Quotes / Equivalent Exchange

"The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings."

Hohenheim: This world is tragically violent. Throughout the course of this war millions of people have been killed with the use of highly toxic gases, but the single most terrifying instrument of death is yet to come. You saw it in the gate, didn't you? [Edward remembers an image of the atomic bomb cloud above Nagasaki.] The lives of those that have died and will die in this world become the energy for the alchemy used in ours.
Edward: The energy? That doesn't make sense...What about the-
Hohenheim: -law of Equivalent Exchange? There's something you don't understand. It takes more than equal mass to restore a broken radio. The energy used to put it back together must come from somewhere, too. And energy cannot be created or destroyed; only redirected.
— Hohenheim revealing the limitations of this trope as a law in Fullmetal Alchemist

"Energy can neither be created nor destroyed, only changed in form."
Law of Conservation of Energy

"To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions."
Newton's Third Law of Motion

"Alchemy: the science of understanding, deconstructing, and reconstructing matter. However, it is not an all-powerful art; it is impossible to create something out of nothing. If one wishes to obtain something, something of equal value must be given. This is the Law of Equivalent Exchange, the basis of all alchemy. In accordance with this law, there is a taboo among alchemists: human transmutation is strictly forbidden - for what could equal the value of a human soul...?"

Ed: What I seek was just ahead... the truth about human transmutation! Please, show it to me again!
Truth: I can't. I can only show you this much for the toll you've paid.
Ed: Toll?
Truth: Yes, toll. [Ed's leg disappears] It's an equivalent exchange, right? Alchemist?

"Oh, you could do it all by magic, you certainly could. You could wave a wand and get twinkly stars and a fresh-baked loaf. You could make fish jump out of the sea already cooked. And then, somewhere, somehow, magic would present its bill, which was always more than you could afford."

"There ain't no such thing as a free lunch."

"All magic comes with a price!"
Rumpelstiltzkin, Once Upon a Time

And so, this is what the Pearl Satraps do. On one hand, they please themselves above all others. They go out in the world and what they see, they want, and what they want, they purchase. It's a mad game to serve their vanity, but what does one have if one is without the joy of conceit? One Satrap sees a silver locket around a woman's neck, and that locket holds the picture of a dearly departed husband. Oh, but the Satrap wants it, and the woman assures him she'll never give it up. But she will. Maybe money will do the trick (people love money more than they care to admit, the Satraps say). If not that, then something else. The return of a lost child? A threat against her dear friend? Revenge against a cruel boss? She'll give the locket up when the Satrap sounds the right price. And he'll take it only when she's conceded to that price; no Satrap will accept something without first paying the proper cost. Nor will he ever steal, for thievery is anathema to this noble order. Nothing is free. To act as if it is means a wilful refutation of those principles the Satrapy holds dear.
Changeling: The Lost, writeup for the Satrapy Of Pearls group

"There's light, and there's darkness. Cause and effect. There's guilt and there's atonement. But the scales always need to balance. Everything has a price."
Alan Wake, Alan Wake

Every wish comes with hidden costs beyond the blood cast into the waters. The reason is balance: in some manner, the quarry conspires with the universe to grant wishes, but the rewards aren't simply conjured out of thin air. If someone asks for $100, the money comes from somewhere; it doesn't just appear, it's pulled from someone's wallet or cash drawer. A million dollars works the same way, except more extremely: it has to come from somewhere - an insurance policy, bank vault or some rich person. The universe struggles to stay balance. The good granted by a wish must be equaled by a negative deficit elsewhere.
Translation: wishes cost more than one thinks.
—"The Swimming Hole," Mysterious Places

Only death can pay for life. It is known.
Miri Maz Duur, Game of Thrones