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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2answers
389 views

Is gravity the current limitation to laser cooling?

This is something I've been wondering for a while. I've read about the experiment with NASA to reach unprecedented cold temperatures in space because of the microgravity environment not being such a ...
0
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0answers
36 views

Uncertainty in orientation of angular momentum

To calculate the uncertainty it looks like I'm going to find an expression for the root mean square of either $J_x$ or $J_y$, or the $J$ in the x/y plane? But I'm not sure if that's what it means by ...
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0answers
20 views

Gaussian Minimizes Uncertainty - Statement Qualification [duplicate]

On the last page of this paper, the following statements are made (I'll jump right to around the point of interest): Example: Consider $A=p_x$, $B=x$. Then $$\langle A\rangle=\langle ...
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0answers
49 views

Quantum mechanics - “God does not play dice” - does he? Or might he not? [duplicate]

I'm a mechanical engineer by training, so please forgive ignorance in my question. Heisenberg's uncertainty principle states (to my understanding) that one cannot measure both position and momentum ...
5
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1answer
65 views

Butterfly and quantum uncertainty

I'm sorry for the long question. In Brian Greene's book 'The Hidden Reality' he gives a nice illustration of the uncertainty principle. Imagine a butterfly flying around in a room. We would like to ...
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1answer
74 views

How does the uncertainty principle relate to quantum fluctuations?

I found a webpage that just kind of mentions the uncertainty principle lightly but doesn't really go into detail as to why we need it in the first place when considering quantum fluctuations and ...
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0answers
18 views

Is there a limit to the frequency of light? [duplicate]

I am assuming that light frequency would eventually be limited by Planck distance and/or Heisenberg limitations. Could this frequency ever be approached in practical terms?
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1answer
40 views

“Everything is Uncertain.” Heisenberg Uncertainty Principle Question [closed]

I'm new to the concept and only understand that nothing can be measured accurately simultaneously. Is the statement (in title post) true? Can you also use an example from Quantum Mechanics for the ...
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1answer
57 views

Mathematical proof of Bohr's complementarity principle

Complementarity principle, in physics, tenet that a complete knowledge of phenomena on atomic dimensions requires a description of both wave and particle properties. Depending on the experimental ...
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0answers
49 views

Calculating Natural Broadening of Emission Lines

I'm trying to demonstrate the small effect of Natural Broadening as compared to other types of broadening (Doppler, Stark, van der Waals, etc.) and my calculations don't match the accepted values. My ...
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0answers
49 views

Heisenberg theory of uncertainty

I was watching a video on YouTube about uncertainty theory of Heisenberg it said that there is a relation between momentum (multiple of mass and speed) and wave length. And the relation is that if ...
2
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1answer
21 views

Point source of monochromatic photons - self-contradictory in QM?

Suppose we have a point source of photons located somewhere in space. So when the photons are released their location is well known, $\Delta x \approx 0, \Delta y \approx 0, \Delta z \approx 0$ ...
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4answers
381 views

Heisenberg's uncertainty principle for mean deviation?

The Heisenberg uncertainty principle states that $$\sigma_x \sigma_p \ge \frac{\hbar}{2}$$ However, this is only for the standard deviation. What is the inequality if the mean deviation, defined as ...
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1answer
51 views

Uncertainty relation and quantum gravity

Suppose a quantum version of gravity exists (which I don´t think). What will be the quantities in the uncertainty relation connected with this quantum gravity? Some time ago I sent a letter to Lee ...
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1answer
63 views

Would two identical universes evolve identically? [duplicate]

What if there were 2 universes (completely disconnected - not part of the same multiverse) which were identical and a given point in time (say when they first began). Would these 2 universes evolve in ...
3
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2answers
215 views

Aharonov Bohm Effect Interaction Energy Interpretation: $\vec E_m = -∇Φ - D\vec A/Dt$?

