Michael Chase: Notes on PWL, Quantum Physics and Epistemic Modesty

15th session of the PWL International Seminar, hosted by Michael Chase (CNRS Centre Jean Pépin, Paris / Max Planck Institute for the History of Science, Berlin) who talked about “Notes on PWL, Quantum Physics and Epistemic Modesty”. The session took place on July 17, 2024.

The PWL International Seminar is held virtually once a month and takes place within the scope of the activities of the exploratory project Mapping Philosophy as a Way of Life: An Ancient Model, A Contemporary Approach, coordinated by Marta Faustino (CultureLab/IFILNOVA), and the activities of the research group Forms of Life and Practices of Philosophy, coordinated by Bartholomew Ryan (CultureLab/IFILNOVA).

[Achrononmaster]

Really nice talk and discussion. Thanks IFILNOVA.

[Achrononmaster]

@10:20 a _providential universe_ is neither quaint nor outdated, rather it is merely suppressed by modern culture. From a modern understanding of nature the idea does indeed seem quaint and naïve, but that is only because people have shifted predominant worldviews to materialism. If the physical existence is only a means to an end, and we cannot perceive the greater ends, then it can sure seem like the universe is nasty, cruel and hostile and therefore devoid of any providential intent. But if physical existence is not the _be all and end all_ then things take on an entirely different complexion. The soul/spirit cannot progress without tests. Part of the progress of a soul is in knowing one has progressed.

[Achrononmaster]

@28:00 Heisenberg Uncertainty applies to classical mechanics. But we can ignore it because *_classical_* classical mechanics simply asserts ħ = 0. It is an error. So the Lie algebra brackets for the _classical_ symmetry groups vanish. But why is it "ok"? The answer is that for any system where entanglement structure is washed out by many-body statistics we simply do not need to solve the QM equations of motion. su(2)xu(1) is an algebra contained within the classical spacetime algebra of rotors (rotation generators are the bivectors) and the pseudoscalar. su(3) is an algebra with a tensor product structure in spacetime, i.e., non-trivial topology. These are "quantum" only because they apply to local degrees of freedom on spacetime, not global, i.e., to local nontrivial (non-Minkowski) topology.
Note the best way to formulate GR is by starting with fermions, not a metric. The metric is a square root of the position covariant gauge field, so the latter is "more fundamental". Fermions are deeply GR/spacetime structure. They are really classical operators. (The _spinors_ are not "the particles." They are mathematical representations of instructions to transform frames. Scaled rotors.) The "quantum" nature of the spinors is again due to the fact they represent local degrees of freedom, or local transforms, i.e., "particle" interactions and they carry a statistical scale factor √ρ (accounting for nondeterminism) --- the particle interaction regime is where if you erroneously set the Lie commutators to zero (ħ=0) will result in a poor theory that is predictively wrong. The so-called quantum--classical transition is an inherently messy statistical thing, it is the question of when can you ignore the non-zero commutators? and _deliberately_ make the error of setting them to zero without messing up model accuracy.

[Achrononmaster]

@1:24:00 that's wrong. The "quantum state" is best understood from the spacetime algebra formulation, where it becomes clear the object 'ψ' is just an instruction to rotate and dilate. A transformation instruction is not an element of reality, it is "secondary" ontology at best. The elementary particle is what is real, not 'ψ'. What the wavefunction or spinor provides is a way of transforming from a laboratory frame to the elementary particle's frame. This 'Clifford' spacetime algebra view also more clearly shows you why the unitary groups play a fundamental role. Or as Misha Gromov would say, "matrices are stupid."

[Achrononmaster]

@31:00 Heisenberg was wrong about that imho. The distinction is not that of one between "real" and "objective". It is between "recorded" and "not recorded" and between "time evolution" and "the atemporal". If we do not watch a particle over very small time intervals, then we do not know of it's objective real trajectory, but it does have a real trajectory. The lack of even the possibility of knowledge of an elementary particle trajectory is due to the atemporal, the closed timelike curves, which imply global spacetime is non-orientable. If we insist on a Hamiltonian time evolution story then we invite the unavoidable apparatus of a stochastic dynamics that is non-Markov (not divisible). Thing is, for we mere mortals stuck in psychological time evolution, we cannot do much better than providing such a story. You can try to tell a non-time oriented story, but then you have to know the future! Not sure anyone will ever manage that except by non-veridical dreams.

[Achrononmaster]

@25:50 Doh! Neither of those aspects of quantum mechanics challenge objectivity. QM formally is completely observer independent. A "measurement process" is _anything_ that breaks entanglement (or if at a classical level the usual notion where ħ →0). No "mind" or observer is required. For sure, humans "do measurements" all the time, but so do viruses and amoeba, even single atoms. Whenever there is a record trace in a spacetime cobordism which would allow something to know the value of some dynamical variable, then that is a measurement. The mystery (in QM) is _what is entanglement?_ and how is entanglement broken? The recent ER=EPR conjectures provide a possibly beautiful account --- minimal ER bridges _are_ entanglement, and topology of spacetime locally can change. Meaning there must exist closed timelike curves, albeit highly constrained to scales where a Planck scale wormhole cannot Hawking evaporate due to conservation laws (i.e., unitarity). There is a topological censorship conjecture due to Geroch: any attempt to probe a Planck scale wormhole will collapse the thing. So no scifi time travel nerds, sorry. But at least we recover local causality and objective physics. The _Mind_ is not a thing in the physical realm yo.

[Achrononmaster]

@1:02:30 That's not right. Science is a proper subset of philosophy. A scientist who claims their business is not philosophical is like a ice figure-skater who claims they are not involved in sport, but rather art. Well... you can do both at once.

[Achrononmaster]

@1:06:00 physics has never concluded time is not real. All good predictive theories start with Minkowski space as a base. While the laws of physics are supposed to be coordinate covariant, time itself cannot be erased, since at least globally all successful theories have a pseudo-Riemannian structure (which coordinates are not needed to define). You can adopt a Kuhnian or Feyerabend stance and claim this is just our present paradigm, but seriously dudes, are you really going to envisage this baby ever getting thrown out with the bathwater? Rovelli is is an ideologue. He misses the insight that general relativity was already a quantum theory (one must augment GR with local nontrivial topology to have "particles". That implies quantum logic. See Mark Hadley's old but highly underappreciated work.)