energy" has been trying to have it both ways ever since it was born: parading as a technical term, but deriving its energy (so to speak) from being associated with superhuman powers.