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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Extension of uncertainty principle to mixed-states

In his Lectures on Quantum Theory, Isham states the generalized uncertainty principle for two observables $O_1$ and $O_2$ for a pure state $|\psi\rangle$ as $$\Delta_\psi O_1~\Delta_\psi O_2 \ge {1\...
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Does Heisenberg uncertainty affect Snells law?

Assuming an ideal single frequency plane wave, we can determine the angle of retraction for the light beam. But the more I make my pulse shorter, the less certain I am in the frequency and thus the ...
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Looking for a very cheap heuristic demonstration (in a few lines) of Heisenberg inequality

While I perfectly know the true demonstration of Heisenberg uncertainty principle (from the full QM machinery), I'm looking for a very cheap heuristic way of getting $$\Delta x \, \Delta p \ge h, \tag{...
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Entangled photons and CCD

Its a question about entangled pairs and double slit experiment. I have seen and read many such on the stackexchange but I can not really understand what is happening! So please don't stop the ...
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Does the Heisenberg's uncertainty equation holds when one of the observable have zero variance?

From this link Heisenberg uncertainty principle, It says: Clearly, when $\Delta p_x$ shrinks, $\Delta x$ has to grow larger and larger in order to satisfy the Heisenberg inequality. For example, a ...
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Use Heisenberg’s Uncertainty Principle to caculate the accuracy of simultaneously observe the spin in the $z$ and $x$ directions [closed]

It's actually an exercise from Quantum Computing for Computer Scientists,I know how to caculate it, but I don't know if I was wrong, can someone show me a complete solution? Here is the original ...
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An alternative approach to proving the generalized uncertainty relation? [duplicate]

I am looking through some notes for a quantum chemistry course and I encountered this explanation of the proof of the generalized uncertainty relation, which appears to take a different approach from ...
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An alternative proof of the generalized uncertainty principle? [closed]

I am looking through some notes for a quantum chemistry course and I encountered this question: $\Delta A\Delta B\geq\frac{1}{2}\left|\left<[\hat{A},\hat{B}]\right>\right|$ (for given state $\...
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Is every pair of conjugate variables associated with a Fourier transform?

For example, in quantum mechanics, the commutator of the position and momentum is $$[\hat{P_i} ;\hat{Q_j} ] =i\hbar\delta_{ij}\neq 0, i\neq j$$ I know that the position space representation of the ...
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Wave Nature of Matter in the Macroscopic World [duplicate]

Let us say that two macroscopic objects are at rest with respect to one another. Then we can see that $\Delta p$ is zero, because $v$ is zero. To compensate $\Delta x$ has to be infinity (according to ...
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TISE and uncertainty in energy

We use time independent schrodinger equation to find Stationary state solution for some potentials. My question is that, these Stationary state solutions are physically reliable or not? I am asking ...
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Can current and voltage be linked by an uncertainty relation when electrons tunnel through a barrier?

Quantum tunneling has been shown to be linked to uncertainty relations for some observables involved in the system. For instance, if we consider electrons tunneling through a potential barrier it can ...
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Heisenberg's Uncertainty Principle : How is particle position determined more accurately with shorter wavelengths? [duplicate]

In this principle, how can shorter wavelengths on the particle leads to determine more accurate position of the particle? I think it is somewhere related to reflection of the light from the particle, ...
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Why do we use ΔxΔp≥ℏ instead of ΔxΔp≥ℏ/2 to calculate the minimum uncertainty in momentum?

I came across a question in which we were asked to calculate the minimum uncertainty in the momentum of a particle. The solution showed that the min. uncertainty is found using the formula ΔxΔp≥ℏ ...
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Neutrino Helicity and Uncertainty

In the context of non relativistic quantum mechanics, or better, if I consider the neutrino's mass to be zero, the phrase Neutrino are left-handed. The spin is in the opposite direction of motion. ...
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Quantum tunneling for bound states

In QM, take a particle in a bound state in $\mathbb{R}^n$ subject to a potential (need not be smooth and not necessarily bounded above, but is bounded from below, say, something that might roughly ...
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Why can't we directly measure the internal energy and entropy?

