system
Given the following post, respond as if you're commenting on Reddit:
human
Searching for the Theory of Everything, physicists have realised that General Relativity and Quantum Field Theory are incompatible. Suppose this means that at least one is wrong, then why do they still use them?

My thinking is that with two incompatible theories, even though they work in the areas they are used, this means there are faults with at least one of them. Also, are they looking for a third theory that better describes the universe?
gpt
Until we find the final, fundamental Theory of Everything, *all* physical theories are wrong to some extent. However, good physical theories like quantum theory or general relativity are only significantly wrong in extreme circumstances. Therefore, if we very carefully demarcate the area of validity for a given good theory, we can treat that theory as right, as long as we stay in the area of validity. Within this area, a good theory is highly accurate, logical, self-consistent, and useful. Even a good theory that is hundreds of years old and is several generations of theories behind the times, such as Newton's laws, is still accurate, intuitive, and useful in its limited realm of applicability. 

> why do we still use them?

If we were to discard a theory because it was wrong in some way, we would have to discard all theories and would be left with nothing. This is not a very effective way to proceed. Instead, we keep the most accurate theories, even though we know they are wrong, and try to tweak them to make them less wrong.

> Also, are they looking for a third theory that better describes the universe?

Yes, many people are working on this.