Let

Ok when I say “let,” i’m just defining something to be another thing.

Example:

Let blorple be blue\begin{gather*} \text{Let blorple be blue} \end{gather*}

Now if i say “the sky is blorple” then i actually mean that it is blue.

This is the foundation of mathematics. Mathematics is largely axiomatic which means it is created on axioms which we "let" be true.

Physics uses mathematics to describe and model systems in real life.