Hup Definition and 68 Threads

HUP for spins reads $$\langle\sigma_z^2\rangle\langle\sigma_x^2\rangle \ge \frac{1}{4}|\langle\sigma_y\rangle|^2$$ Right after measuring ##\sigma_z##, we know it exactly, and so ##\langle\sigma_z^2\rangle=0##. However, HUP then implies that ##\langle\sigma_y^2\rangle=\infty## Even if we say...

Position and momentum are the popular pairs of properties with uncertainty we often hear about, for example that we cannot know with precision where an electron is and its momentum at the same time. What are others? Such as an example of an energy and a time that we cannot know both...

Hi HUP states that if i know the exact position of a particle there must be infinite uncertainty in its momentum. What about if i apply HUP to myself ? Is it not possible for me to know that i am standing at a specified position and not moving ; implying zero uncertainty in both position and...

The observer effect results from the interaction of a quantum system with a measurement device. The HUP is more fundamental: it results from the fact that certain quantum measurements cannot be made simultaneously (or, equivalently: certain quantum observables do not commute, most famously -...

a) Consider a dust grain of mass 0.1µg whose position is known to a distance of 1µm. How precisely can its velocity be known? b) A company claims to have invented a device that can measure the momentum of objects inside it with extreme accuracy. The device fits within a matchbox, and the...

Hello everyone, If something is a principle of reality, then its absence means reality will not be reality anymore. This is my point of view on what a principle means. Heisenberg’s uncertainty principle, as Bohr stated, is not an indication of our ignorance, but what reality is. If this is...

I'm a student in South Korea(It is my first English question ever). I found descriptions of quantum tunneling explained by the uncertainty principle in Korea. There are two kinds of descriptions to explain quantum tunneling; position-momentum and time-energy uncertainty principle. First...

If I understand it correctly, a particle doesn't have a definite momentum and a definite position, but is in a superposition of multiple positions and momenta. And when we measure either of the two quantities, say, position, the wavefunction collapses to tell us where the particle is. Now when...

I'm asking this after some previous thread about the HUP. If I understand well, the HUP is basically about measurements, that is, it imposes limitations to the quality of the information any observer may attempt to obtain about the universe. My question is, how should we understand the HUP in...

The question relates to the deterministic views of people like Descartes or Pierre de Laplace, the infamous "an omniscient intelligence who could know precisely the position and momentum of every single particle in the universe would be able to predict the future with total accuracy, past...

If we measure one conjugate variable in an uncertainty relation precisely , i.e., so its standard deviation is zero, then by the HUP the sd of the other one is either infinite or undefined. But what about the cases when the other conjugate variable has limits: e.g., there cannot be an infinite...

Hi all, Yet another question: if the universe is finite, then linear momentum should be quantized (I assume in a similar manner to an infinite potential well since there are boundary conditions). My question is, then, if one computes a value for ##\Delta p## (momentum variance), is the variance...

Is there any mistake in Heisenberg's uncertainty principle?

In non-relativistic QM, wave functions are represented as a superposition of complex exponentials in which the energy/frequency is a function only of momentum/wave number (dispersion relation). This seems to imply that under the HUP, precise momentum guarantees precise energy. Are there any...

HUP was taught at least to me, as a brute fact that came into existence when my lecturer wrote it on the board...with chalk. I was fortunate enough to have already had some background in Fourier Transforms. When doing a basic course on SWE and the link between it and wave solutions, the HUP...

I understand this topic has been brought up before, however there appears to be "truth" or "lies" and very little in between when it comes to explaining the Heisenberg Uncertainty Principle (HUP) to students of freshman chemistry. I'm teaching university general chemistry to students who've had...

I'm a QM noob/newb trying to understand the physical implication of a wave packet, in my mind it is something like this: On the x-axis there is displacement (vibration), probability on the y. I Imagine stretching and compressing the wave packet. When I stretch it out, the amplitude must...

