Quantum Definition and 998 Threads

I had read up on identical particles and their associated symmetric/antisymmetric wavefunctions a while back and solved a few problems. It seems like I'm still confused on some fronts. I have picked here two solved problems from Zettili's QM book (Edition 3) that I believe illustrate the part I...

How to derive orbital angular momentum of spins in quantum mechanics? Make up for some lost things in Griffiths QM 3rd Ed. Equation (4.134) in Griffiths QM 3rd Ed. was given but no explanation. Please explain how to derive this equation in detail or provide references that by reading them one...

Hi everyone,:peace: Thank you immensely for having me, darkmatyr

Hi. Following the classical mech. g=-GM/R^2, for quantum distances the gravity force would be strong. What are the quantum mechanisms that cause the effects of gravity to vanish? The position uncertainty or the probabilistic wave function can be a justification for suppressing strong...

Greetings scientits and science enthuiasts Im Cosmos_ a 15yr old boy quite crazily in love with Physics especially quantum physics and astrophysics,i might ask some Annoyingky curious questions about the bssic or fundsmnetals of Physics.

I don't know why, but I purchased Quantum Field Theory As Simple As Possible by Andrew Zee. I actually like it (not so much his other book Quantum Field Theory In A Nutshell). The purpose of this post is to mention that while math is required, it is nothing beyond a HS or even advanced middle...

Hi all, I just want to know what you suggest to the arxiv papers of Prof. G. Bianconi. Especially these two: Gravity from Entropy Quantum entropy couples matter with geometry Thanks in advance.

Taking a course In quantum mechanics to review my old courses in physics, they are going to use landau books , should I also consider Griffith Best Regards H

[Moderator's note: Personal speculation deleted.]

A Segunda Lei da Termodinâmica afirma que a entropia total de um sistema isolado nunca diminui. Mas em um experimento de reversão de tempo em sistemas quânticos, seria possível observar uma diminuição efetiva na entropia? Como isso se reconcilia com a visão clássica da irreversibilidade?

Is there any work that tries/ed to incorporate one theory into the other, just like in the papers where Witten published back at the start of 00's ? BTW, how did this work pan out? does it have any implications in nowadays String theory? There's this an attempt which constituted as a published...

I know that the word 'postulate' means something without explanation, so probably there are no words like 'electrons have stable orbits and radiate only when transiting from one to another, because .....' in quantum mechanics books, but were there at least worthy of mentioning attempts to...

Dear PF Forum, It's been a while since I logged in. And I hope everybody is in good health. Here I have a question concerning quantum computer. First, I'm no unfamiliar with a computer. I'm a computer programmer, but I don't know any physics. How can a quantum computer be a lot faster then an...

There are several interpretations of quantum mechanics, most of which are in contradiction to each other, e.g. whether or not the wave function collapses, is ontic, has to be understood in the instrumentalist's view and so forth. My question refers to the meaning of the term "interpretation"...

I was just skimming some reading on Bohmian mechanics and for some reason decided to check on Basil Hiley. He was co-author and close friend of Bohm. I just noticed he died a couple of weeks ago. He was supposed to hosting some event on Bohm's next month. Quite champion of the field. Hopefully...

https://arxiv.org/abs/2406.15345 Trapping molecules to perform quantum operations. By carefully controlling how the molecules rotated with respect to one another, the team managed to entangle two molecules, creating a quantum state known as a two-qubit Bell state with 94 percent accuracy. The...

This isn't really homework but rather me working through my quantum textbook and coming across something I don't understand. Consider the potential function $$V(x)=\begin{cases}0&x<0\\V&x\geq0\end{cases}$$ where ##V## is a constant. If the energy of the incident particle ##E## is less than...

The states of the Schroedinger atom are indicated by several quantum numbers - principle, azimuthal, magnetic, and spin. From the point of view of differential equations, the first three can be derived by using radius and two angles and solving for seperable solutions. One then has what amounts...

From Griffiths 3rd edition quantum pg 45 The bottom two lines. Why can the general solution be expressed as that sum of separable solutions? Griffith doesn't seem to explain this step. What am I missing? Thank you.

Hello all, glad to be here I'm passionate of physics, especially quantum physics since my youth decades ago, and have come to the point to be able to introduce myself as a living example that one can come to a basic understanding of quantum physics with very little mathematics. It's possible...

Is it okay to assume that the Newtonian formula $$ F = G \ \dfrac{ m_{_1} m_{_2} }{d^2} $$ is itself a theory of quantum gravity ?

Hello everyone. I have the following questions: 1. How and why did the theory of quantum gravity begin? 2. What is the objective of those who are dedicated to this research?

I'm just here to learn and contribute my understanding of quantum physics and mechanics to science and engineering for the world. I don't claim to be the best, I only claim to be able to contribute what I understand

Does it make sense to ask what the quantum wavelength of gravitation is? If it does make sense, is an explicit and quantitative determination possible?

Hello all, I am Patrick R. I am a independent researcher. I dabble in physics and numerous fields hoping to help humans all the way down to plants.

On pages 94-96 of Helgoland, Rovelli explains Bell violations according to relational QM. He speaks of spacelike separated measurements, one in Beijing and the other in Vienna. He says any talk of correlations between the 2 is meaningless, specifically: "it makes no sense to ask whether the...

