I've recently started my journey in understanding the math of quantum mechanics and I've noticed a strange pattern. (I'm not saying that the popular interpretation of quantum physics is wrong or anything. I'm just genuinely curious about this aspect of it.)
All of the descriptions of experiments that I've seen are spoken about as if measuring a particle doesn't affect the particle. A lot of the conclusions regarding the interpretation of the experimental results seem to be based on the assumption that measurement doesn't affect particles.
But isn't it obviously the case the measurement always affects the particle?
A polarizer will always reorient the polarization of a photon (basically every light experiment involving polarization).
Beam splitters affect the photons going through them, each exiting beam having different properties created by and/or filtered by the splitter (basically every light experiment).
A magnetic field will reorient a particle that has something like magnetic poles (Stern-Gerlach experiment and such).
And so on...
That last one in particular bothers me, especially when someone says that an electron's spin is "always up" or "always down" and never in between, despite the fact that measuring it intuitively appears to force it to be up or down regardless of whether or not it was somewhere in between before being measured.
However, I've never seen any physicists talking about how measurement affects the particles being measured or its impact on interpretation. Every time I ask about it, I never get a clear answer (but then again, I've only had access to physics professors).
And it seems like acknowledging the intrusiveness of measurement makes the experimental results much more intuitive than my teachers and popular physics videos seem to claim. They say "that's weird", but assuming the measurement affects the particles makes it not seem weird at all.
Is there a reason that measurement is talked about as not being intrusive, despite the obvious instinct being that it is?
Have we been able to demonstrate that it isn't intrusive somehow? Or do we know that it's intrusive, but we don't know how so we don't talk about it? Or is it something else?
Note: I'm not asking about the Uncertainty Principle. I'm totally comfortable with the implications of wave-particle duality.