For people with two hands, one is usually dominant. On a molecular level, life takes this to the extreme. All of the DNA in earthly living things twists to the right, whereas the protein building blocks favor a kind of left-handed chemistry. But in recent years, scientists have worked toward a kind of mirror version of life. The technology to make mirror life likely won't exist for at least a decade. Still, a group of concerned scientists published a 299-page technical report calling for a stop to the science. New York Times science columnist Carl Zimmer explains how a mirror microbe could wreak havoc on life on Earth in the future.