MATHEMATICS SPACE AND TIME A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site mirror reversal problem Why does a mirror reverse right and left, but not up and down? This question crops up perennially in the letters and queries columns of magazines and newspapers. It was the inspiration for Lewis Carroll's Alice Through the Looking Glass. Alice Raikes (not to be confused with Alice Liddell after whom the fictional Alice was modeled) was another of Carroll's young friends. On one occasion, in 1868, Carroll put an orange in her right hand and then asked her to stand in front of a mirror and say which hand the reflection had the orange in. She said the left hand and Carroll asked her to explain. She finally replied "If I was on the other side of the glass, wouldn't the orange still be in my right hand?" Carroll said this was the best answer he'd had and later said it gave him the idea for his book. Others have struggled harder but not always convincingly to explain the phenomenon, appealing variously to gravity, the psychology of perception, and philosophy. Why does a mirror reverse right and left, but not up and down? A frequently given answer is that a mirror doesn't reverse right and left. It reverses front and back. This is certainly true: the looking-glass you is facing in the opposite direction to the "real" you. But this short, crisp explanation doesn't completely dispel the mystery. The fact is that, if you imagine that the mirror is not there and that instead you are looking at a real flesh-and-blood twin of yourself, that twin is differently handed. If you have a watch on your left wrist, the person you are facing has his/her watch on the right wrist. The mirror has done a left-right swap, surely! At any rate, something has happened to left and right that hasn't happened to up and down. To be more convinced of this, hold this book up to the mirror and try to read it. If no left-right swap has happened, why is the reflected writing so hard to read? Firstly, remember that you are only looking at an image! The mirror hasn't (Carrollian fantasies aside) created something of opposite handedness. Secondly, appreciate how the writing appears in the mirror's frame of reference. This is easy to do by looking at the writing from the other side of the page (i.e. back to front, thus undoing the back to front reversal caused by the reflection). From the mirror's point of view the writing looks perfectly normal. Related entry    • enantiomers Related categories    • MATHEMATICS    • SPACE AND TIME Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP