· Black Holes
Penrose Diagrams Explained: All of Spacetime on One Page
How do you draw the whole of space and time, out to infinity, on one sheet of paper? Roger Penrose found a way: shrink distances but keep every angle, so light rays stay at 45 degrees. Here are the two coordinate steps behind the trick, how to read the corners of the diagram, and why it helped show that black holes really form.