What makes an observation an observation?

“What Is an ‘observer’, what is a ‘measurement’?”

The notions of “observer” and “measurement” are taken as primitive, the very starting point of the theory. This is an unsettling situation! Shouldn’t physics be talking about what is before it starts talking about what will be seen and who will see it?¹

Is reality created through observation?

There is a quote, popularly but unverifiedly attributed to Einstein, that illustrates the “problem”. It reflects a naive disbelief in the indeterminism of quantum mechanics, in the dualistic superposition:

“Do you really believe the moon only exists when you look at it?”

This “argument” about the moon oversimplifies the construct of quantum mechanics and can be refuted with some considerations, as John Bell also expressed. Of course, the moon does not cease to exist simply because an individual is not observing it. It is important to clarify what the words “measurement” or “observation” actually mean. To quote Bell in his own words:

What exactly qualifies some physical systems to play the role of ‘measurer’? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system … with a PhD? If the theory is to apply to anything but highly idealised laboratory operations, are we not obliged to admit that more or less ‘measurement-like’ processes are going on more or less all the time, more or less everywhere? 
– John Bell, 1990

Following Bell’s argumentation, the moon should exist as soon as it is “measured,” which in this context means that it interacts in some way with another (physical) system. Its existence would be justified solely by the fact that the moon has effects on the Earth’s tidal system, thereby exerting both direct and indirect influences on countless processes of flora and fauna.

A measurement qualifies not only as a visual observation (interpretation of photons on the retina) by a human individual. Instead, any type of interaction between two physical systems could be considered sufficient to collapse a wave function and create reality. This applies equally to inanimate objects as it does to virtually any type of living being that can perceive, register, or even interpret stimuli (vibrations/waves). The extent to which this constitutes an “objective reality” i.e., matches the reality of other individuals, is a matter of debate among experts.
The thought experiment by Eugene Wigner (Wigner’s friend) addresses precisely this question of what reality might look like in which the objective realities of two individuals differ. Recent studies contradict each other and arrive at different conclusions, partly because they are based on different fundamental assumptions of quantum mechanics (Allard Guérin et al., 2021; Bong et al., 2020; Wigner, 1963).

For physicists are indeed in agreement today that our world is built on quantum mechanics (Quantum fundamentalism), yet there is disagreement about what this ultimately means for our world – and our concept of reality.
(Smolin, 2019; wZinkernagel, 2016a)

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Footnotes

1. Fuchs (2010) QBism - the Perimeter of Quantum Bayesianism ↩