Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
1answer
39 views

Can the problem of the infinite energy of an electron's point charge be solved by applying time constrains?

Just because an electron's energy and mass appear to be infinite does not necessarily mean you would measure infinite energy and mass. Since measuring the mass of something generally involves you to ...
0
votes
1answer
23 views

Explanation of Different factor of $2$ in Formulas for the Uncertainty Principle [duplicate]

I am readind about Heisenberg's Uncertainty Principle and although the main formula most texts use is $$\Delta x\Delta p_{x}\geq \frac{\hbar}{2}$$ or equivalently $$\Delta x\Delta p_{x}\geq \frac{h}...
1
vote
1answer
29 views

Clarification on Heisenberg thought experiment

Heisenberg imagined a high energy photon was absorbed by an electron, but in order to make a measurement on that electron it will have to absorb another photon which means it velocity gets higher but ...
-1
votes
1answer
51 views

A question on Heisenberg's uncertainty principle [on hold]

According to Heisenberg's uncertainty principle it is impossible to determine accurately momentum and position of an electron simultaneously. Whereas it's not much of a problem in case of a football ...
0
votes
1answer
32 views

minimum uncertainty in measurement of position

Suppose, I made a measurement of the position of an electron using a photon. How the minimum uncertainty in the measurement of the position be one wave length? Also how do we use waves to measure the ...
1
vote
0answers
73 views

How does Heisenberg's uncertainty work with more than one quantum field?

How does Heisenberg's uncertainty principle work with more than one quantum field? I am specifically asking about the time-energy uncertainty: $$\Delta E \Delta t \ge \frac {\hbar}{2}\tag{1}$$ Imagine ...
19
votes
5answers
4k views

If perfect blackness violates the Uncertainty Principle, how isn't dark matter a violation?

In a recent tweet, Dr. Michio Kaku stated that perfect blackness would violate the Heisenberg Uncertainty Principle, i.e. every object must emit some radiation. I have two questions regarding this ...
0
votes
1answer
46 views

How to get the radius of Bohr from the uncertainty principle?

I would like to know how to get the following result: \begin{eqnarray} a_0=\frac{4\pi\varepsilon_0 \hbar^2}{\mu e^2} \end{eqnarray} from the beginning of the uncertainty of heisenberg. If possible, I ...
2
votes
0answers
33 views

Are phase and particle (photon) number in QED conjugated variables?

I found in A. Zee's book "QFT in a nutshell" (1.edition) the interesting relation (8) respectively (9) in chapter III section 5 (p.173) which states that in a collective of non-relativistic bosons the ...
1
vote
1answer
68 views

What is 'definite' variable in QM?

I have gone through a few of the questions on the website regarding this particular query, but I have not understood what they meant. When a question says that a particle has definite momentum, are ...
0
votes
1answer
65 views

I have a thought experiment that defies the uncertainty principle - what's wrong with it?

There's a particle somewhere on the x-axis (this whole thing is 1-dimensional) at x0, which we do not yet know. I fire a photon at it from the origin with a known speed (c) and a known wavelength λ1 ...
0
votes
1answer
65 views

How can electron have known momentum?

In many exercises it is given that electron has a know speed, e.g. 5*10^3 m/s. But how is this possible when we deal with Heisenberg principle?
3
votes
2answers
148 views

Bond breaking stretch length with QM

In QM and assuming you could repeat the same exact bond-breaking experiment arbitrary number of times, do bonds always break at the same stretch length, or does the uncertainty principle require some ...
1
vote
2answers
84 views

Notation in Heisenberg Uncertainty Relation: greater than with tilde: $\gtrsim$

In "The Road to Reality" (pg. 523), Roger Penrose writes: Heisenberg's uncertainty relation tells us that the product of these spreads cannot be smaller than the order of Planck's constant, and ...
2
votes
1answer
54 views

Would a neutron star-like celestial body made of bosons collapse because of missing Pauli repulsion?

Imagine the neutron star-like celestial body would be built up of bosons (assume that neutrons would be bosons). In that case there would be no Pauli repulsion (the exchange force of the exchange ...
1
vote
1answer
56 views

Is there an Heisenberg uncertainty relation for light polarisation?

While reading some questions about the polarisation of a photon, I was wondering about its quantum mechanical representation as a classical vector in the electromagnetic field operator : \begin{...
0
votes
1answer
41 views

Finding the uncertainty from a probability distribution?

