Relativity reveals the fundamental nature of the world, the four-dimensional space-time universe. This, however, is only part of the picture. Taking quantum theory at face value, it means we live in the domain of all possible worlds. This is the meaning of Everett’s famous many-worlds theory. So these two extraordinary concepts are the essential, imagination-wrenching adjustments to our worldview. Not only is the universe incomprehensibly vast, but also every possible version of the world exists within it. The latter may sound too weird to be believable, but this is increasingly understood to be the only tenable interpretation of quantum theory, as described in The Case for Parallel Universes in Scientific American.
All Here and Now
The next point, which is no less tricky to grasp, is that all these worlds are here and now. They are not somewhere else, off in the distance. They are parallel realities, slightly different versions of the whole world, that exist exactly where we are. In this sense it is just like the parallel worlds in The Long Earth science-fiction series by Terry Pratchett and Stephen Baxter. The final point is the strangest of all. As described by Max Tegmark in Parallel Universes (pdf), one actually exists in a very large number of these worlds; this is an inevitable consequence of the new physics.
As cosmologist Max Tegmark (2003) describes in his article Parallel Universes, all possible worlds exist in the universe. And as he explains, this means there is a vast number of identical copies of you. This is simply because every possible variation of a world that contains you, exactly as you are here and now, must actually exist in the universe.
There is no question all these copies are the same person. As Deutsch reflects, given that there all these identical copies of oneself:
… which one am I? I am, of course, all of them. Each of them has just asked that question, ‘which one am I?’, and any true way of answering that question must give each one of them the same answer. (1997, 279)
Obviously, therefore, your world hologram exists in all those worlds. But since all these worlds are coincident and superposed, this means that there is only one inside view in all of these worlds: when you superpose copies of a structure of information, you just get that structure of information. In other words, there is in fact only one world hologram, one structure of information, that happens to exist in all these worlds, all at the same time.
The net result is that to experience this inside view is to experience the superposition of all of these worlds. In other words, the physical reality of this inside view is all of these worlds, superimposed. Therefore, since this is the view of reality you are actually experiencing, you actually live in a world superposition. This means your world works exactly like QBism describes.
Suppose there is a butterfly perched behind me sunning himself; I cannot see the position of his wings. For every possible position he may have adopted, there is a version of the world in which I exist. The net result in my physical reality – the superworld – is the sum of all these versions, as illustrated by the last image in the picture below. In other words, in my physical reality, the position of his wings is indeterminate.
This is the physical reality of the world of the individual. Everything I observe is determinate, but everything unobserved is a superposition of all possible variations of how it could be. This is what quantum theory is telling us. Here, however, we have a simple rationale for this weird concept, and a physical basis for the bizarre definition of the world in QBism.
This of course sounds all wrong because it seems so obvious the world we are actually living in must be an ordinary world, all there, real and solid. And it is. But the physical reality you encounter, the superworld, is the simultaneous existence of a great number of these worlds. And in this domain only what you have observed is determinate.
The things you have not observed are different in these different worlds, therefore, like the wings of the butterfly, these aspects of the world are all the different possibilities superposed, and the net result is indeterminate. In other words, exactly as described in QBism, other than that which is directly observed, everything is indeterminate. This means it is defined solely in terms of probabilities. In all likelihood the butterfly has his wings wide open for display, so this is the most likely observation for me if I turn and look. But before I do, the real physical situation is not just unknown, it is indeterminate. This is the many-worlds reality, the result of the superposition of worlds to form the superworld.
The Deep Things
The key point is that this resolves the great paradoxes of quantum theory, as the authors of QBism show. What is more, nothing else does according to a hundred years of research. In other words, taking the physical reality encountered, subjectively, at the second level of logical type, to be a superposition of worlds is a logical resolution of the fearsome paradoxes that have defeated comprehension of the quantum theory all this time.
It is certainly very weird but it is enormously significant. As stated by von Baeyer, quoted on the Home page, the general consensus is that the deep things quantum theory is so urgently trying to tell us about our world are irrelevant to everyday life, and too weird to matter. As shown here such perceptions are utterly false. The things the science is trying to tell us are certainly very weird because they are exactly the opposite of what seems so obviously to be true. But they could not be more relevant. As described in the following pages, one is deeply connected with the personal world because effectively one is constantly interacting with what is likely to be experienced happening in this world, everywhere, very slightly, all the time. All this is simply taking quantum theory at face value, as described in detail in this section of the site. But in order for the implications to make sense we have to understand the nature of the conscious individual, who we actually are. You are The World Hologram.