My question is: Is my picture of what happens as something approaches an event horizon accurate - and are there any citations describing it? I got my "picture" from a PBS broadcast several years ago. It was since mentioned in these forums, but I haven't been able to find an explicit mention...

By solving the schrodinger equation, we get atmost two solutions for wavefunctions with definite wavenumber and definite wavelength. Thus, we know specifically the momentum of the particle. But this is contradicted by HUP. Please explain. I would appreciate an explanation in the context of a...

I am not going to look up specific threads to support that assertion because I assume they have been seen by all those who regularly read threads on the HUP. If necessary, I'll dig up a few. The two points of view expressed in various threads are as follows 1) Simultaneous measurements for...

Electrons emit and absorb photons all the time. I heard that each electron is surrounded by a cloud of 10^{20} photons. That suggests to me that the rest mass of an electron must fluctuate, and that raises the prospect of uncertainty. My questions: Is the rest mass of an electron really...

Novice questions: 1. All complimentarities seems to be an expression of HUP... (for example from some of the quantum eraser experiments such as DCQE) Is that correct? I.e. Complimentarity is NOT a phenomena/mystery that is seperate/different from HUP 2. Can we derive/conclude...

HUP --> Heisenberg Uncertainty Principle The below questions maybe a bit amateurish. 1. Can two photons be entangled on both position and momentum?...for a same time period I think not because: To entangle on momentum (or any property) we need a broad distribution of momentum for the photon...

I have a question about the HUP. As I understand the HUP, it only applies to conjugate attributes that do not commute, such as position and momentum. However, many good quantum numbers do commute, so does this mean that the HUP does not apply to simultaneous measurement of such good quantum...

The HUP says that I can not know the position and the momentum of a particle simultaneously, therefore, from time T1 to time T2 I cannot predict its position. How does this not violate the law of conservation of momentum? If you cannot know its position and momentum exactly that how do we know...

Now, I am lost, I am stuck with the Heisenberg principle.. Seriously, the more I read papers, standard textbooks, or any books on it, I find I am more lost, nearly all seem to contradict all. *http://www.kevinaylward.co.uk/qm/ballentine_ensemble_interpretation_1970.pdf In page 365, This...

Consider the following video... http://www.youtube.com/watch?feature=player_embedded&v=0FGo8mi-5w4 Am I really seeing a demonstration of the HUP or am I just seeing diffraction? In this instance, is it just different models with different terminology describing the same thing? If so, what...

A number of threads in this forum oscillate between pure mathematical descriptions of the HUP and QM generally, while others *try* to provide a physical, visualisable causal model to explain them. Heisenberg's original quantum microscope explanation for the HUP was such an example which...

Hi, I have a question about reconciling two pictures of virtual particles and the Heisenberg Uncertainty Principle (HUP). In QFT "virtual particles" show up in perturbative calculations. We try to calculate an amplitude in interacting theories, this can not be done in an exact way, so we...

Hi everyone, I know this topic has been discussed quite a bit -- and in particular it's been done in this thread and this thread. But there are still some things I want to talk about in order to (hopefully) clarify my own thoughts. One of the threads discusses this Ballentine article in which...

Violation of Heisenberg's Measurement-Disturbance Relationship by Weak Measurements Lee A. Rozema, Ardavan Darabi, Dylan H. Mahler, Alex Hayat, Yasaman Soudagar, Aephraim M. Steinberg http://arxiv.org/abs/1208.0034 This paper says there are two forms of the Heisenberg uncertainty principle...

BBC NEws Story "refuting" HUP http://www.bbc.co.uk/news/science-environment-19489385 I did a double take when I read this, can someone please explain what it's all about?

Is "nothing" an unstable thing that violates HUP? I am trying to understand the logic behind the likelihood of creatio ex nihilo. Does QM tell us that it isn't possible for something to have position and velocity both be 0 at the same time, which is what "nothing" would suggest?

