Qm Definition and 1000 Threads

What are the active questions/topics in QM?

A beam of neutrons with energy E runs horizontally into a crystal. The crystal transmits half the neutrons and deflects the other half vertically upwards. After climbing to height H these neutrons are deflected through 90 degrees onto a horizontal path parallel to the originally transmitted...

To my understanding you can believe in the multiverse theory without subscribing to many-worlds interpretation of quantum mechanics. But can you subscribe to the many-worlds interpretation while also believing there is only this one universe (and that it just has hidden dimensions). Can...

QM: The "double square well" potential Homework Statement Consider the "double square well" potential below. Qualitively (no calculations) how do the energies of the ground state and the first excited state vary as b goes from zero to infinity (i.e. the two wells become further and further...

some, like momentum appear to be, but are all of them?

Hi everybody, I have been looking over a number of papers by Alexey Kryukov and I have some questions. I have been in some brief correspondence with him about some of my questions but I wanted to ask the forums. Consider this paper...

http://www.esa.int/esaCP/SEM5B34TBPG_index_0.html "ESA’s Integral gamma-ray observatory has provided results that will dramatically affect the search for physics beyond Einstein. It has shown that any underlying quantum ‘graininess’ of space must be at much smaller scales than previously...

I'm reading Daniel T. Gillespie's A QM Primer: An Elementary Introduction to the Formal Theory of QM. In the section on continuous eigenvalues, he admits to playing "fast and loose" with the laws of calculus, with respect to the Dirac delta function. I'd like to understand it better, or, if such...

hello I started to read ‘QFT in a Nutshell’ by A. Zee. In the introduction to the path integral formulation of quantum mechanics there is the story about a particle going through a series of screens with holes drilled through them. Then the number of holes in each screen is increased. This...

Hi there, I am on high school physics level and came here to have a few questions answered that keep boggling my mind and challenging my standards of logic... please keep explanations simple, since I don't have any extensive knowledge of QM and English is not native to me, thanks...

In Fredrik's recent thread: https://www.physicsforums.com/showthread.php?t=506326 some questions arose about this paper: J. B. Hartle, "Quantum Mechanics of Individual Systems", Am. J. Phys., vol 36, no 8, (1968), pp704-712. [For other readers, you'll need to have read or be able to...

I think I may be over-thinking this as I have had one formal course in QM and an independent study course in QM, but any help is MORE THAN GREATLY APPRECIATED! Homework Statement Prove that |-V> = -|V> Homework Equations He instructs us to begin with |V> + (-|V>) = 0|V> = |0>...

As far as explaining the refraction of light through glass (as an example), does the Huygens-Fresnel principle serve any purpose in the quantum mechanical (or the quantum electrodynamical) model? http://en.wikipedia.org/wiki/File:Refraction_-_Huygens-Fresnel_principle.svg Is the Huygens...

Does someone know a textbook that treats QM without relying on representations much? I mean like saying "lets show that this commutator (momentum and position etc.) is reasonable and then derive everything from that without ever talking about representation much". Moreover is it possible to...

At least, according to this paper - http://arxiv.org/ftp/quant-ph/papers/0206/0206190.pdf - nonlocality isn't real in QM. Thoughts?

Homework Statement Consider an electron of mass m=9*10^-30 kg in an infinite box of dimension a=10^-9 m. What is the energy difference between the ground state and the first excited state? Express your answer in eV. Homework Equations E_n = \frac{\hbar^2\pi^2n^2}{2ma^2} The Attempt at a...

Homework Statement The Hamiltonian of a quantum-mechanical system has only two energy eigenstates, namely |1> and |2>. The system has three other properties, denoted by the observables A, B, and C, respectively. The normalized eigenstates |1> and |2> may or may not be eigenstates of A, B, or...

Hi! I got a Barnes & Noble gift card for my birthday yesterday, and am wondering how to spend it on an introductory book or books about QM. My math background was sufficient to get an ME degree in 1958, and that litttle knowledge is now pretty rusty. I would appreciate any advice concerning...

Hi, I understand that we use i\hbar\partial/\partial t and -i\hbar\nabla for the energy and momentum operator but I would like to know how this identification is made. I can see that it works for a wave of the form e^{i(kx-\omega t)} and using the relation E=\hbar\omega and the relation...

Here's an idea I came up with recently, that I wanted to share: No true black holes exist. Every "apparent" event horizon is really a separation of two universes, where the outside universe is entangled geometrically with the inside universe. The Hubble volume is sitting inside of an...

Hello Forum, I've been reading about MWI, the Bohm interpretation, and Feynman QED. Combining elements from these interpretations, I've been building up my own simple mental model of 'how to picture the state of affairs', and I've been speculating about the feasibility of interpretations...

Hello! I'm quite familiar with non-realtivistic QM and particle phenomenology. What I do really miss is a text, which builds on the postulates of quantum mechanics and stresses the similarities and differences between "single particle" nonrelativistic QM and QFT. I want to read about...

Hi, I am new to QM, so advanced apologies for the dumb questions to follow. What does "the spectrum of boundstates is non-degenerate" mean? And why is the time-independent Schrodinger eqn reflection invariant? (I'm not sure I quite know what that means either...) Thanks!

I watched The Elegant Universe, and it was somewhat disappointing. At the current moment, I only know some of the math of SR, no math of GR, and no math of QM. The special kept giving vague overviews of why GR and QM don't mix. I do know some of the concepts for GR and QM, and I do not see why...

Homework Statement Folks, I am looking at a past exam question regarding the Harmonic Oscillator. The question ask 'Justify that the ground state of a harmonic oscillator a_\psi_0=0 equation 2.58 on page 45 of griffiths. THis was not covered in my notes. Any ideas how to justify this...

