I read a book many years ago that talks about the shortest distance between two points being a line, and if you held a string between those points you can fold the string to connect the points. The book is about teleportation and space travel, and I believe it has a purple cover. Anyone know of this book?
Are you thinking of A Wrinkle in Time? Three kids are teleported around space by a trio of supernatural aliens using folds or wrinkles in space-time.
Could it be Robert Heinlein's "Tunnel in the Sky", one of the original covers was sort of a purplish pink color. It's about teleportation as a means of space travel to colonize far off planets.
The main character is a high school boy who is taking a survival test, him and his team are supposed to be teleported to a distant primitive planet and survive 10 days, but something goes wrong and they are accidentally sent to an unknown planet for far longer and must learn to survive.
I don't specifically remember the scene with the string as reference to space travel, but it could be in there.
The first instance that I remember of that type of scene is in the movie Event Horizon with a piece of paper and then again in I think Interstellar. But I haven't read it in a book.