ALICE and Bob are having an argument. They are looking at the same space, but while Alice sees only emptiness Bob sees lots of particles. Alice whips out a thermometer which registers zero temperature, but Bob’s registers heat from the motion of the particles. Who is right? They both are. If you’ve been thinking that a particle’s existence is independent of who sees it, time to think again. Existence, it seems, is all in the eye of the beholder.
Is this so very strange? We already know from quantum theory that something can be either a particle or a wave…
