Steven Pinker -- How the Mind Works - Hampshire High Italian ...

276 | HOW THE MIND WORKSWhen Cooper and Shepard measured how long it took people topress the button, they observed a clear signature of mental rotation. Thefarther the letter was misoriented from the upright, the longer peopletook. That's exactly what you would expect if people gradually dialed animage of the letter to the upright; the more it has to be turned, the longerthe turning takes. Maybe, then, people recognize shapes by turning themover in their minds.But maybe not. People were not just recognizing shapes; they werediscriminating them from their mirror images. Mirror images are special.It is fitting that the sequel to Alice's Adventures in Wonderland was calledThrough the Looking-Glass. The relation of a shape to its mirror imagegives rise to surprises, even paradoxes, in many branches of science.(They are explored in fascinating books by Martin Gardner and byMichael Corballis and Ivan Beale.) Consider the detached right and lefthands of a mannequin. In one sense they are identical: each has four fingersand a thumb attached to a palm and a wrist. In another sense theyare utterly different; one shape cannot be superimposed on the other.The difference lies only in how the parts are aligned with respect to aframe of reference in which all three axes are labeled with directions: updown,frontward-backward, left-right. When a right hand is pointing fingers-uppalm-frontward (as in a "halt" gesture), its thumb points left;when a left hand is pointing fingers-up palm-frontward, its thumb pointsright. That's the only difference, but it is real. The molecules of life havea handedness; their mirror images often do not exist in nature and wouldnot work in bodies.A fundamental discovery of twentieth-century physics is that the universehas a handedness, too. At first that sounds absurd. For any objectand event in the cosmos, you have no way of knowing whether you areseeing the actual event or its reflection in a mirror. You may protest thatorganic molecules and human-made objects like letters of the alphabetare an exception. The standard versions are all over the place and familiar;the mirror images are rare and can easily be recognized. But for aphysicist, they don't count, because their handedness is a historical accident,not something ruled out by the laws of physics. On another planet,or on this one if we could rewind the tape of evolution and let it happenagain, they could just as easily go the other way. Physicists used to thinkthat this was true for everything in the universe. Wolfgang Pauli wrote, "Ido not believe that the Lord is a weak left-hander," and Richard Feynmanbet fifty dollars to one (he was unwilling to bet a hundred) that no exper-