Something Deeply Hidden
On Many Worlds and Consistent Histories interpretations of quantum mechanics
At last, I managed to read Something Deeply Hidden by Sean Carroll. This book had been patiently waiting its turn on my bookshelf for quite some time.
This is already at least the tenth popular science book on the subject of quantum mechanics that I have read so far. I've learned to be skeptical of such books because each author—consciously or not—takes on the role of a salesperson for their favorite interpretation of quantum mechanics. Unfortunately, Carroll does the same with the many-worlds interpretation.
The sophistical trick the author uses involves presenting his own theory against the convenient backdrop of another, very weak theory. This way, he can demonstrate its many advantages, freedom from paradoxes and difficulties, and internal coherence. "Look at the absurdities and inconsistencies in this theory! My theory is free from all of them. Simply a gem!" says the author, although he knows perfectly well that it would be much more difficult and less convincing if he chose the strongest competing theory instead of the weakest. The interpretation Carroll chose for that purpose is the still popular Copenhagen interpretation of quantum mechanics.
I do not deny that the many-worlds interpretation has many advantages. It avoids paradoxes and absurdities, is simple, and does not require unnecessary assumptions. Undoubtedly, it is an interpretation close to the correct solution. However, what repels me is the concept of multiple worlds. Not that the idea itself scares me. I am convinced that we live in some kind of multiverse, although I'm not convinced that it's precisely the one postulated by the many-worlds interpretation. The reason is that I consider the postulated multiplicity of worlds to be an unnecessary addition that can be relatively easily discarded.
The many-worlds interpretation states that when a quantum system in superposition is observed, first, entanglement occurs between the observer (who is also a quantum system, like everything else) and the system. Then, rapid decoherence of this entangled system with the observer occurs due to interaction with the environment, which causes reality to split into equally real branches. In other words, every possible measurement outcome is observed but on separate branches where observers are unaware of each other.
Another sophistical trick used by the author is showing the consequences of the interpretation through the least problematic examples. The author discusses how measuring the spin of a particle along one axis splits reality into two branches. However, he doesn't mention that attempting to localize an electron orbiting an atomic nucleus presents not two different possibilities but billions. For the purposes of this discussion, let's say a billion. If we wanted to localize an electron in a hundred consecutive atoms, we would split reality into a billion to the power of a billion to the power of a billion, and so on ninety-seven more times. This is true madness of creation.
Returning to the assumption that all branches are equally real—what exactly does that mean? How do we even know they truly exist? It seems to me like a dogma that isn't required to understand reality through the prism of quantum mechanics. Can't we, for example, assume that decoherence doesn't cause reality to split into an enormous number of really existing worlds, but that these are simply potential possibilities for the development of the situation, of which only one is realized with a probability given by the Born rule? Such a description of the world would be much more economical and wouldn't cause any additional problems.
This could be interpreted as a mechanism by which the creator of the Universe—a non-personal God manifesting according to its nature—made the Universe indeterministic. After all, if the Universe were to be indeterministic in its "design," this postulate must be physically realized somehow. It wouldn't happen just like that, by itself.
This does not, of course, mean that the many-worlds interpretation is wrong. It simply assumes much more than is required to sensibly capture what we observe in experiments in the microscopic world. And worst of all, this additional baggage is impossible to observe. I believe that the principle of economy of thought requires us to prefer the Consistent Histories interpretation (which I described above) over the Many Worlds interpretation.
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