Maudlin writes about the proponents of the different interpretations of QM (Quantum Non-Locality and Relativity):
They may correctly note that according to every one of their rival theories, God was malicious, and having thus eliminated every other possibility, claim their own theory the victor. The problem is that every partisan can argue in this way since every theory posits some funny business on the part of the Deity.
Peter Donis wrote the equivalent earlier in this thread (#69):
The problem is not that nobody has come up with alternatives. The problem is that none of the alternatives satisfy everybody; every single one has some showstopper that makes some segment of the physics community simply refuse to buy into it.
and it summarizes the quagmire of quantum foundations.
In response, Rovelli wrote (
https://arxiv.org/abs/quant-ph/9609002):
[Q]uantum mechanics will cease to look puzzling only when we will be able to derive the formalism of the theory from a set of simple physical assertions ("postulates", "principles") about the world. Therefore, we should not try to append a reasonable interpretation to the quantum mechanics formalism, but rather to derive the formalism from a set of experimentally motivated postulates.
The reasons for exploring such a strategy are illuminated by an obvious historical precedent: special relativity. ... Special relativity is a well understood physical theory, appropriately credited to Einstein’s 1905 celebrated paper. The formal content of special relativity, however, is coded into the Lorentz transformations, written by Lorentz, not by Einstein, and before 1905. So, what was Einstein's contribution? It was to understand the physical meaning of the Lorentz transformations.
In other words, Rovelli challenged the foundations community to render QM a "principle theory" like SR (see quote below), which was spawned from a similar quagmire in the late 19th century.
In that situation, physicists were trying to find a causal mechanism ("constructive efforts" per Einstein, see quote below) like the luminiferous aether responsible for length contraction that would then account for the fact that everyone measures the same value for the speed of light c, regardless of their relative motions (observer-independence of c). Einstein played this game himself before giving up, writing (What is the Theory of Relativity? 1919):
By and by I despaired of the possibility of discovering the true laws by means of constructive efforts based on known facts. The longer and the more despairingly I tried, the more I came to the conviction that only the discovery of a universal formal principle could lead us to assured results.
Instead of a "constructive" (causal) account:
aether --> length contraction --> observer-independence of c
he formulated a "principle" account:
Relativity principle --> observer-independence of c --> length contraction.
Here is the distinction between constructive and principle theories per Einstein (What is the Theory of Relativity? 1919):
We can distinguish various kinds of theories in physics. Most of them are constructive. They attempt to build up a picture of the more complex phenomena out of the materials of a relatively simple formal scheme from which they start out. Thus the kinetic theory of gases seeks to reduce mechanical, thermal, and diffusional processes to movements of molecules – i.e., to build them up out of the hypothesis of molecular motion. When we say that we have succeeded in understanding a group of natural processes, we invariably mean that a constructive theory has been found which covers the processes in question.
Along with this most important class of theories there exists a second, which I will call "principle-theories." These employ the analytic, not the synthetic, method. The elements which form their basis and starting point are not hypothetically constructed but empirically discovered ones, general characteristics of natural processes, principles that give rise to mathematically formulated criteria which the separate processes or the theoretical representations of them have to satisfy. Thus the science of thermodynamics seeks by analytical means to deduce necessary conditions, which separate events have to satisfy, from the universally experienced fact that perpetual motion is impossible.
Accordingly, SR is a principle theory since its kinematic formalism (Lorentz transformations) follows from an empirically discovered fact ("experimentally motivated postulate" per Rovelli), i.e., the observer-independence of c (light postulate). Of course, the light postulate follows from the relativity principle and Maxwell's equations, e.g., from Physics for Scientists and Engineers with Modern Physics 5e, R. Knight Pearson, San Francisco p. 1057 (2022):
and from Physics for Scientists and Engineers with Modern Physics, R. Serway and J. Jewett, Cengage, Boston
10th ed., Section 38.3 (2019):
Accordingly, length contraction is not a dynamical effect due to some causal mechanism like the luminiferous aether, it is a kinematic fact following from the relativity principle and Maxwell's equations. Now let's return to QM.
Quantum information theorists have since satisfied Rovelli's challenge and rendered QM a principle theory whose kinematic formalism (Hilbert space) follows from the empirically discovered fact called Information Invariance & Continuity (Brukner & Zeilinger,
https://arxiv.org/abs/0905.0653):
The total information of one bit is invariant under a continuous change between different complete sets of mutually complementary measurements.
Essentially, that just says the quantum bit of information (qubit) exhibits quantum superposition. The rest of Hilbert space is built starting with the qubit, so quantum entanglement follows from quantum superposition. Of course, the quantum foundations community already knew that the mystery of entanglement follows from the mystery of superposition, so this did nothing to solve the mystery of entanglement. But, it's easy to show that qubit superposition follows from the observer-independence of Planck's constant h between reference frames related by spatial rotations and translations, which can obviously be justified by the relativity principle just like the light postulate ("Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit", Oxford UP, 2024;
https://iopscience.iop.org/article/10.1088/1742-6596/2948/1/012009).
Consequently, quantum entanglement is not a dynamical effect due to some nonlocal or superdeterministic or retro causal mechanism, it is a kinematic fact following from the the relativity principle and Planck's radiation law (where h was introduced as a constant of Nature).
So, the bottom line is that quantum entanglement does not entail "spooky actions at a distance" or causes from the future with effects in the present or conspiratorial causal control over experimental procedures or infinitely many realities or the violation of intersubjective agreement (a la QBism). Just as physicists long ago accepted length contraction and time dilation as kinematic facts rather than dynamical effects, it is perhaps time to do the same with quantum superposition and entanglement. But, that's up to you :-)
