Qm Definition and 1000 Threads

Is there a maximum size an object can have above which it won't follow the laws of quantum mechanics anymore? e.g. could the double slit experiment in theory work with macroscopic objects?

I am interested in knowing that in QM what vector/tensor operators are? In fact how do they differ from scalar operators?

Question on the "probabilistic" nature of QM I read very recently something that I interpreted as stating that certain quantum-mechanical phenomena are necessarily probability-based: for instance the exact path traversed by a photon/electron in the double-slit experiment. That's all well and...

Many popularized accounts of the development of quantum theory generally go like this: • Maxwell shows that all electromagnetic radiation is a variant of one phenomenon. • Experimental results measuring black body radiation are inconsistent with the radiation theory as understood. • Planck...

My understanding of the main problem with adding gravity to quantum theory is that gravity is proportional to 1/distance squared. And so for particles that have no size (like electrons), their gravity is effectively infinite in a collision. Or in quantum terms, the equations don't converge on...

Do you think Hamilton's principle from classical mechanics can be deduced from Feynman's path integral in quantum mechanics? (We get across this question in another discussion: https://www.physicsforums.com/showthread.php?t=609087&page=5) Of course, there is a loose connection, since...

I have a cursory understanding of QM which (as far as I know) fails to provide causation for certain events such as neutron decay and electron leaps to lower orbits. My understanding is that there is (currently) no know "cause" for these, and other, events - they simply happen. We cannot, for...

One of the most frequent questions in this forum is why there is a contradiction between General Relativity and Quantum Mechanics. The most frequent answer is that, in high-energy conditions, some integrals diverge, giving nonsense. I could not find a mention of which integrals one is talking...

If you Lorentz transform a scalar: U^{-1}(\Lambda)\phi(x)U(\Lambda)=\phi(\Lambda^{-1}x) If you now perform another Lorentz transform, would it it look like this: U^{-1}(\Lambda')U^{-1}(\Lambda)\phi(x)U(\Lambda)U(\Lambda')=\phi(\Lambda'^{-1}\Lambda^{-1}x) ? But isn't this wrong...

I watched this video http://www.youtube.com/watch?v=aJ0FVez0FSc&list=UU_fHG6JygMd7oIvQ5S_cSIg&index=7&feature=plcp and the guy says that we don't know wether probability is a fundamental description of the particle or wether it is because of our lack of knowledge of the underlying system (ie as...

Hello to everyone, while solving homework course Nanotechnology and Nanocomponents, I have encountered a problem in FD method that is applied in even potential. In my homework assignment it is explicitly said that it must be done only in x>0 part of the domain, where my problem starts with...

I'm a chemical engineering major and I have to take one of these. Is QM more theory heavy or are they about the same in that regard? I am leaning more towards QM. my only exposure so far has been with the "modern physics" part of general physics

Which is more difficult to understand general relativity or Quantum Mechanics. Neil de Grasse Tyson basically straight-up contradicted himself in a docu on Einstein. In the beginning he said, GR is so complex that only a few people can understand it. At the end he said GR is simple, profound...

I have a good enough grasp of basics of QM at the level of Griffiths and Binney. Anyways, I want to start a more advanced book. I have my heart set at starting one of the following Dirac's "Principles of QM" John von Neumann's "Mathematical Foundations of QM" L. Ballentine's "QM: A Modern...

Homework Statement The hamiltonian for a given interaction is H=-\frac{\hbar \omega}{2} \hat{\sigma_y} where \sigma_y = \left( \begin{array}{cc} 0 & i \\ -i & 0 \end{array} \right) the pauli Y matrix Homework EquationsThe Attempt at a Solution So from the time dependant schrodinger...

I make way too many mistakes in calc so I'm going to go back and brush up so as to prepare for the exciting moment when I finally start studying QM. I'm using the Thomas text on calc, it's contents are listed below. What sections do you think I should really master. Plus David Griffiths' book...

