This tag is for Heisenberg quantum mechanical uncertainty principle.
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Determining the spin of wavefunction
We all know that by uncertainty principle, location of a wave-particle is perfectly determined when uncertainty of momentum becomes infinite. (I also heard that in reality, it is almost impossible to ...
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1answer
240 views
Applying uncertainty principle and the difference in $\Delta x$
These two questions seem to be very similar, but the textbook uses a bit different methods for calculating $\Delta x$ of uncertainty principle.
Question A) Suppose that there is a room with the same ...
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1answer
305 views
Momentum in quantum mechanics
In quantum mechanics, we can have some superposition of matter waves that have different wavelengths. If then, can't momentum of a particle change every time measurement takes place? Or should I ...
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1answer
141 views
electrons in an atom and uncertainty principle
Electrons in an atom have quantized energy quantity. Can uncertainty principle be applied in this case, then?
How does this work?
As energy is fixed, this seems to disobey $\Delta E \Delta t \geq ...
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1answer
162 views
EPR paradox and uncertainty principle
In Wikipedia article EPR paradox,
The original paper purports to describe what must happen to "two systems I and II, which we permit to interact ...", and, after some time, "we suppose that there ...
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2answers
205 views
Why is $\Delta x \Delta k \approx 1$ in any pulse?
In my physics textbook, it says that for any pulse, if $\Delta x$ becomes smaller, $\Delta k$ becomes larger where $k$ refers to $2\pi/\lambda$ and $x$ is x-axis displacement, as described by $\Delta ...
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3answers
111 views
uncertainty of fields with many harmonic modes
In most basic level introduction to the quantum harmonic oscillator formulation of fields, it is assumed that the commuting variables for the fields $p_m$, $q_m$ are
$$ \lbrack p_m , q_n \rbrack = ...
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2answers
482 views
what is expectation values of this anti-commutator?
what is expectation values of this anti-commutator?
$$\langle \{ \Delta \hat x,\Delta \hat p\} \rangle$$
where the $\Delta \hat p=\hat p-\langle \hat p \rangle$ and $\hat p$ is momentum operator and ...
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4answers
913 views
What is meant by “Nothing” in Physics/Quantum Mechanics(QM)?
I am not a phycisist, so please forgive my ignorance. This is related to my posts and this.
I am trying to undertand what is meant by the term "Nothing" in physics or Quantum Mechanics since it seems ...
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2answers
307 views
Naive question on quantum mechanics and uncertainty principle
This is a follow up on this question, the answer of which points towards Quantum Mechanics.
As stated I am not a phycisist so please forgive my ignorance.
I will try to understand the issue by going ...
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1answer
92 views
problem with the last terms of uncertainty principle
i've problem with the last terms of uncertainty principle:
1. are these equalities true:
$$\langle \{\Delta \hat A,\Delta \hat B\} \rangle=\langle \{\hat A, \hat B \}\rangle$$
$$\langle [\Delta \hat ...
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2answers
134 views
is there any uncertainty on the free particle with a definite momentum $\vec p$?
The probability amplitude for a free particle with momentum $\ p$ and energy $E$ is the complex wave function:
$$\psi_{(\vec x , t)}=e^{i(\vec k\cdot \vec x -\omega t)}$$
is there any uncertainty on ...
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1answer
167 views
Will photon's energy be exactly same after million years?
If photon will travel for million years without collisions, what
subtle effects can be accumulated ?
Gravity fields affect trajectory, but is energy completely intact after fly by ?
Photon has its ...
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1answer
175 views
Change In Momentum In Uncertainty Principle
The most basic explanation for the Heisenberg Uncertainty Principle is that the momentum and position of a quantum particle is not very distinct when an attempt is made to measure them together. But ...
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1answer
924 views
How does position uncertainty change in time?
I have an online homework for my Modern Physics class, that requires me to find the uncertainty in velocity and position of a duck. The question is as below:
Suppose a duck lives in a universe in ...
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1answer
286 views
Uncertainty principle in infinite potential well
Consider infinite potential well i.e. Hilbert space $L^2 \bigl([0,1]\bigr)$. Next we consider subset $$D_\theta = \left\{ \psi \in L^2 \bigl([0,1]\bigr) | \; \psi \; \text{is absolutely continuos and ...
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3answers
353 views
Generalizing Heisenberg Uncertainty Priniciple
Writing the relationship between canonical momenta $\pi _i$ and canonical coordinates $x_i$
$$\pi _i =\text{ }\frac{\partial \mathcal{L}}{\partial \left(\frac{\partial x_i}{\partial t}\right)}$$
...
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3answers
569 views
Concept of a point particle in quantum mechanics
A point particle is usually thought of as structureless and without dimension. However, given that Heisenberg's uncertainty principle prohibits us from knowing the position of a particle exactly, what ...
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2answers
395 views
Operators Uncertainty
$\hat A$ is an operator.
