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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Uncertainty principle for single slit diffraction

Let's suppose there is an aperture of diameter $d$. If particles undergoes diffraction at the aperture, since uncertainty in the "x-coordinate" is $\Delta x = d/2$, by the Uncertainty ...
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I can't track too many particle ==> Statistical Mechanics OR Quantum uncertainity ==> Statistical Mechanics

I'm sort of confused with these two ideas. We start by saying that the trajectory of the particle can be described by giving the phase space coordinate $(q,p)$. So Given the initial condition, I can ...
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Why we can stand on the floor? [duplicate]

Feynman (Volume 1, 38-4) seems to explain the normal force of a floor acting on a table as quantum mechanical, arising from the Pauli Exclusion Principle and also, the Heisenberg Uncertainty Principle....
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Is it possible the quantum world to be actually deterministic after all? [closed]

Possible the "Heisenberg Uncertainty Principle" (HUP) describes the fact that we are not able to probe beyond a small size scale into the quantum world because the relative long light waves ...
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Doubt about the Gaussian state

I am reading an article that makes an application using the Gaussian state. The author of the article writes the Gaussian state as follows: $$\psi(q) = [2\pi(\Delta q)^2]^{-\frac{1}{4}}e^{-\frac{q^2}{...
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Uncertainty principle and multiple-slit diffraction

Most of the quantum mechanics textbooks mention the single-slit diffraction phenomenon and explain it with uncertainty principle to obtain the $b\sin(\theta)=n\lambda$ law. But how does one explain ...
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Are velocity and position complementary properties in quantum mechanics?

I know that it is frequently said that velocity and position are complementary properties i.e. subject to the uncertainty principle. But the more accurate statement, or so I am told, is that momentum ...
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Does a quantum commutator exist for energy and time? [duplicate]

In quantum mechanics the position operator $\hat{x}$ and the momentum operator $\hat{p}$ have a commutator $$ [\hat{x}, \hat{p}] = i\hbar $$ Does a similar commutator also exist for the uncertainty ...
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Would the Heisenberg uncertainty principle give mass to massless particles?

Background I am self-studying QFT and I was learning about the Higgs field (lectures 7 - 8 in the link), and I learned how massless particles behave in the Higgs field. What I saw was that they follow ...
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Interpretation of 2nd law of thermodynamics and observation in quantum mechanics

The fundamental lesson of quantum mechanics has been that an observation "disturbs" the system under analysis as exemplified in Schrodinger's cat thought experiment or wave-function collapse ...
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Action of classical mechanics is bounded from below by the Planck constant

I was wondering about the dimensions of the Planck constant ($h$) and the dimensions of the action, which are obviously same. Then a train of thought led me to conclude that uncertainty principle can ...
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Does the effect of the mass of one particle always have some uncertainty?

the gravity effect of the mass of an object is depends on the location of the object and it mass ,but the problem is that the mass also depends on the speed of the object (relativistic mass). since ...
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How does Heisenberg uncertainity principle apply here?

Heisenberg's uncertainity principle states that we can't mutually determine both the trajectory and momentum of a subatomic particle. BUT when dealing with moving charges and magnetism we do problems ...
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If electron moved in a definite orbit, would that violate Heisenberg uncertainty principle? [duplicate]

If hypothetically a electron does manage to move in a specified orbit (we always find it anywhere on a particular locus), would it break Heisenberg uncertainty principle?
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Is uncertainty necessarily nonzero for non-eigenstates?

Is uncertainty necessarily nonzero for an operator acting upon a state which is not one of its eigenfunctions? For instance, if a wave function representing a state is not an eigenfunction of the ...
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1answer
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What does $\Delta p$ in uncertainty principle mean?

What does the $\Delta p$ in uncertainty principle mean? Is it standard deviation? I have seen few videos on youtube as well as in our high school textbooks, it was proved that the electrons don't ...
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Heisenberg and the Electron

The Penning trap can confine a free (I believe) Electron. The optics world has made great advancements, can we sow some doubt on the Heisenberg principle by nailing down the location and vector or ...
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89 views

How precisely can particle position be measured in a laboratory?

