An event is always either the cause or the effect of another - this should be a principle of physics. But at the quantum level this is not always true.
One of the fundamental principles in physics is that of direct causation. This states that an event is always either the cause of another or caused by it. In elaborate quantum experiments, however, researchers are creating situations in which the relationship between cause and effect between events is no longer clearly defined. The findings could be useful for more efficient computations on quantum computers and provide new insights into the interface of quantum physics and general relativity.