This is a small book, in the genre of possible science. Rovelli has his ideas about the existence of “white holes” and explains the development of the theory in a rather charming way, citing Dante most of the way through the process. While I was able to follow along with his reasoning I wasn’t convinced about his theory. He says the math stands on its own, but I would know nothing about that.
Essentially, the life of a black hole is finite and when it ends, the star that began the process has collapsed to become a “Planck star” at which point it rebounds and over time becomes a white hole which, as you may guess, it the opposite of a black hole. It has a horizon, it has mass and information but the cycle is reversed in that it will ultimately give up all the information that went into the original black hole, minus the Hawking radiation.
It is an interesting read and I enjoyed both his writing and his physics.