If we have any given particle, such as a photon or an electron (it doesn't really matter what for the sake of the question), how precisely can modern physics devices measure their position? ...
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Heisenberg's Uncertainty Principle (Beginner)

I was reading through my class book about Heisenberg's uncertainty principle and I was hoping you clarify this for me without recurring to advanced mathematics, please do it in a beginner's level. ...
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The matter wave concept, convergence in the macroscopic world and the contradiction

One of the postulates of quantum mechanics states that as the system of interest goes from the microscopic world to the macroscopic world, the quantum physical laws converge to classical physics. I ...
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Position/number uncertainty relation for the eigenstate of a Harmonic oscillator

Position and number operators for a Harmonic oscillator manifestly do not commute: $$ \hat{n}=a^\dagger a,\\ \hat{x}=\sqrt{\frac{\hbar}{2m\omega_0}}(a + a^\dagger),\\ [\hat{x},\hat{n}]= \sqrt{\frac{\...
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Why don't we observe quantum effects for large massive objects at rest? [duplicate]

The de Broglie wavelength of any massive particle is $\lambda = \frac{h}{p}$. We know that if a large object (say, a baseball) is at rest, it will have $p=0$ and hence $\lambda$ will be infinite. This ...
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How could theoretical physics without experimentalists aid distinguish observer effect from Kennard's uncertainty principle?

Regarding this experiment which was carried out in 2012: https://arxiv.org/abs/1208.0034 I'm wondering how could the scientific society be totally convinced(prior to this paper being published) based ...
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Is it an assumption that Heisenberg's uncertainty principles applies to the vacuum or is there proof?

The Heisenberg uncertainty principle was found to apply to all particles in physics. Was it an assumption that it should also apply to the vacuum? One of the consequence of this extrapolation is that ...
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What are Uncertainties in Quantum Mechanics intuitively? [duplicate]

So $\Delta x$ and $\Delta p$ are uncertainties in quantum mechanics. What exactly does the term "uncertainties" mean?
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Possibility of staying within nucleus for a electron according to Uncertainty Principle

Academic Problem: According to Uncertainty Principle, show that electron can't stay within nucleus. That's a general problem indeed. Anyway, we know that uncertainty of position in this case can't ...
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Are “intelligent” systems able to bypass the uncertainty principle?

This paper talks about finding theoretical correlations to experiential phenomena in quantum mechanical experiments using artificial intelligence (AI). If AI applications can be sufficiently well ...
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Why isn't the final screen in the double slit experiment a 'detector' which would collapse the wave function retroactively?

I'm sorry if this is a stupid question but I'm someone who is not from the physics world trying to learn about this for the first time (I'm reading Daniel Golding's Quantum Physics for Beginners and ...
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Interfering alternatives and identical particles in Feynman and Hibbs

I am currently self-studying Feynman and Hibbs, and in his first chapter, Feynman talked about 'alternatives' like the various possibilities or paths an experiment can take. He defined two different ...
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1answer
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Feynman's non-rigid double slit experiment

I am currently reading Quantum Mechanics and Path Integrals by Feynman and Hibbs, and in the very first chapter, Feynman qualitatively tries to motivate the Uncertainty Principle. He started out with ...
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Subsequent measurement of energy [duplicate]

I am interested in the subsequent measurement of energy, like assume the energy of the electron was measured to be $E_1$ and the wavefunction of the electron is described by a finite superposition of ...
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What does it “physically” mean, in terms of uncertainty and measurements, for a commutator to be different than zero in quantum mechanics?

Let's consider the commutator $[L_i,L_j] = i \hbar L_k$ of the angular momentum. The consequence of this equation is that two components of the angular momentum cannot be simultaneously measured. I ...
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Does the Kalman filter incorporate a Heisenberg-like uncertainty principle?

In the case of mechanical systems, applying the Kalman filter involves combining model based prediction (using an apriori known dynamical model) with real-world noisy observations of the positions and ...
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The frequency spread of a wavepacket from a femtosecond laser pulse

I want to ask a question about the frequency spread of a wavepacket from a femtosecond laser pulse. I was presented with the following question today: Compute the frequency spread of a wavepacket ...
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3answers
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If Heisenberg uncertainty principle involves the standard deviation of quantities then why do we use it in a different way as here?

