Here's a simple explanation, with pictures: http://visualrelativity.com/LIGHTCONE/schwarzschild.html http://visualrelativity.com/LIGHTCONE/schwarzschild.html

Here's a simple explanation, with pictures: http://visualrelativity.com/LIGHTCONE/schwarzschild.html http://visualrelativity.com/LIGHTCONE/schwarzschild.html And here's a more technical one: https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes