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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How close to reality is my handwaving argument about Fabry Perot interferometers?
Under this answer to https://astronomy.stackexchange.com/q/55437/7982 I wrote a comment where propose the uncertainty inequality roughly written1 as $\Delta E \Delta t \ge h$ or for photons $\Delta \...
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Is the space between plates, in Casimir effect, empty of momentum?
Please correct me if I am wrong. In Casimir effect, when two plates are brought very close to each other, there is a Force felt. This force is due to quantum fluctuations.
The space between plates is ...
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Find the uncertainty in the velocity of an electron and alpha particle respectively when they are located within 15×10^(-8) cm [closed]
recently I was solving questions on uncertainty principle but never came across questions involving system of particles like combination of electron and alpha particle.
I wanted to understand how to ...
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Uncertainty on the sum of two non-commuting operators
Suppose that I have an observable
$$
\hat{E} = \sin(\alpha) \hat{Q} + \cos({\alpha}) \hat{P}
$$
with $\hat{Q}, \hat{P}$ being non-commuting operators satisfying
$$
[\hat{Q}, \hat{P}] = i \hbar
$$
It ...
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The uncertainty principle and magnetic bar
As far as I know, the magnetic properties of a bar magnet is due to the alignment of electronic spins of all the atoms. According to the uncertainty principle the electronic spin is randomly up or ...
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How to Derive the Minimum Time for $⟨ψ_0|A(t)|ψ_0⟩$ to Vanish Using Uncertainty Principle?
I am trying to work through some bookwork, and I am stuck on the titular question. The scenario is as follows:
In a generic finite dimensional Hilbert space $\mathcal{H}$, define the operator $A(t) ≡ ...
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Is it possible to shift frame of reference to an electron?
We can see the world from different perspectives, from inertial frames to non-inertial frames. All that works very well but suppose I want to see the world from electron’s perspective then would I be ...
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Youtube video claims 2023 physics Nobel prize winners proved Heisenberg wrong
This video claims (scroll to 11:22 frame), that inventors/improvers of a unique attosecond pulse generation which enables us to monitor atom dynamics proved that Heisenberg was wrong (citation from ...
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The Uncertainty in momentum and the de Broglie wavelength
I'd like to pose a straightforward question by providing a brief example to determine whether my current approach is correct or incorrect.
Imagine I have an electron confined within a box measuring $1\...
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Heisenberg's microscope and gravity [closed]
Is the Heisenberg's microscope gedanken experiment valid when considering spacetime kinematics?
That is, if we consider a small region of space and try to measure its curvature, then we may use ...
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Feynman on Heisenberg's Uncertainty Principle
In 1964, Feynman stated that
"Heisenberg noticed, when he discovered the laws of quantum mechanics, that the new laws of nature that he'd discovered could only be consistent if there was some ...
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Simultaneity and The Uncertainty Principle
So, the uncertainty principle states that one can not measure momentum and position with accuracy simultaneously. However, we know from relativity that simultaneously is something frame dependent in ...
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Heisenberg's Uncertainity Principle Disproved? [closed]
Heisenberg's uncertainty principle states that we can't mutually determine both the trajectory and momentum of a subatomic particle.
According to Einstein,
If we take two particles with different ...
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QM from the uncertainty principle?
In a book Quantum Mechanics with Applications (1970) by D.B. Beard and G.B. Beard, the authors wrote on page 34:
"By methods beyond the scope of this text, one could state the uncertainty ...
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How did Cohen-Tannoudji (QM) manipulated this? [closed]
In the first chapter of Cohen-Tannoudji’s Quantum Mechanics Book, there's this part of the chapter called "Time evolution of a free wave-packet". So one starts with the wave packet given by
$...
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How is the RMS energy of a nucleon in a nucleus of mass number A in its ground state depend on mass number of the nucleus?
So, in my book it's said that the RMS energy of a nucleon in a nucleus of mass number A in its ground state varies as A^(-1/3). Can you please explain how did we arrive at this? Are nucleons ...
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Can I upper-bound uncertainties of $B$ in an eigenstate of $A$ using an appropriate norm of $[A,B]$?
There are times when I would really like a "reverse" uncertainty principle to hold, allowing me to upper-bound certain uncertainties in terms of properties of commutators. I'll try to ...
