Non-Empirical Theory Construction

The search for an empirically adequate theory of quantum gravity - i.e., a theory that should cover a range of validity in which both quantum mechanical and gravitational aspects are traditionally relevant - has been dragging on now since the 1930s: There are some theoretical candidates for a quantum gravity theory, albeit not completely worked out (such as string theory and loop quantum gravity); but at the same time, the range of application of the desired theory, far, far away from experimentally accessible scales, still makes testing of these candidates seem almost impossible until the near future. (Based on current knowledge, it would take an estimated ring particle accelerator in the style of the Large Hadron Collider at CERN with diameter one-tenth of the Earth-Sun distance to reach the characteristic energy scales of quantum gravity. See Zimmermann (2018).)

In this context, an empirically adequate theory of quantum gravity is hoped to provide answers not only to intriguing questions about the interior of black holes and the nature of the Big Bang in the standard cosmological model; but also about the nature of space and time in general. Indeed, much from the already known candidate theories suggests that space and time are not only fundamentally discrete in nature, but that space and time emerge derivatively from non-spacetime structure (keyword: emergence).

The project addresses methodological-conceptual issues in theory development and pursuit of a theory of quantum gravity, including: (1) Can candidates be meaningfully tested or compared before the actual experiment? (2) How systematically have known candidates been found? (3) Have meaningful directions of theory development been disregarded for purely contingent but substantively unjustified reasons?

Reference: Zimmermann, Frank. "Future colliders for particle physics-"Big and small." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 909 (2018): 33-37.