Uncertainty principle Definition and 528 Threads

We have an electron pulse of width 1 nanosecond and with kinetic energy of 1keV. We have to calculate Δx and Δp. I have a question regarding this problem. If they give us the kinetic energy of the electron pulse then we know exactly the momentum right? And so the uncertainty of momentum would...

The principle states: δxδp≥h/4π I understand what it means and I've seen in proven both theoretically and expiamentally, so I am not questioning the inequality here. My question is: If there was a very narrow tube that had a vacuum inside it and a laser attached at one end that shoots...

I'm not certain as to the true meaning of the Heisenberg Uncertainty Principle, and wonder if anyone can provide insight. I understand that there is a reciprocal relation between the certainties as to the position and momentum of a particle such as an electron; the more precisely position is...

All of the statements of Heisenberg's uncertainty principle that I've read seem to state that there is a fundamental limit on the precision to which you can measure the values of conjugate pairs (like position and momentum) at the same time. So is this simultaneity necessary? I ask because...

Homework Statement Show that (\Delta A)^{2} = \langle \psi |A^{2}| \psi \rangle - \langle \psi |A| \psi \rangle ^{2}\\ \phantom{(\Delta A)^{2} }=\langle \psi | (A - \langle A \rangle )^{2} | \psi \rangle , where \Delta A is the uncertainty of an operator A and \langle A \rangle is the...

At our QM intro our professor said that we derive uncertainty principle using the integral of plane waves ##\psi = \psi_0(k) e^{i(kx - \omega t)}## over wave numbers ##k##. We do it at ##t=0## hence ##\psi = \psi_0(k) e^{ikx}## \psi = \int\limits_{-\infty}^{+\infty} \psi_0\!(k) \cdot...

Heisenberg's uncertainty principle asserts a fundamental limit to the precision with which certain pairs of physical properties of a particle, such as position and momentum, can be known simultaneously. The more you know about one, the less you know about the other. Why does the following...

I'm trying to understand the uncertainty principle. ΔxΔp >= h/4∏ from my understanding of the concept, its not possible to know the value of the position and the momentum simultaneously. yet the problems that i see floating around on the internet seem to just plug in values for mass and...

A photon is considered as a quantum particle, right? However since we know the speed of a photon(speed of light) and hence can predict its position, isn't it violating the Heisenberg Uncertainty Principle? Where am I going wrong? Is it false to believe that a photon is a quantum particle?

This question may have been posted before, but I didn't have much luck finding it. We can't know the momentum and position of a particle at the same time, but if one were to entangle two particles (I.e. photons), wouldn't it be possible to measure one quality on each and thus deduce both the...

Hi does anyone know how bogulobov transformations are related to the Heisenberg uncertainty principle?

According to this article, scientists were able to bypass the Heisenberg Uncertainty Principle, creating relative certainty in measurement of both position and momentum. Any thoughts, objections, comments?

As my knowledge of an electric field strength becomes more precise, what physical quantity becomes correspondingly less precisely known?

Consider two hermitian operators A and B. Imagine a system is in state |\psi\rangle ,then we have: \langle \psi|[A,B]|\psi\rangle=\langle \psi|AB-BA|\psi\rangle=B^{\dagger}A^{\dagger}|\psi\rangle-BA|\psi\rangle=BA|\psi\rangle-BA|\psi\rangle=0 This just seems a little strange,for example...

Say you have a particle in a one-dimensional box of length L. The particle can only have momentum values of the form p_{n} = \frac{nh}{2L} according to the De Broglie standing wave condition. Now say I don't measure the position of the particle, but I know for certain that it is in the box...

hi pf, i am so confused with this energy time uncertainty principle. Somewhere i find that this means law of conservation of energy can be violated for a while and somewhere i find this still being a mystery? please help me out.

Hi, Consider a laser source of frequency f. This source is projected to a target at a distance D, so that the light needs time T = D/C to reach the target. I will consider the particle behavior of light in this situation. I will study the motion of one of the photons. At the exact time T/2...

Doubts about wave particle duality I know that a wave packet is formed by superposition of several individual waves having different wavelength.And the resultant wave has varying amplitudes.And from these amplitudes we can find the likeliness of the object to be in that position. My doubt is...

