This tag is for Heisenberg quantum mechanical uncertainty principle.

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Group velocity and calculating wavelength [closed]

A stone tossed into a body of water creates a disturbance at the point of impact that lasts for Dt = 4.0s. Measurements indicates that the wave speed is v = 25 cm/s. (a) Over what distance on ...
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Why uncertainty principle on a large scale doesn't impose limitations on precision?

The question is By choosing reasonable numerical values for mass and velocity, show that $\Delta x \Delta p >=\frac{ \hbar}{2}$ doesn't impose any limitations on the precision with which the ...
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Are the authors saying that the observer effect plays no role in Bohr's thought experiment of the Heisenberg uncertainty principle?

Here is an excerpt from Eisberg & Resnick's Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles. Here is introducing Bohr's though experiment to establish a physical origin for the ...
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Uncertainty principle and measurement

I would like to really understand how the uncertainty principle in QM works, from a practical point of view. So this is my narrative of how an experiment goes, and I'm quickly in trouble: we prepare ...
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wormhole time machine and violation of uncertainty? [duplicate]

Let's asssume we have a wormhole that allows sending info to the past and receiving information from the future. Next, we have a particle moving in two dimensions, for which we can evaluate $ p_{y} $ ...
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Heisenberg uncertainty and probabilistic nature of QM

I am trying to understand whether the HUP and the probabilistic nature of QM are orthogonal or not. By that I mean that the HUP fundamentally derives from operators not commuting, which is the ...
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2answers
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RH side of the Uncertainty principle: when is it a number and when an expectation value?

The uncertainty principle between the position $x$ and the momentum $p$ is given by: $$ \sigma_x \sigma_p \geq \hbar/2,$$ whereas for the $x$ and $y$ components of the angular momentum is given by: ...
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Is there a prediction of quantum mechanics that could be construed as representing an “energy-time uncertainty relation?” [duplicate]

As the title suggests. Is there a prediction of quantum mechanics that could be construed as representing an "energy-time uncertainty relation?" Does there exist any reference to such a prediction, or ...
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Diffraction from a single slit experiment and Heisenberg's uncertainty principle [duplicate]

Practically how to separated between Fraunhofer and Fresnel diffraction? Do all diffraction fringes from single slit have same peaks? Why?
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110 views

Energy of system in eigenstate of Hamiltonian

I know how to find the spectrum of the Hamiltonian to get the allowed energies for a system. If the spectrum is quantized, I can get definite values for each energy level. But when the system is in ...
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1answer
71 views

Why can't we define a unique wavelength for a short wave train? [duplicate]

Here we encounter a strange thing about waves; a very simple thing . . .namely, we cannot define a unique wavelength for a short wave train. Such a wave train does not have a definite wavelength; ...
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63 views

Quantum relativistic effects

I was performing a thought experiment: let us assume an object is traveling so close to the speed of light that the length of the object is small enough for quantum effects to become noticeable to a ...
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1answer
89 views

electrons inside nucleus and uncertainty principle [closed]

State the assumptions of the proton-electron model of the nucleus. Show that if one uses the Heisenberg uncertainty relation to estimate the speed of an electron inside a nucleus with a diameter of ...
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189 views

The uncertainty principle and spin

I realize that this may be a very basic question, but I've been unable to find the answer elsewhere so thanks in advance for the help. Suppose an electron's spin is measured about an axis, and then ...
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76 views

Can mass be uncertain?

If you can have uncertainty in momentum, then wouldn't you have uncertainty in mass and velocity? Why can't mass be uncertain?
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6answers
571 views

Explanation for the EPR-like paradox

I am trying to understand the process of Quantum Entanglement for use in Quantum computers. The problem I have is this: Suppose some nuclear process emits an electron-positron pair. Now after ...
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1answer
75 views

Can we put $\Delta p, \Delta x, \Delta E, \Delta t$ into one big uncertainty equation?

According to my calculations $x$ * $p$ has unit $[kg m^2/s]$ which is what we would get if we multiply $E$ by $t$ So $$ Et = xp$$ Starting from here, can we some how derive a formula that puts all ...
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117 views

Why only 1 component of angular momentum?

