Qm Definition and 1000 Threads

I recently, via Zoom, watched a lecture on QM at Chapman University, supposedly on philosophy and QM. It was by Matt Leifer, a mathematician, so it didn't contain much philosophy but was mostly the math of QM. He talked about several things, but one was a book cited a lot in the literature -...

Hello, Springer books are on sale this week so I wanted to buy some textbooks to support my studies and (eventual) future career. I'm an undergrad (in europe) and my courses next year will be QM, GR and statistical mechanics, so I was looking for books about these topics, but any suggestion on...

Strictly speaking, this isn't about interpretations; it's about whether there is a way to justify QM formalism more intuitively. I put it here because it may help when discussing interpretations. I will let others decide on its implications or even if it is a valid way of viewing it...

I recently finished reading a current novel whose main plot device depended on the Many Worlds interpretation as well as Observer-Created Reality. I wasn't too put off because every science fiction - type story is allowed a certain degree of temporary suspension of disbelief. As I plowed on...

I'll risk a quick off-topic answer here, since I think it's straightforward QM, not vague "interpretation" stuff. :oldbiggrin: In QM (e.g., Ballentine p81), for a free particle, ##H = \frac12 \, M\, V\cdot V + E_0##. So in the ground state ##|E_0\rangle## we have ##H|E_0\rangle = E_0...

Could you tell me if I have understood following about operators in QM correctly? Wavefunction takes all generalized coordinates of the system as arguments. for example if we have a system of proton and electron (in 3-dimensional space) then the wavefunction of this system has 7 arguments...

This paper claims that the double slit experiment can be used to distinguish between QM interpretations: https://arxiv.org/abs/2301.02641 IMO, the paper goes astray right at the start, when it points out that time is a parameter in the Schrodinger equation, not an operator, so that equation...

Am looking at page 13 of QM by Griffiths - have become stuck on minor point. He is proving that a normalised solution of Schrodingers eqn stays normalised. The bit I don't get is how can you just take the complex conjugate of Schrodingers eqn and assume its true. (ie how does he get from Eqn...

This screenshot contains the original assignment statement and I need help to solve it. I have also attached my attempt below. I need to know if my matrices were correct and my method and algebra to solve the problem was correct...

"One way to ground everything in reality is to think purely about the records of experiments that are stored in computer memory. Very often, that's a list of times at which events happened." -- Peter Morgan, old thread meaning-of-wave-function-collapse "If we are to understand the relationship...

Hi For an operator A we have Aψn = anψn ; the matrix elements of the operator A are given by Amn= anδmn My question is : is this an abuse of Einstein summation convention or is that convention not used in QM ? Thanks

We are all familiar with ladder operators, such as QM harmonic oscillators or in QFT to produce energy states which are interpreted as particles. But when a creation operator raises the energy level of a system, where does that energy come from?

Hi PF. I desire deeper understanding of fundamental physics, and quantum mechanics can be a challenge for me (compared to other topics in physics). I read in the intro of the physics textbook chapter that QM explains many phenomena, e.g. why copper conducts electricity and glass does not. In...

I was recently trying to understand how Bohmian Mechanics could model quantum theory. In an old lecture of Sidney Coleman's called "Quantum Theory with the Gloves off" available here: https://www.damtp.cam.ac.uk/user/ho/Coleman.pdf He shows with a "physicist's proof" that QM predicts truly...

We were discussing how much weight it would take to stop the mechanism from rotating in this thread: https://www.physicsforums.com/threads/weight-required-to-hang-straight-down-with-known-torque.1016470/#post-6646777 I wondered if there were actually a range of weights that would stop it...

I do not like superdeterminism because it makes reality Newtonian. However, the objection that superdeterminism means that there is no free will and free will is required for science is silly. Computers lack free will, but they still figure out what's going on. from the introduction to the...

I have approached this question step by step as shown in the image attached. I request someone to please guide if I have approached the (incomplete) solution correctly and also guide towards the complete solution, by helping me to rectify any mistakes I may have made. I'm still unsure how to...

Hi. I have attached a neatly done solution to the above question. I request someone to please check my solution and help me rectify any possible mistakes that I may have made.

In the last few years, many of us have heard of GPT-3, a "language model" trained on terabytes of Internet prose, with a remarkable ability to generate essays, dialogues, and other original works. There is a similar but less powerful model called GPT-J which can be accessed freely at the...

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck. Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments? By this, I mean: 1. Particles are real and...

Summary:: I understand the consensus on PF about studying for knowledge and not merely for "cracking Semester Exams" but I urge you all to go through below thread before attaching to that feeling in my case. Hi. So I have my Exams on Intro QM approaching very soon, which will be a combination...

Below I have attached an image of my possible solution. I have replaced all the relevant limits. For some reason, I am getting the final value for (i) part as ψ(x)= with an additional √2pi in the denominator. Have I made any errors or is it fine if I take it within the constant A.. In...

So I have come up with my solution(attempt) which is: where ( $$\psi_ 1 \triangleq Asin(kx),0<x<L$$ $$\psi_ 2 \triangleq Be^{-sx},x>L$$ $$k \triangleq \sqrt{\frac{2mE}{\hbar^2}} $$ $$s \triangleq \sqrt{\frac{2m(V-E)}{\hbar^2}} $$) But this has a serious problem about boundary: I think...

