H Stands for Hydrogen…and Humility

Simplicity need not be trivial. Simplicity can be profound. The hydrogen atom is Nature's simplest atom: a single proton surrounded by a solitary electron. This simplicity, however, belies the importance of hydrogen for 20th century science and technology. It is hydrogen that provides the most striking example of how experimental data and physical theory work together to advance our understanding of physical phenomena. Repeatedly the hydrogen atom has surprised physicists and, in the process, has brought basic new insights into the workings of Nature. Hydrogen has also humbled physicists as it has defied their most confident predictions. Through the simple hydrogen atom the door was opened to nuclear magnetic resonance (NMR) and the powerful diagnostic medical tool MRI; through hydrogen the door was opened to atomic clocks. The role of hydrogen has been prominent in working out details of atomic structure and has made seminal contributions to the understanding of nuclear structure. The hydrogen atom has enabled us to map the Milky Way and probe galactic structure. The hydrogen atom has provided an empirical check on Big Bang cosmology. And yet, the hydrogen atom still beckons, still calls for our attention. Whenever scientists are tempted to think they have a hammer-lock on Nature, it would be good to remember that H stands for hydrogen and humility.