When coming up with a physics formulation and theory..how do you combine two theories..?

Question

Like for instance E=mc(squared) how would a physicist combine that with another law? What would be the process, and how do you check your work?

Answer 1

It's not that simple. Combining theories isn't like mixing chemicals. The best current example is the efforts (including those of Einstein) to find some laws of physics that work in both domains of relativity and quantum mechanics. No one has yet succeeded, but the candidate which looks promising is Superstring Theory or its many variants. The ideal way is to study and understand all of the relevant existing theories, know where they fail, and try to think of an explanation that is still correct where the other theories are correct, but doesn't fail.

You check your work by applying the new theory and seeing if its predictions match reality. Then, you publish your work and get your peers to do the same checks. With relativity and string theory, it gets really hard to find experiments where the new theory makes a difference.

Answer 2

Carefully & carefully.