Uncertainty principle Definition and 541 Threads

Homework Statement A beam of 50eV electrons travel in the x direction towards a slit of width 6 micro metres which is parallel to the y direction. The diffraction pattern is observed on a screen 2 metres away. Use the Heisenberg uncertainty principle to estimate the minimum uncertainty in the...

I am looking at the derivation of the Heisenberg Uncertainty Principle presented here: http://socrates.berkeley.edu/~jemoore/p137a/uncertaintynotes.pdf and am confused about line (21)... I do not understand why AB and BA are complex conjugates of each other... (I'm still in high school so I...

Which of them comes first,(I mean the concept or the theory)? Did Heisenberg come up with the idea of uncertainty principle because of the discover of the wave particle duality? Thanks for paying attention~

My friend and I had this argument about whether or not the uncertainty principle is applicable to stationary particles. I maintain that it is, because the principle is really about predictability ( isn't it?) But he maintains that it doesn't. So I would just like to clear things up . Does it or...

Homework Statement A bullet is shot from a rifle. 1) if the position of the centre of mass of the bullet perpendicular to its motion is known to have an accuracy of 0.01 cm, what is the corresponding uncertainty in its momentum? 2) If the accuracy of the bullet were determined only by the...

Can one use uncertainty principle for Classical mechanic wave and still get the same equation for Quantum mechanics, as in (root-mean square uncertainty of position) (" of momentum) > hbar/2? It's just that V(x) [Potential equation] is same for both Classical and Quantum mechanics so I wonder if...

Homework Statement Hopefully it is not a faux pas to post two questions relatively close together in time. This is more of a conceptual question than a calculation based question. An electron is confined to a region of space of the size of an atom (0.1 nm). a) What is the uncertainty in the...

Homework Statement The square of a wave function gives the probability of finding a particle at a given point. What is the probability of finding an electron in a 1s orbital within a volume of 1pm^3, centred at: a) the nucleus b) 50pm away from the nucleus? Homework Equations...

Definition/Summary This is a derivation of the Uncertainty Principle based on the properties of non-commuting Hermitian operators. Equations \langle (\Delta A)^2 \rangle \langle (\Delta B)^2 \rangle \geq \frac{1}{4} |\langle [A,B] \rangle | ^2 \langle (\Delta x_i)^2 \rangle...

For the infinite square well in one-dimension the wavefunctions have the form Acos(kx) where k is the wavenumber which is proportional to momentum. Now due to H.U.P. if Δx is fixed as the infinite well size we can't know the exact momentum. I presume this is because the wavefunction exists as a...

I have been reading and would be interested in feedback to the comments that I make, below. One of the points made in this paper is that the interpretation of the uncertainty relation needs to be re-examined in its relation to the viability of having simultaneous measurements of A & B. For...

I was watching a YouTube video about Heisenberg's uncertainty principle and was wondering if it only works for position and momentum or does it work for any other two measurable quantities?

I know this may sound strange, given that we cannot really work out where in space a photon is because it cannot be completely stopped. But here's a thought. Let us assume that a photon has been emitted in vacuum going in a straight line. At any given moment in time, this photon will have...

Hello, i'm solving some quite simple problems using the uncertainty principle, but I don't have access to the solutions and I really don't have a feel for what a 'sensible' answer is... When finding the minimum uncertainty in velocity, I end up with things greater than the speed of light, so I...

Uncertainty principle -- Nature of observer About the fact that electrons have a determined position only after having been observed/measured, I don't understand how they make the difference between being watched by an eye/instrument or any non-measuring object just sitting there.

In an explanation to distinguish the Heisenberg Uncertainty Principle from the Observer Effect, on p. 89 of "Quantum Computation and Quantum Information", Nielsen and Chuang start by writing: "The correct interpretation of the uncertainty principle is that if we prepare a large number of...

Hi Guys, Newbie question from a layperson so please don't beat me up! :D I know that Heisenberg's Uncertainty Principle relates to measurement/observation of particles with regard to quantum physics. My question is whether or not it applies to measuring anything in the observable...