Hello! I have a doubt about Heisenberg uncertainty principle. Suppose that a particle moves along x-axis with a given uncertainty in velocity. Can I say something about its motion along y-axis? Thanks

Homework Statement The problem and its solution are attached as TheProblemAndSolution.jpg. Homework Equations Δx = λ/sinθ Δp_x = 2h/λ sinθ The Attempt at a Solution In the equation given in the problem (Δx = λ/sinθ), why is the uncertainty of the ELECTRON written as a function of the...

Homework Statement I was looking at a solution inmy notes which begins: ΔE = hc/λ -1st eqn ΔEΔt ~ (h-bar)/E -2nd eqn Δt ~ (h-bar)/ (hc/λ) Δt ~ λ/2∏c (where 'c' is the speed of light) What formula has been used to go from: Δt ~ (h-bar)/ (hc/λ) to Δt ~ λ/2∏c...

In statistical mechanics, nearly all the textbooks say that the volume of the smallest cell in the phase space of a N-particle system is h^{rN} where h is the Planck Constant, r is the degree of freedom. Also these books say that this comes from the uncertainty principle. However, the...

Homework Statement Assume that a particle travels with a certain known (average) velocity ##v = \left\langle\hat{p}/m\right\rangle##. You know it's position with an uncertainty ##Δx##. Use the uncertainty principle to determine the least possible value for the article's kinetic energy...

Probably, the essence of quantum theory (QT) is principle of uncertainty (HUP). The essence of QT is also the fact that Fourier transformation of wave function in phase(?) space gives wave function in momentum space. If one wave function is Gaussian (and so both ones) this gives HUP. Very...

Ground State Wave Equation: ψ0=(a/∏)(1/4)e(-ax2/2) Prove the Heisenberg Uncertainty principle ≥h(bar)/2 by way of expectation values. First I found <x>=0 because it was an odd function then I found <Px>=0 because it was an odd function Then <x2>=∫(a/∏)(1/2)x2e(-ax2)/2dx=1/2a by way of...

How sound do you think the following research is? http://phys.org/news/2012-09-scientists-renowned-uncertainty-principle.html

Should relativity be factored into the uncertainty principle. I can't move faster than c so should that affect the measurement process? Should time dilation and length contraction be considered or maybe some of these factors cancel when 2 effects are considered.

This is problem 25 in chapter 4 of Modern Physics 2nd edition by Serway, Moses, and Moyer. I have changed the wording, but not the meaning I hope. Homework Statement A person drops an object of mass m from a height H. Show that the miss distance must be at least \Delta x =...

How can one operate the deltas of the uncertainty relation? I know they're supposed to be the standard dev, but how are they operated in physical reality? Is there some sort of function to make them have a physical meaning?

Hi physicists, How can two atomic-scale particles interact through gravitation (Gm1m2/r^2) or any other force that is a function of r if r isn't know with complete certainty. Is it that the force itself also comprises uncertainty in its value? Thanks

Homework Statement This is not a problem as such. Just a derivation for which I've been given a solution which I cannot seem to find. Homework Equations Ke = 1/2 mv2 = ρ2/2m hbar << 2ΔxΔp Δp≈p as the average magnitude of p is small. The Attempt at a Solution p >> hbar/2Δx p2...

We are often told one reason why an electron does not fall to the centre of atoms is because it would then have a well-defined position. Any two particle which comes into contact define each others positions and so their momentum becomes very large. How then is it, according to the Exclusion...

ΔxΔp ≥ \frac{h}{4\pi} Since Δx=ct for a photon and Δp=(mv_{f}-mv_{i}) Then ct(mv_{f}-mv_{i}) ≥ \frac{h}{4\pi} Since mv=\frac{h}{\lambda} You have ct(\Delta\lambda)^{-1}h ≥ \frac{h}{4\pi} Planck's constant cancels, move the c over \lambda, \frac{c}{\lambda}=f This leaves you...

