Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [wavefunction-collapse]

Wavefunction collapse amounts to the apparent reduction of a wavefunction consisting of a superposition of several eigenstates to a single eigenstate (by "observation"). It underlies measurement in quantum mechanics and connects the wave function with classical observables, in a thermodynamically irreversible interaction with a classical environment, normally disfavoring future QM interference.

0
votes
1answer
38 views

Does measurement of momentum always collapse the wave function into a plane wave?

When you measure $\vec p$ the wave function collapses to an eigenstate of the momentum operator. These eigenfunctions are always plane waves, correct? Does it mean that momentum always collapses into ...
0
votes
1answer
113 views

Doubt about the probabilistic nature of quantum stuff and the field theory

To the quantum field theory, is it like there's "two layers of reality", one in which things are just probabilities waves that collapses into the quantum fields or is the quantum field and its waves ...
-3
votes
2answers
54 views

Does Quantum Entanglement happen between two wavefunctions? [closed]

Does the entanglement happen between two particles or two wavefunctions? If it's wavefunction then what happens to the two wavefuntions after getting entangled?
4
votes
3answers
973 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 ...
2
votes
1answer
89 views

Why doesn't observing a photon collapse it's wave function into a B or W3 boson?

According to electroweak theory, the photon ($\gamma^0$) and weak bosons ($W^+, W^-, Z^0$) are all linear combinations or superpositions of the weak hypercharge boson ($B$) and the weak isospin bosons ...
1
vote
1answer
68 views

Annihilation Operator on Entangled State - How Does This Not Break No-Communication Theorem?

If I have the state $$|\psi\rangle=\frac{1}{\sqrt{2}}\left(|2\rangle_{A}|0\rangle_{B}+|0\rangle_{A}|2\rangle_{B}\right)$$ and apply the annihilation operator to B $$a_{B}|\psi\rangle=|\phi\rangle=\...
-1
votes
1answer
40 views

Could we interpret search for the Pitch as a process similar to the collapse of the wave function?

According to Wikipedia: In quantum mechanics, wave function collapse is said to occur when a wave function—initially in a superposition of several eigenstates—appears to reduce to a single eigenstate ...
0
votes
0answers
32 views

Collapse of quantum state after measurement of degenerated eigenvalue (From textbook Shankar) (Closed)

I want to ask an easy question from Problem 4.2.1, Quantum Mechanics(2nd) by Shankar. Let's say Operators, $L_{x}$, $L_{y}$, $L_{z}$ are $$L_{x}$ = $1/2^{1/2}$ $\begin{pmatrix} 0& 1 &0 \\ ...
1
vote
1answer
69 views

Why does superposition principle and Copenhagen interpretation not contradict with themselves?

In quantum mechanics, when we say that a particle in a state $|x_1\rangle$, physically the states $|x_1 \rangle $ and $c |x_1\rangle$ (for some $c\not = 0\in \mathbb{C}$) are the same, i.e they ...
-1
votes
1answer
95 views
1
vote
1answer
111 views

Double slit experiment with only ONE detector [closed]

Suppose one sets up a double-slit experiment, but with only ONE detector behind one of the slits (the left one, let's say). Now suppose the dots that appear on the screen are ERASED (by the ...
5
votes
1answer
274 views

Wave particle duality and gravity

Is a particle's center of gravity at the center of its wave function or is it where we would measure the particle to be? When we measure a particle does its center of gravity shift to where the ...
11
votes
5answers
2k views

How can two electrons repel if it's impossible for free electrons to absorb or emit energy?

There is no acceptable/viable mechanism for a free electron to absorb or emit energy, without violating energy or momentum conservation. So its wavefunction cannot collapse into becoming a particle, ...
2
votes
1answer
68 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
80 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 ...
1
vote
2answers
90 views

Does basic QM allow for superluminal “particle movement” during wavefunction collapse?

