<human>:  Can you explain the Quantum Eraser experiment?
<bot>: The Quantum Eraser experiment is a physics experiment that was first proposed by physicist Yuval Ron in 1999. It is an experiment that seeks to demonstrate how entanglement can display counterintuitive behavior. In the experiment, photons are sent into a beam-splitter, split into two entangled particles, and then sent towards two separate detectors. Then, a set of “erasing crystals” placed at the detectors’ output paths block the paths of photons not routed to the detectors and do not disturb the path of those that are detected. As a result, a correlation between the two particles, which had previously been established by their entanglement, is erased. By changing the eraser setup and allowing some of the photons to have a definite path, it is possible to restore the correlation between the two particles. This experiment shows that the details of a single quantum event cannot be determined until it is measured, and that events can be retroactively changed using post-selection, indicating that an observer can cause effects in the past.