Qm Definition and 1000 Threads

I claim that an experimental demonstration of interference using single particles like photons is also an experimental demonstration of the validity of QM on the macro scale. The idea is that any which path information will destroy the interference pattern. Formally, the visibility of the...

Hi all, I'm studying Quantum mechanics and there seems to be a lot of conceptual concepts involved. Some of it can be a bit dry and I find myself getting easily distracted. What is the best way to study such a subject? Any feedback would be greatly appreciated. Thanks.

Greetings, In trying to even ask this question it’s obvious I don’t understand enough about the topic of QM and light. Here is my attempt at my question: If I shine a laser beam at a target or sensor – the electronics every time detects the beam. How do the Schrodinger wave equation...

Does the notion that a mechanical resonator following the laws of quantum mechanics imply that a similar logic should be used to understand micro and macro events? If there is no border, then why should the logic be different? In other words, if macro events are based on QM, yet they are...

My friend and I were talking , and my friend said that the laws of QM break down at large scales , But i was thinking that they don’t break down the probabilities just become smaller and it becomes harder to use QM . So what do you guys think

Please tell me how conservation of energy and mass apply in QM. I want to confirm something I read somewhere about QM not conserving energy.

Homework Statement I'm trying to follow the solution to a homework problem in QM, and I don't fully understand this step. Where does the factor (2\pi)^3 come from? \int...

hello, is there a reference book in linar algebra that covers topics found in studying quantum mechanics like: vector spaces, operators , matrix , eigenvectors and eigenvalues. i mean not a physics book, i want a mathematics book that talks about these notions and others in an abstarct way...

A buddy of mine asked me to explain QM. I don't by any means tout myself as having any sort of worthwhile knowledge about it so I was a little surprised he asked me. But nevertheless, I explained it to the best of my ability. I'm hoping you guys can tell me if I've royally messed anything up...

So I was checking out some cool videos on youtube of helium in superfluid state and I have a question about it. How exactly does this superfluid have both zero and non-zero viscosity at the same time? The evidence seems pretty clear that it exhibits zero viscosity since it forms a Rollin...

I always thought superposition principle is a consequence of the linearity of Schrodinger's equation, but it's not, instead it's a fundamental principle in QM according to some references I read recently. However I did not find any detailed explanation about this, could someone kindly explain to...

Dear users, I wonder if there is anybody who can give me a hint on how to handle the following situation: In the 2+1 dimensional Klein-Gordon equation with coordinates (t,x,y), I use as initial condition for \Psi(x,0) a spherically symmetric Gaussian. The relativistic dispersion relation...

Homework Statement For l=1 the angular momentum components can be represented by the matrices: \hat{L_{x}} = \hbar \left[ \begin{array}{ccc} 0 & \sqrt{\frac{1}{2}} & 0 \\ \sqrt{\frac{1}{2}} & 0 & \sqrt{\frac{1}{2}} \\ 0 & \sqrt{\frac{1}{2}} & 0 \end{array} \right] \hat{L_{y}} =...

We've been watching this development taking shape ever since the tentative Gambini Pullin papers about it in 2006. It represents a fundamentally new way to address the problem of interpreting Quantum Mechanics. One person who worked on this back in 2006, with Gambini and Pullin, used to post...

In BLACK HOLES AND TIME WARPS by Kip Thorne there is a fascinating discussion about how electron degeneracy pressure fights gravity in dense stars, beginning on page 146. He says the following (abbreviated excerpts) : "..Quantum mechanics insists that when already dense matter is compressed...

Hi All, In quantum mechanics, related to photon, we have these two equations as valid ones: E = h x f p = h / lambda But we have in vacuum the dispersion relation c = lambda x f. 1) How these relations change when the dispersion relation change ? 2) Is it universally correct to...

The algebraic formulation of quantum mechanics (and related stuff, like quantum thermodynamics & dynamical systems etc.) via C*-algebras provides a viewpoint based mostly on abstract functional analysis. However, I've yet to see a working application of this approach, i.e. an example of a...

