QBism: Is quantum uncertainty all in the mind?
By Matthew Chalmers It’s not quantum theory that’s uncertain (Image: Matt Murphy) The microscopic world described by quantum theory seems a strange, confusing place – but some physicists argue it’s just us who are uncertain SNATCH a toy from the tiniest of infants, and the reaction is likely to disappoint you. Most seem to conclude that the object has simply ceased to exist. This rapidly changes. Within the first year or so, playing peekaboo also becomes fun. As babies, we soon grasp that stuff persists unchanged even when we are not looking at it. Granted, at that age we know nothing of quantum theory. In the standard telling, this most well-tested of physical theories – fount of the computers, lasers and cellphones that our adult souls delight in – informs us that reality’s basic building blocks take on a very different, nebulous form when no one is looking. Electrons, quarks or entire atoms can easily be in two different places at once, or have many properties simultaneously. We cannot predict with certainty which of the many possibilities we will see: that is all down to the random hand of probability. That’s not the way our grown-up, classical world seems to work, and physicists have been scrabbling around for the best part of a century to explain the puzzling mismatch. To no avail. Faced with reality at its most fundamental, we end up babbling baby talk again. David Mermin thinks he has something sensible to say. An atomic physicist at Cornell University in Ithaca, New York,