Hi, could anyone try to explain one thing about the Heisenberg Uncertainty Principle I don't understand? The principle says is impossible to measure the position and momentum of a small particle with absolute accuracy. But this doesn't mean the particle doesn't have a definite position and...

I'm given a form of Heisenberg's uncertainty principle in the form of: \Delta E\Delta t\geq h I need to determine a time interval which would allow a laser to cover the whole visible spectrum, from 400 to 700nm. Now given the relationship is on on a relative scale I used the approximation...

i've seen both: ΔxΔp >= h/2 and ΔxΔp >= hbar/ 2 used, and I'm not sure which is correct. my physics textbook uses h/2, but wiki and other online rescources seem to use hbar/2 do they apply to different situations? (if so, where do you use hbar and where do you use h?) or is one...

Homework Statement The position and momentum of a 1.00 KeV electron are simultaneously determined. If the position is located to within 0.100 nm, what is the percentage of uncertainty in its momentum? (Arthur Beiser - Concepts of modern Physics, 3rd Part exercise 33)Homework Equations...

Homework Statement I'm looking for graphs or other sources of uncertainty principle visualization (I'm suppose to use a Fourier transform to solve it and present visualization in MS Excel... but one thing at a time). Homework Equations The Attempt at a Solution Digged google in 3 languages. I...

Homework Statement Assume speed of 435g football is known with 1mm/s uncertainty. What is the minimum uncertainty in its position? Homework Equations I'm not quite sure... I know p=mv, and I know that Heisenberg's uncertainty principle states that certain parameters of quantum...

Hi, I'm working on a homework for my solid state physics class and I'm having trouble with this question: Homework Statement "We have seen many cases in solid state physics in which you can apply the concept of uncertainty principle to estimate some quantity. Describe two examples of a...

http://quantummechanics.ucsd.edu/ph130a/130_notes/node98.html Can someone help me understand what's going on here? He says "The idea is that the radius must be larger than the spread in position, and the momentum must be larger than the spread in momentum." which I suppose must be true in...

Heisenburg Uncertainty Principle - Seems like an easy question?? Homework Statement The position of a 900 kg boulder's center of mass has been determined to within an uncertainty of 1.0 nm. (a) What is the minimum uncertainty in the boulder's velocity? (b) Repeat the calculation, but for a...

According to the De Broglie-Bohm theory, is the universe, in its current state, the only one that could have evolved from its early conditions? In other words, because in the theory, each particle actually possesses well-defined position/momentum/trajectory, does the theory imply that the...

i tried to apply uncertainty principle to an electron confined in a 3d box of size 1fm. i got uncertainty in velocity Δv to be of the order 1010 m/sec.so i thought maybe i should have taken relativistic mass instead of rest mass. but i realized that for calculating relativistic mass we...

I had a quick question on the uncertainty principle. I'm not a physicist but I'm familiar with the basic theories. I've never had anyone explain it to me like this, but this seems to be an intuitive way to look at it. So I need to know if I'm framing this right. In classical, you start...

The general definition is that we cannot determine the location and velocity of a particle at any given moment. However, my intuition is to assume this is due to shortcomings in technology and measurement, but apparently that's false. This is a rule of nature. Can you explain what exactly the...

When I read about the uncertainty principle, I keep reading about these experiments where they fire electrons through a single or double slit and observe the diffraction but I can't these experiments relate to Heisenbergs uncertainty principle. So when they fire the electrons, they know their...

Homework Statement If the uncertainty in the location of a nonrelativistic particle is about equal to twice its de-Broglie wavelength, show that the uncertainty in its velocity is greater than about 4% of its velocity. Homework Equations ΔpΔx>h/4Pi p=mv Δx=2nλ The Attempt at a...

1. Homework Statement The figure shows 1.0*10^-6 m diameter dust particles in a vacuum chamber. The dust particles are released from rest above a 1.0*10^-6 m diameter hole, fall through the hole (there's just barely room for the particles to go through), and land on a detector at distance d...

As you know,a pure sine wave extends infinitely in both directions and a wave which is the composition of some different frequencies,has a limited extent.Does it mean that such a wave is a pulse moving in space or it has limited range?(I know its crazy to talk about the range of light,but I've...