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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What is The Heisenberg Uncertainty Principle Making Statements About?

Non-physicist here, trying to understand details about Heisenberg's uncertainty principle: Watching the The more general uncertainty principle, beyond quantum about the uncertainty principle I came ...
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14 views

Time Dependence of Momentum Uncertainty for a Free Particle

Question: Show that in a free-particle wave packet the momentum uncertainty $∆p$ does not change in time. I am not sure how to solve for the time derivative of the momentum uncertainty $ ∆p $. I am ...
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How will the uncertainty principle broaden emission spectrums?

I have been told in a lecture that the broadening of peaks detected from photon emission in a hydrogen lamp is due to the uncertainty principle, but can’t work out how it does or find any equation ...
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An uncertainty principle modification of GR? [closed]

Can we modify the GR field equations to contain uncertainty and then use an assumption that the uncertainities are somehow related? Are there any known attempts that try to extend the established ...
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1answer
45 views

Query about Heisenberg uncertainty principle

acoording to heisenbergy uncertainty principle if the electrons change the radius of their orbit, then it is like making transition even though the change in radius is small and they should emit ...
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1answer
40 views

Uncertainty about the ensemble average?

Does an uncertainty in momentum of $\Delta p$ mean that the actual momentum is in the range $\langle p \rangle - \Delta p\space <p< \langle p\rangle+\Delta p\space$ ? Or does it mean that the ...
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Does uncertainty principle imply that the past history of universe is also undetermined?

I read the page here: Is the Uncertainty Principle valid for information about the past?, but I am still somewhat confused. If you measure the momentum/position (with uncertainty) of a particle, what ...
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61 views

Can one find the uncertainty of a particle from Schrödinger's wave equation? [closed]

Right now I am studying quantum mechanics and I'm having trouble understanding what exactly $\Psi$ is in Schrodinger's equation $\Psi(x) = A\sin(kx) + B\cos(kx)$. After doing some googling I learned ...
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1answer
57 views

What does “An experiment performed with certainty has results with uncertainty.” mean? [closed]

A physics book says: An experiment performed with certainty has results with uncertainty. What does this mean?
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40 views

Heisenberg uncertainty principle on bosons at absolute zero [duplicate]

Bosons obey Heisenberg's uncertainty principle but not Pauli's exclusion principle. In Bose-Einstein Condensation quantum effects are much more important and here we get a large number of particles ...
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64 views

Why the ground state energy of bosons are 0 at T=0K ? Does it violate Heisenberg's Uncertainity Principle at 0K?

Bosons obey Heisenberg's Uncertainity Principle but do not Pauli's Exclusion Principle. That's why in Bose Condensation we get a large amount of particles in a single state i.e. ground state at T=0K. ...
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Does the Copenhagen interpretation (+ “quasi-classical apparatus”) allow one to bypass a derivation's objection? [closed]

Background I asked this question, where I'm thinking about this joshphysics's answer: And the gist of what I get is (from the answers and the chatroom) within interpretations of quantum mechanics ...
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What is uncertainty in position of electron when it is revolving around the nucleus?

Consider an electron revolving around the nucleus in a circle of radius $r$. We need to apply Heisenberg's uncertainty principle on it. What exactly do we take $\Delta x $ to be? One way to think ...
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148 views

Validity of the derivation of time-energy uncertainty principle?

Background The top voted answer to this question seems to make some assumptions I'm uncertain about (to say the least): What is $\Delta t$ in the time-energy uncertainty principle? Assumptions The ...
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15 views

Deriving a non trivial pair of observables whose product of variances is EQUAL to position and momentum?

I'm operating in the schrodinger model, where my position space is $\mathbb{R}^1$. I'm looking for a pair of operators $O_1, O_2$ such that $$ \sigma_{O_1}^2 \sigma_{O_2}^2 = \sigma_x^2 \sigma_p^2 $...
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Correct form of Uncertainty Principle [duplicate]

In a book of mine, the author wrote that $$\Delta x \Delta p_x \geq h$$ However the usual form of the Uncertainty Principle I saw in many places is $$\Delta x \Delta p_x \geq \frac{h}{4\pi}$$ So I ...
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Heisenberg's uncertainty principle: what is the correct interpretation?