Can particles move superluminally away from their "expected values" using basic quantum theory? Here's an example: The eigenstates of a harmonic oscillator are defined from $(-\infty, \infty)$. This ...
0
votes
2answers
90 views

In the double-slit experiment of electrons (observed by photons), is it correct to say the collapse is caused by the momentum of the photons?

I'm working off the article, The Double Slit Experiment Demystified. Disproving the Quantum Consciousness connection. I think it's well-written, but I'm not convinced about this part: So what is ...
-1
votes
1answer
30 views

Where is the difference to a quantum mechanic system with collapsing wavefunction in this experimental setup?

Let us have a disc throwning system, where two porcelain plates where throwning at once and in different directions, one with its axis horizontal and the other vertical. To catch ple plates we use a ...
3
votes
1answer
59 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
58 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
vote
0answers
53 views

Is it certain that “experimental physics has not already detected an unexpected spontaneous collapse”

The WikiPedia page for the Ghirardi–Rimini–Weber theory states that "experimental physics has not already detected an unexpected spontaneous collapse". Is this really true? What would be 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 ...
1
vote
2answers
121 views

Does entangled states must become non entangled states after the measurement?

In tensor notation. A state vector $|uv\rangle$ is a tensor product(non entangled states) if and only if there is $A\in E_1(u)$ and $B\in E_2(v)$ such that $A\otimes B$. So by postulate of quantum ...
2
votes
1answer
171 views

How does the “many worlds” interpretation follow from the “universal wavefunction” idea?

So, I took this class some time ago where we discussed Hugh Everett's approach to QM. The premise seemed very logical to me: Isolated systems evolve according to the Schrödinger Equation. Of course ...
0
votes
2answers
81 views

Question regarding the projection postulate of quantum mechanics

In Quantum Mechanics, McIntyre states the projection postulate like so: After a measurement of $A$ that yields the result $a_n$, the quantum system is in a new state that is the normalized ...
4
votes
2answers
150 views

Why do we need the third axiom of QM to explain the wave function collapse? Why don't we use the decoherence process as an axiom?

I've always seen the standard interpretation and axioms of QM as in some way tricky on a philosophical level. They state the collapse of the wave function is caused by the measurement. 3.b If $A$ ...
-1
votes
1answer
133 views

Does the Copenhagen interpretation really predict that Schrödinger's cat is both alive and dead?

Accoring to the Wikipedia article Schrödinger's cat, the answer is yes. I really don't think so. I don't think Schrödinger's cat is a good example because in fact, it's not the case that it will with ...
6
votes
3answers
171 views

Is it really right to say that we never measure anything exactly in QM?

In reference to this elaborate answer by @DanielSank, I would like to pose the following question(s) in order to verify my understanding of the subject matter--in particular, that of the nature of ...
2
votes
3answers
106 views

Collapse of Wavefunction, and Subsequent Time Evolution

To keep it simple, suppose the system is the well-known particle in a 1D infinite potential well. Suppose the wavefunction is $ a|1\rangle + b|2 \rangle + c|3\rangle$, where the $|i\rangle$ are ...
0
votes
0answers
35 views

Wave function collapse when it is spread over large space

Imagine there is an atom whose wavefunction is uniformly spread across a whole room. Can we estimate the time it will take for the atom interact with other atoms in the room leading to the collapse of ...
0
votes
2answers
69 views

Difference between decoherence and wave function collapse

What's the difference between The phenomenon of decoherence and the quantum wave function collapse ?
-2
votes
1answer
76 views

Wave-function collapse query

A distant star emits photons towards Earth, where they can be detected and observed, however there is a very dense object (a galaxy) directly between the distant light source and our observation ...
0
votes
1answer
72 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)...
0
votes
0answers
30 views

Is there a collapse of wavefunction in scattering processes?