I want to go about learning quantum mechanics in a way that I can learn it in detail eventually. And I was wondering if someone could give me some advice or advice for how they learn't it, should I start learning calculus and the mathematics needed for understanding it or get one of these...

In Dirac's "The Principles of Quantum Mechanics", in chapter V on the equations of motion Dirac proceeds with a line of reasoning that is something along the following lines (I've modified it a bit to coincide with what's taught in the course I'm taking) 1. We assume that the motion...

I was trying to think of QM in the context of different possible spatial curvatures since the standard cosmology (FRW model) admits at least in principle that 3-space can have positive, negative or no curvature, even if the flat space is favored by the CMB WMAP-COBE observations etc, when I...

Wave functions and their exp(-ipx) are base of quantum mechanics and QFT. But how to derive them the most simply that we will understand why they are base of QM? It is interesting that Feynman in his book "QED: The Strange Theory of Light and Matter" very simplifies QED, but he did not give a...

I'm looking for a good book on QM to study from (at the advanced undergrad level), but the caveat is that it must be concise. What do you recommend?

These are the contents of the books I'm going to be reading to prepare myself for Quantum Mechanics. I was wondering if there any chapters that are not really necessary to learn. For instance, in studying Calculus it seems unlikely to me that infinite series will every be useful, though I...

Consider one particle traveling at a relativistic velocity in 3-space. Then the configuration space of the system consisting of that one particle would have 3 degrees of freedom – 1 particle times 3 dimensions. Because of its high energy, the particle decays into, say, 2 particles. Now the...

If your major is basically going to be mechanical engineering, but you take electives that have to do with physics.. would those electives help you do MS in Quantum mechanics easily?

Which and why do you believe will turn out to be more 'fundamental' (in the sense that one will prove to be the foundation of a theory which goes beyond the SM, while the other will be explained away by it). Or maybe both, or neither?

Whats the difference between Many Worlds Interpretation and Relational QM. Here is what I understand in few words: MWI: The whole universe system evolves with Schrodinger Equation without Quantum Collapse, but when a subsystem interacts with other subsystem, it seems like Quantum Collapse...

Dear forumers, I have a question about taking direct sums and products of state spaces in QM. Picture I have a state space that describes two (indistinguishable) particles which is a direct sum of two one-particles spaces: \epsilon_t = \epsilon_1 \oplus \epsilon_2 Furthermore, picture that...

Couple noob questions. 1.What is quantum mechanical definition of an observer? 2.Why is looking at the double slit experiment with your eyes while the electron goes through any different than a camera looking? Each one is looking, one can just see better. Is it the fact that the outcome...

Hi folks. I'm wondering who does a good job of explaining this limit, preferably with a good set of examples. It doesn't need to be too basic, but it'd be nice if it went through the phase space stuff a little (I get the impression that my grad prof didn't do a great job with some details based...

Hi, I am trying to get a few fundamental concepts sorted out in my mind associated with the maths of non-commutative operators and the physical implications on QM. As such, I am simply looking for confirmation, clarification or corrections to any of the following issues. One of the most...

In relativity, things like gravity are suppose to be time frame independent, i.e. even if time stopped they would still exist frozen as they did before since a gravitational field instantaneously correlates over the distance it covers. However, in the new standard model, forces like gravity are...

I am currently in my second undergraduate quantum course and just finished studying the addition of angular momenta. I am also in my third abstract algebra course and am now covering product groups and group actions. In my QM book (griffiths) there was a reference made to group theory. it said "...

Hi Consider a small system A which is described by quantum mechanics. A large system B is surrounding A and this large system is described by classical physics. What kind of interactions has the system B to the small qm system? Compared to B is A very small so I guess one can neglect...

I'm wondering whether physicists in the 1930's ever had experimental reason to interpret, for example, Schrödinger's cat, as a true paradox (because of the role of a human observer). Why didn't they default to Bohr's interpretation, that an interaction with a geiger-counter, or any classically...

