“Einstein and his colleagues made the perfectly reasonable assumption of locality: that the properties of a particle are localized on that particle, and what happens here can’t affect what happens there without some way of transmitting the effects across the intervening space. It seems so self-evident that it hardly appears to be an assumption at all. But this locality is just what quantum entanglement undermines – which is why ‘spooky action at a distance’ is precisely the wrong way to look at it. We can’t regard particle A and particle B in the EPR experiment as separate entities, even though they are separated in space. As far as quantum mechanics is concerned, entanglement makes them both parts of a single object. Or to put it another way, the spin of particle A is not located solely on A in the way that the redness of a cricket ball is located on the cricket ball. In quantum mechanics, properties can be non-local. Only if we accept Einstein’s assumption of locality do we need to tell the story in terms of a measurement on particle A ‘influencing’ the spin of particle B. Quantum non-locality is the alternative to that view.”