"The history of philosophy provides many responses: atoms and void, ONE, numbers, four elements, geometry, substrata, mind-stuff (truly the funda-mentalists!), states-of-affairs, etc. Physics often informs (and perhaps corrects) these fundamental theories, for naturalists at least; but physics in this case is not considered to provide the most fundamental description of reality: it leaves too much out." Whereas all the responses given by philosophy are invalid, physics provides fundamental descriptions of reality. And why has philosophy failed? Feynman gives some thoughts about this: "what is an object? Philosophers are always saying, "Well, just take a chair for example." The moment they say that, you know that they do not know what they are talking about any more."
Of course, there are cosmologists sharing similar levels of ignorance about the nature of reality; Lawrence Krauss is a notable example. David Albert doesn't show a much better level of understanding either; his review of Krauss' book is an example of it.
The idea that nature has infinite layers is not a scientific notion of reality.
"A philosopher might think, "why spend all that money on particle accelerators when you could pay just me to think, with no equipment other than my brain, to find out what is truly the fundamental structure of reality?"", because the money spend on the philosopher would be lost money, as the history of philosophy shows. One cannot find the fundamental structure of reality without first describing reality, and philosophers fail at this, as Feynman mentioned.
"It is a widespread assumption that scientific progress means finding more basic constituents." Not even close. There are lots of progress made on studying new properties of existing constituents or new ways of combining existing constituents. There are even new scientific disciplines built around such matters! Stating there is no scientific progress if no new fundamental particle has been discovered is ab incorrect conception of science, even if we reduce science to mean only physics.
"physics (elementary particle physics, or something like it) should (and can) furnish a complete account of the world: any and all things should be traceable back to the fundamental layer". This is the older reductionist picture, which has been disproved time ago. This picture doesn't present science not even physics alone.
"The idea is, of course, that the compositional structure of physical reality is something like stacking blocks of Lego to produce a bigger, more complicated object possessing different properties to those found at the level of individual Legos. But we aren't supposed to ask what the blocks are made of, since we would have to then ask the question again, possibly ad infinitum. The fundamentalist intuition is that there must be some end to the questioning." This is not about intuition; it is about being practical, a concept is often missing in the philosophers toolkit.
"So why believe that there is a fundamental level? Why not an infinite descending hierarchy of levels?" One can imagine the existence of infinite layers of existence, an infinite sequence of turtles --paraphrasing that old lady--, but those infinite layers cannot be detected or refuted by us, finite beings living in a finite place. So if one cannot confirm the existence of an infinite layers of existence, debating about them is a waste of time, and the best we (scientists) can do is to propose some fundamental layer as hypothesis and see if we can disprove that hypothesis by founding data that requires a more fundamental layer of existence. What if some day we find some layer that explains all that we know up to that moment? Would we take that layer as truly fundamental or would we play philosophers' games and imagine more turtles?
The "atomic principle" and the "Parmenidean principle" correspond to the synthetic and analytic components of science, but in science we are fully aware that the intermediate states are so fully real as the extremes. We scientists must consider elementary particles as fundamental entities, but we don't consider nuclei, atoms, molecules, cells, planets or any other combination of particles as "mere 'appearance'".
"Fundamental" refers to the foundations of something, or the basis on which other things rest (fundare= 'to found'). Hence it often implies that something is being generated (built) from it, or being made to rest on it (i.e. reduced to it). There exists a dependence relation between less and more fundamental things that define 'levels' of reality." There is only one level of reality. Elementary particles and clusters of macromolecules represent one and the same reality, not two different 'levels'. We can represent this unity using equations as AB=A+B.
"What can be reduced (what has parts) is not fundamental according to this mindset. [...] If something can be reduced, then it is often asserted that that thing does not really exist (mere appearance versus reality)---less derogatory is to say that it is emergent, or scale-dependent". Same missunderstanding again. As stated above composite objects really exist. Reality is unique, there is no scale-dependent reality. The Milky Way, at the cosmological level of sizes, is so real as H2O at the atomic-molecular level. And the concept of emergence is better left to characterize properties of the composite object that don't exist at the components level.
"thus, we might say: `I believe that Max Tegmark is really a bunch of excitations of quantum fields'; or, if we have read Tegmark's book, `I believe that Max Tegmark is really a mathematical sub-structure in a multiverse of such structures.' It is rare these days to find people espousing this radical eliminitivism". Maybe it is rare because people today is better informed and knows that such claims are incorrect.
"The mereological account, of reduction to simples, is already in trouble in standard quantum field theory in which there is, strictly speaking, no basic, elementary, eternally persisting, concrete, physical stuff" as such." At contrary, the basic elementary physical stuff are elementary particles and, so far as we know, everything in the universe is made of them:
"The theories and discoveries of thousands of physicists since the 1930s have resulted in a remarkable insight into the fundamental structure of matter: everything in the universe is found to be made from a few basic building blocks called fundamental particles, governed by four fundamental forces."
https://home.cern/about/physics/standard-model
Dirac didn't discover antimatter. In fact, he believed the mysterious positive charge particle appearing in his flawed equation would be the proton.
