What is Polchinski's paradox?

Polchinski's paradox is a thought experiment in theoretical physics that raises questions about the nature of black holes, information, and quantum mechanics. It was proposed by physicist Joseph Polchinski in the context of string theory and black hole thermodynamics. The paradox involves an imaginary scenario where a scientist throws a baseball into a black hole. As the baseball crosses the event horizon, it seemingly disappears from the outside universe. According to the principles of quantum mechanics, information about the state of that baseball should not be lost, even if the baseball becomes part of the black hole. Here's the crux of the paradox: If the black hole eventually evaporates through Hawking radiation, it appears that all information about the baseball (and anything else that fell into the black hole) is lost. This conclusion clashes with the unitarity of quantum mechanics, which states that information cannot be destroyed. The thought experiment highlights the tension between general relativity, which describes gravity and black holes, and quantum mechanics, which governs the behavior of particles at the smallest scales. This paradox is part of the broader discussion around the black hole information paradox, which has led to various proposals and theories in the realm of theoretical physics, including ideas about how information might be preserved or encoded in the Hawking radiation itself. Efforts to resolve Polchinski's paradox and the information paradox in general have led to significant research in areas like holography, quantum entanglement, and the foundations of quantum mechanics.