I Simultaneous measurements of 1 observable

[Ghost Quartz]

TL;DR Summary

some doubts about the measurement of observables

Hi. I'm new to the forum and and I am currently studying quantum mechanics.
According Sakurai, page 24, "When the measurement is performed, the system is" thrown into" one of eigenstates of observable". This raised some questions for me:

Is possible two measurements simultaneous of one observable?
If yes, then will the eigenvalue be equal in both measurements? if they will be the equal, why will they be the equal?

If not, then why not? I do not remember it well, but I believe I have heard somewhere that it is impossible for two photons to interact simultaneously with an electron. Is there any relation?

i am not a graduate student in physics, then I don't know the correct level of this thread. When in doubt I put A, sorry for this.

 

[Nugatory]

i am not a graduate student in physics, then I don't know the correct level of this thread. When in doubt I put A, sorry for this.

”I” for general college level is about right, and it’s no problem - just a few mouse clicks to change, probably the most common edit I make.

 

[PeroK]

According Sakurai, page 24, "When the measurement is performed, the system is" thrown into" one of eigenstates of observable". This raised some questions for me:

Is possible two measurements simultaneous of one observable?

If you think of QM as describing nature at an elementary level, then it's not possible. Two observers can independently and simultaneously measure the velocity and position of a car, for example, because the car can be bombarded by light from all directions without significantly changing its position or momentum.

You can't do that to a electron. The position measurement of an electron must be deduced indirectly by the scattering of a single photon, say. That's a whole different game.

The role of measurement in QM is subtle and somewhat problematic. For the time being, I would assume that a system in QM is subject to one measurement at a time.