Look in the mirror. Looks like you – but it’s not you. It’s your mirror image. What’s the difference? Left and right are exchanged. My shirt buttons are on the right side of my shirt. His are on the left. He’s got his watch and wedding ring on his right hand. And he’s a mimic – always doing exactly what I do. Who is this guy? I wonder what he does when I’m not around – what his life is like. He certainly looks like me but is not quite the same.
When the great French scientist Louis Pasteur (who was later to give us Pasteurization of milk and vaccination against rabies and the debunking of spontaneous generation of life among other great discoveries) was still in his twenties and hardly known, he was trying to figure out how to help French wines avoid tartrates, crystals that form in wine. Although they are harmless, it is annoying to have something requiring chewing come along with the smooth flow of the wine. Pasteur had a microscope. Others had microscopes also and had looked at the tartrate crystals but no one had noticed what Pasteur noticed. Some of the crystals were mirror images of other crystals. Pasteur picked up each crystal with a pair of tweezers and looked at it under the microscope. He put each mirror image type crystal in separate piles, so he had two piles. He then dissolved each pile in some water and did an experiment that showed that the molecules in each pile were mirror images of the molecules in the other pile. Yes, just as you and I have mirror images that are different from us, many molecules also have mirror images that are different. So what?
Scientists know that the original molecules on earth billions of years ago, which evolved to become life, to become eventually us, had mirror images, and that both mirror images, just as for Pasteur’s crystals, were present in equal amounts. But the problem is that in all living organisms, whenever a molecule has the possibility of a mirror image, only one mirror image is present, just as each of us has a mirror image that is not independently alive. In fact, if you look at the molecules in the food we eat and all the molecules that we are made of, only one mirror form is there. Sure, you can use scientific methods to reflect the molecule in a mirror and see its image – but the image, just as our image in the mirror is only a reflection. It can not be found in something alive.
People want to know why and how this happened, considering that both mirror images of the molecules from which life evolved were there to begin with. Why not have life made of both mirror forms? And would that mean that we would all have twins running around, twins that were our mirror images. What a weird idea.
In Lewis Carroll’s “Through the Looking Glass”, Alice innocently wonders at one point whether looking-glass milk is good to drink. I’m afraid it’s not good to drink Alice because when life is made of one mirror image, the other mirror image is not compatible with our biological mechanisms. We couldn’t digest mirror image milk. If mirror image people were walking around on earth, we would have to have different farms to feed them with mirror image cows and pigs and, well you get the idea. This is serious business because sometimes the mirror images of a molecule can have different effects on people. The reason for this is the same as trying to put a left and right handed glove on your right hand. The pharmaceutical industry has to be careful about this. It all came to a head in the late 1950s when a drug given to women for morning sickness during early pregnancy, thalidomide, turned out to cause defects; otherwise healthy children were born with all kinds of heart breaking birth deformations. The drug companies had marketed both mirror images of the drug. One mirror image did the intended job – the other caused the birth defects. There is now a multi-billion dollar industry doing what Pasteur did, separating mirror image drugs, but not with a pair of tweezers.
But some drugs are still sold as mixtures of mirror image forms because dangerous differences are not found. One example is ibuprofen (Nurofen, Advil, and Motrin). For this drug the body takes the mirror image that is not a pain killer and converts it to its mirror image, the pain killer. That conversion would be tough to do for you and your mirror image but is sometimes possible with molecules. So the drug company can sell the mixture. But for every drug marketed, for which mirror forms are possible, the question has to be asked how do the two mirror forms differ in their effect on the body.
Some scientists think that in the early evolutionary period of life, both mirror forms of life coexisted but somewhere along the line, one won out over the other – a competition for resources or even a fight. Some scientists think that we may eventually find fossils of the losing mirror image life forms and other scientists think that discovery of life on other planets may uncover a mirror image world. Many scientists disagree. Nobody knows the answer.