Theory Definition and 1000 Threads

I understand how do 3 no. equation come from 1 & 2 no. equation. But I am struggling to understand how do 4 no. equation come from 3 no. equation. Will anyone do the steps between 3 no. equation and 4 no. equation, please ?

How did you find PF?: Searching a way to share own thoughts I was wondering if we could gather all the laws of the universe and try to link anything to everything. I'm thinking of the possibility of finding links between quantum physics and the theory of evolution. It reminds me of the...

Suppose we have a hamiltonian $$H_0$$ and we know the eigenvectors/values: $$H_0 |E_i \rangle = E_i|E_i \rangle $$ We then add to it another perturbing Hamiltonian: $$H’$$ which commutes with $$H_0.$$ According to nondegenerate first order perturbation theory: $$\langle H \rangle \approx...

Summary:: I say the answer is A because these are reactive components that take and give back energy from the circuit so no voltage drop across the 2- L & C. Please let me know yours thoughts- thanks Hello I am a newby to electronics taking a class. Please review my thinking on this problem. I...

Hi, smart people This quarantine has got me thinking: Can we get people in the air? I have 3 questions that may or may not help answer this question. But I do appreciate any insight. 1. How would one accelerate (the average human) 100 feet in the air and sustain their position? Under normal...

Hello, I'm trying to make sense of some of the group theoretic discussion found in Griffith's Introduction to Elementary Particles. I have had a fair amount of exposure to elementary group theory, but no representation theory, and have some specific questions related to this which refer to the...

Does anybody know of a derivation of the van der Waals equation from the molecular kinetic theory of gases, but without using the tools of statistical physics (such as partition functions)?

Eric Weinstein finally released a video of his 2013 Oxford talk on "geometric unity". There are many fans and skeptics out there, looking in vain for a genuinely informed assessment of the idea. I admit that so far I have only skimmed the transcript of the video, being very pressed for...

Hi, I'm not sure if it's a good idea to start a thread about the following problem but I didn't want to PM anyone. Some time ago I came across a thread which had stats related to the problems faced by students learning the theory of relativity. It showed like how many undergraduates really...

I have been following the book called "Conformal Field Theories" by Francesco, also known as "the yellow pages". I do this for fun but, of course, sometimes it gets rather technical. Do there exist solutions to the problems in this book? I haven't found a solutions manual available. