Law of Conservation of Energy

This law governs all natural phenomena that are known to date. There is no known exception to this law.

It states that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes.

Law of Conservation of Energy

The total energy of an isolated system will remain constant.

Idea from Richard Feynman:

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.