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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Measurement Problem Explained by Interaction of Operator With Adjoint Having Larger Domain?

Quantum physics axiomatically uses a self-adjoint operator for a measurement. In general, the adjoint of an operator has a larger domain than an operator. Could it be that the "measurement ...
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Is the measurement problem an interpretation or practical problem?

According to Wikipedia: In quantum mechanics, the measurement problem is the problem of how, or whether, wave function collapse occurs. Is the measurement problem an interpretation problem or a ...
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Is the many-worlds interpretation less ill-defined than the Copenhagen interpretation? [closed]

In my understanding, the Copenhagen interpretation is ill-defined in the following way. The interpretation says that wavefunctions collapse when a measurement is performed. But the Copenhagen ...
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Can gravity cause a wave function to collapse?

Assume the Copenhagen interpretation. Suppose that a particle, for example an electron, has a wavefunction. If a heavy object, like the Earth, is close by, then that object interacts with the electron ...
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How to describe collective spin measurement in QM?

What is the QM description for measuring the collective magnetisation of an abitrary number $N$ of protons? For example, say that the density matrix is separable (no initial entanglement between ...
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Is a PBS a measuring device without observer?

Let a photon In superposition of v and h polarization is going through a Polarizing beam splitter PBS. If it passes, it is in h polarization on path A, otherwise is in v on path B. Let have a detector ...
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Testability of consciousness-causes-collapse interpretation

The consciousness causes collapse a.k.a. Von Neumann–Wigner interpretation says that the wavefunction collapse occur only at the point when a conscious being observes the result. I myself find it ...
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Average value of 3 measurements [closed]

Some physical quantity was measured two times. It’s average value is equal to 5. The reading of the third measurement is equal to 2. What is the average value based on the results of three ...
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Where no observer exists, does this mean the wavefunction never collapses?

In most places across the universe, there is no conceivably sentient candidate to act as an "observer" to this system. Are we to believe that, in the emptiness of intergalactic space, or ...
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Who caused first collapse of wave function?

With my wife we discuss a quantum theory and wonder whether a wave function could collapse without an observer - meaning a human/or any other living beings. If so we could make a conclusion that there ...
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Meaning of eigenvalue of the position operator $\hat{x}$?

Apologies for asking a question which may be too basic. I understand at the conceptual level that a measurement collapses a wavefunction into a single spike, which will then evolve again immediately ...
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What is an agent in the Quantum Bayesianism/Relational Quantum mechanics-like interpretations?

In interpretations like Quantum Basyesianism, Relational interpretation, Information Theory interpretation, etc, the wavefunction represents the probabilistic knowledge that an agent holds about a ...
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Nature of expectation values and Born's rule and the measurement problem

Suppose we take a normalised quantum mechanical wave function of $\Psi (\mathbf{r} ,t)$. If we expand it in a certain form of spatial functions $\psi_{n} (r)$ which is complete orthonormal. Then we ...
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Does the inside of a solid object not interact with the outside environment? But how does quantum decoherence happen?

We have learned that quantum decoherence is caused by interaction with the environment. However, inside our body, there is no interaction with photons or air molecules in the environment, so how does ...
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How can the Copenhagen interpretation possibly be redeemed of this contradiction? [closed]

It seems like the Copenhagen interpretation is just self contradictory. These two axioms are contradictory: Quantum Mechanics describes all the particles in the universe Measurement devices evolve ...
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Is the Born rule a red herring in explaining the measurement problem? [closed]

Many explanations of the measurement problem try to derive the Born rule from Schrodinger evolution, for example Many worlds. I have two reasons to think the Born rule isn't fundamentally related to ...
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Have physicists yet ruled out if wavefunction collapse happens due to the potential from the measurement apparatus?

Suppose there is an electron in a state $|\psi \rangle$, and there is a measurement apparatus whose atoms have a joint wavefunction $|m\rangle$. In experiments, we always know the initial value of $|\...
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Why does GRW theory choose position as a 'special' basis in which to localize?

GRW theory attempts to solve the measurement problem by positing that 'localization' events, where a particle's position wavefunction becomes localized (effectively, measured), happen at random times ...
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If measurement causes entanglement with the observer, is any further measurement possible?

When an observer measures a system, the systems wavefunction collapses and they become entangled. Does this mean that any further measurement by the observer on the system is impossible, as the system ...
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The state at wave function collapse [duplicate]

In the double slit experiment, why does the wave function collapse into the coordinate base? Why not into something else? How does the particle know that its position is measured (hence, it gets "...
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Replacement of Born rule to understand consciousness [closed]

This postulate should replace the Born rule as it makes the Born rule precise w.r.t. decoherence: "If a consciousness is in a superposition $\sum |k_i \rangle$, such that $\langle k_i|k_j\rangle=...
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Have we actually verified the claim that macroscopic objects collapse wavefunctions?

Copenhagen interpretation claims this, but have we actually verified this? There exist two options: Objective collapse: Consider a large isolated box inside which there is a macroscopic classical ...
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Projection Postulate of Quantum Mechanics. Where does the Projection occur in the detection process?

This question is about a specific instance of the measurement problem. Let's say we excite a single emitter producing a single photon (described by state $ |\psi_{i}>$), which then "travels&...
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What is the unitary operator which describes a measurement in the Many Worlds Interpretation?

According to the Copenhagen interpretation, the process of measurement is described by the collapse of the wavefunction, which is a non-unitary process. The Hermiticity of a Hamiltonian guarantees ...
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Understanding the Measurement Problem - Is this a good analogy? [closed]

I have asked the question in a better way: Does Vantage Point explain Bell's Inequality's Experimental Results? This question may remain closed. It can be head-melting to conceive of many ...
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Measurement in QM as an approximate form of unitary evolution

It is tempting to describe the wave function collapse / the measurement procedure as an approximate form of unitary evolution of a composite system consisting of a simple subsystem (being measured) ...
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What is the state of the art (potential) answers to the measurement problem of quantum mechanics?

