The wavefunction of quantum mechanics is not simply a statistical tool that reflects our ignorance of the particles being measured, but is physically real, according to physicists at Imperial College London.

Action at a distance occurs when pairs of quantum particles become entangled. The paper suggests that if a quantum wavefunction were purely a statistical tool, even quantum states that are unconnected across space and time would be able to communicate with each other. As that seems very unlikely, the researchers conclude that the wavefunction must be physically real after all.

Theoretical physicist Antony Valentini believes that this result may be the most important general theorem relating to the foundations of quantum mechanics since Bell’s theorem.

Robert Spekkens, a physicist at the Perimeter Institute for Theoretical Physics, says he expects the theorem to have broader consequences for physics, as have Bell’s and other fundamental theorems. No one foresaw in 1964 that Bell’s theorem would sow the seeds for quantum information theory and quantum cryptography — both of which rely on phenomena that aren’t possible in classical physics.

Physics bloggers Scott Aaronson, Lubos Motl, David Wallace and Matt Leifer have posted detailed reviews with different opinions. — Ed.

Ref.: Matthew F. Pusey, Jonathan Barrett, Terry Rudolph, The quantum state cannot be interpreted statistically, 2011, http://lanl.arxiv.org/abs/1111.3328