![]() ![]() That radiation will have a different electromagnetic field depending on which way Alice’s particle went. No matter how carefully Alice sets up her experiment, her particle will always emit a tiny amount of radiation as she moves it, the physicists showed. The rescue came from the fact that charged particles radiate, or emit light, when shaken. “It must be that there’s an effect that no one has calculated in these theories that comes to the rescue,” Danielson says. ![]() The team then guessed at a possible solution to that paradox: The black hole itself forces the quantum state of Alice’s particle to collapse, whether Bob is there or not. But we just made up a scenario in which, definitely, the experiment will be affected.” The paradox is solved if the black hole acts like an ‘observer’ “Nothing done in the interior of a black hole can affect my experiment that I do in the exterior. “The paradox is that black holes are a one-way street,” Satishchandran says. By the laws of physics, Bob should not be able to communicate with Alice at all. But that’s a paradox - nothing done inside a black hole should affect the outside. That would also let Alice know Bob is there, messing up her experiment. When Bob observes which slit Alice’s particle went through, the particle’s quantum state will collapse. ![]() “At the horizon, you wouldn’t even know you fell in,” Satishchandran says. ![]() The laws of physics behave the same just inside the horizon as outside. Even though Bob is doomed, he can still make measurements ( SN: 5/16/14). Then the team imagined another person, Bob, sitting just inside a black hole’s event horizon - the boundary beyond which not even light can escape the black hole’s gravity. The particle’s quantum state of apparently being in two places at once collapses. But if someone, or some device, measures the particle’s path, it will register as having gone through one slit or the other. If no one observes the particle’s progress, an interference pattern typical of waves appears on a screen on the other side of the barrier, as if the particle went through both slits at once ( SN: 5/3/19). In this classic example of quantum physics, a scientist sends a particle, like an electron or a photon, toward a pair of slits in a solid barrier. A quantum experiment near a black hole creates a paradoxįirst the team imagined a person, call her Alice, performing the famous double-slit experiment in a lab orbiting a black hole ( SN: 11/5/10). Here’s how Satishchandran, along with theoretical physicists Daine Danielson and Robert Wald, both of the University of Chicago, did just that. “The idea is to use properties of the that you understand, which quantum mechanics and gravity, to probe aspects of the fundamental theory,” which is quantum gravity, says theoretical physicist Gautam Satishchandran of Princeton University. These sought-after theories aim to unite quantum mechanics, the set of rules governing subatomic particles, and general relativity, which describes how mass moves on cosmic scales. That destruction could have implications for future theories of quantum gravity. ![]()
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