The stratification problem refers to the way that C20th physics has different operating rules over three or four different scale ranges. The result is a layered system of physics in which different rules and laws apply at different scales, with the transitions between scales decided pragamtically.
Stratification across different physical scales
- Large-scale – Cosmology
- Cosmological horizons appear to function as acoustic horizons (which seems ot make their bulk behaviour statistically compatible with quantum mechanics), and their recession-velocity/redshift relationship is different to that of special relativity.
- Mid-scale – Gravity, GR
- GR1960's gravitational velocity-shift relationship is inherited from special relativity. This disagrees with the cosmologically-derived relationship, and generates different horizon behaviour – while cosmological horizons fluctuate and radiate in accordance with QM, GR1960 horizons don't, and are not QM-compatible.
- Human-scale - Simple mechanics
- Special relativity is assumed to operate over scales where the gravitational fields effects of bodies are not obvious. It shares shift relationships with Einstein's general theory, but has very different founding principles. Where Einstein's GR makes inertial and gravitational descriptions interchangeable – no inertial mass without gravitational mass – special relativity assumes that arbitrarily-high concentrations of energy have zero effect on spacetime curvature. as well as being logically incompatible, SR and the GPoR also turn out to be geometrically incompatible.
- Small-scale - Quantum mechanics
- Quantum mechanics describes the statistical behaviour of atomic and subatomic-scale physics, in which signal absorption and emission is quantised. This description is obviously very different to that of SR and C20th textbook GR, and according to the Copenhagen interpretation, Quantum and classical physics are simply different beasts with different rules. However, the statistical laws of QM can be used to derive a hypothetical underlying layer of classical physics, which is then quantised to produced QM. The properties of this QM-compatible classical model are not those of SR, but do seem to be those of an "acoustic" general theory, which would seem to agree with cosmological horizon behaviour, but not with SR/GR1960.
Summary of scale-stratification
If we label these four scales 1-4', with 1 being QM and 4 being cosmology, then the adjacent 2&3 share a shift relationship that disagrees with 4 (and possibly 1). 1 and 4 are compatible with an acoustic model, which then conflicts with 2 (SR), and with 3 (SR-based GR). 3 and 1 make different predictions for black hole radiation.
|“||The multitude of layers discussed above corresponds to the several stages of progress which have resulted from the struggle for unity in the course of development. As regards the final aim, intermediary layers are only of temporary nature. They must eventually disappear as irrelevant.||”|
|— Albert Einstein, "Stratification of the scientific system", in "Physics and Reality", 1936|
C20th theoretical physics also has a degree of theoretical stratification. Newtonian theory is derived for simple mechanics, but is not compatible with flat spacetime. Special relativity is derived for flat spacetime, and modifies the equations of NM with a Lorentz factor - for low velocities this gives "effective" NM behaviour as a physical limiting case. Since gravitation and relative acceleration involve curvature, which requires an additional layer of theory on top of SR, GR(C20th).
Since GR(C20th) is then incompatible with quantum mechanics, we then require an additional layer of theory, quantum gravity, which is expected to somehow include both QM and GR1960 inside a larger structure without amending either.
Although theoretical stratification is useful in that it allows an incremental approach to physics, a total theory with more layers appears more arbitrary and less minimalistic – and therefore less fundamental – than one with fewer layers.
Advanced general relativity replaces the C20th system's four scale-dependent layers with a single-layer theory, plus quantisation. Eliminating the SR layer reduces the total number of levels from four to three, "GR without SR" then ends up using a relativistic acoustic metric, which then merges the gravitational and cosmological behaviours and equations (giving only two layers), and the resulting "rewritten" GR, with fluctuating and radiating horizons, then also appears to be compatible with QM statistics, opening the door to a single-layer classical theory, which, with quantisation, appears to generate QM.