The universe really is weird, and a landmark quantum experiment proves it
Howard Wiseman, The Conversation
Local causality is a very natural scientific assumption and it holds in all modern scientific theories, except quantum mechanics. Thus, because local causality is such a natural hypothesis about the world, there have been decades of experiments looking for, and finding, the very particular predictions of quantum mechanics that John Bell discovered in 1964. To close the first loophole, it is necessary that the laboratories be far enough apart (well separated). This has been a problem with experiments using photons (quantum particles of light) because often a photon will not be detected at all. Alice and Bob then each choose a setting and measure their electrons while Juanita performs a joint measurement on the two photons.