Constructor theory turns this approach on its head. Deutsch’s new fundamental principle is that all laws of physics are expressible entirely in terms of the physical transformations that are possible and those that are impossible.

In other words, the laws of physics do not tell you what is possible and impossible, they are the result of what is possible and impossible. So reasoning about the physical transformations that are possible and impossible leads to the laws of physics.

The analogy that he draws is with conservation laws such as the conservation of energy. This is not a law of physics like quantum mechanics or relativity but a principle that all other laws must follow. As energy is converted from chemical to electrical to kinetic to potential energy and so on, its behaviour is governed by all kinds of different laws of physics. But they must all obey the principle that energy is conserved.

“Thus the conservation law, though not an a priori mathematical truth, provides an explanation of aspects of motion that is deeper than laws of motion,” say Deutsch.