Entanglement is a phenomenon in quantum mechanics where two or more particles become correlated in such a way that the state of one particle cannot be described independently of the state of the other(s). When entangled particles are separated, the measurement of one particle's properties instantaneously affects the properties of the other particle, regardless of the distance between them. This phenomenon has been experimentally verified and is a fundamental aspect of quantum mechanics.
If two entangled particles are separated and one of them passes beyond an event horizon, which is the boundary beyond which nothing can escape the gravitational pull of a black hole, it poses an interesting question. Once a particle passes the event horizon, classical information about the particle, including its state and properties, cannot be observed from outside the black hole.
From a quantum mechanical perspective, the fate of entanglement across an event horizon is still an active topic of research and debate. One possibility is that the entanglement between the two particles would be disrupted or "severed" once one of them enters the black hole. This would result in the loss of entanglement and a breakdown of the correlation between the particles.
Another possibility, suggested by some theoretical approaches, is that the entanglement could somehow survive even across the event horizon. This would imply that the particles' quantum states remain correlated, despite the separation caused by the black hole. However, it is important to note that the details of how this would occur and how the information might be retrieved from the black hole are still highly speculative and an active area of research.
Understanding the behavior of entanglement in the vicinity of black holes is a challenging task, as it requires the combination of quantum mechanics and general relativity, which are two fundamental theories of physics that are not yet fully reconciled. Further research, particularly in the field of quantum gravity, is necessary to deepen our understanding of these complex phenomena.