So I think I use the right approach and I get uncertainty like this: And it's interval irrelevant(ofc), So what kind of wave function gives us \h_bar / 2 ? I guess a normal curve? if so, why is normal curve could be? if not then what's kind of wave function can reach the lower bound

I assume most people when they refer to Quantum Theory, they sort of referring to QFT. So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

Given what we know about special relativity and its implication for time and the observer, could this in any way be linked to why the isolated processes of QM are exhibiting everything happening at once and then collapsing to classical physics when bigger objects interact - the measurement...

As a spin out of How to calculate these odds? https://www.physicsforums.com/threads/how-to-calculate-these-odds.1012014/ I have a question for quantum objects. Question : An atom system has 16 different energy levels filled with 16 electron pairs of opposite spin direction. We pick up or...

Since QM is not deterministic, the future state B is not determined by the previous state A (at time A, B was only a possibility, not a certainty). Then, when we are at time B, and assuming we could move back in time (of course, we cannot do that, but let us make a Gedankenexperiment), it just...

In non-relativity then there is QM, but in relativistic regime then there is QFT. Then what is useful role of Relativistics QM nowaday, or it is only has a historical meaning?Does non-existance wave function in relativistic regime make RQM meaningless?

Rovelli, in his recent paper, writes: https://arxiv.org/pdf/2109.09170.pdf Do you think Rovelli is correct in implying the wave function is redundant and misleading? If we disregard the wave function's significance, beyond convenience, say we forgot it even existed, how would that change (or...

Various people like VN,Wigner thinks QM links to mental states,we know that. People introduced decoherence to kick consciousness out of the realm,as we widely accept.But even Zurek himself admits that there is a fundamental problem of why we only perceive one state and that solving the problem...

In Quantum Mechanics, how can you justify the use of distributions like the delta functional without introducing a rigged Hilbert space? I see that some texts do not make any reference to this subject.

Is Modern Quantum Mechanics, 3rd Edition, by J. J. Sakurai and Jim Napolitano a good book to learn quantum mechanics from?

Hi all, I have a simple question (apologies of this has been asked elsewhere, I am new here): I am looking for a source on Quantum Mechanics for non-physicists. A little more detail on what I am looking for: I am a PhD in Discrete Maths/Optimization and I come from a pure Computer Science...

Hi Pfs. I think that QM can explain the classical things explained by classical physics. Using mean values and so on. We know that in a constant magnetic field an electron will rotate on a circle (at the macroscopic scale approximation) I have the answer for the Larmor precession but how to...

Can we tell, given the ample accuracy of formal quantum mechanics, that the (formal) theory is correct in its entirety?

I was on you-tube and saw a video from Oxford on QM foundations. I didn't agree with it, but that is not an issue - I disagree with a lot of interpretational stuff. The video mentioned a paper they thought essential reading...

New physics guy.(This means totally unknowledged and ignorant.) I've been surfing google scholar,researchgate etc. Seeing many exotic articles,claming things like 1.unitary quantum mechanics fails to describe dynamics,so is ruled out. 2.quantum randomness is illusional! 3.we can recover...

Hi,new college guy here,previewing next year's work. Been seeing these articles,written by reputed physicists. 1. https://www.mdpi.com/1099-4300/23/5/519 this one claims that quantum randomness is false.does this argument be strong enough to rule out QM's so-called randomness?I understand that...

I read in an article that "Quantum physics is a highly mathematical theory that describes the nature of reality at the atomic and subatomic level". I also read another article that says quantum physics does not tell anything about reality. Can you give me some context about it in a way that is...

I understand that QM identifies the nature of the universe as being granular (discrete?) rather than continuous. In Xeno's race, it seems Achilles problem is he must divide distance an infinite number of times before chasing down that speeding tortoise. But I understand that 'Plank Length' is...

I can remember reading something about a future experiment which alledgely could decide if there is an underlying deterministic layer governing quantum phenomena or if pure, empty chance rules suppreme (which I can't imagine). It had something to do with arrival times but I can't imagine how...

Hello. I should find the energy aproximatelly using the variational approximation for this physical hamiltonian: ##bx^4 + p²/2m## Imediatally, i thought that the better trial wave function would be the one correspondent to the ground state of the harmonic quantum oscilator. THe problem is, in...

I was thinking a little about how the absorption of angular momentum occurs from the point of view of QM. For example, suppose we have an atom A and an electron $e^-$. The electron $e^-$ is ejected from a source radially in direction of the center of the atom. Suppose that the atom has net...

I recently came across the following lecture on what QM is: I was shocked by how close it is to my view. What do others think? Thanks Bill

I started reading about the “relational” interpretation of QM (RQM). I’m stuck on what appears to be a contradiction. The simplest way I can think to explain it is with a slight complication added to the Wigner’s friend experiment, adding an extra operation after the friend F measures the...

In adding some detail to a question about mass, I gave a link to an article by Sean Carrol: https://www.preposterousuniverse.com/blog/2013/06/20/how-quantum-field-theory-becomes-effective/ 'Nowadays we know you can start with just about anything, and at low energies, the effective theory will...

Reading the very interesting thread that @Demystifier started, I was hoping to get a better understanding of certain ideas. I don't think these questions would be suitable for that particular thread. The first such question pertains to the following exchange between DarMM and Demystifier. Are...

While classical mechanics uses single action optimizing trajectory, QM can be formulated as Feynman ensemble of trajectories. As in derivation of Brownian motion, mathematically it is convenient to use nonphysical: nowhere differentiable trajectories - should it be so? Can this connection be...

I started another thread on this but it went off into other topics. Hoping to focus on the math here, specifically whether or not the model presented in here is consistent with QM. Let's measure the polarization at the same angle ##\alpha = \beta = \pi/3## (##\varphi_1=0...