I recently finished my undergraduate quantum mechanics course, and we used Griffiths' introductory textbook. One of the "open questions" within the book (and the course overall), was that of ...
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Pulse Area Uncertainty for a given Sample Rate and Bit Resolution

I'm recording pulses and want to approximately know how precise I can measure this with my Oscilloscope. I'm recording with 15 bit vertical resolution -> 1/(2^15) and a sample rate of 125 MS/s ->...
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In quantum experiments are we measuring the quantum state of a system or are we measuring the effect of the measurement on the quantum state?

At the macro classical world, measurements in experiments when done correctly interfere very little with the state of the system under investigation. As an example a digital ohmmeter with very high ...
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How to add markers to IR photographs

I'm using an IR camera to identify thermal patterns. The thermal images are similar to this [LINK] image. I'd like to add markers to the area being measured to determine dimensions and normalize the ...
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Trouble understanding the math of the preferred basis problem

I've been trying to understand the preferred-basis problem in QM, specifally in the Everettian intepretation. To quote an answer to another question which discusses this: In my opinion, the situation ...
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Is the uncertainity principle explained by disturbances or only by the Fourier picture?

Qualitatively, the tradeoff in uncertainty between two non-commuting observables $\hat{x}$ and $\hat{y}$, could be explained by... the Fourier picture where the more one variable is defined (i.e., ...
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Why macroscopic bodies should exist as wavepacket?

Based on my understanding, we assume that the electrons, exist as wavepackets in the solids while deriving the transport equations for transistors, we create wavepackets out of momentum eigenstates ...
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Have objective collapse theories been ruled out by recent experiments?

Have objective collapse theories been ruled out by recent experiments, such as the entanglement of macroscopic objects? (vibrating drumheads)
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I don't understand Wigner's friend paradox

The Wigner's friend experiment goes like this: Say Wigner instructed his friend to perform Schrödinger's cat experiment in a laboratory while he work from home, his friend made the measurement and ...
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Are quantum experiments superdeterministic? [closed]

Lately this recent video of Dr. Sabine Hossenfelder made me think if this theory deserves a serious review and has substantial ground. What are the rigorous arguments against this theory today? Please ...
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How is quantum "measurement" actually done?

There is a lot of talk in the fundamentals of QM about "measurement" and "observation", but never much specificity in what is going on at a basic level. For example, an electron ...
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Copenhagen interpetation applied to a video recording [duplicate]

I always get a little confused when it comes to the Copenhagen interpretation, and especially the fact that (for instance as per this article https://medium.com/science-and-philosophy/the-copenhagen-...
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Can weak measurement principles of Quantum mechanics be used in similar questions in classical estimation problems?

This is a surface level question and I don't want to go into detail. Imagine an algorithm which when used with a sensor output gives the statistical moments of a variable in nature (for example mean ...
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Spacetime of a quantum measurement

In a classical(or wave) picture, when we measure a doppler effect from a receding galaxy, we are working on two wave crests essentially. Therefore, there are two events in spacetime for such detection....
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Any unique or unified definition of measurement in physics?

I have not found any unique or unified definition of measurement in physics, and it seems that there isn't one. What is a unique or unified definition of measurement in physics?
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Kochen-Specker theorem and measurement map in the formalism of QM

There is (or rather was) a famous debate between Born and Einstein about interpretational issues of Quantum Mechanics. In this debate Einstein was advocating the so called theory of hidden variables. ...
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I'm not seeing any measurement/wave function collapse issue in quantum mechanics

The information about a particle is contained in a vector of unit-norm called the wave function. One postulates says that this wave function is supposed to evolve with time as the particle interacts ...
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Why is there a measurement problem? [closed]

From what I understand, the measurement problem seems to be a problem of humans limitations and nothing more. It seems to be pretty egocentric. We're saying, because we can only observe one probable ...
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Does the Many Worlds Interpretation make any distinction between entangling processes and measurement?

Suppose I have a qubit in the state $\alpha|0\rangle + \beta|1\rangle$. In the many worlds/relative state formulation of QM, if I measure this qubit with a measuring device in some initial state $|\...
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Stern Gerlach and interference

I recently came across this experiment: a beam of spin 1/2 particles pass through a Stern Gerlach apparatus oriented in the z direction. After passing through it and splitting, the beams are again ...
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Does quantum mechanics tell us when the next measurement will occur?

In many interpretations of quantum mechanics, the result of a measurement is regarded as non-deterministic. However, my question is: is the time at which a measurement occurs deterministic? To be ...
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When does the interference pattern of DSE disappear as size of "projectile" is increased? [closed]

In trying to learn about Quantum mechanics (QM) from popular science books and Stack Exchange (I of course expect my knowledge to be anything but complete) I regularly come up with seemingly childish ...
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Wigner friend experiment with qbits

Suppose that in his isolated box, Wigner's friend measures a qbit in state $|→⟩=\dfrac{|↑⟩+|↓⟩}{\sqrt{2}}$ along the vertical axe. Then, he sends Wigner (who remains outside the box) a qbit in the ...
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How do Heisenberg Uncertainty and Quantum Decoherence coexist? [closed]

I have a question that's intrigued me for awhile. How do Heisenberg Uncertainty and Quantum Decoherence coexist? I know in the early days of QM, a common reaction to the measurement problem was to say ...

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