If Copenhagen interpretation of quantum mechanics is to be believed, nothing exists in reality until a measurement is carried out. In the double slit experiment carried out by John Wheeler, post-selection can be made to work, after the experiment is finished, and that by delaying the observation after the photon has purportedly passed through the slits. Now, if post-selection is to work, there must be a change in the properties in the past. This has been experimentally proved by physicists like Jean-François Roch at the Ecole Normale Supérieure in Cachan, France. This is weird, but invoking the quantum entanglement and throwing it up for grabs against the philosophic principle of causality surprises. If the experimental set up impacts the future course of outcome, quantum particles in a most whimsical manner are susceptible to negate it. This happens due to the mathematics governing these particle, which enable or rather disable them to differentiate between the course of sense they are supposed to undertake. In short, what happens in the future could determine the past….
….If particles are caught up in quantum entanglement, the measurement of one immediately affects the other, some kind of a Einsteinian spooky action at a distance.