Kate McAlpine at PhysicsWorld writes: ''Since quantum mechanics was first formulated, a string of physicists including Albert Einstein have been uncomfortable with the idea of entanglement – whereby a group of quantum particles have a closer relationship than allowed by classical physics. As a result, some physicists have proposed alternative theories that allow such close relationships without the need for quantum mechanics. While it has been difficult to test these theories, researchers in the UK have used "twisted light" to make an important measurement that backs up quantum theory. ''