This is a very brilliant book by a very clever man.
It's a mind boggling odyssey through the four different and discrete ways in which our universe is myriad.
1. The physical universe may well be infinite.
2. The physical universe may well be a slice of a more complex physical universe, with varying physical constants.
3. The many worlds interpretation of quantum physics is easily solved by anther level of universal multiplicity.
4. Everything discussed up to this point may be a single mathematical abstraction, and therefore one of an infinite number of said abstractions.
The chances of all four categories of multiverse being wrong is close to zero, the possibility that all four may be correct is actually quite high.
That means that everything that is happening, is happening elsewhere, either infinitely, on each level, or just a staggeringly high amount.
The consequences are examined too.
That's where it gets really crazy. Very possibly every choice we make, we also don't make.
Every time we die, we also don't die, and when the dust has settled, whichever one of us survives is the one we perceive ourselves to be.
It get's weirder. The implications regarding suicide are very disturbing.
I know I've had about 6 very close brushes with death, accidental and intentional, and the very real possibility that each time, there's a whole tranche of universes in which I did die, makes me feel very melancholy.
If you've seen The Prestige or the Vat of Acid Episode of Rick and Morty
Well, imagine that, only for real, because the universe plays out every possibility.
I can't really do it justice in a short blog review.