My response to that is that there are no grounds for treating the PLA any more or less heuristically than any other law of nature — MetaphysicsNow
It's off topic, so I'll keep it short, even though it is the topic I'm focused on currently.
Even if all laws are heuristic, the PLA is a principle and so distinct in being foundational to laws generally. There seem to be three such guiding principles - the PLA, the cosmological principle, and the principle of locality. My particular interest here is how they fit together.
The PLA becomes truly mysterious and non-local in quantum physics. The path integral or sum over histories formalism suggests events take the least action path over all their possible states. Quantum gravity would (likely) have to see even time and space as emergent in this manner.
A nice intro is Metaphysics of the Principle of Least Action, Vladislav Terekhovich -
https://arxiv.org/pdf/1511.03429.pdf
As regards the constraints based ontology you talk about, could you expand a little on this and specifically what you mean by "material sponaneity" and "formal limitation"?
Do you regard the formal limitations as capable of evolution, or are they fixed and immutable? — MetaphysicsNow
Again, keeping it short, I am arguing for a holistic metaphysics in opposition to the usual reductionist story. So I am arguing for an Aristotelian "four causes" or hylomorphic understanding of Being. As well as the bottom-up constructing causes of efficient/material causality, there is the top-down constraining causes of form/finality.
This is a systems science or hierarchy theory approach. And with CS Peirce, it becomes a semiotic approach where the top-down becomes understood as the informational aspect of reality, the bottom-up as the material or dynamical aspect of reality.
Peirce added the further critical logical wrinkle of understanding reality as a process of rational development - what we would call today, order from chaos or self-organising criticality. The thermodynamic or condensed matter approach to physical structure. So Peirce added Vagueness as a category of logic, a ground of being. A system crisply organised according to the four causes could have the appropriate kind of "nothingness" from which it could actually arise.
So this all cashes out as a general story where reality is the result of the development of constraints that organise a systems degrees of freedoms (and organises them in the precise evolutionary fashion that causes those freedoms, that resulting play of events, to cause the whole system itself to stably persist).
So it is an autopoietic story, a story of ontic structural realism, a story of dissipative structure, to name-check a few of the expressions of the general idea that might be familiar.
To make the contrast with reductionism - and nominalism, atomism, mechanicalism, etc - the systems view does see laws as "merely" the expression of collective behaviour. Peirce called them habits. But then the collective behaviour exerts the constraints that shape the parts making the system. So there is a cybernetic loop. There is feedback that limits the freedoms of the system's events so that they become the kind of thing that are the right stuff to keep the general show going.
From here, it is easy to see why symmetry principles become the governing factor of existence - hence the cosmological principle. At an almost Platonic level, there are logical forms that chaos cannot avoid falling into. For instance, a vortex or whorl is found everywhere in nature where there is dissipation to be done. It is the least action structure. Similarly for fractal branching.
And this is where logic comes in - as an unavoidable form. Logic expresses a least action principle in that is represents a maximal breaking of states of vagueness or uncertainty. It represents the symmetry-breaking which is a binary yes or no, true or false, present or absent.
And quantum interpretations are now picking up on this angle. Wheeler put it nicely with his "it from bit" papers...
This report reviews what quantum physics and information theory have to tell us about the age-old question, How come existence?
No escape is evident from four conclusions: (1) The world cannot be a giant machine, ruled by any preestablished continuum physical law.
(2) There is no such thing at the microscopic level as space or time or spacetime continuum.
(3) The familiar probability function or functional, and wave equation or functional wave equation, of standard quantum theory provide mere continuum idealizations and by reason of this circumstance conceal the information-theoretic source from which they derive.
(4) No element in the description of physics shows itself as closer to primordial than the elementary quantum phenomenon, that is, the elementary device-intermediated act of posing a yes-no physical question and eliciting an answer or, in brief, the elementary act of observer-participancy.
Otherwise stated, every physical quantity, every it, derives its ultimate significance from bits, binary yes-or-no indications, a conclusion which we epitomize in the phrase, it from bit.
http://cqi.inf.usi.ch/qic/wheeler.pdf
So it boils down to the idea that logic - as a Platonic-strength limitation on uncertainty or vagueness - can conjure existence into substantial being simply by applying its PLA-style constraints on naked or chaotic possibility.
Lewis and other nominalists/reductionists take a different view of possibilia in treating them as already definite and crisp degrees of freedom. Reality is a statistical ensemble of already concretely bounded alternatives. That assumption is explicit in modal realism's talk of "worlds". And the ensemble view is also what leads many to a Many Worlds Interpretation of QM.
But I am taking the alternative holistic view where possibility is more basic than that. It starts out as pure unformed potential - an indeterminate and unsubstantial vagueness. Then it starts to develop lawfulness or order as all its unlimited variety gets sieved according to a unifying principle of least action. You get a world that evolves into concrete form as it dissipates its early confusion and erases whole constellations of possibilities with every now definite physical event.
If my eye absorbs that photon from a distant star a billion light years away, then that is it. The event fixes a history. Time has been added to in a concrete fashion that forever limits any alternative result.
So we end up with just the one world creating itself by erasing possibilities. You don't have a modal realism/MWI story of whole new worlds being created every time there is a possible logical fork in the road. Instead, localised events are a non-local or contextual collapse of every other alternative.
The mystery of the PLA is that all the other alternatives did weigh in the balance. They were real in the sense that they really were there in a way that just got eliminated in a systematic and forever fashion. Until my eye did decohere that photon, the Universe was that fraction more uncertain. The alternative outcomes still existed as a fuzzy set of freedoms. And QM gives you a way to measure that kind of concrete possibilia. You can see it as a "block" of unrealised choices - the wavefunction.
Anyway, a short post has grown long. These are exciting times for metaphysics.
:)