The Wheeler-DeWitt equation (1967)
Bryce DeWitt applied the canonical quantization procedure—the standard recipe for turning a classical theory into a quantum one—to Einstein's general relativity. The result was an equation analogous to the Schrödinger equation but for the entire universe's geometry. John Archibald Wheeler championed the approach, and the equation bears both their names.
The equation proved mathematically ill-defined in the general case, producing intractable infinities. It could not be solved for realistic physical situations.
Despite its technical problems, the Wheeler-DeWitt equation established the template for all subsequent quantum gravity attempts: take a classical description of spacetime, apply quantum rules, and see what changes. Every major approach since—string theory, loop quantum gravity, and now the q-desic equation—follows this basic logic.
The TU Wien team's q-desic equation succeeds where the Wheeler-DeWitt equation struggled by narrowing the problem to a specific, solvable case (spherically symmetric, time-independent fields) and extracting concrete, potentially measurable predictions rather than attempting a general solution.