When I originally wrote this book, I only briefly mentioned gravitational waves. Space was tight, and at the time there was only indirect evidence for their existence. On 11 February 2016, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) team announced they had detected gravitational waves from the merger of two black holes. The press release stated:
“For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.”
This historic discovery warrants more coverage than my original few lines, so I have now included a short additional chapter on gravitational waves. There’s a link to this new chapter here and on the home page.