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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How to calculate the amount of photons relased in an atom in an atomic reaction? [closed]

Each atom has an definite amount of neutrons released in nuclear fission and fusion. How is the photons calculated in the release of the sub-atomic particles?
Justintimeforfun's user avatar
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3 answers
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What happens if two people have different knowledge about a state in a quantum mechanical system?

Let’s say I measure the spin of an electron, but I don’t tell you what it is and you don’t measure it yourself. Does that change the wave function for you or does it remain the same either way? If it ...
Name's user avatar
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Does a Quantum System Really "Jump" to an Eigenstate When Observed?

Warning: This is a highly hypothetical question. I am bothered with Dirac's description of the system when making a measurement. Without quoting his statement (from The Principles of Quantum Mechanics,...
Con's user avatar
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7 votes
1 answer
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On the Measurement Problem

In the orthodox interpretation of quantum mechanics, the following three assumptions are made (please correct me if I am wrong): Every physical system is completely specified by a state $\lvert\psi\...
Davyz2's user avatar
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Is the collapse of the wavefunction relativistic?

If a stationary observer, 'A', observes the collapse of a wavefunction, does an observer, 'B', traveling at relativistic speed observe a different collapse of the same wavefunction? What do all the ...
Marco Fabbri's user avatar
-3 votes
2 answers
150 views

Position operator action on a wavefunction [closed]

In a 1 dimensional infinite potential well with width $a$, the ground state wave-function is given by $$\psi(x) = \sqrt{\frac{2}{a}}\sin(\frac{\pi}{a}x)$$ The action of the position operator in the ...
Anky Physics's user avatar
5 votes
3 answers
786 views

Exact time evolution of Stern-Gerlach (SG) apparatus

Background: I was always under the impression that when considering the Stern-Gerlach (SG) Experiment, the interpretation of the split of the beams is that the spin $1/2$ particle get measured the ...
2000mg Haigo 's user avatar
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3 answers
174 views

Doubts on my interpretation of Wigner’s friend scenario

I have some doubts regarding my personal interpretation that i was contemplating about in the context of Wigner's friend experiment (also tested in the laboratory).Could it be that a system is always ...
Marco Fabbri's user avatar
4 votes
1 answer
135 views

Understanding Wigner’s friend scenario

I recently watched this video https://youtu.be/Wsjgtp9XZxo?si=sIRlAbvAm2wjXRNP and tried (unsuccessfully, because i don’t have the knowledge required) to read Bruckner’s paper. What i am missing, is ...
Marco Fabbri's user avatar
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2 answers
170 views

Ontologically speaking, does single-shot quantum interference occur in pairs of possibilities?

I've been perplexed by the semantics used in Science 329, 418-421(2010), where they state that according to Born’s rule and its square exponent, interference always occurs in pairs of possibilities. ...
Tfovid's user avatar
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Andromeda paradox and quantum mechanics

Roger Penrose introduced the Andromeda Paradox as a thought experiment that delves into the implications of relativity and quantum mechanics on our understanding of simultaneity and reality. The ...
Marco Fabbri's user avatar
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1 answer
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Fundamental randomness unprovable? [closed]

Is it too strong a claim (i.e. unprovable) to say that no being (hypothetical or otherwise) could possibly predict the outcome of every individual measurement of any quantum system with certainty? ...
Joseph Robert Jepson's user avatar
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2 answers
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How can the Copenhagen and Everett interpretations of quantum mechanics make the same predictions?

Suppose we have a spin $\frac{1}{2}$ particle in the spin-up state along the $z$-axis, $\lvert \uparrow \rangle$, and after $t$ seconds of evolution under the Schrodinger equation it is in state $\...
MBar2269's user avatar
1 vote
3 answers
154 views

Shouldn't any measurement cause all wavefunctions to collapse?

Given the fact that every wavefunction exists everywhere in space, shouldn't a measurement at any location cause all wave functions to collapse since a measurement at any point measures all ...
Chris Laforet's user avatar
2 votes
1 answer
236 views

What exactly is a "measurement" in quantum mechanics?

*I can't see immediately whether or not this post constitutes as a duplicate, but I wouldn't be surprised if it does. If that is the case, then please reference me the post that I'm duplicating so ...
Joseph_Kopp's user avatar
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Do objective collapse equations actually collapse the state?

