The essence of the experiment is that a beam of light is directed onto an opaque screen-screen with two parallel slots, behind which there is another, projection screen. The feature of the slots is that their width is approximately equal to the wavelength of the emitted light. It would be logical to assume that photons should pass through the gaps, creating two parallel streaks of light on the rear screen. But instead, light propagates in the form of bands in which sections of light and darkness alternate, that is, light behaves like a wave. This phenomenon is called “interference, ” and it was his demonstration by Thomas Young that proved the validity of the wave theory. Rethinking this experiment could combine quantum mechanics with another pillar of theoretical physics, Einstein's general theory of relativity, a challenge that still remains unsolvable in practice.

In order to calculate the probability of a photon appearing in one place or another on the screen, physicists use a principle called the Bourne rule. However, there is no reason for this - the experiment always goes the same way, but no one knows why. Some enthusiasts tried to explain this phenomenon from the interpretation of the quantum-mechanical theory of "multiple worlds", in which it is assumed that all possible states of a quantum system can exist in parallel universes, but these attempts did not lead to anything.

This circumstance allows us to use the Born rule as evidence of the inconsistencies in the quantum theory. In order to combine quantum mechanics, which operates on a narrow time scale of the Universe, and the general theory of relativity, which works with huge intervals of time, one of the theories must give way. If the Bourne rule is incorrect, then this will be the first step to the study of quantum gravity. “If the Bourne rule is violated, the fundamental axiom of quantum mechanics will be violated, and we will find out where to find the answer to theories of quantum gravity, ” says James Quotch of the Institute of Science and Technology in Spain.

Quotch proposed a new way to test the Bourne rule. He proceeded from the idea of the physicist Feynman: in order to calculate the probability of a particle occurring at one point or another on the screen, you must take into account all the possible ways in which this can happen, even if they seem ridiculous. “Even the probability that a particle reaches the moon and returns will be taken into account, ” says Quotch. Almost none of the paths will affect the final location of the photon, but some very unusual ones can ultimately change its coordinates. For example, suppose we have three ways in which a particle can fly through the screen instead of two obvious ones (i.e. instead of one or another gap). The Bourne rule in this case allows us to consider the interference that may occur between two obvious options, but not between all three.

James showed that if all possible deviations are taken into account, the final probability that the photon will hit point X will differ from the result that the Born rule implies. He suggested using a wandering zigzag as the third path: for example, a particle passes first through the left hole, then through the right, and only then goes to the screen. If the third path interferes with the first two, the result of the calculations will also change. Quotch’s work aroused great interest, and Aninda Sinha at the Indian Institute of Science in Bangalore, a member of the team that first proposed using the winding, “unconventional” paths to refute Bourne’s rules, completely agree with her. However, the scientist also points out that there are too many unaccounted probabilities for now to speak about the purity of the experiment. Be that as it may, the results of this work will open the door to humanity in the field of a deeper understanding of reality.

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