> In the decades since the establishment of these theories, both the continuous (classical) spacetime of general relativity and discrete matter of quantum mecha

> In the decades since the establishment of these theories, both the continuous (classical) spacetime of general relativity and discrete matter of quantum mechanics, the world has changed in rather significant ways. It was essentially a historical accident that the first systems where quantum mechanics was studied extensively (black-body radiation and atomic spectra) were ones in which quantum effects ended up discretizing something which was continuous in classical mechanics. Quantum mechanics does not generally impose, require or even match having things be discrete. You can very easily have quantum systems where the relevant quantities are continuous, rather than discrete (wiki link: https://en.wikipedia.org/wiki/Continuous-variable_quantum_information https://en.wikipedia.org/wiki/Continuous-variable_quantum_in...). Simple theoretical examples like the particle living on a 1d line or in 3d space are easy to understand, there are many (many many many) more complicated examples. TLDR: there is no fundamental link between things being quantum-mechanical and things being discrete. Quantum mechanics makes some things discrete, but not everything.