Why are objective collapse theories stated to collapse the state from a superposition to a single eigenstate (corresponding to the measured eigenvalue)? For this discussion, we are focusing on the ...
Jahn Dorian's user avatar
-1 votes
1 answer
68 views

Quantum Collapse during the Measurement of the spectrum of hydrogen [closed]

We have hydrogen inside a tube, and we induce a voltage on it; a current passes through it and light is emitted. The frequencies of light correspond to the differences of the eigenvalues of the energy ...
Zatrapilla's user avatar
1 vote
2 answers
186 views

Measurement problem and precise mathematical calculation

The infamous measurement problem is a problem in the foundations of quantum mechanics: different people have different views how to understand this problem: some people even deny that there is any ...
truebaran's user avatar
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2 answers
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Are there any other nondeterministic processes than measurement in quantum theory?

Nondeterministic refers to a system or process that does not have a single predictable outcome. In other words, when a system is nondeterministic, it means that multiple outcomes are possible for a ...
Kid A's user avatar
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How to obtain quantum-state purity and concurrence by measurement on quantum computer?

My whole question is aimed at the implementation on quantum computers utilizing quantum circuits, i.e. we can assume, that I can prepare several "copies" of the same state, without really ...
Eenoku's user avatar
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2 answers
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Quantum Measurement and the law of thermodynamics

When discussing the conceptual issues of quantum mechanics, concepts like Bell's inequality, non-locality, and the Kochen-Specker theorem are often brought up. Many physicists have dedicated time to ...
raskolnikov's user avatar
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Why is this a correct explanation for the Uncertainty Principle? [duplicate]

There's this really common explanation for Heisenberg's Uncertainty Principle, but I quote it from Classical Dynamics by Marion and Thornton: The wave character of the photon precludes an exact ...
Ambica Govind's user avatar
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4 answers
166 views

Is projective measurement a channel that results from a unitary evolution on both the system and the apparatus?

I was researching the motivation behind introducing quantum channels and this is essentially what I've gathered. Suppose we have two subsystems, the system we're interested in where states exist in ...
Adrien Amour's user avatar
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1 answer
63 views

Will the electron interference remain if the photon scattering method doesn't include a photo-detector? Is it an example of quantum entanglement?

It is actually not a question. I am giving a chain of arguments here , I believe at some point I made a mistake. I want the mistake to be pointed out. /1. The probability of an event in an ideal ...
SURYABARTA SAHA's user avatar
2 votes
1 answer
317 views

Nielsen and Chuang general measurements and POVM

I'm reading Nielsen and Chuang's famous book on Quantum Computation and Information. In section 2.2 on the postulates of quantum mechanics, they talk about quantum measurements starting with Postulate ...
Dimitri's user avatar
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1 answer
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What is the 'charge' and 'mass' of an electron means before measurement?

What I have learnt: We can't talk about an electron's position,momentum,angular momentum,energy...anything 'before the measurement'. An electron simply doesn't have these physical parameters before ...
SURYABARTA SAHA's user avatar
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1 answer
108 views

Ideal quantum measurement

Schlosshauer (in Decoherence and the Quantum-to-Classical Transition) defines ideal quantum measurement as a von-Neumann measurement in which (1) the apparatus states correspond 1-to-1 to given system ...
EE18's user avatar
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2 answers
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On the field leakage problem in quantum experiments

In a quantum experiment, does the leakage of the electromagnetic fields lead to the suppression of quantum effects? For example if I have an electron in a box, in some quantum superposition. Can I use ...
Mauricio's user avatar
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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 ...
EEatWork's user avatar
2 votes
3 answers
239 views

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 ...
Riemann's user avatar
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4 answers
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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 ...
Riemann's user avatar
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2 votes
3 answers
569 views

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 ...
Riemann's user avatar
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1 vote
0 answers
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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 ...
Mercury's user avatar
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1 vote
5 answers
513 views

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 ...
Daniel's user avatar
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-2 votes
2 answers
93 views

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 ...
Zehra 's user avatar
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1 answer
124 views

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 ...
James's user avatar
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1 vote
1 answer
114 views

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 ...
Jirka Meluzin's user avatar
3 votes
4 answers
498 views

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 ...
James's user avatar
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0 answers
118 views

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 ...
Ryder Rude's user avatar
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1 vote
3 answers
196 views

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 ...
ludwigvan's user avatar
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1 answer
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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 ...
Nunes's user avatar
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-5 votes
1 answer
132 views

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 ...
Leopard Mamba's user avatar
0 votes
1 answer
105 views

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 ...
Leopard Mamba's user avatar
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3 answers
281 views

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 $|\...
Leopard Mamba's user avatar
1 vote
2 answers
169 views

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 ...
William Elderfield's user avatar
2 votes
2 answers
217 views

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 "...
wawa's user avatar
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-3 votes
1 answer
99 views

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=...
Leopard Mamba's user avatar
0 votes
1 answer
179 views

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 ...
Leopard Mamba's user avatar
1 vote
1 answer
190 views

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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