Harry Desmond

The galaxy NGC 1560 is a modest island of stars and gas ten million light-years away. Its rotation curve, first measured in 1991, became an icon for those seeking an alternative to dark matter. The plot of rotation speed versus radius shows bends that seem to exactly mirror the bends in the distribution of ordinary matter.

The cosmological community has been living in a state of quiet civil war for several years. Two camps measure the expansion rate of the Universe and get different answers. Planck, peering at the cosmic microwave background, says 67.4 km/s/Mpc. SH0ES, climbing the distance ladder from Cepheids to supernovae, insists on 73.2.

Astronomers, like chefs, have long been preparing a description of the Universe using the same cumbersome recipes. These recipes — complex mathematical formulas — estimated how many galaxies of different luminosity and mass fill the cosmos, as well as how the invisible frameworks of dark matter are distributed. But the dishes lacked accuracy.

Astronomers debate the age of the universe as passionately as 19th-century geologists argued over the age of the Earth. Direct measurements give contradictory numbers: Edwin Hubble's law and the cosmic microwave background paint different cosmic chronologies.

The standard cosmological model ΛCDM, where dark matter and dark energy act as the chief architects of the cosmos, has predicted astronomical data with Swiss-watch precision for decades. Its foundation was laid by three geniuses.