How to Measure the Expansion Rate of the Universe Without Knowing Its Age
The universe is expanding, and galaxies are flying apart like raisins in rising dough. The rate of this expansion, the Hubble constant, is a key number in cosmology.
Cosmic Lightning: How Fast Radio Bursts Illuminate Hidden Baryons
Half a century ago, Fritz Zwicky noticed that the visible matter in galaxy clusters was catastrophically insufficient to explain gravity.