If you have two properties, $A$ and $B$, that do not commute, and thus have a commutator $C$, and the uncertainties $\Delta A$ and $\Delta B$ obey the relation $$(\Delta A)(\Delta B)\geq \frac{1}{2}|C|...
-1
votes
1answer
59 views

How to determine the approximate order of the strength of nuclear force from Heisenberg's Uncertainty Principle

Today I came across a question , where I was asked to find the Strength of nuclear force from Heisenberg's Uncertainty Principle... Please can anyone help me out... I have come across a solution ...
0
votes
0answers
17 views

Does diffraction change longitudinal component of k?

Say a monochromatic wave in 2D travelling in the $x$ direction passes an aperture of width $a$ at $x=0$. The amplitude distribution in $k_y$ afterwards will follow the Fourier transform of the shape ...
2
votes
2answers
49 views

Relation between momentum and momentum uncertainty

I have read the following sentence in a section which is explaining why particle accelerators need such high energy: As we require high precision position measurement, the Heisenberg uncertainty ...
2
votes
3answers
139 views

What is the meaning of natural line broadening?

I have recently found one exercise in an exercise book: During the transition from the first excited state of a hydrogen atom into the ground state, photons with a wavelength of 121.5 nm are ...
2
votes
0answers
34 views

Different statements of the Heisenberg's uncertainty principle [duplicate]

In different books, but also websites, there are different expressions for the Heisenberg's uncertainty principle. For example, $\Delta x \Delta p \ge h$ (from The Physics of Atoms and Quanta) $\...
6
votes
3answers
374 views

Zero uncertainity in components of angular momentum in Hydrogen atom

It is given that L and Lz,Lx,Ly commute.(L is total angular momentum, Lx is angular momentum along x axis). So, I can simultaneously know the value of let's say L and Lz. But, if I perform huge no of ...
2
votes
2answers
109 views

Heisenberg uncertainty principle

Is it true that an electron is fundamentally probabilistic in nature? That the Heisenberg uncertainty principle is not describing our limited ability to measure the particle's position and momentum ...
1
vote
2answers
80 views

Paragraph from a Stephen Hawking's Book (Uncertainty Principle)

This is from a Stephen Hawking's Book (Uncertainty Principle). I would like to know how does the Uncertainty Principle impose a limit on the size. What does he mean? From Hawking's book: It turns ...
0
votes
1answer
48 views

Confinement energy of an electron in the nucleus

Hullo, I've got a relatively simple question in my homework and yet I can't seem to find a proper answer I need to find the confinement energy of an electron in a Deuterium nucleus with the radius ...
-4
votes
1answer
89 views

Is the uncertainty principle a circular argument? [closed]

Uncertainty is due to the measurement techniques humans tend to use requiring photoelectric effect. The Planck constant is due to the photoelectric effect. If the standard deviation of measurement was ...
17
votes
2answers
7k views

Uncertainty principle for a sitting person

If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths. What am I missing? Do ...
2
votes
4answers
105 views

QFT and vacuum energy [duplicate]

According to Quantum Field Theory, all 'particles' are oscillations in their own fields. And according to Vacuum Zero Point Energy and the Heisenberg Uncertainty Principle, these fields have ...
2
votes
0answers
43 views

Spread of the (smeared) field observable under time-evolution

Setup: Essentially, I'm interested in performing an analysis which is completely standard in QM, but I've never seen the analogue in QFT: Given I measure a system to have some value of its canonical ...
10
votes
3answers
666 views

Heisenberg energy uncertainty [duplicate]

I am biologist and just new to the field of quantum mechanics and trying to understand the subject by reading. It is said that virtual particles are created due to the uncertainty of energy when ...
-1
votes
1answer
77 views

Uncertainty Principle - Accuracy or Precision? [closed]

While discussing about the Uncertainty Principle, some books use the word 'accuracy' and some other books use the word 'precision'. Some even use them both interchangeably. For instance, in Griffiths' ...
0
votes
2answers
48 views

Is information lost in the Heisenberg's uncertainty?

If I set a particle at a known momentum and a known position, then I would expect that I know the precise position and momentum upon measurement (assuming I can measure that well). The uncertainty ...
1
vote
1answer
25 views

How can the derivation of the energy of an electron in a Fermi gas using the Heisenberg uncertainty principle be made rigorous?

