I want to talk briefly about a couple of reasons that physicists are so weirded out by quantum mechanics.

Now, I want to hasten to say that quantum theories give REALLY good predictions. FANTASTICALLY good. So why are they a source of such discomfort?

Keep in mind, this is all my opinion. Others might disagree or think other reasons are more important.

But here we go!

1. The theories are mathematical messes.

Although renormalization is now much better understood, it is still a weird technique, and there's little to no reason, mathematically, to expect that the perturbation series converge. So... are the theories even mathematically consistent? Nobody knows!

However, I would argue that this is a relatively minor problem! Because we can probably fix them up when we understand things better. For example, loop quantum gravity and string theory both give ways to get rid of the divergences which plague quantum field theory.

Deeper problem forthcoming:

2. Nobody knows what the fuck measurement means.

One of the Von Neumann's axioms about quantum theories involves measurements. The problem is that nobody can define what a measurement is.

What's more, Von Neumann proved that, basically, YOU CANNOT DISTINGUISH DIFFERENT PROPOSALS FOR WHAT A MEASUREMENT IS, EXPERIMENTALLY.

That is weird as fuck for people used to being purely empirical!

Note: Von Neumann's conclusion seems not to quite qualify when we start working quantum erasure into the picture, but I don't want to get into that at the moment.

Anyway, various proposals have been made for what a measurement is. Including some that totally rework the theory, like De Broglie-Bohm theories... but they give identical empirical predictions!

Ok, now here's where things get even worse:

3. Regardless of what measurement really is, it somehow violates a cherished notion of classical physics and causal ordering.

See, the universe has, on a classical level, a 'light cone structure.' In theory, no causal influence should be possible, except forward in the light cone. But measurements have to have causal influences outside the light cone.

This is a consequence of Bell's inequality, which has been experimentally verified.

Note that this does NOT mean that relativistic physics is wrong about the nature of time as a dimension. But it means that at the very least...

... causal ordering and chronological ordering are not exactly the same.

Physicists are so uncomfortable with this conclusion that I've seen them make some REALLY BATSHIT attempts to avoid it. Basically they amount to ignoring the problem

Parenthetically, Rovelli, a famous physicist, is guilty of having a logically inconsistent resolution to this problem.

I wrote a paper that included a description of the inconsistency, but the journal rejected it. Possibly because Rovelli was the chief editor of the journal

And since the paper was kind of silly I didn't bother trying to publish it elsewhere