What is Quantum mechahnics: Definition and 188 Discussions

Hi Guys, at the moment I got a bit confused about the notation in some QM textbooks. Some say the operators should be symmetric, some say they should be self-adjoint (or in many cases hermitian what maybe means symmetric or maybe self-adjoint). Which condition do we need for our observables...

I mean for the free electron Dirac equation the charge (e or q) does not appear in the equation. It only appears after its interaction with EM field. So it seams the electron does not have the intrinsic property of charge, either that or the EM is integral to the electron. Any idea?

Photon energy E_p= hv=hc/lamda taking lamda= h/mc which is the electron Compton wavelength and substituting in above E_p=mc^2 L(angular momentum)=r X P=(Lamda/2)*(E_p/c)=h/2 are these results coincident or have any physical meaning, they relate a photon wavelength equal to an electron...

I have tried to solve a scattering problem of two particles in one dimension, following the T operator theory, after to write the system in the center of mass reference. I have used the square potential \begin{equation} U(x) = \left\{ {\begin{array}{cc} U_0 & 0 < x < a \\ 0 & \rm{Otherwise}...

At the moment I'm working with the https://en.wikipedia.org/wiki/Schwinger's_quantum_action_principle']quantum[/PLAIN] action principle of J. Schwinger. For this I read several paper and books (like: Quantum kinematics and dynamics by J. Schwinger, Schwinger's Quantum action principle by K.A...

Hi all, Given that usually the most recent subject taught in a standard undergraduate curriculum is quantum mechanics, which was developed in the first half of the twentieth century, when did it become a standard part of the curriculum for undergraduates?

Hello. I'm new to this forum and to Physics and Chemistry in general and I have a question that's making me go crazy: why does the potential energy decrease as two atoms (say, hydrogen atoms) get closer to form a molecule? I'm talking about this graphic: I've read that it's related to the...

Does the electron field has information about its charge(strength) throughout space and if not why not? I hope this question is not vague.

On page 9 of *Quantum theory of many-particle systems* by Alexander L. Fetter and John Dirk Walecka, during the derivation of the second-quantised kinetic term, there is an equality equation below: >\begin{align} \sum_{k=1}^{N} \sum_{W} & \langle E_k|T|W\rangle C(E_1, ..., E_{k-1}, W...

Hi. I have a rather silly question. When speaking about a single photon? What do people mean when they speak of the polarization of a single photon. For instance, in classic electromagnetic theory, this would be the direction in which the electric field of the wave is oscillating . But does...

Homework Statement An excited hydrogen atom can emit photons of various wavelengths. a) What is the maximum wavelength of the Balmer series (in nm) (5pt) b) What is the minimum wavelength of the Balmer series (in nm) (5pt) c) Corresponding to part b), what is the kinetic energy of the recoil...

Are All symmetric matrices with real number entires Hermitian? What about the other way around-are all Hermitian matrices symmetric?

I've heard good things about A Modern Approach to Quantum Mechanics by Townsend and Quantum Mechanics by Mcintyre. They use the same spin approach, but what are the pros and cons of each book?

origin page : http://www.physicspages.com/2012/08/08/finite-step-potential-scattering/ No quite understand how the solution come from this equation

Hi! I'm going on to the masters year of a theoretical physics course and I need some inspiration for my dissertation. Last year I did a one semester long project on quantum computation. (More specifically I discussed the general idea of a qubit, a simple method of realising a qubit using spin...

Everybody knows what is the Wave Function is. $$\Psi=\space e^{i(kx-\omega t)}$$ or $$\Psi=\space cos{(kx-\omega t)} \space - \space isin{(kx-\omega t)}$$ But can anyone tell me how it is derived. Since Schrodinger Equation is derived so easily using this Wave Function. I think it is necessary...

Hello! So if I want to describe dΨ(x)/dt can I use 1D wave equation?

Einstein's relativity of simultaneity & quantum measurement paradox. Suppose a rocket traveling close to the velocity of light which emits a single photon from its midpoint at point A, illustrated below. The rocket is equipped with a single detector drawn in green at the front of the rocket...

How does one write a Lagrangian of a coherent state of vector fields (of differing energy levels) in terms of the the individual Lagrangians? I desperately need to know how to know to do this, for a theory of mine to make any progress. Please stick with me, if I didn't make sense just ask...

