One of the central themes presented here is that the current paradigm is not actually wrong, it is just incomplete. The world one lives in is an ordinary physical world, but the full definition of this world is a superposition of many ordinary worlds. This is well illustrated by the famous idea of Schrödinger’s Cat.
This is a thought experiment by Erwin Schrödinger, the Nobel Prize-winning physicist who discovered the fundamental mathematics of quantum mechanics, the wave equation of physical reality. He produced this idea in order to demonstrate the absurdity of quantum theory; it means the cat has to be alive and dead at the same time.
Essentially, a cat in a closed box has a fifty-fifty chance of being killed by a quantum device. According to the principle of superposition, fundamental to quantum mechanics, unless it is observed, the cat is in a superposed state of being both alive and dead. Of course, when someone looks inside the box, the cat is either alive or dead; but that action is an observation, and according to quantum theory it is observation that makes things determinate. The big question is, what state is the cat in before, unobserved? Obviously, it cannot be both alive and dead at the same time.
Given QBism, the answer is simple indeed. The state of the cat is indeterminate, alive and dead, in the world of the scientist. But not, of course, in the world of the cat. The concept of world superposition explains exactly why this is the case. Taking quantum theory literally, as defined by the wave function of the universe, all possible versions of the world exist. Therefore there is a version of the world in which the cat dies, and a version in which it lives. The scientist exists in both of these versions of the world simultaneously; he exists in every possible version of the world where he carried out the experiment. So his world, his physical reality, is the sum of the two worlds added together, just as in the first picture. So in his world, the state of the cat is indeterminate because his physical reality is the superposed sum of both versions.
This gives us a proper physical explanation of this strange-seeming state of affairs. But that is only true until he looks in the box. As soon as he looks in the box he exists only in one or other of the two versions of the world, shown as separate in the second picture.
Quantum reality works like picture slides. You put two of them together and you get the superimposed sum of the content, as in the first picture. The general assumption in physics is that as an observer one is necessarily present only in one specific version of the many worlds. And with respect to the observer as defined by Everett, the physical body-mind, this is as true as it seems obvious. However, as the entity defined by the record of observations that Everett defines as the experiences of the observer, here the world hologram, one is necessarily present in a great number of worlds, as described in The Indeterminate World. Thus, for this kind of entity, the cat is both alive and dead at the same time.
The same is true of everything that has not been observed, not just cats in experiments for mad scientists. The person making the observation exists in so many ordinary worlds that every possible variation of things which have not been observed, is the case in some of them. As a result, the real world is like the first picture, with respect to everything that has not been observed. In other words, the physical reality encountered is the superposed sum of all these worlds, and it is indeterminate with respect to all the things which have not been observed. Every possible variation of these things is present, superposed, in the resulting physical reality. Thus the reality is determinate only where observed, as stated in QBism. This is the many-worlds reality.