In the following lecture of Feynman https://youtu.be/ZcpwnozMh2U?t=16m33s a student says "we look in nature an find the first order term", referring to a particular scattering process characterised by ...
2
votes
0answers
98 views

Quantum Observation

Bear with me if I present a lack of knowledge - QM is not my field. There's a common notion in QM that until a particle is observed (measured), its properties are not definite, but rather are spread ...
1
vote
1answer
146 views

Is this assertion by Landau and Lifshitz's QM equivalent to the axiom that state spaces are vector spaces?

Many expositions of Quantum Mechanics begin by stating axioms of the following type: "The state of a quantum mechanical system is given by a nonzero vector in a complex vector (or Hilbert space) ...
3
votes
2answers
109 views

Spontaneous collapse of the universal wavefunction

How did the Hatley-Hawking wavefunction of the whole universe, as defined on the minisuperspace of all possible homogeneous and isotropic three geometries and matter fields, experience a collapse, ...
0
votes
1answer
52 views

When does the wave function collapse in the EPR paradox experiment? Shouldn't this depend on the reference frame?

Suppose you have two entangled particles. Particle A, and Particle B. If the spin of particle A is up, then the spin of particle B must be down and vice versa. Now suppose you measure the spin of A ...
-1
votes
1answer
110 views

Dice roll wave function [closed]

How looks the wave function for dice roll? How to calculate probability from it? Thank you very much for help.
2
votes
4answers
222 views

Does the wave function collapse cause information to be created?

If I understand correctly, a principle of physics is that information is never created or destroyed. And, unless information is defined differently in physics, according to information theory there is ...
1
vote
1answer
92 views

What is the relation between a measurement and an observable?

Observables are represented by Hermitian operators. First of all, it's a little strange (to me) that some measurable physical quantity is represented by a transformation (or linear map), given that I ...
1
vote
1answer
207 views

All of the postulates of quantum mechanics without additional information [closed]

$\newcommand{\braket}[2]{\left<#1|#2\right>}% \newcommand{\bra}[1]{\left<#1\right|}% \newcommand{\ket}[1]{\left|#1\right>}% $As an undergraduate who's trying to learn quantum mechanics it'...
0
votes
0answers
66 views

Wave function collapse, when spectrum is continuous

Is known that when measuring position the possible measurement values are eigenvalues of the position operator. Before measurement the particle is supposed to be in a physical state (wave function) ...
0
votes
1answer
89 views

What is the physical basis of Born's interpretations?

Did anyone has any idea how Born came up with the probabilistic interpretation of quantum mechanics. It is by all means very bizarre. And then it leads to the idea of copenhagen interpretation. Also ...
1
vote
1answer
117 views

How does one make the wavefunction collapse into an eigenstate of a particular operator?

Say one has an unperturbed system that can be described with a wavefunction that is a superposition of many eigenstates. How does one make the wavefunction collapse into an eigenstate of say, the ...
2
votes
1answer
114 views

Does a photon's spin wavefunction collapse when detected by a photon detector?

Assume two entangled photons A and B have the same spin but travel in different directions. When Photon A is detected by photon detector (e.g. photomultiplier) on its path, does Photon B's spin wave ...
1
vote
1answer
70 views

Wave function collapse, EPR paradox and information transfer

For a classical formulation of the EPR paradox, two particles are produced, with total momentum zero and separated by a long distance. So say we measure the momentum of one particle first, and measure ...
2
votes
3answers
80 views

Is there an objective asymmetry between a collapsed and un-collapsed wave function?

In a quantum double slit experiment, one starts at t0 with a wave function that propagates through two slits, interferes, and probabilities for various positions at the final stage at t1 can be ...
20
votes
3answers
647 views

What are the strongest objections to be made against decoherence as an explanation of “collapse?”

When we measure an observable A of a quantum system, we get an eigenvalue of A. Without worrying about connotations of Copenhagen vs. MWI, etc., let's just call this "collapse." Question: Among ...
2
votes
1answer
89 views

Measurement of wavefunction collapse

I read in Griffith's quantum mechanics that In a particular system, the second time measurement of the position (say) would yield the same result (the same collapse or the same spike) given that ...