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.

Filter by
Sorted by
Tagged with
-4
votes
0answers
23 views

Planck's circumference [on hold]

Theoretically speaking what would be the smallest diameter of a circumference drawn on the Planck's scale and what would it look like, and what about Pi? (using only Planck's length) Rephrasing (I ...
0
votes
1answer
22 views

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 ...
3
votes
2answers
155 views

If the wavefunction is continuous how can the many-worlds be discrete?

Preamble for clarity: The many worlds interpretation is usually used to explain the measurement of a 2 level system ($|0\rangle$ or $|1\rangle$) as: $$\frac{1}{\sqrt{2}}(|0\rangle+|1\rangle)|\text{...
0
votes
2answers
52 views

What is in physical term meaning of penetration of a potential barrier?

While solving the quantum mechanical case of potential barrier meaning - $$\text{E} <\text{V} $$ The transmission coefficient is nonzero. My problem is what is happening with particle motion Has ...
4
votes
2answers
107 views

Are superpositions contagious?

Does quantum mechanics really predict that a particle prepared in a state of superposition of spin will result, after being measured by an appropriate instrument (Stern-Gerlach device), in a ...
-2
votes
1answer
81 views

Quantum mechanics limits to understanding the Universe [closed]

By definition, a wave function does not describe a particle's state exactly, we can only know that information when we make measurements and thus collapse the wave function. This gives us a lot of ...
3
votes
1answer
72 views

Can we craft a Hamiltonian such that the measurement is consistent with the discrete measurement taught in Quantum physics?

So the way I understand this, the way measurement is taught is that you have a wave function $\Psi(t)$. It's evolution over time is : $$i \hbar \frac{d}{d t}\vert\Psi(t)\rangle = \hat H(t)\vert\Psi(t)...
0
votes
1answer
79 views

In QM does the observer really perturb the system to make a measurement?

It is commonly taught in introductory QM courses that in order to get to know the position or momentum of a particle, be it by "sending a photon" or similar experiments, the measurement necessarily ...
6
votes
1answer
471 views

Is the Born rule indeed wrong?

This is a question about the validity of a preprint, arXiv:quant-ph/0509089, which claims that the "Copenhagen Interpretation of QM is incorrect" (same title, authored by Guang-Liang Li and Victor O.K....
3
votes
0answers
93 views

What is the simplest model of a quantum measurement on a 2 level system

What is the simplest physical system which can be used to model the quantum measurement of a 2 level system? For example, can the following, spin coupled to a harmonic bath, be used to model a ...
2
votes
2answers
91 views

Does observation in quantum theories always imply interaction (affecting quantum system with photons, electromagnetic fields, etc.)?

The term observation is obscure. As I see so far, observation is always done by means of affecting (!) the quantum system by some means - often photons or electromagnetic waves or whatever else. ...
1
vote
0answers
95 views

Measurement problem: Origin of probabilities in Many-Worlds Interpretation

As far as I can tell there appears to be an active group of academics (including the likes of Sean Carrol) who believe in the Many-Worlds Interpretation of quantum mechanics, but feel that the origin ...
0
votes
0answers
61 views

Can wave collapse during measurement be avoided with a better experiment / measurement apparatus?

Or to restate the question, does quantum mechanics or the quantum field theory state or imply that we can only observe the wave in a collapsed state? And if they don't, do we have any promising ...
3
votes
1answer
76 views

Why does the interaction with environment remove the basis ambiguity : decoherence theory

In decoherence theory, we try to remove the measurement postulate from Q.M to replace it by unitary evolutions. Consider a two level system $S$, an apparatus $A$ and the environment $E$. A first ...
2
votes
2answers
100 views

Is this decoherence?

I have a very basic understanting of decoherence (i.e. I,ve read the Wikipedia page), but I was recently reading Heisenberg's The Physical Principles of the Quantum Theory and I came across a thought ...
3
votes
1answer
118 views

Full Hilbert space of a particle

Given the Hilbert space $H$ of a single particle, we know we can write \begin{equation} H = H_{spatial}\otimes H_{other} \end{equation} where $H_{spatial}$ is spanned by the possible position states ...
51
votes
5answers
6k views

Why aren't particles constantly “measured” by the whole universe?