Homework Statement Using the Uncertainty Principle show arithmetically that neutrons can't be formed by a proton and an electron. Homework Equations The Attempt at a Solution I can see that if neutrons were made out of a proton and an electron they would just attract each until...

Homework Statement Explain, using the Heisenberg Uncertainty Principle, how classical physics is reached a a limit of quantum physics when (h-bar) tends to 0. Homework Equations ΔxΔp(x) ≥ (h-bar)/2 The Attempt at a Solution The only reasonable answer I can formulate is the fact that when...

According to the uncertainty principle Δp*Δx≥h/2pi, now suppose we measure a particle in a very tiny area(if x is tiny enough), s.t. Δp ≥ h/(2xpi) ≥ mc then v > c. But in fact, the velocity can not be faster than light. So how can we compromise these two statement?

This could be one of those questions where I'm hindered by my lack of knowledge on the subject, being only a freshman in college, but recently we learned the uncertainty principle which states that: ΔE*Δt ≥ h/4π Given this, I'm assuming it'd be accurate to rewrite ΔE as Δm*c2, which would...

The uncertainty in this principle is talking about uncertainty of measurement or particle itself?

Homework Statement Laser can now be designed to emit pulses of light smaller than 30 microns wide in their direction of motion. (a) Estimate the uncertainty in the momentum of a photon in such a pulse. (b) The momentum of a photon is p=h/λ. Estimate the uncertainty in the...

if you know the position why can't you know the momentum isnt p=mv and v=dx/dt its the only doubt i have so far please help

For those who read carefully the paper by Esther Hänggi and Stephanie Wehner: "A violation of the uncertainty principle implies a violation of the second law of thermodynamics": 1. Can you elaborate how extra work can be extracted if the UP is violated? 2. Does the paper implies that...

Homework Statement Derive from the uncertainty principle a formula for the relative spread of the spectral line that corresponds to the longest wavelength of the Lyman series. Homework Equations uncertainty principle: σxσp≥\hbar/2 planck constant \hbar=h/2pi h=λp Lyman series...

I don't know much about physics but just had this idea: As I understand it the HUP prevents good accuracy of a small object's momentum and position at the same time. Assume trying to measure the momentum and position of a single atom. In theory, can't we get a very good idea of both of...

I know I have seen this before a few time done a few different ways/starting points and I am always blown away when I see it worked out. Don't know why but I love seeing this derivation. Does anyone want to post the derivation for all to see, it being done a few different ways would be great.

My source is the high school chemistry textbook: General Chemistry, 2nd Edition, by Donald A. McQuarrie and Peter A. Rock, published 1987 (This is not for a high school homework assignment.) According to Heisenberg's Uncertainty Principle, the product of the uncertainty in the momentum...

Homework Statement So here's the question An electron is confined within a region of width 1 X 10^-10 meters. Estimate the uncertainty in the x component of the electrons momentum Homework Equations ΔPΔx\geq(1/2)(h/2pi) The Attempt at a Solution The problem appears pretty...

Hello, Recently I've learned about Fourier Transform, and the uncertainty principle that is arose from it. According to Fourier Transform, if there is only one pulse in a signal, then it is composed from a lot more frequencies, compared to the number of frequencies that are building a...

An article at physicsworld.com suggests that arbitrarily small measurements can be made. Ozawa: "My theory suggests if you use your measuring apparatus as suggested by the maker, you can make better measurement than Heisenberg's relation" Regarding his opposition: "They now prove that if...

I read the Quantum Physics section of the online version of Feynman lectures http://feynmanlectures.caltech.edu/I_02.html#Ch2-S3 and I don't understand how he can deduce electron momentum from the Uncertainty Principle. I agree that the momentum is uncertain but how can he deduce that it is very...

We take for granted the fact that we can infer more about the past than the future. Considering the only difference between past and future is entropy, I wonder if the reason it is possible to have records of the past and not the future is entropy related. At the quantum level is the...

