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Questions tagged [heisenberg-uncertainty-principle]

This tag is for Heisenberg's quantum mechanical uncertainty principle. DO NOT USE THIS TAG for uncertainty in a non-quantum measurement.

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Why does zero $x$ angular momentum imply nonzero $z$ angular momentum?

Assume we have a state $\psi =|n, L =1, L_x =0\rangle$. If we compute it's reprentation in $L_z$ basis we get: $$\psi = \frac{1}{\sqrt{2}}|n, L =1, L_z =1\rangle - \frac{1}{\sqrt{2}}|n, L =1, L_z =-1\...
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0answers
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Negative Quantum Space-Time? [on hold]

What is the Uncertainty Principle telling us? Is it saying the power of observation/measurement of a quantum object is not enough to make it a genuine 3D + 1 space-time object? If something on our ...
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2answers
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Can you help me clear up the double slit experiment?

So I know what happens in a double slit experiment and that if you put an observer, it changes the outcome of the experiment. It has to do with Heisenberg's uncertainty, but how does his uncertainty ...
2
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0answers
33 views

Uncertainty Principle for a Particle on a Ring [duplicate]

In the case of a particle on a line, if I prepare an (although non-normalizable) eigenstate of the momentum so that the uncertainty in the measurement of the momentum vanishes, the uncertainty ...
2
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1answer
54 views

Quantum state where uncertainty in kinetic energy is zero?

While reading Shankar's book on Quantum Mechanics, I encountered an interesting problem: Compute $\Delta T\cdot\Delta X$, where $T = P^2/2m$. I found several solutions online which arrive at the ...
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2answers
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Heisenberg's Uncertainty Principle about electrons [on hold]

According to Heisenberg's Uncertainty Principle when we shoot or project photons on an electron from one side then there is 100% possibility that there is some error in calculating the position and ...
0
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1answer
33 views

Uncertainty principle for a particle of known momentum

For a particle of known momentum we know the wave function. But why is that in that case we have uncertainty in momentum then according to uncertainty principle ∆x∆p>=h/2π? If so then uncertainty in ...
0
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1answer
33 views

Can faster sampling frequency solve the x-ray diffraction phase problem?

In the x-ray diffraction, only the intensity the light that hits the detector is captured while the phase of the light is not determined. The energy flux of the light is the Poynting vector. For a ...
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0answers
11 views

Heisenberg's Microscope and the Compton effect

https://www.youtube.com/watch?v=dgoA_jmGIcA&t=459s Hi, this is my first question on physics stack exchange. I'm in my second year in college and I'm currently learning quantum/nuclear physics. So ...
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0answers
17 views

Doubt on application of uncertainty principle for an ion trap

Ion trap involves the application of an electromagnetic field to suspend and confine a charged particle. At the centre of this picture, you see a saddle shape. This means that the ions are pushed ...
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1answer
64 views

Is this explanation for the uncertainty principle correct?

In a pre-print I read that "The position of the particle is indeterminate as it could be anywhere along the wave packet. Hence compressing the wave packet to reduce the indeterminacy in position will ...
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1answer
69 views

Uncertainty principle in classical mechanics and quantum mechanics

I was just listening to the Leonard Susskind lectures on youtube on qunatum mechanics basics. He said that uncertainty principle in classical mechanics is completely different from that of quantum ...
8
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1answer
356 views

Physical interpretation of eliminating the real component when deriving the uncertainty principle

I've been working on some quantum information theory problems and I've revisited Griffith's Quantum Mechanics. On page 109, he derives the uncertainty principle. He goes through the steps: For ...
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1answer
45 views

Does wave-particle duality rely on accepting the Copenhagen interpretation?

If you're a scientist that subscribes to the many worlds theorem, does that mean you do not accept wave particle duality? Seeing as MW postulates that the wave or particle form has always existed that ...
2
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2answers
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What is exactly a quantum fluctuation?

According to the quantum fluctuation by Heisenberg Uncertainty Principle, matters and antimatters are created and disappearing by colliding in an almost complete vacuumed area of space near the event ...
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3answers
129 views

In Bohmian mechanics, do electrons move inside an atom?

