Is there a compelling reason why physicists believe that there must exist a single theory which subsumes both General Relativity and Quantum theories into a united whole?

Or is it merely some vague belief in the symmetry of nature on all scales?

11 minutes ago, Xerxes said:

Is there a compelling reason why physicists believe that there must exist a single theory which subsumes both General Relativity and Quantum theories into a united whole?

Or is it merely some vague belief in the symmetry of nature on all scales?

I'm no physicist but I had understood there is an unresolved incompatibility between the two, i.e. as the two theories stand today if one is right then the other can't be, and that is why there is a search for a resolution that unifies them. But no doubt a physicist will show up and explain.

1 hour ago, Xerxes said:

Is there a compelling reason why physicists believe that there must exist a single theory which subsumes both General Relativity and Quantum theories into a united whole?

Or is it merely some vague belief in the symmetry of nature on all scales?

I’m not sure it’s vague. Electricity and magnetism were unified (Maxwell and Einstein), and then we had electroweak unification at higher energies emerge in the 60s. So unifying with the strong force, and also with gravity, are seen as “next steps”

exchemist noted the fact that QM and gravity are incompatible where you have very strong gravity, which is a separate reconciliation that simply has to have a resolution. QM still works in strongly curved spacetime, so we expect to have a mathematical description.

10 hours ago, Xerxes said:

Is there a compelling reason why physicists believe that there must exist a single theory

The fact that all known forces 'seem' to converge to equal strength at Planck scale, implies that all forces may unify at Planck energies.
IOW, unification of gravity with color-electro-weak at approx. 1.2 x !0^28 eV.
( way beyond our reach )

18 hours ago, Xerxes said:

Or is it merely some vague belief in the symmetry of nature on all scales?

The problem is mostly that there exist situations in nature where both gravity and quantum effects appear to be simultaneously non-negligible. Thus, it is reasonable to assume that there should exist some mathematical framework that can describe such situations in an internally self-consistent way. But you are right in that this framework taking the form of a single unified theory is largely an assumption based on what happened with the other fundamental interactions. Though I must say it is difficult to see what a possible alternative might look like.

8 hours ago, Markus Hanke said:

The problem is mostly that there exist situations in nature where both gravity and quantum effects appear to be simultaneously non-negligible. Thus, it is reasonable to assume that there should exist some mathematical framework that can describe such situations in an internally self-consistent way. But you are right in that this framework taking the form of a single unified theory is largely an assumption based on what happened with the other fundamental interactions. Though I must say it is difficult to see what a possible alternative might look like.

I tried to find a concrete example of physically meaningful scenario where math suppose to brake but I couldn't...
Maybe someone of you guys can give an example?