The Wang paper "An experimental proposal to test the physical effect of the vector potential" proposes an experiment to decide between two interpretations of the Aharonov-Bohm effect: “the ...
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4answers
192 views

Could the Heisenberg uncertainty principle be derived from the speed of light limit? [closed]

Background: As I was thinking about an alternative approach to the question: "why is there a finite speed of light, and why its magnitude corresponds to c?" –ultimately, I was trying to understand ...
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1answer
70 views

A thought experiment about Heisenberg's Uncertainty Principle

If there is a box full of magnetized particles which are taking random movement continuously, then I put a coil connected to a device that can detect the value of current in it and it's designed to ...
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0answers
128 views

The integration of Einstein's equations [closed]

Einstein's equation is $$G_{\mu\nu} + \Lambda g_{\mu\nu} = {8 \pi G \over c^4} T_{\mu\nu}$$ where $G_{\mu\nu} = R_{\mu\nu} - (1/2)g_{\mu\nu}\,R$ is the Einstein tensor, which combines the Ricci ...
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4answers
2k views

Uncertainty in Uncertainty?

I was reading about how the Planck's Constant can be measured with LEDs, which made me think about this question. The Heisenberg Uncertainty Principle states that: $$\Delta x \Delta p \ge ...
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0answers
102 views

Heisenberg's uncertainty principle at the Planck scale

A particle of mass has a reduced Compton wavelength $$\overline{\lambda}_{C} = \frac {\lambda_{C}}{2 \pi} = \frac {\hbar}{m c}$$ Schwarzschild radius of the particle is $$r_s = ...
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0answers
36 views

How do we know that there is a wavefunction which collapse?

How do we know that there actually is a wavefunction in the first place which collapse. How do we know that there is a transition from some linear combination of the eigenfunctions to a single one? ...
0
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1answer
149 views

Could the uncertainty principle create matter in the Universe?

According to quantum mechanics we have the uncertainty principle: $$\Delta E \ \Delta t \geq \frac{\hbar}{2}$$ Near the beginning of the Universe $\Delta t$ is very small and therefore $\Delta E$ is ...
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0answers
25 views

How to estimate the ground state of a potential well when a confinement dimension is added

I have a finite harmonic potential where I trap an electron. The confinement length changes in size. Now, I'm interested in the ground state energy, so I have this 1D Poisson solver which gives me the ...
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1answer
27 views

Distinguish statistical uncertaincy from noise disturbance relation in slit gedankenexperiment

I am just reading the "Statistical Interpretation of Quantum Mechanics" from L. Ballentine. In section 3.2. he discusses the difference between the observer effect and the statistical ...
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0answers
18 views

Application of uncertainty principle [duplicate]

why doesn't Heisenberg's uncertainty principle also work for macroscopic bodies which are in-turn made up of quantum-particles? ps: if proof is provided it will be a lot more useful.
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1answer
58 views

Reason behind the uncertainty principle [duplicate]

I know that Heisenberg Uncertainty principles states that the momentum and position of a quantum object can not be determined at the same time. This is very strange to me. I want the basic reason ...
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1answer
21 views

Finding natural linewidth's

I want to check whether my fit parameter for the width of a Lorentzian fit on my digital spectroscopy data for Helium (the 5875 Angstrom line) is what you would expect from the uncertainty principle, ...
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5answers
203 views

Quantum Theory just lazy physics?

Is it true that physicists decided that because they couldn't predict with certainty the location of an electron at any given time, that they just created equations using probability instead, still ...
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1answer
81 views

Relationship between Quantum superposition and Uncertainty principle

I'm an amateur in quantum mechanics. I am confused after reading the following in the wikipedia article about quantum superposition: If the operators corresponding to two observables do not ...
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3answers
74 views

Decrease of uncertainty of momentum with increase of width of infinite well in QM(intuition)

Why does the uncertainty in the momentum decrease with the increase of the width for an energy eigenstate in the classic problem if the infinite well in Quantum Mechanics? I have worked out the ...
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6answers
2k views

Is there something behind non-commuting observables?

Consider a quantum system described by the Hilbert space $\mathcal{H}$ and consider $A,B\in \mathcal{L}(\mathcal{H},\mathcal{H})$ to be observables. If those observables do not commute there's no ...
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1answer
89 views

Is there a simple way to explain quantised conductance? [closed]

I am biologist and I need to pass a nanotechnology class. I am stuck with this term of quantum resistance. Basically this appears to me as normal Ohm's law, except that takes into account Heisenberg ...
3
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1answer
106 views

Why doesn't $σ_xσ_p$ change with the width of the well in the infinite square well problem (intuition)?

