Einstein’s paradox, Podolsky, Rose – 03/05/2024 – Marcelo Viana

In 1935, Albert Einstein, Boris Podolsky and Nathan Rose published an article in the scientific journal Physical Review entitled “Can the description of physical reality given by quantum mechanics be considered complete?”.

The uncertainty principle, formulated eight years earlier by Werner Heisenberg, implies that the position and momentum (mass x velocity) of a subatomic particle can never be simultaneously determined with precision: any experiment to measure either of these values ​​perturbs the particle, making the value of the other inaccurate.

The prevailing interpretation at the time, led by Niels Bohr, was that these quantities have no physical meaning in themselves: it would be the experiment that, when measuring one of them, gives it physical existence, to the detriment of the other.

Einstein, Podolsky and Rose rejected this idea that physical reality is determined by the observer, stating that the problem would be that quantum mechanics would not cover all of reality: there would be “hidden variables” not included in the theory that would explain the behavior of the nature of more reasonable way.

To prove their thesis, they proposed the following thought experiment: Consider two particles, A and B, that interact for a brief moment and then move apart. They showed that by measuring the position of A it is possible to determine the position of B and, analogously, by measuring the momentum of A we can determine the momentum of B, without doing any experiment with B, even if the two particles are millions of light years away!

Since information cannot be transmitted instantly from A to B, as nothing moves faster than light, the position and momentum values ​​of B cannot be the result of measurement at A, they have to have real existence.

Bohr responded in an article with the same title, published in the same year in the same periodical. His arguments convinced experts that Einstein, Podolsky, and Rose’s argument was not the deathblow to quantum mechanics that the three authors intended. But he did not satisfactorily address the most important question for Einstein: how can we explain that what we do with A here determines the reality of B elsewhere, in a “spooky action at a distance”?

Physicists had just discovered the idea of ​​entanglement, and the universe was getting really weird. In the end, the dispute between Bohr and Einstein would be resolved by a mathematical theorem. But my space for today is over.

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