If I want to measure the position of a particle, and to do so I bombard it with a photon. What attributes of the particle will this interaction affect? I would think that it could affect both the particle's direction and its mass, which in turn would have an effect on both its position and its...

in q zeno effect, measuring, or observing a particle will effect its outcome. however, its been said on this forum that the hup is there whether we observe it or not. contradiction?

does the hup essentially represent the "wall" or "curtain" of the universe? what i mean is, when you don't have any observable ability of what's going on behind a white curtain, if occurrences behind the curtain produce spots on the curtain which we see but we do no see their cause, we can only...

Measuring with great precision the position of a particle, requires high momentum ( and thus energy) of a second particle, that probes the first. That is because when you want to guide a particle to a precise position, then you need to give it high momentum, so it has enough leeway to spread...

Greeting to everyone. This is my first time here (A bit nervous) According to many sources, many books, "Heisenberg uncertainty principle" tells us that it is impossible to measure anything exactly. I agree as the proving equation does not apply any measuring instrument at all which means...

I was watching one of Susskind's videos and I had some questions: Briefly summarizing from the video: E = hf (Planck's constant times frequency) E = cp (speed of light times momentum) or p = E/c = hf/c And we know that if we have wavelength lambda, then if t = 1/f and vel = dist/time...

A beam of light from a laser projected on a screen with a very small hole in it will spread after it traverses the pin hole because of the HUP: Measuring position so accurately causes loss of information about the momentum. I believe that in the case of laser light, only information about the...

According to this article, researchers have obtained measurements with an accuracy larger than the upper bound set by HUP. http://physicsworld.com/cws/article/news/45535 My first thought is that this is not a violation, since we are talking about a finite number of measurements, but then...

I've been thinking about what Bose-Einstein Condensates means in terms of the Heisenberg Uncertainty Principle. When a cluster of atoms is made very cold the particles lose momentum, relative to the other particles in the cluster. This causes the position of the particles to become uncertain...

An alpha-particle produced by radioactive decay leaves a visible continuous track in a Wilson Cloud Chamber. As it collides with and ionizes the molecules of the vapor, its position is constantly being “measured” by the vapor molecules. If a magnetic field is present, its track will be curved...

I know the following question is elementary, but being a dilettante in QM, I am confused on the following. So, I have two questions. The first question is whether the following reasoning is correct, and if not, why not. First, the Heisenberg Uncertainty Principle (HUP) applies to...

There is one thing i always wanted to ask. Since when HUP is so 'easily' allowed to explain the obvious non-conservation of energy? With what justification we say with such an ease that a particle can borrow(wtf does that mean?) energy ΔΕ but it must return it(what...??) in time Δτ? I really...

Hi! Let's say I have a bubble chamber and a particle traveling in it. I know the trajectory of the particle, because I can see the bubbles. But if I measure the time elapsed between the appearance of the first bubble and of the last one, I know how much time the particle took to follow the...

Homework Statement Prove that a 1-d harmonic oscillator in ground state obeys the HUP by computing delta P sub x and delta X Homework Equations delta x = sqrt(<x^2>-<x>^2) delta px = sqrt(<px^2>-<px>^2) The Attempt at a Solution I have absolutely no idea where to start with...

Consider the following double-slit experiment: The source is an optical laser. The beam is, say, ½-inch wide and the laser is located far enough, say 10 yards, from the 2 slits to guarantee a large uncertainty in position (because of the very small uncertainty in the momentum direction)...

Well, I will try to explain it. So, HUP and non-conjugate variables. If we know the position precisely, we don't know the momentum. On the contrary, if we know the momentum, we don't know the position. Sorry for repeating the obvious. Interpret HUP as a spectrum: on one side we know the...

Is it possible to derive Heisenberg's Uncertainty principle just using Schrodinger Equation? If yes, is there any source that you can refer me to?