Richard Feynman famously declared, "I think that I can safely say that nobody really understands quantum mechanics." Sean Carroll lamented the persistence of this sentiment in a recent opinion piece entitled, "Even Physicists Don't Understand Quantum Mechanics. Worse, they don't seem to want to understand it." Quantum mechanics is arguably the greatest achievement of modern science and by and large we absolutely understand quantum theory. Rather, the "understanding" to which these two statements evidently refer concerns the ontological status of theoretical constructs.I agree with this. Quantum mechanics has been well-understood since 1930. It has become fashionable to rant about quantum mysteries, but some very smart physicists pondered those mysteries in the 1930s, and came to conclusions that are much more sensible than anything Carroll and other modern quantum expositors say. That is also Boughn's view:
I confess that during my student days, and even thereafter, I was mightily bothered by these quantum mysteries and enjoyed spending time and effort worrying about them. Of course, as Carroll also laments, I avoided letting this avocation interfere with my regular physics research, otherwise, my academic career undoubtedly would have suffered.4 As I approached the twilight of my career (I'm now retired), I happily resumed my ambition to "understand quantum mechanics" and have ended up writing several papers on the subject.5 Furthermore, as others before me, I now proudly profess that I finally understand quantum mechanics J. Even so, I'm somewhat chagrinned that my understanding is essentially the same as that expressed by Niels Bohr in the 1930s, minus some of Bohr's more philosophical trappings.6 Some have criticized my epiphany with remarks to the effect that I am too dismissive of the wonderful mysteries of quantum mechanics by relegating its role to that of an algorithm for making predictions while at the same time too reverent of insights provided by classical mechanics. I've come to believe that, quite to the contrary, those who still pursue an understanding of Carroll's quantum riddles are burdened with a classical view of reality and fail to truly embrace the fundamental quantum aspects of nature.Again, my experience is similar. I used to accept this story that there are great quantum mysteries that we need to solve with research into quantum foundations. But the problem is that people like Sean M. Carroll just don't want to accept quantum mechanics, and want to fit it into a classical physics paradigm.
Carroll subscribes to many-worlds, and claims that it solves the measurement problem. That is just crackpot stuff. The textbooks of the 1930s were vastly more sensible. There is no sense in which many-worlds solves the measurement problem, or any other problem.
Some people claim that Einstein discovered entanglement in his 1935 EPR paper, but this paper says that Einstein and Bohr were already arguing about entanglement in 1927.