Schools of thought in quantum physics

“You agree, you agree”, launches the chairman of the session to cut short an exchange between Antoine Tilloy and his detractor during the Conference on the foundations of physics which was held in Paris from October 28 to 30. The professor at Mines ParisTech had the boldness to demonstrate an equivalence between two competing theories. The discussion will continue in the gardens. Later, another participant almost apologizes, concluding his intervention: “No, no, I’m not defending one theory over another. “ This is how it has been in quantum land for almost a hundred years. Everyone agrees on the equations, but almost no one on the interpretations to be given.

“For a century, each experiment has only confirmed that the theory works very well, summarizes Carlo Rovelli, professor of physics at Aix-Marseille University. The problem is, she does it in a weird way. We only have information when we look at nature with measuring instruments, but quantum mechanics does not tell us what is happening. “
The theory indeed divides the world in two, by creating a separate category in nature, that of the observer. If it is not there, the particles evolve according to the laws of the founding fathers, with this propensity to be described by probabilities. But if he points the tip of his detector, the particles adopt a very precise configuration, leaving their previous vagueness. As if nature only exists because we look at it. Which made Einstein say: “I like to think the Moon is still there, even though I’m not looking at it. “” It is all the same very unsatisfying not to have a theory which says what the world is, and which creates a particular category of objects, the detectors, which are nevertheless in this world “, sums up Antoine Tilloy.

“Things matter less than the relationships between these things. »Alexei Grinbaum, researcher at CEA and co-organizer of the Paris conference

To get out of this uncomfortable situation, five main options exist: “We don’t care”, “we modify the theory”, “we complete it”, “we believe in it”, “we overthrow”, could we? to summarize. The “who cares” option, probably the majority, consists of adapting to the situation since, in practice, this does not prevent us from experimenting and finding the right results. The option “we modify” adds a mechanism which allows to describe the effect of the measure or to spontaneously remove the famous superimpositions. But many seek experimental evidence without finding it. The “complete” think that there are hidden variables that would explain what is happening. The “we believe in it” take the existence of the wave function literally and see life as a superposition of several possible worlds, each living a different story. The “we overthrow” are ready to abandon well-anchored ideas.

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