A central goal of theoretical physics for nearly a century has been the unification of quantum mechanics and general relativity, but the two most successful theoretical frameworks remain conceptually incompatible. Quantum Field Theory has successfully described the electromagnetic, weak, and strong nuclear forces within the Standard Model, but attempts to quantise gravity using the same techniques have consistently run into intractable mathematical and conceptual problems, suggesting a deep structural mismatch between the quantum and gravitational domains. The core difficulty stems from the non-renormalisability of gravity when treated as a quantum field. Unlike other forces, the graviton (the hypothetical quantum of the gravitational field) gives rise to infinite quantities in loop calculations that cannot be systematically tamed using standard renormalisation procedures. This failure implies that GR, when naively quantised, loses predictive power at high energies or small distances – precisely where a quantum theory of gravity is most needed, such as near black hole singularities or in the early universe.
Several alternative approaches have been developed in response:
String theory posits that the fundamental entities are not point particles but one-dimensional "strings," whose vibrational modes include the graviton. This approach achieves a finite framework that includes gravity, but it requires additional dimensions, supersymmetry, and a vast landscape of possible vacua, many of which are physically untestable.
Loop quantum gravity takes a background-independent approach, attempting to quantise spacetime geometry itself. While conceptually appealing in preserving diffeomorphism invariance, it has yet to deliver a full low-energy limit that recovers classical gravity and quantum field theory in flat spacetime.
Asymptotic safety, causal dynamical triangulations, and emergent gravity models also offer alternatives, but none have yet yielded a universally accepted or empirically confirmed quantum theory of gravity.
This persistent failure to quantise gravity raises the possibility that the gravitational field may not be fundamentally quantum in nature. Some have suggested that gravity may be emergent from deeper, possibly informational or thermodynamic principles, rather than a force to be quantised in the conventional sense. Others propose that QM itself may need revision in order to accommodate a fully relational or background-independent theory of spacetime. At stake is the coherence of our metaphysical picture of reality. If gravity fundamentally resists quantisation, this may indicate that the unification of physics cannot be achieved solely through the tools of 20th-century quantum theory. It may instead require a paradigm shift that reconceptualises either the quantum, the gravitational, or both, as emergent from a deeper substratum.
The long search for quantum gravity usually starts with the assumption that spacetime itself must be quantum. People then try to quantise curvature, treat geometry as a field, or imagine space and time emerging from deeper quantum structures. This effort has continued for decades without consensus on what would even count as the correct explanatory target. In 2PC, the reason is simple: the project begins in the wrong category.
Gravity is not a quantum system waiting for its operator form. It belongs to the classical side of Phase 2, which only comes into being once collapse has already occurred. Before collapse there is no space or time, only a superposed set of possibilities. Geometry does not evolve within Phase 1; it appears when Phase 1 is resolved into Phase 2. Trying to quantise gravity is therefore like trying to quantise the page beneath the equations. It mistakes the background created by collapse for a field inside the superposition.
Penrose treated the problem differently and argued that gravity itself drives collapse. In his picture, superpositions of different curvatures strain against each other, and when the tension grows large enough the state reduces. This makes gravity a pre-existing feature of the world that cannot tolerate incompatible geometries. In 2PC, the causal order is reversed. The world begins without geometry. Collapse occurs when a self-referential observer arises whose valuations cannot remain coherent across branches. That act of resolution instantiates a single classical reality, and gravity follows as its structural consequence, not as a force reaching back into Phase 1 to resolve superpositions. Collapse generates geometry; gravity is the name we give to the structure of that instantiated geometry.
How countless local collapse events coordinate to produce a single, coherent global geometry with uniform curvature is described by Competition Resolved Collapse.