I learned about entropy in chemistry, I saw that we can measure $\Delta H$, but can't directly measure the $H$. So I searched about 'why we can't directly measure the '$H$'?', but I couldn't find the ...
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Designing an (thought) experiment to determine exact position

I know that Heisenberg's Uncertainty Principle prevents us from even theoretically predicting the exact position and momentum of a particle. There is always an uncertainty in one or the other, given ...
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Is monitoring CPU usage a good analogy of uncertainty?

There is a limit to how accurate measurement can be because making a measurement disturbs that which is being measured. This limit means there is inherent uncertainty in any measurement. When you ...
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Is it possible to explain the Quantum tunneling with the uncertainty principle?

I'm a high school student in South Korea(It is my first English question ever). I found descriptions of quantum tunneling with the uncertainty principle in Korea. There are two kinds of descriptions ...
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Applying uncertainty principle to energy states [duplicate]

Often for this I have heard, the longer the lifetime of the energy state, the uncertainty in the energy state decreases as a result of heisenberg's uncertainty principle. However doesn't that look at ...
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What Is the logic and the intuition of the Heisenberg Uncertainty Principle based on? Is it Quantum Superposition or on the electromagnetic spectrum? [duplicate]

With many sources on the internet it has sort of become diluted as to how and why the Heisenberg uncertainty principle still makes sense. One claims that it is due to quantum superposition and that a ...
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Is uncertainty uncertain?

I was thinking about uncertainty and wondered if uncertainty is inherently uncertain. I know in the uncertainty inequality for position and momentum, $\Delta x \Delta p \ge \hbar/2$, the presence of ...
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Does an electron have a fixed orbit in reality? [duplicate]

The Heisenberg's uncertainty principle prevents us from measuring the position and momentum of an electron accurately at the same time. But that is just our inability, right? In reality, would ...
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Why is it commonly said Angular momentum for ground state is zero (for system with rotation invariant potential)? [duplicate]

Neglecting any effect of spin,it is a well known fact,that orbital angular momentum of a system in ground state is zero.(For potential $V=V(r)$ .) The angle-angular momentum uncertainty,gives $\Delta{...
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Is it possible to specify the position of a photon to arbitrary amounts? [closed]

For a photon, $$E = pc$$ from the Einstein Energy Equation. Or $$E = hf$$ with $$p = hf/c$$ From the Heisenberg uncertainty principle $$(\Delta x)*(\Delta p) = h/2$$ The maximum value for $\Delta ...
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(Another) Naive Question About Wavefunctions

I was recently introduced to wavefunctions in my freshman Modern Physics class. I understand that these waves do not- on their own- have a physical interpretation but the square of their magnitude ...
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Why must energy transitions in hydrogen atom be between stationary states?

In Griffiths QM textbook, he said that a hydrogen atom in the ground state may undergo a transition to some other stationary state by absorbing a photon. Why must this transition be to another ...
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Free Particle moving

My class finished the free particle dispersion derivation. Our professor asked us to, as an exercise, modify the derivation to fit a moving particle with a constant velocity. I think I managed it with ...
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Confusion about the description of the uncertainty principle

I have heard two descriptions of the uncertainty principle, and I am quite confused about the uncertainty principle now. The first one is dependent on the wave function of the particle, and it says ...
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Uncertainty of wave function over time [duplicate]

If entropy is the amount of randomness in a certain system, and it has to increase, by the second law of thermodynamics, does that mean that the uncertainty of the state of a particle always increases ...
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1answer
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How can you subtract a value from an operator/matrix?

I'm currently following Quantum Computation and Quantum Information by Nielsen & Chuang. I'm struggling to understand the derivation of The Heisenberg Uncertainty Principle in Box 2.4 page 89. I ...
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On the uncertainty principle when a gamma-ray burst is passing close enough of the magnetic bubbles placed at the edge of a planetary system

I'm going to ask a related question to my past post Collision or impact of a gamma-ray burst against the magnetic bubbles at Solar System's edge on this site Physics Stack Exchange. I have no a good ...
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Does spin $0$ violate the uncertainty principle?