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Connection between quantum non demolition measurement and the Heisenberg limit in metrology
Quantum non demolition measurements are those that do not feed back action noise into the measured observable. For discrete systems, this leads to the somewhat trivial case of where the observable (...
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Does Group Velocity violate Uncertainty Principle?
I've recently begun studying Quantum Mechanics and went through the descriptions of phase and group velocities and the fact the group velocity or the velocity of the resulting wave envelope represents ...
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Commuting operators and their physical interpretation in QM
I'm studying Quantum Mechanics for the first time at the moment and I have a few questions in mind.
So recently, I saw a proof on that if two operators share the same eigenstates is equivalent to the ...
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How does helium 2 at superfluidity occupy the same quantum state
As my question states, at 2K and below, helium 2 is a superfluid that apparently can defy the laws of entropy. This is explained that at this temperature, all atoms are in the same quantum state. ...
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What is meant by the term “borrowing energy from the vacuum” in quantum physics?
What is meant by “borrowing energy from the vacuum” seems like a totally illogical statement and a violation of conservation of energy
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Uncertainty principle, maybe it doesn't forbid simultaneous measurements of position and momentum?
Consider the single-hole diffraction of an electron. We can make the hole as small as we like and determine the electron's position with arbitrary accuracy. When it is in the hole, we can hit it with ...
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Heisenberg uncertainty principle during measurement
I am currently studying quantum mechanics and again came across the uncertainty principle, and I seem to lack any intuition about what it means. I full understand how it can be derived using ...
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Can you use Heisenberg's uncertainty principle to generate infinite energy?
I have been reading a book about quantum mechanics ( In search of Schrodinger's cat by John Gribbin ) and on page 196, it states
An electron does not exist in isolation, because it can borrow energy ...
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Loss of determinism in the uncertainty principle?
I stumbled upon this interview of Teller talking about how Heisenberg and Bohr was suggesting to Einstein the uncertainty principle doesn't disobey causality but merely says the future is always ...
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What is meant by "strongest inequality here" in this proof of generalized uncertainty principle?
In proving a generalized uncertainty principle, Ballentine (page 223 of the first edition) arrives at any expression
$$Tr(\rho A_0^2) +\omega Tr(\rho C)+\omega^2Tr(\rho B_0^2) \geq 0$$
where $A_0 \...
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Causality and uncertainty principle
Suppose one measures the position, then momentum, then position of a particle, and that all these measurements are done in quick succession of one another (ie. arbitrarily close to zero-time as ...
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Understanding the Uncertainly Principle in Stern–Gerlach experiment
Question is at the bottom, some background info
I was watching a lecture where they considered for simplicity sake that the spins were represented as two properties : Hardness (Hard and Soft) and ...
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How does shape of a wavefunction changes as it encounters a potential barrier?
A particle of mass and energy $E > 0$ in one dimension is scattered by the potential
below
If the particle was moving from $x = -\infty$ to $x= +\infty$, which of the following graphs gives
the ...
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Uncertainty of an observable when on energy eigenstate
Suppose we are on an energy eigenstate
$$ \varphi_n $$
We can calculate the expected value
$$ <[\hat H , \hat A ] >_{φ_n} $$ and show that it will be equal to zero.
Now, according to Robertson ...
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Uncertainty principle when in position (or momentum) eigenstate [duplicate]
Suppose we want to calculate the expectation value
$$\langle x|[\hat{x},\hat{p}]|x\rangle,$$
where $|x\rangle$ is an position eigenstate, so that $\hat{x}|x\rangle=x|x\rangle$ and $\langle x|\hat{x} = ...
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DOS in Fermi Golden Rule
I was reading second chapter of Introductory Nuclear Physics by Kenneth S.Krane, and in that chapter he was giving about the logic of why there must be a factor of $\rho(E_{f})$ in the decay ...
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Why is there no uncertainty principle for mass or charge? [closed]
The uncertainty principle holds for pairs of certain observables, such as position and momentum.
All these observables have a relation to spacetime.
Other particle properties, by contrast, such as ...
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Does perfect knowledge of momentum of a free particle imply that there is a finite probability of finding free particle anywhere in the universe?
