Zack Savitsky writes:

After her adventures in Wonderland, the fictional Alice stepped through the mirror above her fireplace in Lewis Carroll’s 1871 novel Through the Looking-Glass to discover how the reflected realm differed from her own. She found that the books were all written in reverse, and the people were “living backwards,” navigating a world where effects preceded their causes.

When objects appear different in the mirror, scientists call them chiral. Hands, for instance, are chiral. Imagine Alice trying to shake hands with her reflection. A right hand in mirror-world becomes a left hand, and there’s no way to align the two perfectly for a handshake because the fingers bend the wrong way. (In fact, the word “chirality” originates from the Greek word for “hand.”)

Alice’s experience reflects something deep about our own universe: Everything is not the same through the looking glass. The behavior of many familiar objects, from molecules to elementary particles, depends on which mirror-image version we interact with.

At the beginning of Through the Looking-Glass, Alice holds her cat Kitty up to the mirror and threatens to push her through to the other side. “I wonder if they’d give you milk in there? Perhaps Looking-glass milk isn’t good to drink,” she says.

Alice was onto something. Just over two decades before the book’s publication, Louis Pasteur discovered while experimenting with some expired wine that certain molecules can be chiral. They can come in distinct left-handed and right-handed structural forms that are impossible to superimpose. Pasteur found that, while they contain all the same components, the mirror versions of chiral molecules can serve distinct chemical functions. [Continue reading…]