Heisenberg uncertainty principle is mathematically given as $$\sigma_x \cdot \sigma_p \ge {{\hbar} \over {2}}$$ The two terms on the left being the standard deviations of position and momentum. But on ...
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Heisenberg uncertainty principle in German [closed]

I have heard that uncertainty was not the actual translation for the word which Heisenberg had used to describe his original principle (in German). The translated meaning is a bit different. What was ...
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Expectation value of the vector potential operator and the classical limit

I'm very much a beginner in QFT and am aiming for intuition and basic understanding. Let's consider a 1D universe and forget about photon polarisation. Imagine the following quantum state: $$|\psi\...
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Can one change the coordinate system of a quantum mechanically modelled particle so that the particle is moving along 1 axis?

I'm currently working with a problem related to quantum field theory (QFT) which could hypothetically be simplified by rotating the cartesian coordinate system so that the momentum is along a ...
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Is there a theoretical or technological limit for arbitrary precise measurement of the position of a point particle in QM?

I have read this question: Where pglpm says: So the answer to your question is that in a single measurement instance we actually can (and do!) measure position and momentum simultaneously and with ...
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1answer
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Proof of uncertainty principle in Nielsen and Chuang

I read the proof of uncertainty principle in Nielsen and Chuang. There is something I don't understand. They use operators $A$ and $B$ respectively as $P - \langle P \rangle$ and $Q - \langle Q \...
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What are $p_a$, $p_b$ and $p_x$ in Feynman's wall with rollers experiment?

Here's Figure 1-6 from section 1-8 of the "Quantum Behavior" chapter from the Feynman Lectures: And the excerpt which my question is about: ... if we determine the momentum of the plate ...
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What is the “total measure of histories” when measuring an electron in quantum?

Excerpt from chapter 12 of David Deutsch's book The Beginning of Infinity (emphasis mine): Although Schrodinger's and Heisenberg's theories seemed to describe very dissimilar worlds, neither of which ...
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Why is it impossible to measure position and momentum at the same time with arbitrary precision?

I'm aware of the uncertainty principle that doesn't allow $\Delta x$ and $\Delta p$ to be both arbitrarily close to zero. I understand this by looking at the wave function and seeing that if one is ...
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Am I misunderstanding something, or are these Wikipedia statements about quantum tunneling wrong? Badly stated?

From https://en.wikipedia.org/wiki/Quantum_tunnelling#Introduction_to_the_concept : The reason for this difference comes from treating matter as having properties of waves and particles. One ...
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Minimization of uncertainty principle for infinite parabolic well (quantum harmonic oscillator)

I've recently had a lecture on how to minimize the uncertainty principle in infinite parabolic well. The analytical solution for $\psi_n$ is $$\psi_n(x)=\frac{1}{\sqrt{\sqrt{\pi}2^nx_0n!}}e^{\frac{-x^...
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Heisenberg uncertainty principle fluctuations and dimensions less than 3+1

I've been looking at the 1+1 dimensional Dirac equation recently and am wondering if the Heisenberg uncertainty principle would allow application of said model to spin-1/2 fermions in 3+1 dimensions ...
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The definition of complementarity principle

I am looking for a precise definition of complementary principle. It is rather briefly mentioned in the textbook, and I feel that authors have deliberately avoided defining it precisely. I'm a math ...
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4answers
91 views

Paradox regarding non-normalizable wavefunctions

Suppose that we have a quantum particle with defined momentum $p=\hbar k$, this means that the particle is in an eigenstates of the momentum operator $|k \rangle$. We can now ask: what is the ...
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Separating Math From Physics In Quantum Mechanics [closed]

So, I'm going through my first quantum mechanics class in university and I feel like there is not a strong distinction made between a purely mathematical system and purely physical system, which are ...
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53 views

Uncertainty principle using fourier transforms

I am trying to show the uncertainty relation of $\Delta x\Delta p = \frac{\hbar}{2}$ using a gaussian wave function and its Fourier transform. I have found correctly the uncertainty in position $\...

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