Hi all I have some questions regarding interpretations of QM. I am not a physicist or mathematician, although I have good general knowledge of science. I'm a philosopher with an interest in the relationships between science, religion and metaphysics. I am trying to link together many...

Retrocausality solves QM problems?? Does retrocausality successfully solve the problems of QM? This recent paper seems to claim it does. http://arxiv.org/abs/1001.5057 Comments, anyone? Also what is the relationship of retrocausality and collapse? TIA Jim Graber

Off pg 977 MTW Gravitation : Consider a classical radiation field whose associated quantum mechanical particles have integer spin S, and zero rest mass. Resolve that radiation field into spherical harmonics - i.e. into multipole moments. all components with l<S will vanish; in general those...

Hi I want to take a year long QM squence at my school but the prereqs is a year long sequence in E&M. I was wondering what skills are picked up from E&M that is used in QM. I have taken modern physics which had light exposure to QM and I did not see much drawn from what little E&M i know...

Hi I was just wondering if someone could explain superposition in QM? Is it to get the probability of finding a particle in a certain state of a wavefunction that would have both positive and negative probabilities?

Hi. I'm studying the transition rates between a state a and a state b in the continuos level. In the book "Physics of atoms and molecules" by Bransden and Joachain it is said: We have to calculate the density of final states. To do this let the volume V be a cube of side L. We can impose...

hi, I'm new to QM and am a lawyer - only an "armchair" physicist. I would be interested in understanding the "views" of subscribers to this site. Specifically: 1. Do you believe in the story of Schorderker's cat? 2. Is Heisenburg's uncertainty principal still valid? 3. Is the Higgs...

I'm sure this has been posted before, but I did a quick search and couldn't spot anything. I was wondering what textbooks I might be able to self-study in order to get up to speed in mathematics and physics so that I might be able to understand GR, SR, and QM. Currently I'm up to speed on...

Questions 3 and 4 in the attachment. The Attempt at a Solution 3. \int d\omega_1 d\omega_2 /|r1-r2|=(2\pi)^2 \int_{0}^{\pi} d\theta_1 \int_{0}^{\pi} d\theta_2 \frac{1}{\sqrt{r_1^2+r_2^2-2r_1r_2cos(\theta_1+\theta_2)} don't know how to proceed from here? for question 4 I got to the...

I was wondering if the following responses, and their line of reasoning, is correct: The wavefunction is 0 at the nucleus for each stationary state of the hydrogen atom. -> False (thinking in terms of the radial distribution, it only approaches 0) The most probable value of the...

So I thought of an easy visual analogy to try and grasp the idea of quantum physics, and I wanted to see if this is accurate or if I am off base in my understanding (As I have mentioned, I'm not a physicist.) Picture a point. Draw lines from that point that moving away that are neither...

[RESOLVED] Quick complex numbers question in QM (probability amplitues) Im a little confused here. I am reading in my textbook about probability amplitudes in Stern Gerlach measurements, and it says this: We find the resulting probabilities for deflection of...

What do you think about Gary Bowman's rather descriptive book "Essential Quantum Mechanics"?

In order to stop hijacking https://www.physicsforums.com/showthread.php?t=361216", I'll restart a discussion here about the role of background assumptions and the conceptual aspects of scientific theories, in particular how the "measurement problem" fits in with quantum mechanics and its...

Hi all, My understanding of the Heisenberg uncertainty principle is this: 1) in order to measure something, we have to hit it with something smaller. 2) in order to know the exact position of something we have to know the exact position of the thing we hit it with. 3) therefore, we cannot...

Homework Statement 1.Consider a one dimensional attraction potential V(x) s.t V(x)<0 for each x. Using the variational principle, show that such a potential has at least one bound state. Hint: use a gaussian in x as a trial functio. 2. A particle with charge e and mass m is confined to...

In thinking about QM, I was wondering if anyone could comment on this? Back in prehistoric times, I did research using bubble chambers. In a bubble chamber, you see a number of curved (because of the magnetic field the chamber is imbedded in) tracks corresponding to different particles...

