This is beyond my level of knowledge, but let's have a go.
Thanks!
"Determinism in classic physics was an assumption that has proved to be invalid regardless of quantum processes and even quantum mechanics."
Not True. The Laws of Newtonian Mechanics work for the overwhelming majority of phenomena.
That's true, in a sense. We can use Newtonian mechanics to create models of systems that are so close to accuracy we often can't even measure the difference. The issue is what we mean by "works". Consider, for example, statistical mechanics. Years before quantum mechanics, physicists realized that many systems were far too complicated to analyze using either Newtonian mechanics or classical electrodynamics. However, a few basic assumptions and simplifications allowed/allow physicists to describe the dynamics of systems otherwise vastly too complex for any conceivable technology to model. Namely, instead of trying to model all the particles of a system using classical mechanics, the dynamics of large numbers of particles (e.g., gaseous molecules in some container) that were sufficiently similar were basically "averaged" and treated singularly. So rather than having describe a system of billions upon billions upon billions of particles in terms of the dynamics of every one, the general behavior of all of them could be treated together.
But most physicists still thought that the systems that couldn't be described by Newtonian mechanics and which required statistical mechanics could, at least in principle, be modeled by Newtonian physics.
This assumption was wrong. Newtonian physics is based fundamentally around a nonlocal, instantaneous-action-at-a-distance ephemeral "force" that doesn't exist, describing point-particles that don't exist, and failed before quantum mechanics because it can't deal with electricity, magnetism, light, atoms, and so on.
The point is that Newtonian Mechanics "works" in the same way that statistical mechanics does: it often yields an answer that is useful and close to being "right". The difference is that not only is statistical mechanics better, but also that nobody ever thought that statistical mechanics actually described reality (as it appears they do with classical mechanics) rather than being a convenient method for predicting, analyzing, and modelling data in/from experiments. This was justified before it was demonstrated that basically every ontological commitment made in classical mechanics is wrong (e.g., that matter consisted of point-like masses; all "waves" were merely excitations, oscillations, or similar perturbations propagating through point-like masses, gravity was a universal force that acted instantaneously-at-a-distance, time and space were absolute, the electrons of all atoms should plunge into their atomic nuclei obliterating basically all matter, etc.) Classical mechanics doesn't work if we want it to tell us about the nature of reality, because it describes reality in terms we now know are false, it is inherently contradictory, it is incomplete, and it contradicts the past century of experiments in countless ways. It DOES work, as you say, to help us get fairly accurate results much of the time. The problem arises when we confuse approximately accurate results with commitments to the reality of the theory that yields them. If we do this, we might as well say that statistical mechanics (which was never intended to be a description of reality) is a better theory of physical reality than classical mechanics.
Relativity dealt with the exceptions to the rule
Relativity is often considered to be part of classical physics. This is because it didn't really challenge or change much, or at least special relativity didn't. But even before relativity Newtonian physics failed to explain light, electricity, and the other things that classical electrodynamics attempted (and failed) to deal with. The "exceptions" to the rule include the most fundamental component of Newtonian physics: gravitation. There is no theory in physics which attempts to reality and which is compatible with Newtonian gravitation. Also, the point-particles of Newtonian physics don't exist, the laws of Newtonian physics are wrong, and in general it posits dynamical laws that aren't accurate to describe classical objects that don't exist.
We're talking about scale.
Only if we abandon the notion that physics should tell us what is real (or at least attempt to). Newtonian mechanics fails at every scale, because it is fundamentally rooted to the commitment of things that don't exist. All of its equations, no matter how accurate, require the existence of fantasies.
"why is it necessary to disregard classical physics for what it works for?"
Statistical mechanics is far, far superior than classical mechanics when it comes to basically any systems of interest. It is impossible to describe the molecules of gas in a very small region using classical mechanics, to describe heat, to describe the flow of air or water, etc. Most of classical physics requires statistical mechanics. The issue is that statistical mechanics is clearly a simplification that nobody would mistake for a description of reality. This isn't true of classical mechanics. It is no more a description of what exists than is statistical mechanics (and doesn't work as well). So when we hold onto classical mechanics or statistical mechanics, we are at best holding onto procedures that yield more or less accurate results, not descriptions of anything real.
how did we reach the conclusion that the failure of classical physics to accurately describe phenemenoa at the qauntum or cosmic level necessarily means that there are no determinisitc laws.