The uncertainty on $\hat{A}$, $\Delta A$ is defined by:
$$\Delta A=\sqrt{\langle\hat A^2\rangle - \langle\hat A\rangle^2}$$
what is difference between
$\langle\hat ...
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3answers
348 views
Why can't we know the speed, $\vec{v}(t)$, and position, $\vec{r}(t)$, of an electron (the two) at the same time $t$?
I've read something about this and I conclude that it happens because of the uncertainty principle. But I don't understand very well the meaning of that.
I mean, it's very abstract that the speed, ...
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1answer
209 views
Heisenberg's principle in Quantum Cryptography
In quantum cryptography why do we need the Heisenberg uncertainty principle?
Edit:
I only know the statement of the Heisenberg uncertainity principle.
As I know that if Eve tries to know the ...
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8answers
585 views
Why do quantum physical properties come in pairs?
Why do quantum physical properties come in pairs, governed by the
uncertainty principle (that is, position and momentum?)
Why not in groups of three, four, etc.?
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4answers
519 views
Uncertainty Principle for a Totally Localized Particle
If a particle is totally localized at $x=0$, its wave function $\Psi(x,t)$ should be a Dirac delta function $\delta(x)$. Accordingly, its Fourier transform $\Phi(p,t)$ would be a constant for all $p$, ...
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2answers
584 views
Who first realized the uncertainty principle allows for virtual particle pair production?
For all I've read about Quantum Field Theory I've never seen the concept of the living vacuum accredited to someone in particular. Given the importance of this very application of the uncertainty ...
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1answer
352 views
Do stationary states with higher energy necessarily have higher position-momentum uncertainty?
For simple potentials like square wells and harmonic oscillators, one can explicitly calculate the product $\Delta x \Delta p$ for stationary states. When you do this, it turns out that higher energy ...
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2answers
865 views
Noether's theorem vs. Heisenberg uncertainty principle
In continuation of another question about Noether's theorem I wonder whether there exists some kind of relationship between this theorem and the Heisenberg uncertainty principle.
Because both the ...
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2answers
570 views
The complementary variable to the qubit and spin-1/2
The qubit is a big topic of quantum information theory. A qubit is a single quantum bit. Physical examples of qubits include the spin-1/2 of an electron, for example, see page 39 of Preskill:
...
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2answers
201 views
electron orbits
Is there an upper limit to the number of orbits an electron can have around say a proton?
Arent there states that are unstable(for n!=1) with corresponding mean/half lives and therefore uncertainty in ...
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1answer
208 views
Uncertainly Principle in orthogonal directions
The Heisenberg Principle states that for each direction, $\Delta x\cdot \Delta p_x \ge \hbar , \Delta y\cdot \Delta p_y \ge \hbar$ and $\Delta z\cdot \Delta p_z \ge \hbar$.
But, can anything be said ...
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6answers
300 views
Does the HUP alone ensure the randomness in QT?
This answer of mine has been strongly criticized on the ground that it is no more than a philosophical blabbering. Well, it may well be. But people seem to be of the opinion that HUP alone does not ...
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5answers
1k views
Does Heisenberg's uncertainty under time evolution always grow?
Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting ...
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3answers
561 views
Causality and Quantum uncertainty [duplicate]
Possible Duplicates:
Why quantum entanglement is considered to be active link between particles?
Why can't the outcome of a QM measurement be calculated a-priori?
Why do some (the majority ...
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1answer
267 views
3D Minimum uncertainty wavepackets
Based on the 1D case mentioned in Griffiths, I decided to try looking at the features of 3D Gaussian wavefunctions, i.e. (position basis) wavefunctions of the form $\psi(\mathbf{r}) = ...
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1answer
429 views
Minimum Uncertainty Wavefunction derivation
Can anyone point me to a reference (preferably either something online or something a small liberal arts school would be likely to have in its library) that goes through a derivation of the minimum ...
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5answers
333 views
Would something like the uncertainty principle arise even if the universe was built on something like Newtonian mechanics?
I am thinking of a (greatly simplified) computer simulation of a universe that followed something like Newtonian rules. Inside the simulation are A.I.s that are made from those same rules, and can ...
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2answers
3k views
Spectral Line Width and Uncertainty principle
so I've been at this for about 3 - 4 hours now. It is an homework assignment (well part of a question which i've already completed). We did not learn this in class. All work is shown below.
An ...
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2answers
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Calculating de Broglie wavelength
Hey,
trying to finish an assignment but having some trouble with it. I will show all my work. The topic is on wave/particle dualty, uncertainty principle (second year modern physics course).
So the ...
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1answer
163 views
Is it possible to determine timescales of electron dynamics from the natural linewidth of an electronic transition?
A lot of work has been done recently on electron dynamics using attosecond pump-probe techniques; for instance in this paper. In this particular paper, the authors photoionized the neutral ...