Look at http://www.bohmian-mechanics.net/whatisbm_pictures_hydrogen.html. It is mentioned that in the rest states of a bound electron, the position of the electron is stationary, since the ...
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2answers
31 views

General commutation question

If I have three general observables, $\hat{C}$, $\hat{H}$, and $\hat{L}$, and the commutation relation between $\hat{C}$ and $\hat{H}$ is given by, $$ [\hat{C}, \hat{H}] = \hbar \hat{L} $$ At the ...
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0answers
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By recombination ion/electron does predominataly the ground level form?

When an electron is near an ion and has small velocity it will be certainly captured and both form an atom. I think that the electron will predominantly release energy dE just the proper quantity ...
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1answer
95 views

What would happen if the opposite complementary variables of two entangled particles were measured at the same time?

Many explanations about the uncertainty principle and its related EPR paradox state that it is impossible to measure opposite complementary variables on different entangled particles; for example, ...
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2answers
36 views

Is polarization complementary along its different axes?

Is polarization complementary along its different axes -- much like the spin of a particle is -- thus implying that the uncertainty principle holds for polarization measurements on these different ...
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2answers
78 views

What does the Heisenberg principle actually mean? [duplicate]

As far as I can understand, the Heisenberg principle limits the possibility of calculating the exact position and momentum of electrons, as the light we use to observe it changes it's velocity. But ...
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0answers
61 views

Virtual pair of particle-antiparticles trajectory [duplicate]

Is it possible to do heuristic calculations on virtual pair of particle-antiparticle trajectories that appear in a vacuum? For example, what is the maximum distance between them during virtual process?...
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1answer
36 views

Why doesn't detecting a photon's position after passing through a narrow slit violate HUP?

I understand that after passing through a narrow slit a photon's momentum is uncertain, however since its position can be inferred from having passed through the slit, a subsequent position ...
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0answers
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Does uncertainty principle truly represent the “lower bound” of the information we can obtained from a pair of noncommunicable operator?

Background I: Suppose the commonly used non commuting operator $\hat p$ and $\hat x$. The uncertainty principle told us that $\sigma_p\sigma_x\geq \frac{\hbar}{2}$. In standard quantum mechanic ...
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53 views

Uncertainty Principle and Commutators

In preparation for an exam I stumbled upon a quantum mechanics task I can´t really solve right know. So i hope someone can maybe give me a hint or two how to understand this. Here is the task: Let $...
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1answer
44 views

Measuring the Momentum of a Quantum System using Position Measurements

A basic way to measure the momentum of a charged particle is to know that (classically) it follows a circular trajectory in a uniform magnetic field perpendicular to the plane of its trajectory, with ...
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1answer
67 views

Can't we see electrons without affecting their movements? [closed]

Can't we see electrons without affecting their movements? I was thinking about the double slit experiment and something is writing on Feynman's book like photons can affect their movements too. But I ...
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0answers
46 views

Energy conservation when exchanging meson

In Prob 1.2 of Griffith's "Introduction to Elementary Particles" 2nd ed., it says that: However, I don't understand why it states that "they must temporarily violate the conservation of energy by ...
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1answer
20 views

Length and velocity of a pulse of particles

We are given a pulse of protons of duration $10^{-7}s$ and energy $2KeV$. I know I am supposed to use the uncertainty principle to solve this. I need to get the length and the indetermination of the ...
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1answer
53 views

Question about point particle vs. wave equation location

Another uncertainty question, this came up in another forum. As I understand it an electron, for example, is a point-like particle. I take this to mean it exhibits dimensionless properties, but ...
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1answer
89 views

A basic question on Heisenberg uncertainty and experiment

I’m not a physicist or anything even close. But what I understand from the reason for the Heisenberg uncertainty is that the photon is changing the volecity/momentum when it hits the particle. ...
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3answers
67 views

Uncertainty Principle for a locally constrained particle

According to the Uncertainty Principle we cannot calculate the precise position or momentum of a quantum particle at the same time, trying to calculate one of them would make the other uncertain. One ...
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3answers
92 views

Heisenberg Uncertainty Principle derivation question [closed]

So I'm rading Shankaar's book and got stuck in this place. $ (\Delta \Omega)^{2}(\Delta \Lambda)^{2} \geq \frac{1}{4}\left\langle\psi\left|[\hat{\Omega}, \widehat{\Lambda}]_{+}\right| \psi\right\...
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1answer
32 views

How in experimental practice does a momentum measurement reduce a state to a momentum eigenfunction?

