Brace yourselves for gravitational waves

[TheRealJoeFish]

Just read about the "L", still not understanding it completely. They shoot lasers down both arms, and if one comes back slightly later, that is what detects the gravitational wave. That confirms what measurement is, the difference. But still don't understand the complete how.

Someone with more knowledge/smarts correct me if I'm wrong, but I'm'a try to come up with an interesting and informative analogy.

Imagine you're standing in the corner of a big box made of rubber.  (I know, I know, stay with me.)  You don't know exactly how big it is, so you take a ruler and, starting at your corner, mark off every foot on the wall with chalk.  You find out that the box is both 20 feet long and 20 feet wide, a perfect square, so there are 20 chalk marks on each wall.

You suspect that someone on the outside might be squeezing the box a little bit, distorting its shape by pressing or pulling on one of the walls.  You can't tell, though, because all you have to go on are the 20 chalk marks on the wall, and you're not fast or precise enough to measure if the box actually changes shape to say, 19 feet 11 inches by 20 feet 1 inch for just a second.

So, you devise a clever experiment.  Standing in your corner, you throw two tennis balls - one along the length (which you think is 20 feet) and one along the width (which you think is 20 feet).  You make sure the tennis balls are exactly the same, and you throw them at the exact same speed. 

Since they're both traveling at exactly the same speed, and presumably going the same distance, they should get back to you at exactly the same time.  However, one gets back to you a second later than the other one.  As far as you can tell, they both went exactly 40 feet (20 marks of chalk to the opposite wall, and 20 marks back).  However, the difference in time means that, indeed, someone must have been squeezing the box a little bit from the outside, making the one wall just a little farther than 20 feet away when the tennis ball hit it.


That was my best shot

(To clarify, the tennis balls are the lasers, throwing one along the width and one along the length is the "L" they're discussing, the room itself is... spacetime, the universe, etc, and the person pushing or pulling the room slightly... is gravity!)