The measurement process therefore is not only an additional assumption that quantum mechanics needs to reproduce what we observe. It is actually incompatible with the Schrödinger equation.Actually, I think it is. Quantum mechanics was created by positivists, and their attitude is to go with what we've got, and not worry too much about purely philosophical objections.
Now, the most obvious way to deal with that is to say, well, the measurement process is something complicated that we do not yet understand, and the wave-function collapse is a placeholder that we use until we will figured out something better.
But that’s not how most physicists deal with it.
Most sign up for what is known as the Copenhagen interpretation, that basically says you’re not supposed to ask what happens during measurement. In this interpretation, quantum mechanics is merely a mathematical machinery that makes predictions and that’s that. The problem with Copenhagen – and with all similar interpretations – is that they require you to give up the idea that what a macroscopic object, like a detector does should be derivable from theory of its microscopic constituents.The positivists would go along with saying that the theory is all about the predictions, but would never say that you are not supposed to ask about the measurement process. Positivists do not tell you what not to do. They talk about what works.
If you believe in the Copenhagen interpretation you have to buy that what the detector does just cannot be derived from the behavior of its microscopic constituents.
She is completely correct that the collapse is observed. Some people complain that Copenhagen is goofy because the collapse is unnatural, but all interpretations have to explain the apparent collapse somehow.
The many world interpretation, now, supposedly does away with the problem of the quantum measurement and it does this by just saying there isn’t such a thing as wavefunction collapse. Instead, many worlds people say, every time you make a measurement, the universe splits into several parallel words, one for each possible measurement outcome. This universe splitting is also sometimes called branching. ...She is right that Many-Worlds does not solve the measurement problem, and really has to have its own sneaky collapse postulate like Copenhagen, even tho the whole point of Many-Worlds was to avoid that.
And because it’s the same thing you already know that you cannot derive this detector definition from the Schrödinger equation. It’s not possible. What the many worlds people are now trying instead is to derive this postulate from rational choice theory. But of course that brings back in macroscopic terms, like actors who make decisions and so on. In other words, this reference to knowledge is equally in conflict with reductionism as is the Copenhagen interpretation.
And that’s why the many worlds interpretation does not solve the measurement problem and therefore it is equally troubled as all other interpretations of quantum mechanics.
However the situation with Many-Worlds is worse than that. Any physical theory could be turned into a Many-Worlds theory by simply introducing a universe splitting for each probabilistic prediction. This can be done with Newtonian celestial mechanics, electromagnetism, relativity, or anything else.
With any of these Many-Worlds theories, you can believe in them if you want, but the split universes have no observable consequences except to reduce or kill the predictive power of your theory. Any freak event can be explained away by splitting to another universe.
So Many-Worlds does not, and cannot, explain anything. It is just smoke and mirrors.
A reader asks:
What is your explanation as to why many people who are obviously very smart, such as Max Tegmark, David Deutsch, Sean Carroll, etc, subscribe to the many-worlds interpretation?Why do so many smart people tell lies about Donald Trump every day?
I wrote a whole book on how Physics has lost its way. There is now a long list of subjects where prominent Physics professors recite nonsense. I hesitate to say that they are all con men, as many appear to be sincerely misguided.