system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it so difficult to find a unifying theory in physics and why is it necessary? Can't it all work separately?
gpt
> Why is it so difficult

I could go into details of examples of current difficulties but that would just lead us astray from the real answer, which is: why should it be easy? 

>Can't it all work separately?

Often it can in practice. For example you could have a theory that works well for slow speeds but badly at high speeds, and another theory that works well at high speeds but badly at low speeds. So if you are working with slow speeds you can use theory 1 and if you are working with high speeds you can use theory 2. But the problem is that in neither case is the theory *exactly* true. So while each might work OK in practice, we *know* that neither theory is the "right" one. This is partly just a point of intellectual curiosity; there is some correct description of nature out there, and we would like to find it. But it also can have practical consequences. For example maybe the right theory predicts other things besides simply being slightly more accurate. Maybe it presents a totally new perspective on the world.