There are other silly objections to EQM, of course. The most popular is probably the complaint that it’s not falsifiable. That truly makes no sense. It’s trivial to falsify EQM — just do an experiment that violates the Schrödinger equation or the principle of superposition, which are the only things the theory assumes. Witness a dynamical collapse, or find a hidden variable. Of course we don’t see the other worlds directly, but — in case we haven’t yet driven home the point loudly enough — those other worlds are not added on to the theory. They come out automatically if you believe in quantum mechanics.This is nonsense. I don't want to keep picking on Carroll, but it seems that more and more physicists are reciting such nonsense in favor of MWI. (Carroll also calls it Everettian quantum mechanics, EQM.)
Lumo explains how Carroll is wrong
At the same time, salesmen like Carroll offer you lots of incredible statements such as the statement that this "many worlds interpretation" directly follows from quantum mechanics, is directly justified by quantum mechanics (more justifiable in quantum mechanics than in classical physics), and unlike proper quantum mechanics, it doesn't introduce any new physical laws. All these statements are untrue. They are really the polar opposite of the truth.The 2013 paper, On Quantum Theory, by Berthold-Georg Englert also explains:
First, many worlds surely don't follow from quantum mechanics.
Quantum mechanics is the universal framework of modern physics which is a natural science. As every natural science, physics predicts or explains the observations that are actually being made in one Universe.
Quantum theory had essentially taken its final shape by the end of the 1920s and, in the more than eighty years since then, has been spectacularly successful and reliable — there is no experimental fact, not a single one, that contradicts a quantum-theoretical prediction. Yet, there is a steady stream of publications that are motivated by alleged fundamental problems: We are told that quantum theory is ill-defined, that its interpretation is unclear, that it is nonlocal, that there is an unresolved “measurement problem,” and so forth.That is correct. Quantum mechanics, as it has been described in textbooks for decades, is a perfectly good theory. It is strikingly successful, and yet from Einstein in the 1930s to many well-known physicists today, they act as if the theory is broken. They even say that realizing that quantum mechanics requires many worlds is like the Copernican revolution.
It may, therefore, be worth reviewing what quantum theory is and what it is about.
This modern rejection of quantum mechanics is just as crazy as if modern physicists went around claiming that particles can go faster than light because they don't believe relativity. I wonder how they ever passed their PhD qualifying exams without understanding quantum mechanics.
Carroll is proof that a physicist can lose the capacity for scientific thinking if his brain is infected with lousy philosophy.
The principle reason for rejecting MWI is that it postulates an infinity of unobservable worlds without any physical benefit. It adds no practical or conceptual advantages over textbook quantum mechanics, and is unscientific in having supernatural beliefs. It even has disadvantages, because it makes probabilities nearly impossible to interpret. Its advocates claim that it cures some philosophical defect of quantum mechanics, but there is no such defect.
The quantum computing folks, like David Deutsch, love MWI because the extra universes are supposedly where the super-Turing computation takes place. No such computation has ever been observed, and the whole field is a big funding scam.