Question: What is theoretical physics

David Ho answered on 8 Nov 2018:

Great question! So in physics, a “theory” means a set of rules that predict what things in the universe will do. Broadly speaking, when we do physics, we make observations about the universe around us, and from patterns in these observations develop a theory as to how it works. This normally takes the form of a set of equations that mean if you can measure some quantities, you can predict what others will be. Then we do experiments, and if the results of the experiments don’t match the predictions of the theory, the theory can’t be correct. If they do, the theory is useful.

In the modern day physics has become such a big project that coming up with the theories and doing the experiments is too much work for one person. So we divide up the work: some people make the theories while other people test them. The people who come up with the theories are “theoretical physicists”, the people who test them (doing experiments) are “experimental physicists”.

Note that in physics, especially theoretical physics, the word “theory” means a slightly different thing to in other areas of science. Other branches of science only call something a theory when there’s overwhelming evidence that it’s true (such as the Theory of Evolution).