- What is a black hole?
- What happens near a black hole?
- How do we know they exist?
- What about wormholes?
In order to explain what black holes are like, I’d like to relate to you the following parable.
A bunch of physicists are up late one night. They’ve been at a party. Most of the guests have left by now, nobody’s noticed that the music has stopped, and the air smells only faintly of sweat and a remarkable range of mind-altering substances. Somebody is passed out on the couch, but no one seems to know who it is. During a lull in the mumbled conversation, one of them happens to look up through a skylight and see the stars. She begins to think about how far that light has travelled to reach Earth, and about why it didn’t just stay where it is. She says so, out loud. One person mumbles in agreement. Another person suggests that maybe some stars don’t allow their light to leave at all. This sparks a two-hour long discussion that includes a whole complement of theories related to this kind of dark star, with names like the no-hair theorem and the information loss paradox. Before the last of them finally falls asleep, he mutters, “Black hole. We can call it a black hole.”
To the best of my knowledge, this is not a true story. But if you learn enough about black holes, you might be tempted to think that this is how people thought up the idea.