Re: The explanation of interference is slightly wrong in the article...
I came to the comment section with this in my copy-and-paste buffer: "mirrors at the end of the tunnels move". In other words, I spotted the same possible wording issue. Minor of course. And debatable.
So... How come the laser beam itself isn't shrunk and stretched in precise lock-step with the 4-km long tunnel?
Must be back to the constancy of 'c'...?