When modeling a large number of non-interacting identical fermions in a potential well of volume $V$ as a harmonic oscillator and assuming the Pauli exclusion principle, it is easily seen that the ...
-1
votes
1answer
55 views

Is it possible to calculate the average value of $x^{2}p^{2}$ for an infinite square well? [duplicate]

If you can only measure either position and momentum in quantum mechanics how would one find the average value of $x^{2}p^{2}$ for an infinite square well?
1
vote
2answers
44 views

Uncertain principle mistake?

I believe I have a hole in my understanding of Heisenberg's Uncertainty Principle, but I'm not sure where it is. 1) Assume you have a source of monochromatic light, a laser, perhaps. 2) Assume it ...
0
votes
2answers
85 views

Heisenberg's uncertainty in nuclear physics

I'm doing a course in Nuclear Physics but I think it focuses more on the experimental side so not everything is that rigorous. In the notes, lecturer gives an argument for why we should use electrons ...
-1
votes
1answer
97 views

Are there any ways to exclude uncertainty in the values of any non-commuting operators? [closed]

If two similar systems are created and In the first system the position is measured with accuracy and in the second one the momentum is measured with accuracy can this avoid the uncertainty in the ...
1
vote
1answer
38 views

Why can't we partition the quantum-mechanical phase space into discrete cells?

Near the bottom of page 2 in this paper, von Neumann states that not only is it impossible to simultaneously measure $x$ and $p$, but also that it is impossible to partition the quantum-mechanical ...
0
votes
1answer
51 views

Definitions of operators and commutativity in quantum mechanics

If $[\hat A,\hat B] = 0$, where $\hat A$ and $\hat B$ are operators, then the operators commute. This also means that, when applied to a wavefunction, that one can measure observables $A$ and $B$ in ...
1
vote
1answer
47 views

$u=(3/2)nRT$ when $T=0$

Why does a body with $0\ K$ temperate does the internal energy NOT become $0\ J$? My lecturer said it had to do with some quantum mechanics, but I never really got any answers from him. I really want ...
0
votes
3answers
54 views

Why does a narrower Gaussian wavepacket correspond to an increased $\Delta k$?

Please answer this question without too much reference to the Uncertainty Principle. I understand it in that respect. I'm just wondering in terms of Fourier analysis. Why does a more localized wave ...
0
votes
0answers
41 views

Finding positional uncertainty from in ground state of $V=-\alpha \delta(x)$

That is the entire problem - I intend to find $\Delta p$ and $\Delta x\Delta p$ once I'm done, but I don't expect that to be difficult (just using the momentum operator instead). I've only found the ...
-1
votes
0answers
35 views

Finding coordinate uncertainty of a particle

I'm given a one-dimensional particle of mass $m$ with "random uncorrelated" $\Delta x_o$ and $\Delta p_o$ and told to find the coordinate uncertainty at time $t$, $\Delta x_t$, then to find the ...
0
votes
0answers
70 views

Are there wavefunctions that don't get more localized as we go backwards in time? [duplicate]

Gaussian wave packets spread as the time passes, which means that as we go backwards in time they get more localized. Therefore, Gaussian wave packets introduce less uncertainty in the position as the ...
8
votes
4answers
3k views

What's the speed of light when viewed from the side?

Suppose a pulse of light is sent from $A$ to $B$ in a rigid triangle $ABC$. While the pulse is moving from $A$ to $B$, what is it's velocity relative to $C$? The special character of the photon among ...
-1
votes
1answer
54 views

Meaning of units in the Heisenberg Uncertainty Principle

So we have the inequality $\Delta x\,\Delta p\geq \hbar/2$ Why is the uncertainty of position in meters? Isn't uncertainty measured in probabiliies? Does it make sense to say that the uncertainty in ...
1
vote
0answers
47 views

The uncertainty principle and probing small scales

The uncertainty principle states that $\Delta x\Delta p \geq \frac{\hbar}{2}$. So if you know momentum to high precision, you can't know position to high precision. In the context of accelerator ...
0
votes
2answers
66 views

Are the fundamental concepts in Heisenberg Picture and Schrodinger Picture different?

In Heisenberg Picture, for a free particle, $[x_i(t),x_i(0)]=\frac{-i\hbar t}{m}$. This relation implies that even if the particle is well localized at t=0, its position becomes more and more ...
0
votes
2answers
34 views

Question About Relation Between Time and Color of a femtosecond Laser Pulse

This is a problem in Tipler's Modern Physics: Laser pulses of femtosecond duration can be produced, but for such brief pulses it makes no sense to speak of the pulse’s color. To demonstrate this, ...