Qm Definition and 1000 Threads

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...

Can somebody help analyzing the outcome of the following thought experiment: 1) A simple setup with a photon source, half-silvered mirror and two photon detectors with counters (on each path - A and B); 2) We adjust the setup to get an equal distribution between the counters on paths A and...

Homework Statement Show that \widehat{A}\Psi(x) = \Psi(x + b), where b is a constant. Homework Equations Given: \widehat{A} = exp(b[d/dx]) The Attempt at a Solution I know I'm supposed to write out the function as a power series expansion, though I'm not sure what I am...

I have a hamiltonian: H = J\left(\frac{1}{2\hbar^2}S_{tot}^2 - \frac{9}{8}\right) where S_{tot} = S_1 + S_2 + S_3 for 3 spin half particles in a cluster. The magnetic properties are governed entirely by their spin. I have set up the possible spin combinations from Clebsch-Gordan to be: From...

All of my questions that follow revolve around the question of atomic geometry/structure as it relates to quantum mechanics. On every high resolution (1 angstrom, and a few less than 1 angstrom) TEM image I have seen, atoms appear as spheres. I then found a website that claims it has visualized...

Can someone please explain to me the sense in teaching quantum mechanics before lagrangian and hamiltonian mechanics? While in undergrad I took a course in intermediate mechanics which was from the first couple of chapters of marion and thornton - like 1-4 or something like that. Then I took...

Homework Statement Determine the momentum proobability distribution function for particles in the n-th energy state in a potential well. Homework Equations a is the width of the well. The answer is:for n odd:|a(p)|^2 = \frac{4an^2\pi}{\hbar}\frac{1}{(\frac{a^2p^2}{\hbar^2}-\pi^2n^2)^2}...

I for one am not satisfied with my professor's presentation of QM. The book she uses for the class is terrible(Peebles) and doesn't do a good job transitioning students from a classical mechanics mindset to a quantum mechanics mindset; Peebles is a graduate level textbook and so many of the...

Can anyone expand on the relationship between Lie groups, Lie algebras, exponential maps and unitary operators in QM? I've been reading lately about Lie groups and exponential maps, and now I'm trying to tie it all together relating it back to QM. I guess I'm trying to make sense of how Lie...

Can anyone tell me how is wavelength defined for a wave associated with a particle? If the wave function we are speaking of has no physical significance,then how can measure its length? tks for any rpl

I posted this question in the homework page but I got no answers, so will try here. Given the wave function of a (spinless) particle I need to expres in terms of \psi(\vec{r}) the probability for simultaneous measurements of X y P_z to yield : x_1 \leq x \leq x_2 p_z \geq 0 I got the...

Homework Statement A 2 MeV (kinetic energy) positron collides with an electron at rest. Find the wavelength of the resulting two gamma rays in the center of mass system. use the fact that E^{2} - p^{2}c^{2} = m^{2}c^{4} is invariant between frames of reference for any system)Homework...

Homework Statement Let \psi(x,y,z)=\psi(\vec{r}) be the normalized wave function of a particle.Express in terms of \psi(\vec{r}) the probability for a simultaneous measurements o X y P_z to yield : x_1 \leq x \leq x_2 p_z \geq 0 Homework Equations...

Homework Statement Consider a quantum system described by a basis \mid 1 \rangle and \mid 2 \rangle. The system is initially in the state: \psi_i = \frac{i}{\sqrt3} \mid 1 \rangle + \sqrt{\frac{2}{3}} \mid 2 \rangle. (a) Find the probability that the initial system is measured to be in...

Homework Statement With the wave function \psi(r) of a particle, one forms the function: D(R,P)=\frac{\int exp(-\frac{i}{\hbar} P\cdot r)\psi^*(R-r/2)\psi (R+r/2) dr}{(2\pi \hbar)^3}, which is the density in phase of a classical statistical mixture associated with this wave function, Show...

Many physicists say that they prefer the "Copenhagen" interpretation of QM, but it does not mean that all these physicists prefer the same (or even a very similar) interpretation. There are at least 4 very different interpretations that are sometimes referred to as "Copenhagen": 1. Shut up...

Hello! I have noticed that most advanced textbooks on QM start the development of the subject with a long review of linear algebra. In particular, they talk about pre-Banach, Banach, pre-Hilbert, Hilbert spaces and so on. Why is it necessary to invoke such abstract spaces in order to describe...

Does quantum theory render null hypothesis obsolete? http://en.wikipedia.org/wiki/Philosophy_of_psychology http://en.wikipedia.org/wiki/Null_hypothesis http://suppes-corpus.stanford.edu/article.html?id=35 Thanks.

Karl Popper, the highly influential philosopher of science was unusual in that, as a philosopher, he had a large impact on science itself. He was actually listened to by physicists! He's best known, of course, for his falsifiability criterion for theories to be considered scientific, which has...

I'm trying to read through Griffiths' QM book, and right now I'm on the series solution to the harmonic oscillator (ch 2). I'm having a hard time following the math (especially after equation 2.81) in this section, so if anyone has read this book, please help. My first question is about the...

What preliminary knowledge of QM should I know before learning QFT, or should I learn QFT in parallel with me learning QM?

On pg. 2, Shankar seems to just assume (I'm guessing) that 1|V\rangle = |V\rangle for all vectors |V\rangle when he does the exercise at the bottom of the page. Is this true, or is it possible to prove 1|V\rangle = |V\rangle from the axioms he lists?