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It seems clear from the Standard Model that all macro-objects (ie, those described by classical mechanics) are ultimately composed of up quarks, down quarks, and electrons. Further, the component structure of all macro-objects is hierarchically organized in terms of atoms --> protons,neutrons,electrons --> quarks.

My question is whether there is an analogous story for macro-events, ultimately terminating with the fundamental interactions between elementary particles. That is, are all macro-events (between macro-objects) ultimately made up of fundamental interactions? If so, is there any indication that the fundamental interactions naturally compose into a hierarchy of more complex interactions? (Macro-events seem describable in terms of electromagnetic & gravitational interactions only, since the strong and weak interactions only operate at small distances, but this involves a partition of fundamental interactions rather than a hierarchy of subevents/subinteractions.)

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  • $\begingroup$ It is in the spirit of a reductionist approach. But it is proven that "more is different". $\endgroup$ Commented Dec 15, 2021 at 17:03
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    $\begingroup$ Yes and no. Complicated macroscopic phenomena exist because the microscopic interactions exist, but they can't necessarily be described in terms of them. $\endgroup$
    – Javier
    Commented Dec 15, 2021 at 17:08

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This is a long comment:

It is simpler to examine in terms of the available physics theories, the emergent ones. Physics theories were invented in order to fit data and observations and predict new data and observations in order to be validated.

We have :

1)the standard model of particle physics

2)quantum electrodynamics

3)classical electrodynamics

4)special relativity

5)general relativity

6)classical mechanics

7)Newtonian gravity

8)thermodynamics

9)....?

In terms of your "macro" and "micro", thermodynamics is the most appropriate analogue. Thermodynamics variables emerge from classical mechanics in a strict mathematical way, it is an emergent theory with different variables and it is very successful in the domain it applies. It is a "macro" theory emergent from the theory for "micro" interactions.

It can be mathematically shown that classical fields emerge from the fields of the quantum field theory used to define "micro" interactions.

Thus the "macro" events/interactions with electricity and magnetism are emergent from the standard model . Gravity is an external force to this.

General relativity reduces to Newtonian gravity and special relativity in the appropriate phase space.

In this sense , as you also observe, the weak and strong interactions are short range, they can be important for cosmological models.In the temperatures and pressures on earth the "macro" events are emergent from the "micro" events/interactions.

The objective of current research is a "theory of everything" which will embed the existing standard model so as to be consistent with data, and include a quantized gravity .

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  • $\begingroup$ Is the interaction between a proton and an electron, say in a hydrogen atom, considered to be a complex or a fundamental interaction? It would seem the underlying electromagnetic interaction is between the 3 quarks and the electron, making the proton-electron interaction complex. Does this sort of difference between fundamental and complex interactions make any sense? $\endgroup$
    – davypough
    Commented Dec 16, 2021 at 18:31
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Probably yes, for example any contact force is caused due to and electron emitting a photon to another electron causing a force that repels the electron. However, there is no proof or a definite answer that tells us it is always possible, but it seems intuitive that it is possible.

This is what a theory of everything tries to achieve, however our best approximation for now is the standard model.

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