It seems that if we have some spin eigenstate $|0\rangle$ for which the square of the total spin operator is $\hat{S}^2|0\rangle = 0$, then we simultaneously know the spin in all three directions, ...
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Virtual particles and Heisenberg's uncertainty principle [duplicate]

Introduction Virtual particles are particles which doesn't obey the energy–momentum relation: \begin{align}E^2=(mc^2)^2+(pc)^2\end{align}This is possible if it happens short enough time. Often ...
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Average Energy in generic radial potential

Given a particle of mass $m$ moving in the radial potential $$ V(r)=-\frac{\lambda}{r^s} \quad, \ \lambda>0$$ I'm asked to compute the $L$-dependence (sign included) of the average kinetic, ...
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What does Heisenberg's uncertainty principle tell about nature? [closed]

I agree with the fact that the principle points out to the inaccuracy in the measurement of the two quantities of the particles (momentum and position). But measurements apart, does it explain ...
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Is the time-energy uncertainty relation affected by the refractive index of materials?

For the time-energy uncertainty relation, is it or is it possible it could be affected by the refractive index of a material? In other words, if you have a material where the speed of light passing ...
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Could uncertainty principle be considered a purely epistemological device?

I am trying to wrap my head around the basics of quantum theory and was wondering if my conclusions are reasonable. From what I understand, as far as quantum theory can be applied, it considers all, ...
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The origin and current status of the equation $\boldsymbol {Et}-\boldsymbol {tE}=\frac{h}{2\pi i}$ [closed]

Heisenberg already in 1927 quotes this equation as a "known equation".[1] I would like to know that what was the original conception behind this equation, and what is its current status. According to ...
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Uncertainty in wavelength of a photon emitted from atom

When an atom emits a photon, for some time the photon is close to its source, the atom, because it takes some time for the photon to move away from the atom. So during that time the uncertainty in the ...
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The Uncertainty Principle [duplicate]

We often say that the conservation of the energy could be violated by a quantity $\Delta E$ but only within a precise interval of time $\Delta t$, dictated by the Heisenberg principle ($\Delta t \...
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Is Heisenberg uncertainty principle really a good justification for the impossibility of$\ 0$ K? [duplicate]

Heisenberg’s uncertainty principle is very commonly used to justify why we can’t get to$\ 0$ Kelvin by saying it is impossible to make particles stand still because they will either have an ...
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Generalized uncertainty principle and relevant energy scales

To include quantum gravity effects, some research works have suggested a deformation of the Heisenberg uncertainty principle. One particular model has, $$[\hat{x},\hat{p}]=i\hbar\left(1+\frac{\beta}{...
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Forming Black Holes

I've read a play (The Square Root of A Sonnet) about the physicist who proposed the Chandrasekhar limit, Subramanyan Chandrasekhar, and had a doubt regarding an argument that was put forward regarding ...
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Is there a Heisenberg Force?

If I read him correctly, in his book Quantum Theory, David Bohm argues that the reason an electron doesn't collapse into the nucleus is there is essentially a pressure due to the uncertainty principle ...
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Heisenberg's principle in classical world [duplicate]

I have a ball with me and I have been observing it's position which remains constant at a place only, hence it must be largely localised, further as it remains on the same place from so long, it's ...
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Contradiction with the uncertainty principle using repeated measurements

The uncertainty principle states that knowing the position of a particle with great accuracy would result in a very low certainty in the momentum of the particle. Suppose I have an experiment where I ...
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What possible variants/permutations/derivatives are there of the Heisenberg uncertainty principle?

Generally, the (Heisenberg) uncertainty principle is stated as: $\Delta x \cdot \Delta p \geq \dfrac{\hbar}{2}$ But sometimes you also encounter a variant of it, placing limits on other entities, such ...
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If an object is large enough and slow enough is there a point that we can say we know its position and momentum?

Let’s say you have a 3000 lb vehicle moving very slow at 1 kilometer per hour. It seems obvious that you could simultaneously determine its position and momentum at any point along the way but does ...

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