In this video: https://www.youtube.com/watch?v=xsnTrAEiyHg Prof. Walter Lewin showed when a laser beam passes through a very narrow slit the projection of it becomes wider. He claims it is because of ...
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1answer
60 views

How can uncertainty be represented as a chance [closed]

How can uncertainty be represented as a chance when we write in Heisenberg's principle? Why do we use Delta for uncertainty and mathematically use it the same way as if it was a change in position or ...
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1answer
29 views

Tracing Path of a Body and Uncertainities Involved [closed]

If for instance suppose we take a situation like this- A satellite just exploded due to some reasons and it's sharpnel are falling in Earth. We have to find out the exact location where they will ...
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23 views

Defining Angle between Observables consistently

Problem Setup: There is a nice proof of the heisenberg uncertianty principle using cauchy-schwarz given here Stated in variance form it is: $$ \sigma_x^2 \sigma_p^2 \ge \frac{\hbar^2}{4} $$ Now ...
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1answer
265 views

If $h/4\pi\to 0$ in the Heisenberg's uncertainty principle what happen?

If in the Heisenberg's uncertainty principle the quantity $$\frac{\hbar}2=\frac{h}{4\pi}$$ is near to $0$, what happen? What is a simple any explanation that could be given to a high school student? ...
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38 views

How short is the time for the manifestation of small amounts of energy to justify the existence of quantum fluctuations?

Uncertainty Principle allows the appearance of small amounts of energy from nothing, always on the condition that they disappear in a very short time. Speaking in seconds, how brief should these ...
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Is vacuum energy transient or permanent?

Vacuum energy is based on Heisenberg's energy–time uncertainty principle which says that $\Delta E$ can exist for $\Delta t$. This $\Delta E$ can produce electron positron pair for $\Delta t$ by ...
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1answer
112 views

Is width of particles a consequence of Heisenberg's uncertainty principle?

The uncertainty principle tells us that $$\sigma_x\sigma_p \geq \frac{\hbar}{2}, $$ which means that the more precisely we measure a particle's position, the more imprecise we will know its momentum. ...
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If Poisson Bracket of Momentum and Position is non-zero, why no Uncertainty Principle?

In Hamiltonian classical mechanics, we have that the Poisson bracket of position and momentum satisfies $$\{q_i, p_j\} = \delta_{ij}$$ But this implies that momentum and position 'generate' changes ...
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3answers
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The use of the commutators in quantum mechanics: explanations [duplicate]

Considering that I've never studied quantum mechanics before I have need to understand the operator commutator. My start is: $[A,B]=AB-BA \tag{a}$ Now, why must be $$\left[\frac{\partial }{\partial ...
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1answer
35 views

Which aspect of light does an ordinary photometer consider?

Most photo detectors uses the wave aspect of light while measuring the intensity of any incident radiation , thus yielding a value in $\text{W/cm}^2$ , also there are photo detectors that shows the ...
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4answers
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Using conserved quantities to violate the Uncertainty Principle

If I have a two-body system (particles A and B) which I measure the total momentum of, can I measure the position of particle A very accurately and the momentum of particle B very accureately, and ...
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The validity of some “applications” of the uncertainty principle

Given a $L^2$ function $f$ with $\int_\mathbb{R}xf(x)dx=0$, define its variance to be $\sigma_f^2=\int_{\mathbb R}x^2f(x)dx$. The uncertainty principle states that $\sigma_f\sigma_\hat f\geq 1/4\pi$,...
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Heisenberg uncertainty principle in daily life

I need some examples of the Heisenberg uncertainty principle on a basic level, or if possible in daily life. Or maybe a simple explanation for validity of the principle in easier words. I cannot get ...
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Why and in what cases we use $E$ instead of $\Delta E$ in energy-time uncertainity relation?

sometimes in problems of energy or time uncertainity we use the value of energy of the particle/system to calculate the delta t. Now what are those cases specific examples, where we can apply this?
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Derivation of Margolus-Levitin bound on the Quantum Speed Limit

In their derivation of the Margolus-Levitin bound on the "quantum speed limit" the authors make use of a trigonometric inequality $\cos x \ge 1-\frac{2}{\pi}(x+\sin x), \quad \forall x\ge0$ Is ...
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1answer
52 views

Different statements of the Heisenberg uncertainty principle [duplicate]

I know that from the Heisenberg uncertainty principle, ∆x∆p=ℏ/2 . And I know that this equation can be rewritten as ∆t∆E=ℏ/2. From QED I also know that the equation ∆t∆E=ℏ/2 claims that some energy ...
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1answer
56 views

Do emitted photons have a well defined frequency or just a spread as per HUP?

