TL;DR: Perspective-based reasoning would suggest interpretations in the spirit of Copenhagen to be most likely correct. Among which Relational-Quantum Mechanics (RQM) is exceptionally compatible. The advantage of perspective-based reasoning is that it easily explains troubling concepts such as “observer” and “measurement”. According to which “It’s not a bug, it’s a feature”.
In sections 8 and 9 I discussed why perspective-based reasoning should reject the Many-World Interpretation and be pessimistic about Bohemian mechanics and GRW theory. It is time to consider how perspective-based reasoning would interpret quantum mechanics.
It might be helpful to keep the interpretive challenges in mind while assessing this interpretation. I find the troubling notions such as “observer”, “measurement”, and non-locality fits extremely well within a perspective-based framework. It goes as follows:
- As usual, it starts with a given perspective and its center.
- From here, any information or knowledge about the world is based on actions upon the perspective center.
- These (inter)actions are the fundamental subject matter of quantum mechanics. The natures and properties of the interactions’ counterparties are deduced based on them.
- The actions are empirically indeterministic.
- Quantum mechanics describes the behavior of these actions upon the perspective center. We can, for example, use it to predict future actions based on past ones, subject to the inherent uncertainty. It also helps to deduce the nature of the interactions’ counterparties, i.e. describe the external environment.
That is it. To clarify it further some foreseeable questions are answered below.
What qualifies as a perspective center?
The perspective center is a reasoning starting point. It is postulated (or primitively defined), not derived. Any physical systems can be proposed as the perspective center. E.g. an electron, a Geiger counter, a person, etc.
What is an “observer” in orthodox interpretations?
The “observer” is the perspective center. Because the subject matter is actions upon it, quantum mechanics do not apply to the observer itself. Therefore it cannot be explained by reductionism using quantum mechanics. Note this does not mean whatever the perspective center is, say a Geiger counter, is physically unanalyzable. It just means the analysis cannot be performed from its own perspective. From a different perspective, e.g. when “the observer” is a person, it can be perfectly explained by quantum mechanics.
What is a “measurement” why does it cause the wave function to collapse?
A measurement is just an action upon the perspective center. Due to their stochastic nature, they cannot be perfectly predicted by quantum mechanics, only probabilistically. It is why the wavefunction is updated when an interaction happens.
Is the wave function epistemic of ontic?
Epistemic.
Is this an instrumental view of quantum mechanics?
It may seem so. But I would argue such a label is not necessary. Many think the role of physics should be, in some metaphysical sense, describe the world instead of merely predict experiment outcomes. That is not in conflict with this interpretation per se. However, perspective-based reasoning suggests a description must originate from a certain viewpoint. It cannot be an aperspectival presentation of reality by an abstract “view from nowhere”. Scientific descriptions should be based on evidence. And the fundamental evidence from any given perspective is actions upon it. e.g. physical systems do not affect these actions cannot be described from the given perspective. In this sense, describing the world and explaining/predicting interactions does not conflict with each other.
How does it explain quantum non-locality?
Easy, quantum mechanics is local. Any notion of non-locality is either caused by not taking a consistent perspective or aperspectival reasoning.
In the famous EPR paradox, the suggested non-locality manifests itself when Alice measures the spin of the entangled electron and gets a result of say, up. Then instantaneously Bob would find his election spins down, no matter the distance separating the two. However, one measurement is an action upon Alice and the other upon Bob. The non-locality cannot be described from either one’s perspective. A perspective switch from Alice to Bob is needed for its formulation. Alternatively, the non-locality can be expressed from a god’s eye view. However, in this description, no action upon the imaginary perspective center is ever needed. It directly presents what happens to Alice and Bob with “a view from nowhere”. Both the perspective switch and the omniscience of god’s eye view traverse distance instantly. The suggested non-locality is caused by them, both incompatible with the perspective-based interpretation.
So quantum mechanics must be used from a consistent perspective?
Yes. It is the common requirement for any perspective-based reasoning. That means conclusions drawn using quantum physics from one perspective cannot be used by another perspective.
One notable paper is Frauchiger & Renner’s Quantum theory cannot consistently describe the use of itself. Which states there are three assumptions (Q, C, S) that cannot be simultaneously true for any interpretation. The requirement of a consistent perspective is rejecting assumption (C). In my opinion, assumption (C) in the paper should be stated in terms of perspectives instead of agents. i.e. “conclusion drawn from one perspective can be used by another perspective.” In doing so, Bohmian mechanics would not satisfy this assumption even though different agents can use each other’s conclusions. Because they all reason from a god’s eye perspective. So they would not conclude Bohmian mechanics have to violate assumption (Q), universality. Which led to the rebuttal by Lazarovici & Hubert in How Quantum Mechanics can consistently describe the use of itself.
Why classical physics do not need to consider perspectives?
Because macroscopic objects are massive. They are almost always interacting with their environment. So they are constantly affecting actions upon the center from any practical perspective. Therefore object permanence is a good approximation no matter which perspective one chooses to take. In such cases reasoning with “a view from nowhere” would not cause any problem.
It is analogous to the idea of absolute space and time in classical physics. It is a good approximation when the relative motions are low speed. If relativity can be regarded as a theory about the behavior of spacetime from any given perspective, then quantum mechanics can be regarded as a theory about the behavior of interactions upon any given perspective. Both help to describe the world, just not in the manner of an aperspectival absolute reality.
So which interpretations are compatible with perspective-based reasoning?
Copenhagen based interpretations. Among which Relational Quantum Mechanics (RQM) is the closest. It also proposed interactions to be the subject matter of physics and “observer” can be any physical system. However, it does not start with perspectives’ fundamental importance. So sometimes it studies the interactions from a god’s eye view, which causes it to confirm quantum nonlocality.