Quantum mechanics Definition and 994 Threads

Hi, I have two questions concerning the double slit experiment in the scenario where we fire one photon at a time and it interacts with itself to create an interference pattern over time: - Does the photon actually interact with itself or with the photons fired before/after it? - What happens...

This problem bothered me many years ago when I was taking a university course in quantum mechanics, but I assumed it was due to an error on my part which I, however, couldn’t locate, and I didn’t ask my course instructor about it. Recently, when researching a q.m. question on the Internet...

Greg Bernhardt submitted a new PF Insights post The Fundamental Difference in Interpretations of Quantum Mechanics Continue reading the Original PF Insights Post.

Hi all, Is there a critical analysis of this work ( https://arxiv.org/abs/1506.00431 ) that claims to develop a new representation of microstate and then using this representation as a reference-and-imbedding-structure, to develop a new foundations of an intelligible reconstruction of the...

Homework Statement Homework EquationsThe Attempt at a Solution ## E \propto n^2 ## ## \frac { \Delta E} E = \frac { 2n +1} {n^2} ## In the limit of large quantum number, ## \frac { \Delta E} E = \frac { 2} {n} ##, option (a).

I would be in college in 2019 (currently I'm in standard 11). I'm greatly interested in Quantum mechanics, QFT, QCD and Quantum Geometerodynamics. Of these, I want to do an internship on the first, because I don't think I'll be able to touch the others till the 2nd year in college. I'm living...

Homework Statement Homework EquationsThe Attempt at a Solution The energy eigen - value of a particle in a box is given by ## E_n = \frac { n^2 h^2}{8mL^2} ## . Now, applying classical mechanics , ## \frac { p^2}{2m} = \frac { n^2 h^2}{8mL^2} ## . ## p \propto \frac { 1} L ## , So...

Homework Statement Homework Equations This is solution of Griffith problem 11.16 The Attempt at a Solution This is procedure to get a 1-D integral form of Schrodinger equation. I don't understand why that contour integral include only one pole for each contour?

Hi, I'm a new member. I joined this forum because I'm interested with astrophysics and cosmology. I'm actually in the field of the Humanities, currently taking up my Master's in Art History. I like physics because I think it is where art and science beautifully intersect. I started to see the...

Homework Statement The answer is as follows: [/B] However they said that time t=0 so I am confused how the exponent has a t in it surely it should be zero. Thanks

Hi everyone, I just have some confusion regarding Planck's and Einstein's equation. The following is an explanation of the photoelectric effect using Einsteins theory: Light is composed of photons. Each photon has energy hf and mass hf/c^2. When ultraviolet photons are brought to rest by zinc...

Homework Statement A particle is restrained to move in 1D between two rigid walls localized in ##x=0## and ##x=a##. For ##t=0##, it’s described by: $$\psi(x,0) = \left[\cos^{2}\left(\frac{\pi}{a}x\right)-\cos\left(\frac{\pi}{a}x\right)\right]\sin\left(\frac{\pi}{a}x\right)+B $$ , determine...

Homework Statement How can we tell that quantum effects do not propagate along forward light-cones that represent two separate events? How do light-cones demonstrate this notion of quantum effects? Homework EquationsThe Attempt at a Solution We don't know which events occur first given...

If Alice and Bob had a large number of particles entangled together (with state of either 0 or 1), could Alice send information by breaking the entanglement of particles with state of 1 (by flipping the state for example) so that Bob measures 50% of particles to be in the state opposite of 0...

If I have a general (not a plain wave) state $$|\psi\rangle$$, then in position space : $$\langle \psi|\psi\rangle = \int^{\infty}_{-\infty}\psi^*(x)\psi(x)dx$$ is the total probability (total absolute, assuming the wave function is normalized) So if the above is correct, does that mean...