Shahar Hod is an Israeli physicist who has specialized in heuristic reasoning about the properties of quantum black holes, one might say in the tradition of Bekenstein and Hawking. By this I mean that, rather than trying to develop a detailed theory of quantum gravity, he has tried to obtain...

Could the numerical value of the Gravitational Constant G have a quantum basis? G=(2pi x h-bar) + h/137

Suppose we have a quantum system ##S##, an apparatus ##A##, and an observer, say Alice, ##O##. WLOG let ##S## be a spin-##1/2##particle in a state ##0.6|\uparrow\rangle+0.8|\downarrow\rangle##. The apparatus measure it in the ##\sigma_z## basis. Then the observer sees the result. According to...

LSU Physics grad, 30+ years as a Health Physicist for the State of Louisiana, retired guardsman of the military intelligence branch. Interested in approaches to quantum gravity, e.g., Maldaxena, Swingle, Preskill, Van Raamsdonk et al. Convinced the cosmological constant problem is rich with...

In relation to travel back in time, we've all heard of the grandfather paradox, whereby killing your grandfather before they sired offspring would preclude your future existence. This contradiction leads to the conclusion that time travel to the past must be impossible. But it doesn't quite end...

I don't have good references yet and am hoping you all can help me understand my pop-sci reading. I have read that quantum mechanics implies that there is a very small probability that I can fall right through my chair, or suddenly appear on the moon among other crazy things. I subscribe to the...

"We present, for the first time, the full history of the evaporation of a large charged black hole." https://arxiv.org/abs/2411.03447 The evaporation of charged black holes Adam R. Brown, Luca V. Iliesiu, Geoff Penington, Mykhaylo Usatyuk Charged particle emission from black holes with...

The internet has a question for the PF members who are also musicians. Is quantum physics easier than playing this guitar piece?

In Peskin's textbook, the coupling factor is given by a constant in the interacting field theory. The scattering matrix ##S## is given by the time-evolution operator, ##\exp(-iHt)##, in the limit of very large t, i.e., ##t\rightarrow \infty##, as expressed in Eq. (4.71). In my mind, the...

Consider an infinite well between ##0## and ##a##, the energy eigen functions are: $$\phi(x)=\sqrt{\frac 2 a}\sin{\frac{n\pi x}a}$$ Since the Hamiltonian of this system is only a function of momentum operator ##(\hat H=\hat p^2/2m)##, we should be able to find a common energy and momentum...

Hi All, We say that the Schroedinger equation stipulates a smooth and unitary evolution for the wave function, and that the measurement causes the wave function to collapse into one of the eigenstates of the operator that represents the observable parameter being measured by the apparatus. My...

In the following thread: https://www.physicsforums.com/threads/particle-movement-in-quantum-mechanics.1054807/ the discussion established/confirmed that the matter of a particle’s continuity of movement in Quantum Mechanics QM is not a scientific question in QM, refer to PeroK post # 6...

As this has been a key point, in several threads in particular the last close one https://www.physicsforums.com/threads/local-mechanism-for-nonlocal-anticorrelations-inside-spin-theory.1066463/ I though I would clarify what this means becuase it is a pity to confuse it with classical (newtons)...

In the standard model fermion field components collect quite a few labels. The basic fermion field has 4 components that obey anti commutation relations. If one has two types of fermions, say electrons and muons. Do these commute or anti commute? Same question for other labels like gauge group...

This page is Quantum mechanics by bransden. My homework is explain why there is no regulation of quantum number n in selection rule. Also explain that by solving that integral of radial part is always non-zero. ∫∞0[rRnl(r)]Rn′l′(r)r2dr (n is different with n') I tried to solve it by just...

Suppose in the presence of an electric field we solve electronic Hamiltonian with eigen energies and corresponding eigenstates ##|\psi\rangle##. The action of momentum operator on the stationary states ##|\psi\rangle## doesn't change by time. So, momentum-change (or acceleration) seems...

https://www.amazon.com/Student-Friendly-Quantum-Field-Theory/dp/0984513957?tag=pfamazon01-20

I want to create a thread about quantum ethology, and don't know whether such thread will be ok for moderators. Can I ask somebody whether I can post it? I wrote a PM to Greg Bernhardt, but he didn't respond, maybe he receives too much messages to read all? Whom of the moderators can I ask such...

My question is about a statement in the book, Many-Body Quantum Theory in Condensed Matter Physics: An Introduction, by Henrik Bruus, Karsten Flensberg in appendix A: In a translation invariant system, any physical observable ##f(\vec r,\vec r')## of two spatial variables ##\vec r## and ##\vec...

It is a giveaway. https://www.amazon.com/Quantum-Field-Theory-Standard-Model/dp/1107034736/?tag=pfamazon01-20

Classics ! James D. Bjorken, Sidney D. Drell - Relativistic Quantum Mechanics (1964) James D. Bjorken, Sidney D. Drell - Relativistic Quantum Fields (1965) Sold as a pair (reasonable infraction on the 1 book/thread guideline) Mint condition

Free electrons can not absorb photons. Otherwise, the 4-momentum will not be conserved. That is what I understood from the very first lecture of QED. However, we do have the semi-classical picture for HHG - electrons are kicked out from the atom and get accelerated by the radiation field. I...

I was pondering the notion of fiction in the multiverse and remembered my fluids dynamics lecturer many years ago telling us all something about quantum mechanics and how the air molecules in the room could all spontaneously move to one side and we would all suffocate. Slightly disturbing and...