Did you feel it?
On May 21, 2019, the mass of eight suns disappeared. In a universe like ours, in which mass and energy are conserved, mass cannot disappear without consequences: and so it went that, as two distant black holes merged, the entire universe vibrated. A powerful gravitational shockwave expanded outwards from the merger, expanding out for billions of years before passing through Earth. On that day, every cell in your body stretched and compressed in four quick successions, as did the atoms of everything else on Earth and in our solar system.
