This is fundamentally true but I think the question being posed by the o.p. is where one theory ends and the other begins, and where there are areas of overlap. And, below that explicit question, is why there are two seemingly incompatible theories which are both, in their respective domains, highly useful in predicting behavior, but break down at some scale.
I’ll point out that there is not conflict between special relativity and quantum field theory, starting with quantum electrodynamics (QED) but eventually extended to the entire Standard Model (of particle physics), albeit with some limitations. QED in particular has made some of the most accurate predictions in all of physics, and has real practical applications in condensed matter physics. (QFD and QCD have far fewer practical applications—essentially no industrial technologies—simply because the energies required to control interactions are too great for modern technology but could be a boon if we developed a way to control them other than randomly smashing highly accelerated particles together.) Admittedly, QED was resolved through the process of renormalization to eliminate infinities in the possible interactions and self-interactions, which while being taught as the standard method is regarded by some physicists as mathematical hocus-pocus; a trick that steps around the philosophical issues of what those infinities actually represent. But it works for electrodynamics, and (again, with some caveats) in quantum chromodynamics.
Renormalization does not, however, work for gravitation, both because the low energy and infinite range of its force carrier, the hypothetical graviton. This doesn’t really matter in practical terms because gravitons will never be observed in isolation due to their low energy, extremely low capture cross section with any normal matter, and because spacetime is flooded with a constant stream of them. Even if gravitation can be formulated as a quantum field theory it would reduce to general relativity under all observable conditions (and to classical Newtonian gravity in locally ‘flat’ space) in all cases except where there are discontinuities in the fundamental plenum of spacetime, such as near the singularity of a black hole.
It should be noted that for as broadly accepted as general relativity is, there is no real explanation for what spacetime actually is other than some kind of manifold upon which the effect of mass and localized energy can describe a curvature in geometric terms. GR treats the topology as smooth and (generally) continuous but we don’t know that to be the case as we can only observe it down to the highest wavelength of electromagnetic radiation that we can measure, and it could totally be discrete beyond that level, just as the “smooth” paint on your car is actually made of discrete molecules. Any physicist who is honest will admit that GR is an incomplete theory in this way, just as in quantum mechanics the fundamental nature of elemental particles is described by a self-consistent model but with no real understanding of what those particles are made of (other than ‘kinks’ or vibrating strings or some equally esoteric analogy to the everyday mechanics of our experience that is probably totally wrong).
There are some luminaries who think that gravity is fundamentally different from the other interactions and that we should not expect or even seek out a quantum theory of gravity, instead looking toward a completely different nature. While this could be true, and there are almost certainly deep connections between gravitation and time, I think it is more likely that both QFTs and general relativity are mean field approximations of some more fundamental underpinning, one that we may never be able to directly interact with or inspect. If quantum mechanics is real, then everything has to obey the rules of QM all the time, but at some resolution it just looks like classical mechanics or general relativity. However, phenomena such as ‘dark energy’ or cosmic strings (if we ever observe one) may give greater insight into the deeper nature of gravity and the possible quantization of spacetime at some extreme energy gradients.
I don’t think this really answered the question of the o.p., and probably cast even more confusion, but that isn’t because the question was stupid or the o.p., despite his begging of pardon, is ignorant; in fact, @Lucas_Jackson is asking the same question that generations of physicists have been ‘ignorantly’ asking since the emergence of quantum mechanics and general relativity, and as yet without a definitive answer.
Stranger
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