A Century of Quantum Mechanics

Physicist Sean M. Carroll writes a high-profile Nature essay:

Why even physicists still don’t understand quantum theory 100 years on

Quantum mechanics depicts a counter-intuitive reality in which the act of observation influences what is observed — and few can agree on what that means.

He did not write those titles. He does not deliver on the titled promises.

PHysicists understand quantum mechanics just fine, and there is broad agreement on what it means. There is a faction of philosopher wannabes like him who believe in many-worlds or some other goofy variant, but the real work is being done by those who follow Copenhagen or say shut up and calculate.

Most of what he writes is reasonable:

It was the German physicist Werner Heisenberg who, in 1925, first put forward a comprehensive version of quantum mechanics. ... So it is fair to celebrate 2025 as the true centenary of quantum theory. ...

Whereas in classical physics, a particle such as an electron has a real, objective position and momentum at any given moment, in quantum mechanics, those quantities don’t, in general, ‘exist’ in any objective way before that measurement. Position and momentum are things that can be observed, but they are not pre-existing facts. That is quite a distinction. The most vivid implication of this situation is Heisenberg’s uncertainty principle, introduced in 1927, which says that there is no state an electron can be in for which we can perfectly predict both its position and its momentum ahead of time2.

This is because position and momentum are non-commuting operators.

He starts to go off the rails:

As a result, the probability of observing one particle to be somewhere can depend on where we observe another particle to be, and this remains true no matter how far apart they are.

Actually, classical probabilities work the same way. Probabilities nearly always depend on other observations.

Bohr, along with Heisenberg, was willing to forgo any talk about what was ‘really happening’, focusing instead on making predictions for what will happen when something is measured.

The bizarre logic of the many-worlds theory

The latter perspective gave rise to ‘epistemic’ interpretations of quantum theory. The views of Bohr and Heisenberg came to be known as the Copenhagen interpretation, which is very close to what physicists teach in textbooks today.

Yes, that is the mainstream view. Science is all about what can be observed, not speculations about imaginary parallel universes.

Mercifully, the paywall blocked me from reading the rest, which presumably rambles into many-worlds nonsense. I can only get the above link to a 2019 essay:

At the beginning of Something Deeply Hidden, Sean Carroll cites the tale of the fox and the grapes from Aesop’s Fables. A hungry fox tries to reach a bunch of grapes dangling from a vine. Finding them beyond his grasp, but refusing to admit failure, the fox declares the grapes to be inedible and turns away. That, Carroll declares, encapsulates how physicists treat the wacky implications of quantum mechanics.

Carroll wants that to stop. The fox can reach the grapes, he argues, with the many-worlds theory.

That is where we get the term "sour grapes". In this case, the many-worlds theory really is inedible. Carroll is misleading everyone.