Is the behaviour of quantum objects described by a simple, classical theory? Or can particles really be in a superposition of different places at once, as quantum theory suggests? In 1985, the physicists Antony James Leggett and Anupam Garg proposed a new way of answering these questions. If the world can be described by a theory that doesn’t feature superposition and other quantum phenomena, Leggett and Garg showed that a certain inequality must be obeyed. If the world really is quantum, though, the inequality will be violated.
Researchers at TU Wien in Austria have now made a new measurement of this so-called Leggett-Garg inequality (LGI) using neutron interferometry. Their verdict is clear: no classical macroscopic theory can truly describe reality. The work also provides further proof that a particle can be in a superposition of two states associated with different locations – even when these locations are centimetres apart.
To read more, click here.