Hi, I don't understand how to use 51 get 66. Can you help me with that?

Currently I am working on a manga/comic of mine which imvolves science, especially stuff related to quantum mechanics. The theme of my manga is based on the 'collapsing of realities'...i.e, realities from different timescales would collapse at one place and try to exist at once, which would...

So this upcoming fall I'm beginning college and decided to pursue a BS in Physics. Although I'm not exactly sure what field I want to pursue in physics, I think I want go into quantum mechanics after I graduate and obtain my PhD. Although I love chemistry, it's not what I want to do as a career...

Hi. I was wondering if experiments on the Planck length (about 10-35 m) are possible or not. If it is possible, what kind of experiment would that be? If it's not, then what is the problem? Or what is need to be done? Thanks.

Homework Statement Question: What is the physical dimension of Probability Current for a particle in 1 dimension? (Quantum Mechanics) Homework Equations Quantum mechanical Probability Current: The Attempt at a Solution I know the physical dimension of mass, that is kg. If I know every...

Homework Statement The Clebsh Gordon coefficient is < 11;00 |11> = < l_1,m_1;l_2m_2 | kq > Homework Equations My professor determined the CG to be 1 The Attempt at a Solution How do we look up these numbers in the table? What is the direct product basis? 1x1? What is JM and what is m_1 and...

Homework Statement Prove that the maximum value of the Von Neumann entropy for a completely random ensemble is ##ln(N)## for some population ##N## Homework Equations ##S = -Tr(ρ~lnρ)## ##<A> = Tr(ρA)## The Attempt at a Solution Using Lagrange multipliers and extremizing S Let ##~S =...

Hello friends. My question consists two parts, 1-What is the difference between an optical and an acoustic phonon? 1-What are the conditions by which we can decide the type of phonon i.e optical or acoustic phonon ? Hope to get the reply soon.

Hi, If I consider for instance N non interacting particles in a box, I can compute the energy spectrum quantum mechanically, and thus the number of (quantum) microstates corresponding to a total energy between $E_0$ and $E_0 + \delta E$. In the limit of large quantum numbers, the result is well...

So I was wandering why it is not possible to use quantum particles to communicate across vast distances. As I understand it we cannot send information using this as it would break the laws of physics but what I was wandering is why can't we us entangled particles in a binary why by changing the...

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of states. This can be easily seen using the projection postulate. Often the topic of decoherence...

Homework Statement I did poorly on my exam, which I thought was very fair, and am now trying to understand certain aspects of perturbation theory. There are a total of three, semi related problems which i have questions about. They are mainly qualitative in nature and involve an intuitive...

Hi everybody, I'm a second semester physics major who was fortunate enough to get a position in a research group at my school. What I want to do is get a head start on learning the physics that this lab studies. Currently, I'm in the honors section of basic E & M and I do well in class, not...

Homework Statement a) Determine the ratio (Em/En) between two energy states of a particle in a one dimensional box of length l. b) Show that this is consistent with the non-relativistic low-energy limit. The attempt at a solution I have figured out a) using the de broglie wave-particle duality...

Hi, in the book 'Introduction to Quantum Mechanics' by Griffiths, on page 71 in the section 'The Delta-Function Potential' he states that the general solution to time independent Schrodinger Equation is $$\psi(x) = Ae^{-\kappa x} + B e^{\kappa x}$$ he then notes that the first term blows up as...

Naive reading on the web says that stellar collapse is halted by quantum mechanical processes called "degenerate pressures" that arise when gravity tries to force fermions such as electrons or neutrons into the same quantum state. White dwarfs are propped up by electrons, neutron stars by...

Looks like the title above is popular among physics philosophers and laymen who are interested in QM. I am neither of them by the way, I am a genuine physics student who just got enticed again with QM despite having taken this course some years ago. I would like to know what's so attractive...

I've been looking over the idea of the multiverse recently. I am trying to grasp exactly why so many physicists believe in the idea when it seems more philosophical than scientific. Are there any good indicators pointing towards the theory from QM or GR? The gripe that I also see with it...

So, after time-independent 1D Schrodinger equation is solved, this is obtained E = n2π2ħ2/(2mL2) This means that the mass of the 'particle' is inversely related to the energy eigenvalue. Does this mean that the actual energy of the particle is inversely related to its mass? Isn't this counter...