Classical physics fails at every level. It fails not because it doesn't yield useful results, but because it does so by requiring things that don't exist and aren't real to be treated as such. Also, in many ways quantum physics is more deterministic than quantum physics.
In terms of Physics, Science and Mechanics, we are still trying to behave like "Leplace's Demon", in the belief the causality works simply in a linear (or mechanistic) fashion.
Laplace's "intellect" fails to deal with classical physics:
"the time evolution of a many-particle system is deterministic on the microscopic level is a metaphysical belief. It cannot, even in principle be shown to be correct. It is a starting assumption on which the subsequent considerations are based, and it is not the result of scientific observations...even simple macroscopic equilibrium systems such as
gases, crystals, or liquids, cannot be fully explained in terms of their constituent particles...
"In classical mechanics, the state of a system can be represented by a point in phase space...Starting from an initial state, Newton’s laws, in the form of Hamilton’s equations, prescribe the future evolution of the system. If the state of the system is represented by a point in phase space, its time evolution is represented by a trajectory in phase space. However, this idea of a deterministic time evolution represented by a trajectory in phase space can only be upheld within the framework of classical mechanics if a point in phase space has infinite precision. If the state of a system had only a finite precision, its future time evolution would no longer be fixed by the initial state, combined with Hamilton’s equations. Instead, many different future time evolutions would be compatible with the initial state. In practice, it is impossible to know, prepare, or measure the state of a system with infinite precision. This would require a brain or another computing device that can store an infinite number of bits, and such a thing does not exist in a finite universe. Here, we see once again that the belief that classical mechanics can provide a valid microscopic description of a thermodynamic system is a metaphysical belief.
History and philosophy of science have taught us that the idealizations that are contained in the theories of physics should not be taken as a faithful and perfect reflection of reality. In classical mechanics, these idealizations include certain concepts of space and time, in addition to a deterministic worldview. The belief that classical mechanics is a faithful and perfect reflection of physical reality was shattered 100 years ago...
From a scientific point of view, we know that Newton’s (or Hamilton’s) equations of motion and the Schrödinger equation are only an approximation to reality. The fact that these two theories work so well for many applications can make us blind to the the possibility that their limited precision may have significant effects in systems that consist of macroscopic numbers of nonlinearly interacting particles. Such complex systems are therefore not simply the sum of their parts, but are governed by new laws that are not contained in a microscopic description."
Drossel, B. (2015). On the relation between the second law of thermodynamics and classical and quantum mechanics. In B. Falkenburg & M. Morrison (Eds.)
Why More Is Different (pp. 41-54). Springer.
"According to determinism, if someone (the Demon) knows the precise location and momentum of every atom in the universe, their past and future values for any given time are entailed; they can be calculated from the laws of
classical mechanics." (
Leplace's Demon)
"any Laplace's demon having all the information about the world now will be unable to predict all the future. In order to answer certain questions about the future it needs to resort occasionally to, or to consult with, a demon of a higher order in the computational hierarchy whose computational powers are beyond that of any Turing machine."
Korolev, A. V. (2007).
The limits of predictability: Indeterminism and undecidability in classical and quantum physics.
"While Laplace’s approach comes closer to the mark than does the previous one, the appeals to an ‘intelligence’ (or ‘demon’ as it is often called) and to the concept of knowledge ought to sound warning bells. Depending upon what powers we endow the demon with, we get different senses of determinism. Endow it with the powers of the latest Cray computer or even with the powers of a universal Turing machine and we get a fairly interesting sense of determinism; but we also get a sense in which it is fairly certain that the universe is ‘non-deterministic’ in that future states are not always computable from present states..."
Earman, J. (1986).
A primer on determinism (Vol. 37). Springer.
Laplacian determinism fails even in classical physics, for it doesn't account for the need for impossibly infinite precision of initial states to make the claim that it is possible to predict future states without exponential errors, or even in principle deterministic prediction.
The reason it works in physics and chemistry
It works well in chemistry. It work
ed well in physics.
[this is getting too long to reply to so here's a few points.]
And my response is getting to long, particularly as I have had to delete large portions in which I explained or presented things in too much detail. I don't mean to ignore the rest of your post, I just ask that you forgive me for addressing it later so that I can give it the consideration it is due. And thanks again for the thoughtful response!
