“But the gravitational wave detection game’s been changing of late, with a recent spate of improvements to our leading ground-based observatory, LIGO, and with the launch of the very first space-based gravitational wave detector, LISA Pathfinder.”

LISA Pathfinder is *not* a space-based gravitational wave detector. It’s…

No-one’s shooting lasers across the continent. They’re shooting lasers in a 4km-long apparatus in Washington, and they’re doing the same thing in Louisiana.

No, they won’t. These gravitational waves are a classical (non-quantum) phenomenon. It’s like detecting electromagnetic waves for the first time (rather than photons).

No, that sentence was badly written. The Washington and Louisiana sites are separate, and there are no lasers being shone between them.

In each site, there’s an L-shaped set of evacuated tubes. A laser beam starts in the common corner, and is split into two beams, each of them going down one arm of the L, bouncing off…

They’re not. The Hanford and Livingston sites are completely separate. *Each of them* has an L-shaped setup (in vacuum) with hanging mirrors at the ends and a laser at the corner, split into two beams that bounce off the mirrors, come back to the corner again and are compared.