# Questions tagged [measurement-problem]

DO NOT USE THIS TAG just because your question involves measurements (either quantum or classical). The measurement problem asks how wave function collapse occurs during measurement in quantum mechanics, and how it can be reconciled with unitary evolution.

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### Why is wave function collapse mysterious?

There are lots of questions and answers on this site about wave function collapse (for example, How does a Wavefunction collapse?, Why does a wavefunction collapse when observation takes place?, How ...
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### Is Uncertainty from a Scalar object using Momentum/Direction from Vector? [closed]

A Scalar Object is a Physical Scalar Volume. I'm asking what causes Uncertainty, not what we already know. Are objects tossed in the double slit, that can't display fringes, subject to the Measurement ...
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### Why does particle measurement cause quantum wavefunctions to collapse

When we attempt to measure a certain property of a particle, how and why does its wave function collapse? I've tried to find answers on my own, but they've been far too complicated for me to ...
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### Why does commutativity mean that two observables can be measured together?

BACKGROUND As far as the Heisenberg uncertainty principle is concerned, my understanding of commuting observables $\hat{A}$ and $\hat{B}$ is that the measurement outcome $a_i$ does not perturb (or ...
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### Can someone explain the measurement problem with little bit of mathematics?

Can someone mathematize the statement of the quantum measurement problem? I am only interested in the statement of the problem (and not its solutions). Thanks. Still confused. Stated in this way (as ...
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### Does the Bell test preclude localism, realism, both, or just one of either (indeterminate)?

I saw this excerpt from the wikipedia article on EPR paradox They postulate that these elements of reality are, in modern terminology, local, in the sense that each belongs to a certain point in ...
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### Can quantum measurements be the origin of thermodynamic arrow of time?

We can practically consider that the microscopic interactions are symmetric with respect to time(as we can neglect weak force for many cases which is the only interaction that can violate $T$ symmetry)...
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### Determine initial permeability from experimental data

How to determine initial permeability of the sample having only its dimensions (ring with $R$ - external radius, $r$ - internal radius, and thickness $h$), the number of coils around it $N$, and only ...
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### Wigner's friend experiment - How is there an apparent paradox?

Wigner's friend thought experiment mentions that there is an apparent paradox - 'when exactly did the collapse occur?'. Whether it occurred when the friend made the measurement, or when Wigner asked ...
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### Wigner's friend question [closed]

This is probably a dumb question, but does anyone know whether both Wigner and Wigner's friend observe the same result once both have been in the room and measured?
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### Electron interference

As I have understood, as per QM, electrons could behave as waves in a double slit experiment, i.e. form dark and bright bands, albeit after sufficient electrons have been shot from the source. Also, I ...
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### Measuring momentum in a 2 height well

In a 2 height finite square well we know that qualitatively the position wavefunction will have a lower amplitude in the side of the well with a smaller potential energy (since it will be travelling ...
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### Many-world interpretation and absolute time

Consider a quantum system $S$ in superposition of two state,with an observer $A$, forming a bigger quantum system $S'$, with observer $B$. At $t=0$, observer $A$ measure $S$ and according to MWI, the ...
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let's define 'a measurement device' as a system which is highly sensitive to the eigenstate of an observable. The sensitivity is quantified let's say by how irreversible and grand the small changes in ...
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### Difference between Phenomenal and Phenomenological in the Context of Physics

I was going through a conference presentation on System of Systems Engineering. In the presentation entitled "Macroscopic Quantum Mechanics and the SoSE Design Approach", I came across a ...
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### Are all processes time/CPT-reversible, e.g. measurement, stimulated emission, state preparation, Big Bang?

"The CPT theorem says that CPT symmetry holds for all physical phenomena, or more precisely, that any Lorentz invariant local quantum field theory with a Hermitian Hamiltonian must have CPT symmetry." ...
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### Penrose experiment

I just read about Penrose interpretation theory about the wave function collapse: https://en.wikipedia.org/wiki/Penrose_interpretation, which could be confirmed/infirmed by the following experiment: ...
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### Measuring small changes in length using the micrometer screw gauge

Which of the following method/instrument cannot be used to measure small changes of the order of a millimeter occurring in a length of about 50cm. 1)spherometer 2)travelling microscope 3)meter ...