Ok, I http://en.wikipedia.org/wiki/Academic_genealogy_of_theoretical_physicists#Arnold_Sommerfeld that Heisenberg had studied under Arnold Sommerfeld, but I have just now learned that Sommerfeld proposed a sort of uncertainty principle in the first Solvay meeting. That was 1911. It seems...

What Uncertainty Principle actually is? I searched on the internet and got an amazing answer that the energy could form out of thin air. Who could explain more specifically to me, who is in year 11.

Problem Find the minimum energy of the hydrogen atom by using uncertainty principle a. Take the uncertainty of the position Δr of the electron to be approximately equal to r b. Approximate the momentum p of the electron as Δp c. Treat the atom as a 1-D system My step 1. Δr Δp ≥...

Hello, I have this exercise and want to check if what i did is correct Homework Statement Nuclei, typically of size $10^{-14}$ m, frequently emit electrons with energies of 1-10 MeV. Use the uncertainty principle to show that electrons of energy 1 MeV could not be contained in the nucleus...

I read somewhere that Heisenberg described his uncertainty principle by saying that you can't measure position more accurately than the wavelength of light (which makes sense), so Δx > λ. This is what I don't get. He then says that p=h/λ, so Δp > h/λ2 Δλ. He the multiplies and sets Δλ ≈ λ to...

Homework Statement A spin-half particle is in a known eigenstate of Sz. Show that the product <S^2_x> < S^2_y> is consistent with the Uncertainty principle Homework Equations The Attempt at a Solution I know that the generalized uncertainty principle gives ΔS_x ΔS_y ≥ |<[S_x...

I have been going through my Physics textbook to brush up on my Quantum Mechanics before starting my next QM course next academic year and the Heisenberg uncertainty principle for position and momentum is written as ΔxΔp ≥ h-bar when I thought it was ΔxΔp ≥ (h-bar)/2. Other sources say it is...

This question is regarding the boson statistics and it’s relation to the uncertainty principle. Consider we have a vacuum state and we apply a field operator on it to create a particle at position x, we end up with state like \begin{array}{l} \left| \psi \right\rangle = {\psi ^\dag...

My qm textbook, aptly named "quantum mechanics", is by McIntyre, though it omits the proof for the uncertainty principle and simply states it as ∆A∆B ≥ 1/2|〈[A,B]〉|. In words, if that's unclear, this is 'the product of the rms deviations of A and B is greater than/equal to one half the absolute...

As a result of some precise experimental data, we now know that the mass of the quark is not naively 1/3 the mass of the proton. The most recent estimates for the mass of the quark is: Masses of the current quarks: = 2 - 8 MeV/c2 = 1.0 - 1.6 GeV/c2 = 168 - 192 GeV/c2...

I really can't understand the uncertainty principle,and now there are some experiment that violate the uncertianty principle, I need deepen understanding of quantum uncertainty,who can give me all the information about the uncertainty principle,such as new ideas,related study or books,thanks

The derivation of the momentum/position Heisenberg Uncertainty Principle (HUP) is based on the statistical interpretation which says that if we have a lot of quantum systems in identical states, and measure the momentum in half of them and get a distribution with standard deviation σp, and...

If we take a narrow aperture(such as the one used in the double slit experiments) and attach a length of optical fibre to it, surely now we know the position (confined by the width of the fibre) and also the momentum(defined by the direction of the fibre). How does the uncertainty principle...

Hi everybody. I have a quick question regarding the relationship between the uncertainty principle and the measurement postulate. According to the former, the higher our certainty is about the position of a particle, the lower our certainty is regarding its momentum, and vice versa. This...

This may be a dumb question, but I am still new the the concept of the quantum world... If we can't measure position and momentum precisely at the same time, why can't we use 2 detectors? One to measure position, and one to measure momentum. Have them take the measurement at the same time, and...

The typical energy needed to ionise an atom is around 5 eV. Use the Uncertainty principle to estimate the size of an atom. Homework Equations E=mc^2 E = p^2/2m Δx.Δp ≥ h/4π The Attempt at a Solution So I got the mass rearranging E = mc^2 m = 5*1.6*10^-19 / (3*10^8)^2...