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If metaphysical naturalism is true, would that mean that Physics is the ultimate discipline that can sufficiently explain everything, and that all other disciplines, including Chemistry, Biology, Cosmology, Geology, Neuroscience, Psychology, Sociology, etc., are just using convenient high-level abstractions/models/approximations that can be traced back and reduced to low-level primitives studied by Physics?

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  • Where does astrophysics fit on such a list? If there are things like initial or accelerated cosmological expansion that depend on enormous amounts of primitives acting in concert, are the laws for those enormous masses over-and-above the primitives or somehow encoded into each primitive from the mass? Jun 29, 2023 at 18:45
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    A computer game can fully be reduced to 1s and 0s and simple arithmetic operations on them. But reducing it down that far would make it rather difficult to understand the behaviour of the bandits who are shooting at you in a detailed 3D world.
    – NotThatGuy
    Jun 30, 2023 at 12:11
  • @NotThatGuy That's more or less what I tried to say when I said "convenient high-level abstractions".
    – Mark
    Jun 30, 2023 at 13:56
  • The "low-level primitives studied by Physics" may be low-level but they are not understood to the bottom and are not fully resolved. They are systematic deductions based on measurements, so the actuality of those phenomena (not 'primitives') is based on the deductive skill of observers and their instituted knowledge. The conditioned phenomena are synthetic, intellectual, theoretical inventions, so metaphysical naturalism is on a sticky wicket. Jul 1, 2023 at 17:29

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Yes*

According to metaphysical naturalism, all matter and their interactions are ultimately a result of the interactions of their material parts (down to atomic particles and such).

Even for most who reject metaphysical naturalism, they still accept to a large degree the idea of that matter can be broken down to its composite physical parts (and specifically down to atomic particles).

For example, it's commonly accepted that the sensation of pain can be reduced to sensory receptors sending signals to our brains via nerve fibres (and then some stuff happening in the brain). Viruses and their interaction with various cells in the body causes disease. We can further break down the physical makeup of these things. It's commonly accepted that matter ultimately consists of atomic particles. When we "touch" something, this is actually electrons repelling one another. And so on.

Where non-naturalists deviate tends to be when it comes to the brain/consciousness and the origins of the universe. I haven't heard notable rejections of the idea that matter consists of atomic particles.


That said, when each person consists of around 7*1027 atoms, you can't plausibly model human-human interactions on an atomic level. The abstractions we use are a little more than convenient, they're necessary, for us to be able to say anything meaningful about the interactions of complex physical objects.

We could say there is weak emergence, which means more complex behaviours can emerge when combining simpler parts, but this can ultimately still be broken down into the component parts.

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  • I tend to agree with this view. What are your thoughts on "emergence", posed by CriglCragl's answer?
    – Mark
    Jun 30, 2023 at 15:21
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    @Mark I'd hold to weak emergence, which means that more complex behaviours can emerge, but these can ultimately still be broken down into component parts.
    – NotThatGuy
    Jun 30, 2023 at 15:34
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No, because of emergence. Saying other sciences are reducible to physics, is like saying literature is reducible to the alphabet.

What did emerge, Earth biology, didn't have to be that way, & the specific nature of a human in a society making sense of it's subjectivity, cannot meaningfully be predicted from physics. See: Is it the job of physics to explain consciousness?

This is also relevant: What are the missing pieces that prevents us from deriving the laws of chemistry from physics?

I would describe the process not as reduction of biology and neurology to physics, but as about getting our domains of concern to interface with a common language where they overlap, discussed here: Is the idea that "Everything is energy" even coherent?

In this answer are details of David Deutsch's attempt to work out the minimum set of domains we need, to form a kind of 'meaning-cosmology' that can account for where we find ourselves: Could a new method of understanding the universe be created? The TLDR is that as well as physics (specifically Many Worlds QM, for him), we need epistemology, evolution, and information theory. He has been working with others on Universal Constructor Theory, which aims to make the emergence of life and information more explicable.

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  • “What did emerge, Earth biology, didn't have to be that way” how do you know? How do you know that it could have been any other way? Jun 30, 2023 at 2:18
  • @thinkingman: Because biology is enourmously, vastly complex: gaelmcgill.artstation.com/projects/Pm0JL1 The scale of contingency is gigantic.
    – CriglCragl
    Jun 30, 2023 at 7:47
  • @CriglCragl Any thoughts on NotThatGuy's answer.
    – Mark
    Jun 30, 2023 at 15:17
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    @Corbin: Knowing an alphabet is not enough to make sense of a work of literature. Just because the work is constituted of letters, does not make it reducible to them. And that is ghe question here.
    – CriglCragl
    Jun 30, 2023 at 16:04
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    @Mark: "sufficiently explain" Everything comes down to how you define that. In the linked answer above about energy, I make the case we aim to have an interface between things like consciousness & physics, but physics is not enough to explain consciousness - because people & chairs are not objects in fundamental physics, they belong to a different mode of explanation. You could use physics to predict what someone will do, say, but not why they are doing something, that belongs in a different explanatory layer of composite conceptual references
    – CriglCragl
    Jun 30, 2023 at 16:11
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Under metaphysical naturalism, does everything boil down to Physics?

TLDR

Depending on one's definition 'boil down', not yes, not no, but partially so!

Explanation

You have one answer that says other fields like chemistry reduce to physics, and one that says emergence prevents that. So, the middle ground is that chemistry partially reduces to physics. In fact, there's a discipline called physical chemistry that has a foot in both domains, which helps to highlight what is in chemistry that is not in physics. Reductions also needn't be strictly hierarchical. Biophysics is a topic that looks at biological principles rooted in physics and isn't as concerned with reduction to biochemistry. What might be helpful to understand is that when we talk about reductionism in a domain, for instance, reductionism in biology (SEP), we can talk about both theoretical and explanatory reduction.

In psychology, we have the experience of heat. Our minds are capable of detecting heat. What is heat? A magical force? Nope. Heat is the psychological manifestation of the biological perception of a concept in thermodynamics, that of statistical kinetic energy of molecules. The famous philosopher Quine talked about 'webs of belief' which is a phrase that invokes the concept of confirmation holism. From WP:

In philosophy of science, confirmation holism, also called epistemological holism, is the view that no individual statement can be confirmed or disconfirmed by an empirical test, but rather that only a set of statements (a whole theory) can be so. It is attributed to Willard Van Orman Quine who motivated his holism through extending Pierre Duhem's problem of underdetermination in physical theory to all knowledge claims.

Thus, it might be best to understand the ambiguous phrase "everything boils down to physics" as the implication that a highly complex set of beliefs and knowledge does seem to have a direction that links together a web of belief such that certain ideas reduce as explanations and theories to others. The mind is studied by psychological principles which are rooted in the biology of the brain which is built out of chemicals which are understood in terms of atoms, and so on. Is pain an atom? No. So pain doesn't reduce to an atom, but through a series of claims, it can be shown that pain can be explained in terms of atoms ultimately.

If you want a great introduction to this sort of topic, consider reading Consilience: The Unity of Knowledge by Edward O. Wilson. From WP:

Consilience: The Unity of Knowledge is a 1998 book by the biologist E. O. Wilson, in which the author discusses methods that have been used to unite the sciences and might in the future unite them with the humanities... Wilson uses the term consilience to describe the synthesis of knowledge from different specialized fields of human endeavor.

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