It's easy to think of ways to reduce the state of a particle to a position eigenfunction (or at least a narrow spread in position space), whether by trapping the particle in a potential well or by ...
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2answers
77 views

Interpretation of the energy-time uncertainty [duplicate]

From the uncertainty relation it follows that: $$\Delta E \ \Delta t = \hbar$$ $\Delta E$ is the energy uncertainty of a state, $\Delta t$ should be the uncertainty of the lifetime $\tau_b$ of the ...
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1answer
89 views

What's the intuitive interpretation of quantum uncertainty $\Delta \hat{A}=\sqrt{\langle\hat{A}^2\rangle-\langle\hat{A}\rangle^2}$?

As per this video, if $\hat{A}$ is a quantum operator, the uncertainty is given by $$\Delta \hat{A}=\sqrt{\langle\hat{A}^2\rangle-\langle\hat{A}\rangle^2}$$ I understand what this expression means ...
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1answer
54 views

Plotting quadrature uncertainties in phase space

In most books like in the picture given below, the uncertainties regarding quantum states like coherent and squeezed states are represented in phase space plot by some area enclosed within a circle or ...
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0answers
35 views

Confused about using uncertainty principle to determining momentum

A question asks to estimate the energy of a neutron, if the neutron is composed of a proton and electron by using the uncertainty principle. The basic idea is to let x = 1 fm and calculate p using: $...
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2answers
79 views

Are superposition and uncertainty principles logically dependent?

If we assume superposition and define an Hilbert space with canonical commutation relations we can derive uncertainty relations. So it seems the uncertainty principle isn't required, or should be ...
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2answers
62 views

What happens to the uncertainty principle when I have a particle contained within an inelastic box?

Say I have a box made of inelastic material such that when a particle hits the box, energy is lost through heat. I then put a particle inside of this box and squeeze the box down. How does this not ...
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3answers
304 views

Understanding the statement of the bandwidth theorem

I know that the Bandwidth Theorem (BT) and the Heisenberg Uncertainty Principle (HUP) are basically the same thing, and stem from the fact that for operators $A,B$, we have: $$\Delta A \Delta B \geq \...
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3answers
175 views

Why do neutron stars with more mass have smaller volume?

I know about Heisenberg uncertainty which makes more localized neutrons have a wider range of undefined momentum, and Pauli exclusion principle which prohibit neutrons from getting too close or "...
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1answer
103 views

Accuracy of Heisenberg Uncertainty Principle for estimating ground state energy of particle in potential well

I've understood the assumptions and logic behind the 'proof' that the ground state of a particle in an infinite potential well has a non-zero energy using the Heisenberg Uncertainty Principle. ...
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1answer
50 views

Momentum uncertainty for a free particle [closed]

Free particle is in state psi k, where k is the wavenumber. Now i am trying to findout uncertainty in its momentum. I know that for free particle position is uncertain (delta x approaches to infinity) ...
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0answers
85 views

Where this interpretation for the field modes comes from?

I'm reading the book "Modeling Black Hole Evaporation" by Alessandro Fabbri and Jose Navarro-Salas, and in section 3.3.2 they talk about wavepackets at $\mathscr{I}^+$. It all starts like this: one ...
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1answer
36 views

What does Hawking mean by “in empty space the field can’t be fixed at 0 because then it’d have both a precise value and a precise rate of change of 0”

Slightly modified the language in the title to make it fit in 150 characters. The above comes up in the part leading up to the explanation of how black holes emit particles.. My impression was that ...
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0answers
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How to get the Number Phase Uncertainty relation from the Energy time relation?

I can arrive at $\Delta H\Delta t \geq \frac{\hbar}{2}$, but how do I get from there to $\Delta N\Delta \phi \geq 1$ for the number states of light? I know we write $H = \hbar \omega (N + \frac{1}{2})...
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1answer
51 views

momentum in calculation of Bohr's radius

Some usual calculations of the Bohr's radius (see 2.5 at Feynman's here, or this text here) starts by defining a radius $a$ ( most probable radius ? average radius ? ). Next, from Heisenberg's ...
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24 views

Why accelerating observer can see Unruh radiation?

I read that uncertainty principle allows a pair of virtual particles to spawn in a vacuum as long as time is $h/E$ and nature forbid negative energy to exist, a accelerating person will see the photon ...
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34 views

Prove a version of the uncertainty principle

Hello this question is about the wave nature of the electron and the uncertainty principle. The question goes as follows: A finite wave train has a constant velocity $v$ and its profile as a ...