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The ultimate transgression of everything that we take to be nature’s immutable laws might be something called delayed-choice quantum erasure, and any plausible theory of post-death reality would almost certainly have to involve something this outlandish. It has been well established that observing a double-slit experiment forces photons to act like particles rather than waves and go through one slit at a time, whereas unobserved photons go through both. And it has been well established that particles “entangled” at the quantum level affect each other instantaneously across any distance, including the entire universe. In an attempt to go back in time and erase reality, physicists combined those two phenomena into one experiment that tested entangled particles on the island of La Palma, in the Canaries archipelago, and on the island of Tenerife, eighty-eight miles distant. (For the brave or merely curious, a slightly abbreviated version of the technical description of this experiment is: “Linearly polarized single photons are sent by a polarization beamsplitter through an interferometer with two spatially separated paths associated with orthogonal S and P polarizations. The movable output beamsplitter consists of the combination of a half-wave plate, a polarization beamsplitter, an electro-optical modulator with its optical axis oriented at 22.5° from input polarizations, and a Wollaston prism. The two beams of the interferometer, which are spatially separated and orthogonally polarized, are first overlapped by the beamsplitter but can still be unambiguously identified by their polarization.”) That is to say, on one island, researchers shot a particle at the double slits, and it passed through both of them as an unobserved wave function. Eighty-eight miles away, via fiber optics cable, they then shot its entangled twin at double slits while observing it with a photon detector; as expected, its wave function collapsed, and it passed through only one slit. But now the universe had a problem: Entangled particles have to do the exact same thing, but the delayed choice had tricked them into acting differently. That was impossible. When researchers checked the strike plate of the first test, though, they found that the wave function had been retroactively collapsed by the second test and forced through a single slit. Quantum information had been erased.
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Sebastian Junger (In My Time of Dying: How I Came Face to Face with the Idea of an Afterlife)