Qm Definition and 1000 Threads

I was taught that a particle is assigned to a unique quantum state. As a specific example, two bound electrons can't have the same quantum numbers in an atom. And likewise one and only bound electron is assigned to one quantum state in an atom. Yet, I am reading several solid state books and...

One of the postulates of QM is that the physical state of any system (with any number of constituent particles) corresponds to a Hilbert state vector ψ. So an isolated system that includes an object to be observed, the observing apparatus, and also the human observer himself is also represented...

Hey, I cannot solve this problem. Please help me. In the H2 molecule, the Pauli exclusion principle demands that the wavefunction of two protons be antisymmetric under the interchange of the two proton coordiates. Based on this, explain the (a) In the spin-triplet states of two protons...

What is the connection between QM and classical mechanics? This has never been obvious to me, but it seems that it would be desirable that we should be able to derive the laws of CM from QM, but I've never really seen that done convincingly. Can you actually show that a very large quantum system...

Several questions. 1. Do different observers (with the same knowledge) in different inertial frames agree on the number of states of some specific system? 2. The same question for the different accelerated frames; 3. The most difficult one Say, Alice observes some system X with N particles...

Hello! I have been told that Zettili's book is the best. How much is that true? And can I follow it and still be capable of solving problems posted in exams (knowing that my Prof is working in other books.. ) I want to be able to solve ANY exercise at the end of the semester. Your...

Just an abstract question here. How different do you think the world would be if we were taught quantum mechanics before classical mechanics, given the prerequisite that we already have a good knowledge of the mathematics? Of course, it's a highly unlikely scenario, but an interesting one none...

Noble prize in QM for 2012 1. Would someone like to summarize the research and results? 2. how can single quantum particles be observed without destroying them? 3. how were they able to show both states at the same time? 4. were the two physicists entangled at 68?...;)

I'm trying to "sure"up my Quantum Mechanics and found an sheet of mostly conceptual review questions. A sort of "Quantum minima". I'd like to check my answers to a couple of these. Firstly: In terms of state vector the wavefunction is the expansion coefficient (probability amplitude) of a...

I'm just wondering... Regarding the single & double slit experiments... Why does every interpretation say that the photographic screen is 'measuring' the position of the particle traveling towards it? Why not say that the photographic screen interacts with an electron that is spread out...

Hi, It's about green's function in the book Messiah - Quantum Mechanics II - Chapter 16.3.2 (see http://books.google.de/books?id=OJ1XQ5hnINwC&pg=PA200&lpg=PA202&ots=NWr6A89Mkt&dq=messiah+quantenmechanik+kapitel+16.3&hl=de). The book actually is in german, but I guess that doesn't matter...

Show G(k)=\sqrt{2π}g1(k)g2(k) Given that G(k) is the Fourier transform of F(x), g1(k) is Fourier trans of f1(x), g2(k) is Fourier trans of f2(X) and F(x)=^{+∞}_{-∞}∫dyf1(y)f2(x-y) SO FAR G(k)=1/\sqrt{2π}^{+∞}_{-∞}∫F(x)e-ikxdx <-def'n of Fourier transform...

I have a question about time dependence in the different pictures of QM. In the Schrodinger Picture, I've read that the time dependence is in the state vector, but one can construct Hamiltonians and other operators that are time dependent in the Schrodinger Picture. For instance, one can...

Hi, I am looking for the operator representing the absolute value of a particle's momentum. In other words: the square root of the laplacian (preferably in 3 dimensions, but 2 would also be fine). I am aware, that integral formulas exist for this operator, but is it possible to express it...

Homework Statement Find the variational parameters \beta, \mu for a particle in one in one dimension whose group-state wave function is given as: \varphi(\beta,\mu)=Asin(βx)exp(-\mux^{2}) for x≥0. The wavefunction is zero for x<0. Homework Equations The Hamiltonian is given as...

Hi, I'm unsure if I'm posting this in the correct place, so apologies in advance if not. I looked at the study board, but the post template doesn't apply to my question. I'm a layperson who had previously only read popular science books on QM, but has recently been watching some more...

Do you still use QM in conjunction with the other theories? Is QM kind of like the basic theory that the others rely on? (Hopefully those questions make sense)

I am an UG student majoring in Physics. I am just starting classical coursework, but I have had, for the past 10 or so years, a great interest in Quantum Theory. I have read nearly every popular-level (read: very little, if any, math) book published in the last 15 years on the subject, but just...

If QM requires a constant universal time, does this rule out closed time-like curves?

Hello all, On one forum I found this link: http://oyhus.no/QM_explaining_many-worlds.html claiming to demonstrate correctness of Many Wordls interpretation of QM. On the one hand - seems like well presented arguments. On the other hand: it claimes to be discovered in 1990,and it seems...

Does anyone know of a psychological study done of the various people who take different positions in the debates about interpretation of quantum mechanics? I mean something that would analyze the philosophical reasons for the arguments, and the emotional drives that might lead physicists to...

Since all the observables in QM is on the form \langle \alpha |A| \beta \rangle where A is an observable, one can transform the observables and states like A \to A' = UAU^{-1} \ \ \ |\beta \rangle \to |\beta '\rangle = U |\beta \rangle where U is a unitary transformatioin. These...

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If such a thing exists, what is a good popular science book for quantum mechanics? Multiple book choices would be accepted. Not looking for textbooks, more something you can lend to people who don't have science degrees but who are keenly interested in the subject. In an ideal world it...

As I see it the unpredictability of clouds can have two causes: 1. quantum indeterminacy or 2. Clouds are classical objects but they are so complicated that they cannot in practice be predicted I'm inclined to think 1 is correct. Correct me if I'm wrong but I'm pretty sure protons'...

