The Looking Glass in Lewis Carroll’s book, Through the Looking Glass, is a mirror, and things are not the same on the other side, in much the same way as they are not the same when observing left- and right-handed molecules, known as chirality, the scientific study of which is called stereochemistry.
For example, if you could somehow drink looking glass milk in the book through a layer of ice, it would not be digestible by humans because it would be the opposite of right-handed lactose, the sugar found in normal milk, and thus not recognised by the body; similarly, molecules such as amino acids, which are the building blocks of all life, always exhibit one of two types of chirality, and this is a fundamental question in the science of what is known as homochirality.
In addition, scientific instruments are also either left- or right-handed, much like a pair of gloves, and this is because they are manufactured to behave in a particular way, and any results obtained from them would be unrepeatable if carried out by a similar instrument with the opposite chirality.