I have read this question: Conservation of Energy in photon exchange between two atoms where Kurshal Shah in a comment says: As per the energy-time uncertainty relation, the emitted photon ...
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23 views

Why does heisenberg uncertainty principle work? [duplicate]

Hiesenberg's Uncertainty Principle states that inaccuracy in momentum and position will always be there and we will never ever be able to get it 100% accurate. Suppose in future millions of years from ...
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1answer
51 views

Does this wave function from Zettili book (Quantum Mechanics) violate uncertainy principle?

I am not sure whether my question counts as homework and exercises or not, because I already know the answer. The problem is, I find Zettili answer rather unsatisfactory. Problem 1.11 (a) Find the ...
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61 views

Hawking temperature, uncertainty principle and size of a black hole

I was playing with the Hawking temperature formula $$T_H = \frac{\hbar\ c^3}{8 \pi\ G\ M\ k_B}$$ and I thought it would be interesting to associate a velocity to this temperature: $$k_B\ T_H = \frac{1}...
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87 views

Hard boundary of Heisenberg's uncertainty principle

Heisenberg's uncertainty principle states that we cannot know the position and momentum of subatomic particles simultaneously...but what exactly is the boundary of size of such a particle? Does such a ...
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2answers
73 views

A doubt on waves

We know that every progressive wave depends on its position X and time variable T. y= Asin (kx- wt) My doubt is "Even an election is a wave (de broglie's hypothesis), but we cannot write its equation ...
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2answers
83 views

schrodinger's cat experiment puzzle [duplicate]

In Schrodinger experiment, the cat is both alive and dead until an observer opens the box to observe the radioactive decay - but why isn't the cat itself an observer?
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What is the characteristic of a property?

Background: The following two observations are , in my understanding, pretty much accepted in quantum theory: Location is a property which is not preexisting but is established by measurement. It is ...
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1answer
45 views

Can momenta eigenstate written in term of $x$ be an eigenfunction of position?

Being non-commuatable operators, momentum and position cannot have simultaneous eigenfunctions. But in "Theoretical Minimum: QM" by Lenny Susskind and Artsy Friedman, in explaining Heisenberg's ...
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1answer
40 views

Can the “external” field in DFT be that of an electron?

In my experience with (Kohn-Sham) density functional theory, the external potential is due to a massive particle like a nucleus or ion. I have never seen an electron be the source of the potential, ...
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3answers
68 views

Quantum Zeno effect and Heisenberg uncertainty principle

The Heisenberg uncertainty principle forbids the existence of static atoms But in the Quantum Zeno effect observing atoms makes them stand still does the Quantum Zeno effect violate the Heisenberg ...
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1answer
96 views

Can measurement of the momentum of a particle can be done without observing its position?

Uncertainty principle says that one cannot measure exactly the position and momentum of a particle at same time. As per common understanding when we are measuring momentum of an object it is ...
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1answer
34 views

Heuristic for large $x$ behavior from small $q$ behavior of Fourier Transform

If I have a function $h(\mathbf x)$ which may be written $$h(\mathbf x)= \int \frac{\text{d}^d\mathbf q}{(2\pi)^d} \, h(\mathbf q) e^{-i \mathbf q \cdot \mathbf x}$$ and assume spherical ...
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1answer
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How can the momentum-position Uncertainty Principle not violate conservation of energy? [duplicate]

As far as I understand, the primary reason why an electron doesn't fall into a nucleus is that, when it gets close, it has a sufficiently high probability of having a lot of momentum to get back to ...
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1answer
56 views

What does it mean to say “since the magnitude of actual momentum is smaller than uncertainty, the value cannot be defined”?

What does it mean to say "since the magnitude of actual momentum is smaller than uncertainty, the value cannot be defined"? Original question: Uncertainty in the momentum of an electron is $ 2.6 \...
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1answer
84 views

Quantum mechanics limits to understanding the Universe [closed]

By definition, a wave function does not describe a particle's state exactly, we can only know that information when we make measurements and thus collapse the wave function. This gives us a lot of ...
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2answers
362 views

How does the Uncertainty Principle work? [duplicate]

In my textbook they have explained the Heisenberg's uncertainty principle using the example where you cannot measure the position of the electron using the photon because the wavelength of the photon ...