Everyone has heard of Alice in Wonderland, but not many know that the book’s author, Lewis Carroll, was actually a mathematician whose real name was Charles Lutwidge Dodgeson. In another book by Lewis Carroll, Through the Looking Glass, Alice speaks to her cat through a mirror.
She describes the room that she and her cat are in and how it appears in the mirror’s reflection and details how the letters in the book in her room appear backwards in the mirror. So, although the room she is in is similar to the room in the mirror, they are in fact not the same. Then, Alice wonders if the milk in the mirror will taste as good as the milk in the room she is standing in. This is a curious question. But to understand this, we need to understand chirality.
To explain chirality, think of the spring in your pen. The spring turns in a specific way. If you run your fingers along the spring it may run clockwise. And this will be true no matter how you hold the spring. However, the same spring in a mirror will turn counter-clockwise. And you cannot change the spring in your hand into the spring in the mirror, i.e. make it turn counter-clockwise. Similarly our hands are mirror images of one another and cannot be superimposed and lack an internal plane of symmetry. One is right-handed and the other left-handed. This is chirality.
Everything around us is made up of molecules of a specific chirality. The mirror image of a right-handed molecule will be left-handed.
Now most non-living things like rocks or cement etc are a 50-50 mix of right and left-handed molecules. Interestingly, all proteins in living substances (humans, dogs, trees, etc) are strictly left-handed and never right-handed. Although the chirality of life is left-handed, scientists can manufacture caraway seed molecules for instance, in their mirror image of right-handed and this molecule tastes like spearmint! This fact that a molecule’s mirror image can be so different can also be detrimental. Like something good can become poisonous.
Thalidomide is well-known story of such a flip. The original drug was made to be all one-handed and was developed to cure morning sickness. But somewhere along the way the molecules making up the drug flipped and its mirror image was extremely poisonous. Women who took that medication had severely deformed babies. The drug of course was discontinued.
What about the difference between us and the person who stares back at us in the mirror then? There is in fact what is known as true-mirrors out there allowing you, for the first time, the ability to see how the world sees you. Most people freak out when they stand in front of such a mirror. So, coming back to Alice, she is quite right. The milk in the mirror she is looking at might not taste anything like the milk she is used to!
The writer is a Ph.D. in Molecular Genetics and Genomics and is working on skin cancer at Novartis
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