Hello, I know that blackbody radiation was one phenomenon whose study contributed to the conceptual development of QM early on. My first question is, what other such systems were considered? I want to know this because I'm closely following the actual order of development of QM concepts, the...

Hi, I have a conceptual question concerning causality and locality in QM. Causality plays a role in second quantization when doing QFT, which one calls "micro-causality"; the commutators between fields disappear when the interval between them is spacelike. However, how does this fit in...

Edit: Sorry I posted this in the wrong forum...I intended to post this in the Quantum Physics forum. Mods would you please move this post to the forum you see most appropriate.I am a newbie in learning quantum mechanics, so please view my opinion lightly: After learning a bit of QM, I feel...

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I have completed Quantum Core courses as well as GR and it seems there is something I am missing before taking QFT/QED courses. Is there another subject between?

Homework Statement A spin-1 particle is measured in a stern gerlach device, set up to measure S_{z}. What are the possible outcomes? In this case, the outcome is zero. The same particle is measured by a second deviced which measures S_{x}. What are the possible outcomes of this...

Hi, a brief question from a confused undergrad, I'm about to start a section of a QM course that deals with the QM nature of condensed matter and think I should get a good idea on this before I start it. I fully understand the wave-particle duality of photon's and electrons and the like, but...

Is it wrong to say that QM is random? Aren't we too ignorant of what's going on at the level of QM to claim with certainty what's going on? How could the Universe be deterministic at the level of GR, but we different at the level of QM. They are both connected, only describing different scales.

Homework Statement Hi Say I have a Hamiltonian given by H = δSz acting on my system, where δ is a random variable controlled by some fluctuations in my environment. I have to show that if I start out with <Sx>=½, then the Hamiltonian will reduce <Sx> to <Sx> = ½<cos(δt)> where the <>...

This is a continuation of discussions from another thread: https://www.physicsforums.com/showthread.php?t=490677&page=2 I believe it deserves its own thread instead of hijacking the other one. "Ref 3" in what follows is this paper: L.E. Ballentine, "The Statistical Interpretation of...

I didn't want to hijack somebody else's thread, so thought I would start a new one for this. There are several interpretations/formulations of QM: Copenhagen, TSQM, MWI, and others. Which one currently has the most favor within the physics community? Why Which one currently has the...

I'm at a UC taking upper division QM, and I get the feeling that the course is designed so as to ignore physical interpretations of equations or the true meaning behind the derivation of the wave function, to the point where I'm having doubts of even my professor's real understanding of the...

The concept of "Center of Mass" is mentioned often in QM literature. I saw one blurb stating that a diatomic molecule could be represented as a SHO vibrating about the "center of mass" between the two atoms. But is there a precise definition of center of mass in QM based solely on the state...

For those of us trapped in a corner with difficult choices of whether to believe many worlds are splitted off billions of times every second or whether there is Godlike power to collapse the wave function in the universe or whether waves can travel forward or backward in time (Transactional) or...

I'm a junior undergraduate who has yet to take quantum mechanics, although I did have a brief introduction to basic wave mechanics (square well, harmonic oscillator, tunneling, the hydrogen atom, etc.) in "modern physics" course. I've also watched and taken notes from the Quantum Mechanics...

I just finished a course on linear algebra. The class was quite slow, and not much material was covered (essentially going as far as diagonalization w/ some applications). Seeing as I will be taking a QM course next semester, I thought that it might be a good idea to advance myself on the math...

.. This thread is intended to focus on arithmetic issues, mainly raised by JesseM, vanesch, DrChinese, ThomasT, in the context of: "What's wrong with this local realistic counter-example to Bell's theorem?" https://www.physicsforums.com/showthread.php?t=475076 : For newcomers to the issues...

.. In his text-book "Quantum Theory: Concepts and Methods", Asher Peres (1995) writes: A: "Bell's theorem is not a property of quantum theory." - (p.162, Peres' emphasis). B: "This conclusion can be succinctly stated: unperformed experiments have no results." - (p.168, Peres' emphasis)...

The commutator for group theory is [X,Y]=X^{-1}Y^{-1}XY whereas the quantum commutator is [X,Y]=XY-YX . At first glance, the two commutators seem to be totally unrelated because the quantum commutator speaks of two binary operations whereas group theory has one binary operation. However...

Hello, I am trying to express a given wavefunction through different basis, momentum and position. Look at 5.2(b) and (c) through the link: http://qis.ucalgary.ca/quantech/443/2011/homework_five.pdf" I complete part (b) by doing the following...

I'm am trying to derive the relations: a|n\rangle=\sqrt{n}|n-1\rangle a^{\dagger}|n\rangle=\sqrt{n+1}|n+1\rangle using just the facts that [a,a+]=1 and N|n>=|n> where N=a^{\dagger}a (which implies \langle n|N|n\rangle=n\geq 0). This is what I've done so far: [a,a^{\dagger}]=1 \Rightarrow...

Someone posted this on another forum, and, not knowing enough about it to supply a satisfying answer, I figured I'd ask you guys.

Hi! I'm struggeling with a quantum mechanical problem. Homework Statement An alpha-particle is "trapped" inside a uraniumcore, and the potential is simplified to 0 for R2 < r V0 for R1<= r <= R2 0 for 0<= r < R1 I have calculated the transmission coefficient T =...

Homework Statement Hi Say I have an operator O, and I find its expectation value <O>. Now, if I wish to find the expectation value of O† († denoting Hermitian conjugate), then will this just equal the complex conjugate of <O>? Niles.

hello, can anyone please share the name(s) of the qualified textbooks for QM? thanks in advance..