Griffiths says that you can have only 1 well defined component of the angular momentum because of the uncertainty principle. From the uncertainty principle, we get that $$ \sigma_{L_x}\sigma_{L_y} ...
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1answer
60 views

On quantum randomness, the longest weather predictions and perfect macroscopic caos

Which is the maximum number of days we can predict future weather conditions with a reasonable degree of accuracy if we knew all of the initial conditions of everything that effects the weather down ...
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Gedankenexperiment to derive the Robertson uncertainty relation without confusing it with the obersver effect

In the last years there seemed to be much activity on the meaning Heisenberg's uncertainty relation. The main point of the discussion was Heisenbergs noise-disturbance-relation (see: ...
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Why isn't the Heisenberg uncertainty principle stated in terms of spacetime?

As I understand it, there are two "versions" of the Heisenberg uncertainty principle: Position-Momentum uncertainty \begin{equation} \sigma_x \sigma_p \geq \frac{\hbar}{2} \end{equation} where ...
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1answer
80 views

In the Heisenberg uncertainty principle

In Heisenberg uncertainty principle why do we only talk about uncertainty in position along $x$ axis, why not along other dimensions as well?
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279 views

Are “uncertainties” in Heisenberg Uncertainity just standard deviations? [closed]

Can someone confirm that the uncertainties in Heisenberg's uncertainty relation are really just standard deviations based on the expectation values? For example, the $\Delta x$ can be computed by ...
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Rectangular window $\psi$ wave-function and the calculus of $\langle p^2\rangle$ for it

I'm currently considering a rectangular window $\psi$ function: $$ \psi(x) = \begin{cases}\left(2a\right)^{-1/2}&\text{for } |x|<a \\ 0&\text{otherwise.} \end{cases} $$ I am interested in ...
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Calculation of $\langle p\rangle$ and $\langle p^2\rangle$ for wave function [closed]

Given the wave function $$\psi(x)=A\exp\left[-a \left(\frac{mx^{2}}{\hbar}+it\right)\right]$$ I would like to calculate $\sigma_{p}$. \begin{align}\langle p\rangle &=\int ...
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Uncertainty Principle - measuring momentum on one entangled particle, position on the other

If two entangled particles are sent far apart and then at exactly the same time the position of one, and the momentum of the other, is measured, won't this mean that, because the corresponding values ...
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1answer
77 views

Could the uncertainty principle theoretically be violated at 0 K? [duplicate]

Ok so please excuse me if the following mental argument is completely ridiculous or obviously flawed :P I was reading about how, even at 0 K (assuming we could experimentally reach such a ...
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Is there a Planck uncertainty?

There are theories which place lower limits on length, time and temperature. Is there a corresponding one for the lower limit for uncertainty? Is there a probability so small it cannot exist in this ...
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1answer
90 views

What is uncertainty principle exactly? [duplicate]

I've learned a little about uncertainty principle. According to words on Internet, it says that the position and the velocity of an object cannot both be measured exactly at the same time. And there ...
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1answer
68 views

Quantum properties of objects with zero velocity

Just curious: What would the Heisenberg Uncertainty Principle and De Broglie Wavelength be for a baseball that is not moving (i.e has zero velocity)? Also, since macroscopic objects like baseballs ...
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Huygens and philosophy of the slit

A single (narrow) slit diffraction pattern, can be explained/described classically with Huygens' principle (1678), and quantum mechanically with the Uncertainty principle. If the pattern on the screen ...
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160 views

Quantum mechanics,and how the law $ΔxΔp≥ℏ/2$ explains the paradox regarding atoms [duplicate]

In Chapter 2-3,Vol I of the Feynman lectures, Feynman talks about a rule in quantum mechanics that says that one cannot know both where something is and how fast it is moving. That the uncertainty of ...
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2answers
70 views

Size of particle so small that it covers large volume?

An electron's "cloud" covers more volume than a proton does due to Heisenberg's uncertainty principle. Δmv*Δx > h an electron has less mass than a proton, so its position is less determinate. ...
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How to minimize the wavepacket dispersion?

