How to explain to an extra-galactic being what we mean by 'left' and 'right'
At the center of a distant galaxy there's a black hole with the mass of several billion suns. And now, for the first time, we can see it.
On the 100th anniversary of Albert Einstein's Theory of General Relativity (gravity), many of the predictions of this theory have been proven correct. Here's the story of one that was wrong.