Strong understanding = unique, well-tested theory that accounts for all the data we have within the domain of applicability (defined by SMC at 14:00).
Consequences: There are no competing theories. Modifications or extensions are feasible, but the domain is "solved." The theory won't be displaced.
Examples: general relativity, Newtonian dynamics, Newtonian gravity.
Weak understanding = more than one theory can account for the data. Unable to discriminate which is relevant since theories make the same predictions. (defined by SMC at 15:44)
Consequences: Not clear theory which is right. Right theory may not have been invented yet.
Examples:
Foundations of quantum mechanics (e.g., Copenhagen interpretation, Bohemian, many worlds, jaggets platz)
dark matter and dark energy in cosmology. Properties are known, but multiple theories
dark matter: WIMPS, axions,
dark energy: vacuum energy, dynamical quintesense-like fields
No understanding = have data but no theory (defined by SMC at 18:20)
Examples: what happens at or before the big bang
SMC's claim: We have either a strong or weak understanding of everything that is accessible through measurement. (at 21:40) There's nothing that's experimentally accessible and not understood. That's new!
Survey of domains and relations
What is it that we know?
Newtonian dynamics. Space is separate from time. Deterministic Laplacian evolution.
Theory of relativity (1905, Einstein) explains space-time (as per Minkowski, 1907). (SMC: 29:22)
Special Relativity: how space-time is when gravity is not important; when space-time is flat. (SMC 30:20)
General Relativity: space-time can be curved and that curvature is gravity. Predicts big bang, black holes. SMC 30:10)