> So measurement is just theoretical concept that relates to system physically getting immensely less fuzzy to a point we can safely assume for the sake of easier calculations that it's not fuzzy at all.
It appears to be more complicated than that, see Wigner's friend[1] thought experiment and a recent experimental realization of it[2].
From the paper's abstract: "In a state-of-the-art 6-photon experiment, we realise this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. If one holds fast to the assumptions of locality and free-choice, this result implies that quantum theory should be interpreted in an observer-dependent way."
Wigner's friend experiment doesn't contradict my interpretation in any way. For me it's not the exchange of information that causes system to become more sharp. It's poking that system with immensely huge stick built out of billions and billions tightly and sharply interacting particles that you have to do to get that information.
So when Wigner's friend makes the measurement of quantum system through interacting with it he causes it to collapse to sharper form. Wigner unaware of the result may still think that there's still some fuzziness in the system that consists of his friend and the experiment he performed. But in fact all the fuzziness was gone when his friend performed the experiment. The fact that Wigner doesn't know that yet, changes nothing in reality. Sure, he can treat his friend and his experiment as if they were quantum system. But they are not. The math I think looks the same if you don't know things about sharp stuff or if you know all there is to know about fuzzy stuff.
The actual 6-photon experiment is a bit too technical for me but I don't supposed "Wigner's friend" in it is built of billions of particles interacting with each other. If the friend is something smaller, like just a few particles that perhaps loosely interact then it's perfectly fine to expect that after measurement of one fuzzy system by another there's plenty of fuzzines left for the macroscopic observer (Wigner) to see.
> For me it's not the exchange of information that causes system to become more sharp. It's poking that system with immensely huge stick built out of billions and billions tightly and sharply interacting particles that you have to do to get that information.
That's exactly what I think about Schrödinger's Cat experiment. It's often implied that the hypothetical cat may be simultaneously both alive and dead, as if there are only two possible states for the cat.
There are approximately 7 x 10^27 atoms in the average human body. The figure for a cat wouldn't be much far from that I suppose. Taking that into account we can safely say that the quantum system (cat + radioactive source + poison) may actually simultaneously be in an abysmally high number of different entangled states, which may converge to, as you say, a "sharp" form.
Doesn't this experiment have a simple explanation that measuring something is essentially entangling yourself with it? So at the end of the thought experiment, both scientists and the test device are in a superposition together...
...except it's not that simple, and here is why I don't like those experiments (and why in reality, they're always realized using atoms, and not cats): there's no Wigner, or Schrödinger's cat, as a unit in physical sense. They're made of atoms. Atoms that interact and radiate information all the time. That box with a cat with it, the cat radiates information at the speed of light, which gets absorbed by the box and reradiated away. If the result of your thought experiment could be changed or confused by the following setup:
- a) put a broad-spectrum camera suite around the box prior to the experiment
- b) have it record data on the hard drive
- c) have the experimenter do their experiment
- d) have someone pull the data from the hard drive and read out the actual state of the experiment subject
... then it means your explanation for the thought experiment is wrong.
Yes it's extremely difficult not to leak (potential) information. This is called decoherence in these situations. It doesn't matter if you don't become conscious of the measurement result as long as some atoms in your body gets contaminated by the measurement they get pulled into the same branch (or whatever concept you subscribe to, it all works the same).
It appears to be more complicated than that, see Wigner's friend[1] thought experiment and a recent experimental realization of it[2].
From the paper's abstract: "In a state-of-the-art 6-photon experiment, we realise this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. If one holds fast to the assumptions of locality and free-choice, this result implies that quantum theory should be interpreted in an observer-dependent way."
[1]: https://en.wikipedia.org/wiki/Wigner%27s_friend
[2]: https://arxiv.org/abs/1902.05080