String theory is based on the misguided idea that the “great pillars of 20th-century science”; quantum mechanics and relativity can be unified. Unified into one theory that explains the quantum theory and relativity.

This is meant to unify physics and allow us to come up with a unified “Theory of Everything“. Or, at least to come up with a unified theory that can be used to explain most/all of physics. It is believed that with this theory, pretty much every other aspect of physics could be derived.

### How do we know that we should try to unify quantum mechanics and relativity?

Even if we assume that these are reasonable theories, how do we know that we can unify them into a good or even coherent theory? Who says such a theory exists?

Many physicists assume that such a theory must exist. However, I see little or no reason to assume that such a theory must exist.

Why do so many believe that it must? Physicists have noticed how successful quantum theory and relativity have been in making astoundingly accurate mathematical predictions. It is rather hard not to. In terms of their powers of mathematically describing relationships, both of these theories are remarkably accurate to very high levels of precision.

And there has certainly been a trend in physics towards increased unification. For instance, electricity and magnetism were once considered to be separate things until it was discovered that they are very closely related and that the same set of equations describe how they both work.

So, it is widely considered that there is this increasing trend toward unifying lots of different things under one theory, all describable by one set of equations. As done with electromagnetism and as physicists believe they accomplished with space and time.

They now want to unify quantum physics and relativity so that one theory explains both of these. And that can describe both with one set of equations. They assume that this is possible and that such a theory must exist. Must it?

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