This article is great but the references to gravitational waves as if they were an observed fact (in 1972) was mystifying to me. It led me down a rabbit hole to Joe Weber, who is name-checked at the end of the Penrose article.

A Fleeting Detection of Gravitational Waves

https://physics.aps.org/story/v16/st19

Gravitational wave blues

https://aeon.co/essays/how-joe-weber-s-gravity-ripples-turne...