How Many Gravitational Waves have we seen?
Last week I got an email from a colleague, asking a question which, on the face of it, should have been easy to answer.
How many gravitational waves have we detected?
However, the fact that they needed to ask helps to reveal that there is not, in fact, a straightforward answer.
This is hopefully a complete, and fairly concise, set of potential answers to the question, along with caveats as appropriate.