In the probabilistic Bohr/Heisenberg Copenhagen Interpretation CI of quantum mechanics from 1930s the word measurement plays a key role, because it is the measurement which decides some actuality out of many possibilities, like the observation of a dead or alive Schrödinger Cat upon opening of the Box somehow deciding an actuality from a possibility of a both alive and dead cat before the opening. The key role of measurement was expressed as follows:
- Bohr: Nothing exists until it is measured. (The Moon does not exist if you are not looking at it)
- Heisenberg: The purpose of quantum mechanics is to predict the outcome of experiments/measurements.
- Bohr: It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.
John Bell (1990) expresses an opposite view in Against Measurement:
- When I say that the word "measurement" is worse than the others, I have in mind its use in the fundamental interpretative rules of quantum mechanics.
- It would seem that the theory is exclusively concerned about 'results of measurement', and has nothing to say about anything else.
- However, the idea that quantum mechanics, our most fundamental physical theory, is exclusively even about the results o f experiments would remain disappointing.
The contradiction between Measurement and Against Measurement has not been resolved. Physicists no longer want to talk about or express belief in CI, like Bell, but have nothing better to offer as concerns the foundations of quantum mechanics, which is left to philosophers pf physics outside physics departments in endless scholastic disputes about the meaning of words without physics as Everett's Many-Worlds and Bohm's Guiding Waves. I wonder what the situation will be 100 years from now.
The lack of progress as concerns the foundations of quantum mechanics is even more paradoxical as the we now pass inte the Second Quantum Revolution heroically pursued by EU in the grand project The Future is Quantum searching new revolutionary applications of the very foundations of quantum mechanics. If the foundations are not well understood, how can they be turned into wonders of quantum computing?
Recall the previous post with a measurement "click" identified as a photon, like the click of passenger counter making the passenger come alive as being counted:
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