Mathias Garny

Two telescopes look at the same Universe and see different expansion rates. Local measurements from supernovae give 73.04 ± 1.04 km/s/Mpc, while cosmic microwave background data within the standard model predict 67.36 ± 0.54.

Dark matter is invisible, but its gravity holds galaxies together. For a long time, it was thought that dark matter particles pass right through each other without noticing. However, in small galaxies, the density of dark matter in the center turns out to be lower than calculations predict.

The cosmological dispute resembles two craftsmen measuring the same room with different tape measures. One, looking at distant galaxies, gets one number. The other, peering into the ancient glow (the cosmic microwave background, the cooled light of the Big Bang) gets another, smaller number.