"the fact that quantum field theory makes any particle a complex dynamical system (of virtual particles which comprise the `physical' particle) implies that A-TOMs are dead". No, he confounds reality with model. Quantum field theory is only an approximated description of reality built around the concept of bare particle. It is only after a renormalization procedure that those unphysical bare particles are surrounded by clouds of virtual particles to generate real particles. The real particles that we measure in experiments aren't the bare particles that one finds in the Lagrangians of quantum field theory. One can formulate the world directly in terms of real particles, one simply abandons quantum field theory by direct-particle interaction theories.
"Nobel prizes are routinely awarded for finding the smaller, simpler constituents of complex systems." Only if one ignores the history of Nobel Prizes.
"Of course, it doesn't show that reduction to more basic elements and laws is impossible, only that generation of complexity from these basic parts is often not possible. This has been taken to indicate that a theory of everything based on these simples and their laws alone would not enable us to `deduce the world.'" That is not the content of Anderson paper. The problem is not computational. The problem is not it is difficult to extract the properties of composite objects from properties of components. The main remark in Anderson's paper is on the existence of emergent properties that don't exist at the component level. So a full understanding/study of components cannot provide a description of the composite object.
Anderson's critique is against classic reductionism, understood as the study of components only, not about the existence of fundamental level of description with entities and associated laws. The reduced theory continues being less fundamental, simply the old reductionist attitude has to be replaced by modern integrationism.
"Hence, such systems are irreducible in the sense that one cannot find a unique micro-grounding which would imply the properties and laws of the macro-level". But this irreducibility is computational rather than ontological. Twenty years ago we could study certain complex systems at the molecular level, because computers lacked the needed performance. Today we can run simulations of those systems. The same happens with systems are too complex for current computers. In 50 years we can run certain simulations thoday we can only dream.
"Basically, the ultimate approach is grounded in mathematical laws that aim to represent a unique system (some basic field or particle): they are specific and are usually based on symmetry principles (with elementarity defined in terms of invariances). In contrast, complex systems, inasmuch as they admit a representation in terms of exact mathematical laws at all, possess much universality or what philosophers call `multiple realizability.'" Again this confounds reality with specific models. Quantum field theory is not an ultimate approach, but a model used in certain situations. There is no objective reason to believe that different complexity layers of description require qualitatively different ways of description. A simple example is classical chaos. The same equations, the same 'mathematical' laws, that describe the simple behavior of an harmonic oscillator, describe the very complex behavior of chaotic systems.
"This indicates that the critical exponents are independent of the microscopic details of the matter, so that the systems occupy the same universality class. Systems at critical points obey conformal symmetry: one can rescale in various ways and the system looks identical
(i.e. it is a fractal). One can adopt the view that it is such symmetry that is doing the work in generating the properties of critical systems, just as it is the symmetries (e.g. U(1), SU(2), and SU(3)) that generate the physics of elementary particles." Those critical exponents are just a consequence of the microscopic details of the matter. What happens is that the system evolves towards a final state where correlations are minimized and different systems satisfy the same symmetries, the symmetries of the state, but the correlations continue here, the physics has not vanished, and the system can evolve to another less-symmetric state if properly perturbed.
"The approach was developed to understand hadrons (which quantum field theory was then struggling with), and supposed that there was an infinite spectrum of particles (laid along a `Regge trajectory,' with ever rising masses), but, crucially, no one was more fundamental than any other,
thus bypassing a standard particle physicist's question: which particles are fundamental and which are composite? One could in fact view the particles as either fundamental (part of a composite system) or composite themselves." And another confusion between model and reality. The S-matrix approach only provides an approximated description of scattering processes. It is this approximated character which does that different Hamiltonians can be equivalent from the point of view of S-matrix theory. By inspecting only the S-matrix we couldn't differentiate certain fundamental from certain non-fundamental entities, which we could differentiate at the Hamiltonian level directly.
Attempts to geometrize physics (e.g. John Wheeler's geometrodynamics, or even Einstein's unified field theory) have failed miserably. Feynman devotes part of his lectures to explain the differences between physics and geometry. Not only that, but Feynman and other demonstrated how one can formulate gravity non-geometrically.
"Bohm had personal reasons for following this `wholeness' view, since he believed that how we conceptualise the fundamental nature of reality has a bearing on how we relate to the world and one another. Viewing the world as so many independent, separate entities leads to an independent, separate existence, with all that entails in terms of divisions. Adopting a mentality of one, unified system eliminates divisions and establishes us as part of the same whole". This is misleading, the atomic-molecular picture of the world, the 'reductionist' approach do not see reality as a collection of independent, separate entities. Universe is not made of a collection of independent particles. So this 'wholeness' view, is unneeded.