Mirror Reversal

WHY ARE OBJECTS LEFT-RIGHT REVERSED IN A MIRROR BUT NOT TOP-BOTTOM REVERSED?



Consider this: you are holding a mug covered in writing parallel in front of a mirror. You can observe that the handle is on the same side you are holding it. But, the writing on the mug appears to be left right reversed - ‘mirror writing’. Why is this the case? This puzzle has long remained a confusing concept among different academic disciplines and has been the idea behind Charles Lutwidge Dodgson’s Alice Through the Looking Glass.

The truth is that the objects are not really left-right reversed but front-back reversed. Picture this, you stand in front of the mirror; it looks as if a person that looks like is standing opposite you. You image that the person walked from where you are standing turned 180 degrees about the vertical axis and faces you. So the person’s left hand is opposite you right hand. You can imagine this by holding an apple in your hand when you look at the mirror. The apple is still on the right but the person in the mirror is holding it with their left.


The interesting bit about this situation is that the reflection did not do a 180 degree turn. It has been reversed front to back with no rotation at all. When your brain assumes that 180 degree turn you assume an apparent left to right reversal.

Furthermore, regarding the ‘mirror writing’ you can think of left and right as directions that are described relative to the observer. Whereas top and bottom are independent of whichever way you are facing, given that your feet remain on the surface of the Earth. Therefore, the text read from the mug reverses from left to right which as we have discussed before is only really reversing front to back. Fascinating.


Laura L, Year 12

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