In Hartree-Fock method, I saw the Fock operator has two integrals: Coulomb integral and exchange integral. One can define two operator. "The exchange operator is no local operator" why? Whats de diference: local and no local operator? And why do the operators have singularities? thanks

and it is free (legal) Quantum Mechanics for Engineers by Dommelen

"... quantum mechanics isn’t a complete physical theory in its own right, but rather a framework for the construction of physical theories." I found this in Michael Nielsen's blog and elsewhere. I am perplexed. In what fundamental way does it differ from Newtonian Mechanics (Theory) in not...

Homework Statement Earlier in the book it was remarked that early in the history of nuclear physics the electrically neutral mass of nuclei now attributed to neutrons was considered to arise from neutral particles composed of combinations of protons and electrons (as opposed to neutrons in...

In the momentum representation, the position operator acts on the wavefunction as 1) ##X_i = i\frac{\partial}{\partial p_i}## Now we want under rotations $U(R)$ the position operator to transform as ##U(R)^{-1}\mathbf{X}U(R) = R\mathbf{X}## How does one show that the position operator as...

Homework Statement [/B] Consider the hydrogen atom in the 42F5/2 state. Take into account the effects of finestructure (spin-orbit coupling). (a) Write down the spectroscopic notation of the state that the 42F5/2 is degenerate with, in the absence of an external magnetic field. (b) Calculate...

Question (a) Write down the quantum numbers for the states described in spectroscopic notation as 2S3/2, 3D2 and 5P3. (b) Determine if any of these states are impossible, and if so, explain why. (Please note that these could describe states with more than one electron.) My Attempt A) I came...

Hi everyone! I'm trying to make a list of recommended books (introductory and advanced). So far, what I was able to search are the following: Particle Physics: - Griffiths: Introduction to Elementary Particles - Thomson: Modern Particle Physics - Nachtmann: Elementary Particle Physics -...

It seems like every argument in favor of the Simulation Hypothesis revolves around the strangeness of Quantum Mechanics. So can the Simulation Interpretation be just as valid of an interpretation as Copenhagen or Many Worlds? If not why not?

Homework Statement Given 3 spins, #1 and #3 are spin-1/2 and #2 is spin-1. The particles have spin operators ## \vec{S}_i, i=1,2,3 ##. The particles are fixed in space. Let ## \vec{S} = \vec{S}_1 + \vec{S}_2 + \vec{S}_3 ## be the total spin operator for the particles. (ii) Find the eigenvalues...

Homework Statement The Hamiltonian of a certain two-level system is: $$\hat H = \epsilon (|1 \rangle \langle 1 | - |2 \rangle \langle 2 | + |1 \rangle \langle 2 | + |2 \rangle \langle 1 |)$$ Where ##|1 \rangle, |2 \rangle## is an orthonormal basis and ##\epsilon## is a number with units of...

1. The problem statement Consider a particle of mass m under the action of the one-dimensional harmonic oscillator potential. The Hamiltonian is given by H = \frac{p^2}{2m} + \frac{m \omega ^2 x^2}{2} Knowing that the ground state of the particle at a certain instant is described by the wave...

Homework Statement Homework Equations in addition to those provided in the questions, I used the following: Tr(B) = sigma<x_j|B|x_j> purity = Tr(rho^2) The Attempt at a Solution [/B] I find calculating trace and purity very confusing. Am I on the right track with question 1? With...

i want an article or video that i can start with at the journy of understanding the basics of quantum physics and quantum mechanics i don't want a book because in my country i would not find this types of books every where it's unique to find them thanks

Hi everyone; A very stupid confusion here. When we want to talk about the most probable radius to find the electron in $1s$ orbital, why do we talk about the radial density and not the probability itself? For instance, the probability of finding the the electron at a radial distance $r$...

Homework Statement A) Show that <x>=<p>=0 hint: use orthogonality B) Use the raising and lowering operators to evaluate an expression for < x2 > Homework Equations Also A- and A+ will definitely come in handy The Attempt at a Solution I tried setting up the equations for <x> and <p> but I...

Homework Statement Show that the virial theorem holds for all harmonic-oscillator states. The identity given in problem 5-10 is helpful. Homework Equations Identity given: ∫ξ2H2n(ξ)e-ξ2dξ = 2nn!(n+1/2)√pi P.S the ξ in the exponent should be raised to the 2nd power. So it should look like ξ2...