Let's say we are doing the double slit experiment with electrons. We get an interference pattern, and if we put detectors at slits, then we get two piles pattern because we measure electrons' ...
5
votes
3answers
1k views

Why is wave-function collapse still being taught in quantum mechanics? [closed]

I don't really understand why wave-function collapse is still being taught while we seem to have better interpretations of QM available nowadays. During the early development of quantum mechanics the ...
9
votes
5answers
227 views

Conceptual understanding of operators in QM

Do operators in QM represent in some fashion the action of the measurement apparatus on a state being measured? Usually operators in QM are introduced as abstract transformations whose eigenvectors/...
3
votes
1answer
58 views

Is sole projection onto a subspace of a system associated with a quantum mechanical measurement?

I'm a little confused about a recent discussion, where a one dimensional wave-function $\Psi(x)$ was considered, associated with a state $$|\Psi\rangle = \int dx \, \Psi(x) |x\rangle .$$ Now ...
0
votes
2answers
72 views

Doing Stern-Gerlach experiment without blocking the atoms in the $-x$ direction

In quantum mechanics, in general, it is stated that the act of measurement changes the state of the system. For example, consider the following Stern-Gerlach setup; A beam of silver atoms first ...
3
votes
1answer
85 views

Is is possible to have a pair commuting observables only in a single direction?

In quantum mechanics, for two observables to be compatible, successive measurements of the observables, say $A$ and $B$, should yield the same result as earlier, i.e if we do the measurements with the ...
3
votes
2answers
82 views

What’s a measurement qualifier in the double-slit experiment

In the double-slit experiment why does the light hitting the back screen not result in a measurement? How far away from the slit can the measurement take place and still cause a wave collapse and is ...
2
votes
1answer
132 views

Simultaneous measurements in Quantum Mechanics

In the notes I am using, it states that if two observables A and B are measured simultaneously, then the measurement of A does not affect the measurement of B, and vice versa. However, why does the ...
2
votes
1answer
74 views

Does the Hermitian Operator Reduce the Non-eigenstate State to the Self-Eigenstate?

Let's consider $\left| \Psi \right> $ some state of quantum system. Let's also consider some Hermitian Operator $\hat{Q}$, with the discrete specrum: $$ \hat{Q}\left| Q_n \right> = Q_n\left| ...
0
votes
1answer
128 views

Finding an energy of a particle in an infinite potential well

This question arises from a discussion I recently had with my friend. We were talking about a particle in an infinite potential well. The particle is in an arbitrary wavefunction $\Psi$. When one ...
3
votes
1answer
64 views

Difference between Wavefunction collapse and throw of dice

It might be a really stupid question and I think I am trivializing it. I am not able the understand the big issue with collapse of wave function. So we have set of probabilities and when you measure ...
1
vote
1answer
69 views

The common wavefunction and annihilation of 1 photon [closed]

QM says that if we have many particles they have a common wavefunction. Also QM says that when you measure a particle or observe it, you collapse its wavefunction. That must be a logical mistake. Now ...
-1
votes
2answers
105 views

Time evolution of stationary states [closed]

Let's say we have a state $ \phi=\sum_i c_i \phi_i $ where the $ \phi_i $ denote energy eigen vectors with non degenerate eigen values. Now if a measurement of the energy is done this state ...
1
vote
1answer
140 views

Heisenberg choice of the observables and different outcomes [duplicate]

Somebody could help me to clarify how its possible that different choices of the observable to measure can lead to different outcomes of the observed system state?
0
votes
1answer
85 views

The many world interpretation and immortality [closed]

This question might not be appropriate as it is philosophical on a similar level as the Schrödinger's cat thought experiment. In any case it might be interesting to think about it nonetheless. The ...
3
votes
3answers
616 views

What constitutes measuring in the double slit experiment? [duplicate]

In the double slit experiment attempting to measure which slit the particle passed through causes the wave function to collapse. According to the question: What is the quantum mechanical definition ...
4
votes
2answers
231 views

Decoherence: faster than light?

The answer to this question suggest that one can solve the measurement problem by decoherence. If I understand it correctly the decoherence appears when the quantum state interacts with the ...
27
votes
3answers
3k views

Would every particle in the universe not have some form of measurement occurring at any given time? [duplicate]

I know this is probably a common point of confusion, but I have a specific question about measurements in Quantum Mechanics. I read an explanation on this, but still have a point of confusion. The ...
0
votes
1answer
90 views

Is there a quantum analogue of Mean Value Theorem theorem?

