More than a hundred years after the first debates on the nature of quantum reality, a team of MIT researchers has just brought a decisive blow to one of the deepest convictions of Albert Einstein. Thanks to an experience of unrivaled precision, using cooled atoms at extreme temperatures, scientists have shown that the father of relativity was wrong on a fundamental aspect of quantum mechanics. This discovery, published in Physical Review Letters, revives a centenary debate and confirms that the quantum universe is even stranger than imagined the greatest genius of the 20th century.
The experience that changed everything in 1801
To understand the magnitude of this discovery, it is necessary to go back to 1801, when Thomas Young made an apparently simple experience but with revolutionary consequences. By projecting the light of a lamp through two parallel slits on a screen, it expected to observe two distinct light strips, in accordance with Newton’s corpuscular theory which described light as a flow of particles.
The result was amazing: instead of two lines, a complex motif of alternation between clear and dark areas appeared on the screen. These interference fringes could only be explained if the light behaved like a wave, capable of dividing and recombining with itself.
But the story did not stop there. When the scientists later tried to observe by which slit effectively passed the light, the motive of interference mysteriously disappeared, giving way to the expected two bands. The simple observation modified the behavior of light, revealing one of the deepest mysteries of quantum physics.
The intellectual duel of the century: Einstein against Bohr
This discovery aroused one of the most passionate scientific debates in modern history. On the one hand, Albert Einstein, despite his fundamental contributions to quantum theory, refused to accept that observation could systematically destroy the observed phenomenon. He imagined sophisticated experimental devices-such as screens mounted on ultra-sensitive springs-which would surreptitiously detect the passage of the photon without disturbing the interference pattern.
On the other side, Niels Bohr was based on the principle of Heisenberg’s uncertainty to demonstrate the theoretical impossibility of such a feat. According to him, any attempt at measure inevitably introduces sufficient disturbance to erase quantum interference.
This philosophical opposition largely exceeded the technical framework: it questioned the very nature of reality and the role of the observer in the physical universe.
The purest experience ever made
MIT researchers, led by Wolfgang Ketterle and Vitaly Fedoseev, have designed what they consider to be the most “idealized” double slit experience. Their revolutionary approach was to replace classic slots with individual atoms.
The team first cooled more than 10,000 atoms at temperatures of a few microkelvin, a few millionths of degrees above absolute zero. At these extreme temperatures, atoms become practically immobile, allowing their handling with extraordinary precision.
Thanks to skillfully orchestrated laser beams, scientists organized these atoms in a perfect crystalline network, each atom being sufficiently isolated from its neighbors to act as an independent quantum entity. In this configuration, the light passing between two adjacent atoms faithfully reproduced the conditions of the classic double slit experience.
Credit: ISTOCK
Credits: Francescoch/Istock
Bohr’s posthumous victory
The crucial innovation of this experience resided in the ability of researchers to adjust the quantum “sharpness” of atoms. By modifying the parameters of the laser trap, they could make the atoms more or less “blurred” from a quantum point of view. More vague atoms were more easily disturbed by the passage of light, increasing the probability that it behaves like a particle rather than a wave.
The results, analyzed by an exceptional sensitivity detector, have unambiguously confirmed the predictions of quantum mechanics. More significantly even, they have shown that even in the most ideal imaginable conditions, it remains impossible to detect the journey of a photon without destroying the reason for interference.
« In many theoretical descriptions, springs play a major role“Explains Fedoseev. “” But we demonstrate that no, the springs do not matter here; Only count the degree of quantum uncertainty of atoms. »
Confirmed quantum strangeness
This experience marks a turning point in our understanding of quantum reality. She confirms that the intuition of Einstein, however brilliant, came up against a fundamental limit of nature. The quantum universe obstinately refuses to reveal some of its secrets, even to the most ingenious observer.
More deeply, this discovery stresses that the quantum correlations between photons and atoms constitute an essential reality, impossible to circumvent by any experimental device whatsoever. Quantum mechanics, despite its counter-intuitive character, remains our best description of reality on a microscopic scale.
A century after its birth, quantum theory continues to challenge our deepest intuitions, reminding us that the universe is decidedly more mysterious than our daily experience suggests.
