(This page can be read alone without going through previous sections. The focus here is perspective-based reasoning in quantum interpretations rather than anthropic reasoning)
(Edit 2022/06/09, see An Alternative Interpretation of Physics for the position of perspective-based reasoning regarding quantum mechanics.)
Perspectives as Fundamentals
Thomas Nagel suggests we come to the notion of objectivity through the following steps[1]:
- Realize (or postulate) that my perceptions are due to the actions of things upon me, though their effect on me.
- Realize (or postulate) the same property that caused actions upon me can also lead to actions on other things.
- Realize (or postulate) the property can exist without causing any action at all, which leads to our conception of a “true nature”, independent of any perspective.
Thomas Nagel calls this “the view from nowhere”, Bernard Williams the “absolute conception”. It represents our ordinary understanding of reality which science should strive to describe.
I think maybe Step 3 is one step too far. Step 1 can be regarded as the realization that I am experiencing the world from a given perspective. Step 2 can be seen as the realization that my perspective is just one of many, that it is not particularly special. Both steps put perspectives in a fundamental position. Then Step 3 suggesting objectivity being perspective-independent seems to be quite a jump.
By rejecting that last postulate, physical properties are no longer fundamentals but derived from actions upon a perspective center. The reality, instead of an absolute conception, needs to be described from some given perspective. Objectivity property is not perspective-independent but rather perspective-invariant. It refers to qualities, methods, and rationales that remains true with perspective changes. I call this idea Perspective-Based Reasoning (PBR).
PBR and Quantum Interpretation
PBR explains troubling concepts in the Copenhagen Interpretation including the “observer”, “measurements”, and quantum nonlocality. It can be summarized as the following:
- 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 actions are the fundamental subject matter. The natures and properties of the actions’ counterparties (other objects) are inferred from them.
- The actions are empirically discrete and indeterministic.
- Quantum mechanics describes the behavior of these actions. We can, for example, use it to predict future actions based on past ones, or give a description of its counterparties.
What qualifies as a perspective center? The perspective center is a logical starting point. It is either primitively identified (in the case of our natural first-person perspective) or postulated (when we choose to reason from other thing’s perspective). It is never derived. In principle, any physical system can be proposed as the perspective center E.g. an electron, a Geiger counter, a person, etc.
What is an “observer” in the Copenhagen interpretation? The “observer” is the perspective center. Since the subject matter is actions upon it, quantum mechanics do not describe the observer itself. Therefore the observer cannot be explained by reductionism using quantum mechanics. This does not mean whatever the perspective center is, say a Geiger counter, is physically unanalyzable. It only 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”? Measurement is an action upon the perspective center. Due to their stochastic nature, they cannot be perfectly predicted by quantum mechanics, only probabilistically using the Born rule. It is why the wavefunction is updated when an action happens.
How does it explain quantum non-locality? It interprets quantum mechanics as local. Any notion of non-locality is either caused by not taking a consistent perspective or aperspectival (view from nowhere) reasoning. In the EPR paradox, the supposed non-locality manifests itself when Alice measures the spin of the entangled particle. Bob would instantaneously have a confirmed measurement outcome, no matter the distance separating the two. However, one is an action upon Alice and the other upon Bob. The non-locality is not present from either one’s perspective.
The criticism of CI being utterly instrumental. This criticism is basing on the notion that physics should be describing reality instead of merely predicting outcomes. Yet if reality cannot be described by “a view from nowhere”, if it has to be described from a given perspective as suggested by PBR, actions upon the perspective center become the basis of such descriptions. Predicting these actions are describing the external reality.
Reasons to Prefer This Idea
Discarding the aperspectival absolute conception has past success. Relativity rejects absolute space and time. It treats spacetime as perspective-dependent. Nonetheless, we still regard relativity as objective because the theory can be applied to different perspectives while remains accurate. It is conceptually similar to the perspective-based interpretation. Even though the description of reality is perspective-dependent, because the method outlined by quantum mechanics remains accurate from different perspectives, it is still an objective (perspective-invariant) theory.
It is worth noting the absolute conception is a good approximation for the perspective-based interpretation in classical settings. Actions caused by a microscopic entity are few and far between. For any given moment, it might be acting upon a certain object while not affecting another. The effect of perspective choice is prominent as they would give significantly different descriptions. In contrast, a macroscopic object is constantly interacting with its environment. Any practical perspective choice would continually experience numerous actions affected by the macroscopic object. The limiting factor of describing these objects is no longer the lack of actions but the ability to perceive and process them. As such, with all available actions considered, different perspectives would give nearly identical descriptions. One can safely use descriptions from other perspectives if it does not wish to capture and analyze the actions upon itself. The absolute, perspective-independent objectivity is an energy-saving shortcut that works well in our daily scales.
Another reason to prefer a perspective-based interpretation is its parsimoniousness. It has been suggested that, in terms of basic ingredients, the Many-Worlds Interpretation (MWI) is as simple as it gets. There are no additional hidden variables nor ad hoc collapse mechanisms. So the MWI should be considered the “default” interpretation unless there is new physical evidence suggesting otherwise. The same argument can be made to support the perspective-based interpretation. It actually involves even fewer assumptions than the MWI because it rejects the commonly accepted postulate in Step 3 above. The same rationale should instead conclude perspective-based reasoning as the “default” interpretation.
The last reason to prefer this interpretation is quite specific. I argue perspective-based reasoning resolves anthropic paradoxes such as the sleeping beauty problem, the doomsday argument, and the presumptuous philosopher, etc. (That’s what this website is about after all). PBR, an independently motivated idea, happens to explain the interpretive challenges of quantum mechanics is just an additional piece of supporting evidence.
Bottomline
We should be more confident about the Copenhagen Interpretation and its variants such as Relational Quantum Mechanics and QBism. On the other hand, we should be more skeptical towards the MWI, collapse theories such as GRW, and hidden variable theories such as Bohmian Mechanics.
[1] Thomas Nagel put the realization that properties can exist without causing action as the second part of Step 2. So in his original formulation Step 3 only involves the realization of the absolute conception. I changed the grouping for ease of expression.