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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Heisenberg's Uncertainty Principle - finding uncertainty in wavelength

I am confused about this problem: I needed to find the uncertainty of a wavelength using Heisenberg's uncertainty principle. In the solution, they differentiated $λ=c/f$ with respect to frequency to ...
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Uncertainty principle for $\Delta\frac{1}{x}\Delta p$

I've tried to determine uncertainty for operators $\xi=\frac{1}{x}$ and $p$. To do so, I used relation that $B^{-1}[A, B]B^{-1} = -[A, B^{-1}]$ and so I got: $$ \frac{1}{x}[p, x]\frac{1}{x} = \frac{-i ...
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Double sit experiment and Uncertainty

If we try to an electron with a high energy photon, we precisely detect its position, while its momentum becomes totally uncertain. On the other hand, if we detect it using a low energy photon, its ...
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1answer
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Is there a uncertainty relation between viscosity and volume in fluids?

If I make no mistake, dynamic viscosity $\eta$ is measured in $ \rm kg /(s\, m) $. And volume is measured in $\rm m^3$. The product of the two has the same units of Planck's quantum of action $\hbar$...
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What does it mean: $[\langle(\Delta x)^2\rangle\langle(\Delta p)^2\rangle](t)$?

I got following expression regarding linear harmonic oscillator in quantum mechanics, and I don't understand what it means. $[\langle(\Delta x)^2\rangle\langle(\Delta p)^2\rangle](t)$ $\Delta x$ ...
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1answer
90 views

Uncertainity relation of Kinetic energy with position

In R. Shankar's Principle of quantum mechanics book in the problem Now $$\Delta T = \frac{-\hbar^2}{2m} \Delta( p^2)$$ And I don't arrive anywhere using this, but I also know that $\Delta A \...
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66 views

Heisenberg's Uncertainty principle: Position of momentum of Electron orbital

I need some clarification in my understanding of HUP with respect to electron in an atom. This is my current understanding, Position of electron here means which orbit (Quatized orbits around nucleus)...
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109 views

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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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 ...
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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 ...
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1answer
77 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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Heisenberg's Uncertainty Principle about electrons [closed]

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 ...
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1answer
34 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 ...
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1answer
43 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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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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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
116 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
218 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 ...
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379 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
49 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 ...
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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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163 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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50 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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43 views

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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114 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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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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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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65 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
40 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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64 views

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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64 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
46 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
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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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58 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
55 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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105 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
88 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
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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
45 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
124 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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116 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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118 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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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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118 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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72 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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851 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
250 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
218 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
151 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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