So, that's the story. Of course, I don't understand the mathematics, but the idea's rather easy to grasp.
10 seconds sound clip from the X Minus 1 - A Gun for Dinosaur by L. Sprague de Camp classic radio drama series.
You can hear this line at 00:26:57 in the radio play.
Quote context
[...]
- Good Lord, look at that. Ghastly, isn't it?
- Ghastly mess. Looks as if every bone was pulverized and every blood vessel burst. I dare say.
- But that's his gun all right. It's James... there's no doubt of it.
- You can't have paradoxes, you know... just isn't done.
- And, you see, I'm a lot more careful now.
[...]