Atoms stick together in different ways to make the molecules that compose everything we touch and see. Our bodies are made of cells. Cells, in turn, are made of lipids, proteins, nucleic acids, metabolites, and water. Every one of those molecules is made from the same handful of atoms. But although the components are the same, the molecules differ in how many atoms they have and how those atoms are arranged in space.

Since the discovery of the DNA double helix, the main molecular repository of genetic information, scientists have been struggling to find ways to efficiently manipulate genes. The ability to mark, modify, or regulate specific sequences of DNA in a controlled fashion is of key importance because of the ways that gene editing could be used to improve human life. For example, genetic therapies are being developed to permanently cure cancer and other life-threatening diseases.

Vision begins when the eye's optical system-the cornea, iris, and crystalline lens-projects an image onto the retina, the thin and nearly transparent sheet of neural tissue that lines the back of the eye (see figure 1). Photoreceptors located at the back of the retina transduce incident photons into neural signals that are relayed to the brain. Those signals form the basis for visual perception. In humans, cone photoreceptors, which number about 6 million, dominate the central region of the visual field and are responsible for color and high-resolution day vision. Rod photoreceptors, which number about 120 million, dominate the periphery and mediate night vision.

Sound waves generated by light are the basis of a sensitive medical imaging technique with applications to cancer diagnosis and treatment.

Biological polymers have a preferred chirality ond can replicate themselves. Physical arguments provide insight into which of these unique and apparently related properties evolved first, and by what mechanism.

Evidence indicates that the collisions of Earth and a large piece of Solar System debris such as a meteoroid, asteroid or comet caused the great extinctions of 65 million years ago, leading to the transition from the age of the dinosaurs to the age of the mammals.

Controlling coherent light across a vast spectral range enables ultraprecise measurements and the quantum control of atomic, molecular, and condensed-matter systems.