Hi, I'm looking for a popular science book on quantum mechanics. That is, a book for the general public without heavy math and other scary stuff for us stupid people. I'm not looking for a textbook, so don't recommend Griffiths. I want a minimum level of math (if at all). The level I want...

This is a whacky idea but i thought why not try it out here and see what folks think. This theory is based on accepting an observer-centric interpretation of qm. Many won't agree with that but its important in order to make sense of my argument. So let's pretend that the existence of an...

Homework Statement Here is the question: how can we know that if we have discrete or continuous spectrum just by looking at the potential graph? Specifically, let`s consider the potential V(x)=-F*x (F:const) . After we solve, we can conclude wavefunctin is airy function, and so both...

Homework Statement I'm trying to find energy level above Ec where electron distribution makes a peak for a nondegenerate semiconductor. For this case we may take GaAs having Eg = 1.42eV at T = 300K. Homework Equations m_e=single isotrophic effective mass or m_0 energy states, g_{c}(E) =...

So I’m trying to visualize what is going on in QM geometrically. More specifically I would like to visualize the time dependent wave equation in 3 dimensions. So let’s start with dimensionality. Normally when I think of a function of some variables, I picture it in a space with the number of...

Homework Statement Consider a state | l, m \rangle, an eigenstate of both \hat{L}^{2} and \hat{L}_{z}. Express \hat{L}_{x} in terms of the commutator of \hat{L}_{y} and \hat{L}_{z}, and use the result to demonstrate that \langle \hat{L}_{x} \rangle is zero. Homework Equations [...

I've just listened to an online lecture where Susskind explained Bell's inequality () Basically he shows that classically A\cap \overline{B}+B\cap \overline{C}\geq A\cap\overline{C} Then he uses spin measurements with 0°, 45°, 90° to the z-axis for A, B, C to measure spins of an electron...

It is my understanding that in classical mechanics, cause and effect are universally accepted. Is it the same in QM? Is causality sound in QM?

I've always been interested and intrigued by the idea of light cones and how they fit in with other theories in physics. I have a couple of questions about them that I hope make sense are easily clarified: (1) I understand why the shape of the Past Light Cone is a Cone. I don't understand how...

Hi, I've got a problem with the following problem. This is 1.8 out of Griffiths QM text, and was previously covered on this forum for another user in https://www.physicsforums.com/showthread.php?t=152775", although that thread doesn't address my problem. 1. Suppose a constant potential...

SR "Reference Frames" in QM ? The SR concept of “Reference Frame” cannot be transferred to the micro-world of QM because, due to the HUP, space and time are blurry in that world. Comments? (Thanks in advance).

The following are the interpretations of QM: Bohmian · CCC · Consistent histories · Copenhagen · Ensemble · Hidden variable theory · Many-worlds · Pondicherry · Quantum logic · Relational · Transactional Which is the most accepted by the theoretical physics community? Obviously all have...

Here's a simple numerical analysis problem that is confusing me. Can someone help me understand what boundary conditions to use here? f''(x) - (x^2 - E_n) * f(x) = 0; Assume f -> 0 as x -> +- inf. This equation comes from Schrodinger's equation for a one dimensional trapping potential...

If a system is in state |\psi> before a meassurement, then after we find a value a_n the system is in state \frac{P_n|\psi>}{\sqrt{<\psi|P_n|\psi>}} so for instance if |\psi>=c_1|a_1>+c_2|a_2>+c_3|a_3> after we find a_1 the system is in the state |\psi>'=e^{i\theta}|a_1> where \theta= is...

Can somebody please explain the following? Given the measurements of 2 different physical properties are represented by two different operators, why is it possible to know exactly and simultaneously the values for both of the measured quantities only if the operators commute?

When solving the quantum harmonic oscillator often ladder operators (that send energy eigenstates to higher or lower energy eigenstates) are introduced that allow one to algebraically solve the system. Similarly (but with much more difficulty) such operators can be introduced to solve the...