Background I was thinking of Mean Value Theorem in the context of classical mechanics I have $2$ points $A$ and $B$ and my particle goes from $A$ to $B$ then I know the velocity of the particle at a ...
3
votes
2answers
167 views

Does Von Neumann entropy fail to account for projective quantum measurements?

I'm trying to understand if this line of reasoning is correct: For a two-state pure quantum system $\left|\psi \right\rangle=\frac{1}{\sqrt{2}} (\left|0 \right\rangle+\left|1 \right\rangle)$, The ...
0
votes
1answer
21 views

Measuring change in magnitude of electric current due to change in conducting material characteristics

I am new to this community and hence may not be aware of all the rules. Please do let me know if you think I am violating any. I will try to get it corrected. I am trying to get an answer to the ...
2
votes
0answers
76 views

Information Centric Interpretation of the Delayed Choice Experiment

The photon travels from the emmitter to the detector. Along the way it bounces off a few mirrors and off or through a beam splitter or two. This journey takes time, but only from OUR perspective/frame....
1
vote
1answer
82 views

A problem in three sequential selective measurements in case of incompatible observables

In case (a) the B filter takes care of B's eigenvalues and we sum all of their probabilities to calculate the probability of obtaining $|c'\rangle$. In case (b) B filter is not used and this creates ...
2
votes
1answer
56 views

Probability of a particle to go from one position to another

In Feynman's lectures on physics Volume:3 Ch:21. Feynman states The amplitude that a particle goes from one place to another along a certain route when there’s a field present is the same as the ...
-4
votes
1answer
101 views

Would Schroedinger's cat smell 50% like death? [duplicate]

If we left Schroedinger's cat in a superposition for a week would it begin to start smelling 50% like a dead cat and 50% like a living cat? Would the smell of death immediately disappear if we opened ...
3
votes
2answers
259 views

How is it possible that a universal wave function is predicted to simulate a continuously branching timeline?

If there was no mistake and it actually is the case that a universal wave function that's in a very ordered state at the beginning of time is predicted to simulate a continuously branching timeline ...
2
votes
1answer
147 views

Is the Everettian interpretation the only 'realist' interpretation which has been actively researched for relativistic quantum theories? [closed]

I take it that quantum interpretations can be roughly classified into realist and instrumentalist interpretations. In the former category we have the De Broglie-Bohm interpretation, Everettian ...
3
votes
3answers
325 views

Does Newton's first law of motion apply to a single moving electron?

That is in a zero electric field, if an electron moving, does it follow rectilinear propagation? Does it follow Newton's first law of motion? I not asking about newtonian mechanics. I am asking ...
3
votes
1answer
202 views

Two Time Correlation function calculated from Born rule

Update Below I'm having a hard time reconciling two different calculations of the quantum two time correlation function. Consider quantum operator $A$ with eigenvectors $\{|\phi_i\rangle\}$ and ...
0
votes
1answer
85 views

Collapse of the wave function and switching off measurement device before particles hit the wall detector

Would collapsing wave function by measuring/observing and then quickly turning off measurement device cause to uncollapse wave function? so it goes like this : wave--->particle---> wave(hits the wall)...
1
vote
2answers
97 views

Current quantum theory does not offer a dynamical mechanism to account for energy transfer in position-measurement, WHY?

In Quantum Mechanics (vol. 1) by Tannoudji et al., there are two pages discussing "perturbation created by a position measurement" (p.278-279). They consider a particle in an infinitely deep potential ...
1
vote
1answer
67 views

What is the relation between uncertainty and information obtained from a measurement?

For ex. if a measurement gives a position with twice the uncertainty as another measurement, how much less information regarding position are you getting? In other words, if uncertainty doubles, is ...
2
votes
7answers
270 views

What do positions in Schrodinger Equation mean (Remember: the particle never has definite position)?

In position or configuration representation, the Hamiltonian operator, and thus the Schrodinger Equation, is expressed in terms of positions. But the particle never has definite position, what do ...
10
votes
5answers
744 views

Measuring quantum mechanics changes the answer and energy?

A thought occured to me thinking about the quantum slit experiment. Upon firing an electron or particle it would impart an opposing force on the machine shooting it. The direction if this force should ...