Do naturalists think that only microscopic physical things exist?

Question

I was reading an article on time in physics, which is meant to emerge at the macroscopic level. This is interpreted as that it does not really exist.

Is that because only microscopic physical things exist?

Answer 1

The view OP is alluding to is called mereological nihilism (mereology is a branch of metaphysics that studies relations between parts and wholes). It is the view that only "simples" (fundamental entities) exist, and composition of simples does not give rise to new objects. Applied consistently this means that, strictly speaking, not only time but chairs and tables do not exist either. Although the view is controversial some philosophers find it attractive, van Inwagen is perhaps the most prominent current defender. To deal with chairs and tables he stipulates that in colloquial contexts "there are tables" is not to be interpreted literally, instead it means "there are simples arranged tablewise". The metaphysical gain is that one does not have to come up with principled "criteria of objecthood" for arrangements of simples, which proved to be notoriously difficult to maintain (is dust bunny an object? how about dust devil? the set of all pencils on Earth?). For more see Liggins's Nihilism without Contradiction.

It is interesting that van Inwagen is not a pure nihilist, unlike for example Unger, he makes one exception for when a composite is a genuine object: "Necessarily, for any non-overlapping xs, there is an object composed of the xs iff either (i) the activities of the xs constitute a life or (ii) there is only one of the xs." In other words, we have a new, emergent object, and not just simples arranged objectwise, when said simples are engaged in a coordinated activity that amounts to producing a living being. One attraction of this view is that it gives some metaphysical substance to the idea that life is "emergent".

Among philosophers of physics, and physicists themselves, mereological nihilism can often be detected as a kind of underlying stereotype that is rarely voiced explicitly. In Everett and Structure Wallace, a well known philosopher of quantum physics, criticizes such view of emergent objects, implicit in Kent, Barrett and others, as "the fallacy of exactness":

"The objection above arises from a view implicit in much discussion of Everett-style interpretations: that certain concepts and objects in quantum mechanics must either enter the theory formally in its axiomatic structure, or be regarded as illusions... Barrett’s quote implies that we face the same dichotomy: either there is some precise truth about transtemporal identity which must be written into the basic formalism of quantum mechanics, or there are simply no facts at all about the past of a given world, or a given observer.

[...] To see why it is reasonable to reject the dichotomy of the previous section, consider that in science there are many examples of objects which are certainly real, but which are not directly represented in the axioms. A dramatic example of such an object is the tiger: tigers are unquestionably real in any reasonable sense of the word, but they are certainly not part of the basic ontology of any physical theory. A tiger, instead, is to be understood as a pattern or structure in the physical state."

Although Wallace asserts without reservations that tigers exist it is unclear that the difference with van Inwagen is more than purely verbal. van Inwagen too can say that "tigers exist" in the sense that there are elementary particles arranged tigerwise (leaving aside the being alive issue), and Wallace himself distinguishes between "basic ontology" and emergent "patterns and structures". Indeed, his arguments for admitting higher-level ontology are pragmatic rather than metaphysical:

"A more effective strategy can be found by studying the structures observable at the multi-trillion-molecule level of description of this ‘swirl of molecules’. At this level, we will observe robust — though not 100% reliable — regularities, which will give us an alternative description of the tiger in a language of cells and molecules... the language of cell biology is both explanatorily far more powerful, and practically far more useful, than the language of physics for describing tiger behaviour."

A mereological nihilist may well accept such pragmatic ontology and claim the benefit of avoiding metaphysical criteria of objecthood in favor of merely pragmatic ones. And this is what Wallace, with credit to Dennett, also suggests:"A macro-object is a pattern, and the existence of a pattern as a real thing depends on the usefulness — in particular, the explanatory power and predictive reliability — of theories which admit that pattern in their ontology."