Even though gravity is pulling inward on space-time - the "fabric" of the cosmos - it keeps expanding outward faster and faster. You can find the original article here.No matter how astrophysicists crunch the numbers, the universe simply doesn't add up. This article is republished from The Conversation under a Creative Commons license. He receives funding from the National Science Foundation. Much remains to be said about the mysterious world of quantum mechanics.Īndreas Muller is an associate professor of physics at the University of South Florida. ![]() Although quantum mechanics can predict the probability of a measurement with incredible accuracy, many researchers remain skeptical that it provides a complete description of reality. Today, physicists continue to research quantum entanglement and investigate potential practical applications. Two parties far apart performing measurements on entangled particles cannot use the phenomenon to pass along information faster than the speed of light. The fact that measurements over vast distances are correlated does not imply that information is transmitted between the particles. Importantly, there is also no conflict with special relativity, which forbids faster-than-light communication. ![]() Objects can be correlated over large distances in ways that physics before quantum mechanics cannot explain. Collectively, these and many follow-up experiments have vindicated quantum mechanics. The results conclusively ruled out the existence of hidden variables, a mysterious attribute that would predetermine the states of entangled particles. The experiments used entangled photons, rather than pairs of an electron and a positron, as in many thought experiments. The experiments of the 2022 Nobel laureates, particularly those of Alain Aspect, were the first tests of the Bell inequality. But at the time, physicists did not have the technology nor a definition of a clear measurement that could test whether quantum theory needed to be modified to include hidden variables. They theorized there was some unknown property - dubbed hidden variables - that determined the state of a particle before measurement. Physicists, including Einstein, proposed a number of alternative interpretations of quantum entanglement in the 1930s. Surely the measured state of one particle cannot instantaneously determine the state of another particle at the far end of the universe? But according to the laws of physics, nothing can travel faster than the speed of light. This seems to suggest that the particles communicate with each other through some means that moves faster than the speed of light. Only when the measurement occurs does the quantum state of the spin "collapse" into either up or down - instantaneously collapsing the other particle into the opposite spin. But because of quantum mechanics, the spin of each particle is both part up and part down until it is measured. This would be fine if the measurement of the electron spin were always up and the measured spin of the positron were always down. This is true even if the particles are billions of miles apart. Therefore, if the electron spin is measured to be up, then the measured spin of the positron could only be down, and vice versa. When this particle decays, it produces an electron and a positron that have opposite spin and are moving away from each other. In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen published a paper that describes a thought experiment designed to illustrate a seeming absurdity of quantum entanglement that challenged a foundational law of the universe.Ī simplified version of this thought experiment, attributed to David Bohm, considers the decay of a particle called the pi meson. And for good reasons - who would dare contradict the great Einstein, who himself doubted it? It took the development of new experimental technology and bold researchers to finally put this mystery to rest. ![]() However, even until the 1970s, researchers were still divided over whether quantum entanglement was a real phenomenon. Thanks to ever more precise and reliable instruments and the work of this year's Nobel winners, Alain Aspect, John Clauser and Anton Zeilinger, physicists now integrate quantum phenomena into their knowledge of the world with an exceptional degree of certainty. Having spent the better part of two decades conducting experiments rooted in quantum mechanics, I have come to accept its strangeness. Albert Einstein famously called the phenomenon "spooky action at a distance." This odd connection between the two particles is instantaneous, seemingly breaking a fundamental law of the universe. The strange part of quantum entanglement is that when you measure something about one particle in an entangled pair, you immediately know something about the other particle, even if they are millions of light years apart.
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