In the case of a free particle, if you have perfect knowledge of its momentum, the uncertainty in its position becomes infinitely large.
Does this imply that there is a finite probability of finding ...
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What's so "quantum" about quantum fluctuations in the CMB?
I've heard that fluctuations in the CMB provide support for inflationary theory, as they are thought to be amplified quantum fluctuations of the inflaton field. My question is, what is so "...
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What has coherence time to do with Energy-time uncertainty?
we know that the coherence time $t=\frac{1}{\Delta f}$can be derived from Fourier transformation.
But if we look at the Energy Time Uncertainty which is given by $\Delta E \Delta t ≥ \frac{h}{4\pi}$ ...
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Can an electron move in a well-defined path? [closed]
Considering the probabilistic relationship between the momentum and position of an electron, are the pictures that show the interaction between electrons and positrons an accurate description of ...
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Is the uncertainty principle a tight bound?
Looking at the proof on Wikipedia, the part that confuses me is as as follows. Firstly, $\sigma_x^2\sigma_p^2\ge |\langle f|g\rangle|^2$. Then, because $$|z|^2=(\text{Re}(z))^2+(\text{Im}(z))^2\ge(\...
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Need help understanding proof of generalised uncertainty principle [closed]
I was watching this video on YouTube: https://www.youtube.com/watch?v=qgkWUuqoSVM&list=PLdgVBOaXkb9Bv466YnyxslT4gIlSZdtjw&index=9&t=557s about the generalised uncertainty principle when at ...
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Proof of the generalised uncertainty principle
The generalised uncertainty principle for any Hermitian operators $\hat{A}$ and $\hat{B}$ can be proven using the fact that the inner product of the following operator is non-negative:
$$\hat{O} = \...
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Deriving the Heisenberg uncertainty principle from the wave packet [closed]
How did we get the C-17, is it possible to derive the Heisenberg uncertainty principle from the wave packet?
could you recommend readings to help me understand this better.
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Why is this a correct explanation for the Uncertainty Principle? [duplicate]
There's this really common explanation for Heisenberg's Uncertainty Principle, but I quote it from Classical Dynamics by Marion and Thornton:
The wave character of the photon precludes an exact ...
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The chance of light being red after 2nd button press if first button gives red light (Richard Feynman: Quantum Mechanical View of Reality)
This question is related to a Richard P. Feynmann lecture on "Quantum Mechanical View of Reality"
There are 3 buttons L, M and R. Each switch is connected to a bulb that can randomly light ...
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After a particle hits a screen and becomes stuck to it, will we know both position and momentum?
After a quantum particle hits a detector screen, we learn two things:
Its position in all 3 dimensions (it's in the bright spot in the screen)
Its momentum in all 3 dimensions (it's stuck in the ...
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Mathematical Expression of Heisenberg's Uncertainty Principle [duplicate]
In some situations the mathematical expression of the principle is $$\Delta x \Delta p \ge \hbar$$
But sometimes it is written as $$\Delta x \Delta p \ge \frac {\hbar}{2}$$
Why such a difference? And ...
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Integral arising from the proof that the quantum harmonic oscillator satisfies Heisenberg's uncertainty principle
I was trying to verify myself that the stationary states of the quantum harmonic oscillator (QHO) always satisfy Heisenberg's uncertainty relation. In doing so, I came across an integral of the form
$$...
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Why doesn't a photon state have to be infinite in length?
In all discussions I've seen so far (old quantum theory, semiclassical QM, QFT), when we talk about photon states, we seem to say they have a definite momentum. At the same time, we also say a photon ...
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Scientific determinism and the Heisenberg's uncertainty principle
I'm reading Brief Answers to the Big Questions by Stephen Hawking. In chapter 4, it discusses whether we can predict the future. As many have known that Laplace put forth that if we knew the positions ...
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The interpretation of Energy-Time uncertainty principle in this article 'Is the universe is a Vaccum Fluctuation?' by Edward Tyron is right or wrong? [duplicate]
This is a screenshot from Edward P Tyron's article "Is The Universe a Vaccum Fluctuation?"
The explanation Energy-time uncertainty principle from Griffiths:
$Δt$ represents the amount of ...
