Black holes can’t trash info about what they swallow—and that’s a problem

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Three numbers.

Just three numbers—that’s all it takes to completely, unequivocally, 100 percent describe a black hole in general relativity. If I tell you the mass, electric charge, and spin (i.e., angular momentum) of a black hole, we’re done. That’s all we’ll ever know about it and all we’ll ever need to describe its features.

Those three numbers allow us to calculate everything about how a black hole will interact with its environment, how objects around it will respond to it, and how the black hole will evolve in the future.