Hello there, I was reading an article on wiki about the Breit equation: http://en.wikipedia.org/wiki/Breit_equation And I'm having a hard time understanding a few thing about this equation. The first thing is that, from what I can gather, the Breit Hamiltonian is basically a Dirac...

Homework Statement Hi In QM we define the force operator F as (in the Heisenberg picture) F = \frac{1}{i\hbar}[p, H] + (d_t F)(t) What I can't understand is that usually (actually, always) we write F = \frac{1}{i\hbar}[p, H] and neglegt the last time derivative. How can we be so certain...

According to Peterdonis in an old thread According to Matterwave in https://www.physicsforums.com/showthread.php?t=573589 msg #11: Peterdonis said Time is a parameter in non-relativistic QM while as a coordinate in relativistic QM/QFT. But Matterwave said parameter and coordinate has...

Hi, I'm looking for a QM mechanics book, which I could use for review and reference. I've took 3 QM courses, the first two was based on Cohen-tannoudji and Sakurai, and the third was about atoms and molecules etc. , although I haven't studied scattering theory and relativistic QM/QFT. (I took...

hello there, i need a place or a book where i can learn the mathematics of QM. I am having trouble with linear operators and matrix formulation. Like how do you represent an operator? How can one jump between operators and then back to matrix formulation. I NEED THE BASICS! Thanks!

Homework Statement http://img4.imageshack.us/img4/224/32665300.png The Attempt at a Solution http://img684.imageshack.us/img684/2920/scan0003xo.jpg I've uploaded my work so far since its much faster than typing and I'm stuck on the last line trying to solve the integral. The first...

For example let's look at a single particle, double slit experiment: we know that the particle (photon/electron) will land up on one of the fringes. however it is commonly understood that we cannot predict which of the fringes will it land up on. one could argue that since there was...

Feynman said that " [the double slit int. pattern contains] the only mystery in QM" was quantum entanglement not established (and bells theorem not postulated) then yet? or did Feynman believe that the explanation for the double slit (interference pattern) would also somehow explain...

In QFT, Lagrangian is often mentioned. While in QM, it's the Hamiltonian, Is the direct answer because in QFT "position" of particle is focused on and Lagrangian is mostly about position and coordinate while in QM, potential is mostly focus on and Hamiltonian is mostly about potential and...

Last night I started reading the section of Brian Cox's "The Quantum Universe" where they discuss how to calculate the probability of a particle being found at a particular position. What he has stated first is if we have an initial position, at any later time we can find the particle at any...

Hi, I am Liu, a undergraduate in mainland China, I post out this idea and want to see how you gentleman think, here it is: Griffiths says, in his book < Introduction to Quantum Mechanics >, if an insect fly in a path perpendicular to the direction in which lightbeam goes, the velocity of...

I'm trying to understand the basics of convensional QFT versus QM. There are too many books about QM in the introductory level for layman but too rare for QFT. But the public needs to be adept about QFT too not just particle-wave duality, entanglement and other attractions in QM. Let's start...

Hi, I am trying to solve the following equation: \Psi(r,t) = \sum_n C_n(t) e^{-i E_n t} \psi(r) to find the C_n(t)s. The system I am modeling is benzene. I can, by Hückel's method, determine the time-independent solution. The apparently obvious transition from time-independent...

Hello there. It's fair to say that QM confuses me, a lot. Does anyone recommend any lectures/documentaries that i could watch to further my understanding of QM I'd prefer to watch lectures if i be honest, because i know that documentaries are dumbed down for the public (lets face it they...

When reading in Griffiths and on Wikipedia about the vector space formulation of wavefunctions, i am constantly faced with the statement that a vector can be expressed in different bases, but that it's still the same vector. However, I'm having a hard time imagining what it is about a vector...

Hello, I am solving schrodinger and poisson's equation in a self consistent way. I solved schrodinger equation and obtained eigen values which are allowed energy states. now I am calculating electron density with n=sum(psi*psi*f(E)) where f(E)=1/(1+exp((E-Ef)/kT)) fermi function. Now...