Homework Statement Show that application of the lowering Operator A- to the n=3 harmonic oscillator wavefunction leads to the result predicted by Equation (5.6.22). Homework Equations Equation (5.6.22): A-Ψn = -iΨn-1√n The Attempt at a Solution I began by saying what the answer should end...

In an experiment involving electron scattering from a finite rectangular well of depth 4 eV, it is found that electrons of energy 5 eV are completely transmitted. What must be the width of the well? At what next higher energy can one expect to again observe T = 1? My Attempt: I used the...

A massless spin 1 particle has 2 degrees of freedom. However, we usually describe it using four-vectors, which have four components. Hence, somehow we must get rid of the superfluous degrees of freedom. This job is done by the Maxwell equations. To quote from Gilmore's "Lie Groups, Physics, and...

Homework Statement Homework EquationsThe Attempt at a Solution This is the Solution. I am having trouble understanding parts of it. The first part I don't get is why the e^i... goes with the -z. Did my professor just choose one at random, or is there a specific reason? The second part...

Homework Statement I am trying to understand a solution to a problem. I may not need to post the entire question, I just need to know if ##-i = e^{\frac{-i*pi}{2}}## Homework EquationsThe Attempt at a Solution the reason for this question is that one step of the problem has a quantity...

Hi fellow thinkers, my main area of interest is in QM. However I am always interested in new discoveries and experimental proofs of outstanding theories. Looking forward to joining the discussion with others who, like me, enjoy absorbing new information... S.P.W...

Hi. From what I read, according to Quantum mechanics "even though it looks like objects are in definite places, when we get down to ridiculously tiny objects (like electrons) they seem to be not he in anyone place. And everything looks like a hazy clouds of probability."...

Homework Statement This is a question asked in a entrance examination[/B] A charged particle is in the ground state of a one-dimensional harmonic oscillator potential, generated by electrical means. If the power is suddenly switched off, so that the potential disappears, then, according to...

Homework Statement A particle with mass m and spin 1/2, it is subject in a spherical potencial step with height ##V_0##. What is the boundary conditions for this eigenfunctions? Find the degeneracy level for the energy, when it is ##E<V_0## Homework Equations Radial equation \begin{equation}...

QM is gradually conquering my mind day by day. i can't think anything expect it. i always thinking while eating,before sleeping,in classroom,while outside. my college performence is badly affecting as QM is not in my course. i just want to understand anyhow_could anybody guides me to understand it.

Urs Schreiber submitted a new PF Insights post Introduction to Perturbative Quantum Field Theory Continue reading the Original PF Insights Post.

Upon reading Landau QM, the Principle of superposition of states, I got confused. It states (and i quote): "Suppose that, in a state with wave function Ψ1(q), some measurement leads with certainty to a definite result 1, while in a state with Ψ2(q) it leads to a different result 2. Then it is...

Homework Statement This is problem (7.1) from John A. Peacock "Cosmological Physics". Show that the first-order perturbation term for quantum mechanics with an electromagnetic field, ##(e/m) \mathbf{A \cdot p}## is proportional to the electric dipole moment. What is the interpretation of the...

Hi! I am starting my Master's in Applied Physics at the TU Delft next week and I have yet to decide a research track (i.e. specialization). I have narrowed my options down to bionanoscience and quantum nanoscience. Of these two, which would be better? Of course, 'better' is a vague term, so what...

I read the forum rules, I hope I am not breaking them as these principle is generally accepted and I am not contradicting mainstream science. "The principle of relativity, according to which the laws of physical phenomena should be the same, whether for an observer fixed, or for an observer...

Homework Statement A few questions: Q1) How does 1.29 flow to 1.30 and 1.31? How was the integral-by-parts done? Q2) The author states that <v> = d<x>/dt represents the expectation value of velocity. What does this actually mean? I tried to rationalise that d<x>/dt represented the velocity...

Demystifier submitted a new PF Insights post How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics Continue reading the Original PF Insights Post.