Ok, if I understood (feel free to school me, i am an absolute amateur):

The fuck is this:

Einstein made a prediction that spacetime gets wibbly wobbly, expanding and contracting, when massive events (supernovas, blackholes colliding, the big bang) occur. and they finally proved it by measuring the wibbly wobblys of an event that occurred billions of years ago, black holes colliding.

How they did that shit:

--a device, an interferometer, shoots a laser at a laser-splitter.

--the two split light-waves bounce off mirrors and return, recombining into a new wave

--as space-time wibbles and wobbles around the machines, the distance these laser beams travel will changes, and thus so does the returning wave patterns.

--by comparing the varying wave patterns, they can create visual representations of an event, like colliding blackholes, in 3fuckingD.

Why that shits cool:

with this technique they can measure events and perceive objects that existed back all the way to and including the big bang, shit that no telescope could ever see. including, maybe, whatever dark matter is.