This is a final exam problem. Here is what I can remember: We know that if an electron's wavefunction starts out as a narrow wavepacket, and moving in a region of constant potential, then the ...
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Non-locality in non-relativistic Quantum Mechanic

I guess the following obvious question is answered by any flavor of relativistic Quantum Mechanics, but I just wanted to check whether I understand correctly: Is it correct that nonrelativistic QM ...
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Must the product of the two complementary quantities in an uncertainty relation have unit $\text{Js}$?

I know that the uncertainty principle is: $$\Delta p\Delta q \ge \frac{\hbar}{2}.$$. But do the units on the left-hand side of the equation always have to equal $\text{Js}$, i.e. $\text{energy} ...
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247 views

QFT and violation of Heisenberg uncertainty principle

In some QFT books is said that a free electron can emit a virtual photon as long as it reabsorbs the photon and returns to its original state within a time: $$\Delta t<\dfrac{\hbar}{2\Delta E}$$ ...
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Electron at rest

David Griffiths suggested a website in his book where I got this paper http://www.hep.princeton.edu/~mcdonald/examples/electronatrest.pdf Here the author says classically a particle at rest(in some ...
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1answer
77 views

How can I prove this inequality for a harmonic oscillator?

I need a hand with this problem. I have to prove that for a particle in any quantum state in an harmonic potential $$ \langle X\rangle \leq2\Delta E\Delta P/(m \omega^2 \hslash) $$ Here's my ...
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281 views

Relationship between Energy and Time [closed]

Is there a relationship between energy and time? What is it?
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116 views

Does every interaction of quantum objects introduce backaction?

The motivation of this question is the following experiment: Assume you have quantum mechanical oscillator, e.g. a particle in a potential $V(q_x)\propto q_x^2$. Now the position of the particle ...
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3answers
93 views

Why do we care about compatible observables?

Going through my first treatment of quantum mechanics at the Griffiths level, and I was wondering why we care about observables being compatible and what is the significance of having an eigenstate ...
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1answer
87 views

Is there uncertainity of position of the perfectly homogenous radiating body?

I heard the standard interpretation of Heisenberg Uncertainty Principle: Just the measurement affects the position of the body because always you want to see a body (=to measure the position), you ...
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Is uncertainty in velocity via HUP reference frame dependent? [duplicate]

Simply put HUP involves position and momentum, further more consider a mass of 1kg. as momentum is mass X velocity = 1X velocity = velocity for calculation purposes. now for a stationary observer the ...
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179 views

Collapse of the wave function and Heisenberg uncertainty

I have been studying quantum mechanics for a few weeks, in particular wave mechanics, as created by Schrodinger, and his equation. As a high school student, I haven't found an answer to this question ...
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2answers
77 views

How can one be 'certain' about anything that has an “Uncertainty Principle” at its core? [closed]

The Uncertainty Principle, which says that more than one aspect of a particle cannot be measured simultaneously, illustrates one of several major differences between quantum physics and classical ...
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3answers
119 views

Question about derivation of the Heisenberg Uncertainty Principle?

I am looking at the derivation presented here. The first thing I am unsure about is where the form of $\psi_0=Ae^{\frac{-m\omega x^2}{2\hbar}}$ came from. Also, is this form for all $\psi$, or just ...
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1answer
114 views

Uncertainty relation for non-simultaneous observation

Heisenberg's uncertainty relation in the Robertson-Schroedinger formulation is written as, $$\sigma_A^2 \sigma_B^2 \geq |\frac{1}{2} \langle\{\hat A, \hat B\}\rangle -\langle \hat A\rangle\langle ...
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What is the experiment used to actually observe the position of the electron in the H atom?

Prior to observation, the electron can be found anywhere (from inside the nucleus to the ends of the universe), but once its position is determined the answer is precise (albeit its momentum is not ...
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139 views

Energy-Time Uncertainty Principle and Photons

Heisenberg's uncertainty principle states that: $$ \Delta E \cdot \Delta t \ge \frac{\hbar}{2} $$ It is clear that this has nothing to do with the accuracy of our measurements, but rather is a ...