I calculated that the product of the uncertainty in position $\sigma_x$ for the ground state of an infinite square well of width $L$ with the uncertainty in the momentum $\sigma_p$ for the same state, ...
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3answers
105 views

Would the uncertainty principle apply to gravitational waves?

The uncertainty principle is one of the most basic rules of quantum mechanics, but Quantum mechanics still has not been unified with general relativity, so would the uncertainty principle apply to ...
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1answer
104 views

What does it mean that an electron's position is described by probability?

I just read an answer to a Phys.SE question about why electrons don't collide with protons where an answering user said: In quantum mechanics, an electron doesn't have a definite position or ...
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2answers
271 views

Does Heisenberg's Uncertainty Principle describe real uncertainty or measured uncertainty?

Some derivations of Hesenberg's Uncertainty principle are based on the momentum of light or particles used in measuring an object's position and momentum. Does this lower limit on uncertainty describe ...
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1answer
83 views

Momentum and position for free particle

In the section of 'The free particle' in 'Introduction to quantum mechanics, second edition' by Griffiths page 65. He has the wave equation as $$\Psi(x,t) = \frac{1}{\sqrt{2 \pi}} ...
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4answers
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What does it mean “not to have a definite trajectory”?

In a comment to my question someone stated the following: "photons do not travel at some definite number of oscillations per second. In fact, they do not "travel" at all, no more than electrons ...
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1answer
59 views

Heisenberg Uncertainty Relation and Relativity

It's well known that in QM the position and momentum of a particle cannot be known simultaneously. It's also well known that in special relativity the idea of simultaneity loses its meaning. Would it ...
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1answer
89 views

What is the Quantum Mechanical Operator for Electric Potential?

I understand that charge and electric potential are conjugate observables in QM. See https://en.wikipedia.org/wiki/Conjugate_variables The quantum mechanical operator for charge, q, is simply equal ...
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0answers
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The link between non-locality and Heisenberg's uncertainty relations

I have recently found out1 that the concepts of non-locality and Heisenberg's uncertainty do not live independently of one another in Quantum Mechanics. In other words, roughly the idea goes as: the ...
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3answers
258 views

How can I solve this quantum mechanical “paradox”?

Let a (free) particle move in $[0,a]$ with cyclic boundary condition $\psi(0)=\psi(a)$. The solution of the Schrödinger-equation can be put in the form of a plane wave. In this state the standard ...
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1answer
52 views

When uncertainty is calculated in non normalized eigenstates it doesn't give zero. Shouldn't it give zero?

Suppose $\Psi$ is an eigenstate of observable $\text H$ with eigenvalue $E_1$. Then uncertainty in the value of $\text H$,$(\Delta E)^2=\langle E^2\rangle-\langle E\rangle^2$ which gives,$(\Delta ...
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1answer
82 views

Apparent paradox concerning Heisenberg's uncertainty principle

I have just begun my Introduction to Quantum Mechanics course in my undergrad and I am trying to understand the uncertainty principle on a fundamental level. I think the best way to understand the ...
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2answers
143 views

Does the uncertainty principle go against chaos theory?

My understanding of the uncertainty principle and quantum physics is that any given object may, without notice or explanation, spontaneously perform an action it previously was unable to do with a ...
3
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0answers
59 views

Simultaneous measurement of non-commuting observables without uncertainty

A pair of non-commuting Observables $\hat{X}$ and $\hat{P}$ does not have a common set of eigenfunctions, i.e., it can not be measured simultaneously. Let us for the sake of simplicity assume that ...
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2answers
175 views

Does relativity violate uncertainty principle?

Let us say I sit on an electron. According to me the electron is at rest. Also, I will know the position of the electron accurately as I can take the electron as the origin. So, I know both position ...
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2answers
145 views

Rigorous Mathematical Proof of the Uncertainty Principle from First Principles

While looking at an intuitive explanation for the Heisenberg Uncertainty Principle (related question below), there was a mention of an axiomatic approach to establishing the uncertainty principle. ...
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3answers
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How does the uncertainty principle make sense of the fact that momentum for massive particles depends in part on position?

The momentum of an object is in part dependent on the change in position meaning the final position minus the initial position. The equation for momentum is $$p=\frac{m \Delta x}{t\sqrt{1-(\Delta ...