Hello all, I will be learning about the path integral formulation, among other topics, in an advanced QM class during this upcoming semester, so I read ahead a little. I understand that, essentially, the propagator between two points in spacetime is the normalized sum of exp(i*2pi*S/h) over...

Lets say I have 2 elevators And I have the same experiment in both. Now the first elevator goes into free fall in a constant gravitational field. Now a little bit later the second elevator goes into free fall. Now as the second elevator goes into free fall its wave function is the same as the...

I was going through Linear Algebra which is recommended as a prerequisite to Quantum Mechanics. The topic of LA is vast and deep. So I wanted to know which (specific) topics of LA should be covered as a prerequisite to QM.

I have been working through a method of solving the Time-Dependent Schrodinger Equation. I'm trying to learn this techniques before I actually jump into my project, however, I have come to an integral that I have been trying to do but can't think of a way to approach it. Mathematica could not...

this is the final chapter of my Linear Algebra book. It looks like they're just exploring how LA is used in other more advanced math. I have a feeling that it is not very useful for QM which is what I want LA for.

Hello! I´m trying to read Georgi's book on Lie algebras in particle physics but am confused about the start of chapter 4. Georgi writes that "A tensor operator is a set of operators that transforms under commutation with the generators of some Lie algebra like an irreducible representation of...

All three seem to be loved, mathematically rigorous, and appropriate as undergraduate-level texts. I have a good knowledge of classical physics, ODEs and PDEs, linear algebra and multivar calculus, but no knowledge of analytical mechanics or QM. Some opinions on these or other recommendations...

Homework Statement Hi I have read a paper, where they want to find the average number of photons in a cavity. They have an expression for \langle{\hat a}\rangle, and then they use \langle{\hat a}\rangle^* = \langle{\hat a^\dagger}\rangle to find \langle{\hat a^\dagger \hat a}\rangle. I agree...

Homework Statement Hi I have a technical question regarding the following paper: http://arxiv.org/pdf/quant-ph/0602170v1.pdf In it they derive an equation for \left\langle a \right\rangle (equation #5) from the master equation (equation #2). My question is how they do this. Here is what...

Homework Statement Hi My book uses the following in a calculation \left\langle a \right\rangle \left\langle {b^\dagger } \right\rangle + \left\langle {a^\dagger } \right\rangle \left\langle b \right\rangle = 2\operatorname{Re} \left[ {\left\langle a \right\rangle \left\langle {b^\dagger...

Which is the role of hermitian and unitary operators in quantum mechanics and which operator is neither hermitian nor unitary

I'm about to take introductory quantum mechanics next semester and was wondering what I should review from linear algebra? I took it 2 years ago

I find this passage from A Brief History of Time a bit hard to believe. When he talks about using imaginary time for the purposes of calculation, is it the same like in the Schro eq which uses an imaginary number? How plausible is the following passage? Is using imaginary time a common practice...

did feynman unify special relativity with QM or was it mostly a group effort and he just made some important contributions? did he make the decisive step just as leibniz and Newton made the decisive step with calculus? i watched a documentary about him and i couldn't get what his central claim...

I've seen quite a few people on this forum agree that Griffiths is not a good book to learn QM from. But I was wondering what reasons people would give for it. (Personally I don't feel I can give an in depth critique since I've only sampled his book. I rather liked his explanation of...

In classical physics, all observables commute and the commutator would be zero. However this is not true in Quantum Mechanics, observables like position and momentum (time and frequency/energy) don't commute. Why? Is it because the (probability) wave functions/forms of position and momentum...

Hi, PF. I've got a question for you. Maybe this would be better posted in the science education or discussion sections, but it's directly related to QM. I'm just finishing up my undergrad coursework and I've taken QM using Griffiths. It's an okay book, but it does a bit of jumping around, and...

Question 1: how is the QM prediction (i.e. cosine curve, shown below) derived for Bell's tests? in layman' termss Question 2: while Malus's law, some physicists say, is not related to this cosine curve. Is there an indirect/lengthy way to connect the two...

moseley did experiments on various elements and showed that the frequency of the k-alpha emission was proportional to the square of the proton no. The formula is (z-1)^2 proportional to the square root of frequency, with the -1 thrown in for the screening effect. The bohr model can explain...

QM seems something out of our everyday experience and to some it might seem unusual/weird/undeliverable/a hoax...yet... perhaps it actually solves some of the conundrums in classical physics Does QM solve/resolve a few philosophical issues in Physics? 1) Classical physics says that every event...

The title says it. I would like to see what knowledgeable people at PF have to say about the QM projection postulate -- primarily understandings of the conceptual reasoning underlying it. But anything anyone has to say about it is welcomed, including opinions that it shouldn't be a part of the...

I'm a little bewildered by my recent dive into QM. I don't really understand what's going on. I'm thinking maybe I should study some wave mechanics first before I try QM proper. I'm not really good at math. I make an enormous number of mistakes and I need to be constantly reminded of what to...

Sorry, I have 2 doubts about the EPR paradox. 1) Just check out if I am ok: What EPR proposed was that QM suggest that if two entagled particles, for example photons, prepaired in some special way, get away from each other then: a) if we measure their x-spin then one particle will get the...

You always hear that GR and QM aren't compatible, but I've never seen an explanation as to why. If I had to guess I would say it's more than quantum mechanics isn't compatible with GR than the other way around, but I really don't know where the conflicts are.

In what sense is QM "not understood"? This is something that I've seen repeated many times, but I'm wondering how accurate it is. I mean, we've got this mathematical framework where we deal with vector spaces, eigenstates, superpositions, mixed states etc. that works to a high degree of...