This law is about the law of equivalent exchange. This law is about casting spells. It says that you must give something up to create something. Both things must be of equal value. This law applies to spells of creation. No trying to create souls! This can and will be fatal to all who try. This has been tryed, a kid was trying to bring back his mom. This can be understood.
I am going to point this out, because I feel I should. The law of equivalent exchange is a thing from Full Metal Alchemist. The scenario is also from Full Metal Alchemist. You don't have to give up much of anything, except energy.
You are refering to an anime called Full Metal Alchemist. The law of eqivalent exchange may be true for creation spells, but the boy trying to bring back his mother was referencing to how Ed and Al Elrick tried to bring their dead mother back to life with alchemy. The story is false, and whether the fact that you are intending to get comments to help you with some sort of research, or that you are trying to warn people about the dangers of the law of eqivalant exchange, or that you just were watching said anime, got bored, then typed this random choice of sentances up. None the matter, I tell you this! The Law of Equivalant Exchange is quite real, and even more so dangerous! If you decide to ebark on the long journey into creation magick, I bid you this one, and ONLY ONE warning: Do not look into the exchange of lives! No Matter how petty. Whether a human or a chipmunk, do not research this form of creation magick.
Equivalent Exchange is only part true. Knowledge is technically free, you simply need to find it. Wisdom is earned, not bought. Life has no price, it cannot be traded for anything nor can anything to traded for it. Your soul is priceless and belongs to you and you alone. The "price" of magic also isn't literal, it's more like you use energy to get the result you want.
Alchemy is real. The law of equivalent exchange is part of alchemy. The story about the boy however is part of Full Metal Alchemist, though it is a good example. Alchemy is what we had before modern science, people would use religion, philosophy, & physics to explain things and create things. People had to practice in secret. Sir Isaac Newton was an alchemist.
Alchemy is governed by multiple laws, these laws can range from the law of polarity, to the Law of Correspondence. The Law of equivalent exchange is ... technically not a real law but a major philosophical point in alchemy, "All is one, One is all" to give you must take, to create you must destroy. This would be the law of equivelent exchange, it would not just focused around the world of magick but also the physical world.
Issac newton being an alchemist had beliefs that latter can be reflected in the natural laws named for him. The laws of motion state that every action has an equal and opposite reaction. Similar to the law of equivalent exchange