Maybe Quantum Mechanics Needs To Be Augmented
With all its mathematical apparatus QM can only predict the outcomes of experiments. This is no mean feat, but QM tells us nothing about what physical processes are going on before the detector registers a result.
In the case of the two-slit experiment discussed in virtually all discussions of QM, standard QM can predict the striped detector results, but it can say virtually nothing about what is going on between the time that the particle leaves the source and when it hits the screen.
If you want an excellent discussion of what QM can do and what it cannot explain read the piece linked below, which is written at a popular level by an expert in QM physics (with positions at the University of Cambridge and the Perimeter institute).
General Relativity is an extensively tested physics theory that does not need smoke and mirrors. It is explicit in its modeling of nature.
Quantum Mechanics is a black box theory that no one really understands, as Feynman pointed out .
It is far more likely that QM is the theory that needs to be “augmented”, i.e., expanded into a complete theory. One way to complete QM was suggested by Bohm and De Broglie. It involved the particle concept being supplanted by an intrinsically linked particle+wave concept: particles guided by waves. This gave the same answers as QM, and explained atomic scale phenomena in a space-time context for the first time. Unfortunately, this theory has some serious drawbacks, but there are other possible particle+wave models that may one day complete QM.
Let’s not endlessly repeat the hackneyed assumption that QM is the best thing since sliced bread and GR must be modified in order to get quantum gravity. There are other, and probably better, approaches to unifying GR and QM.