Guilhem Lavaux

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.

In the first moments after the Big Bang, the universe expanded faster than light could cross it. This expansion left a subtle ripple in the distribution of matter, like the rings on water from a thrown stone. Traces of that ripple are visible today in how galaxies cluster into groups and filaments.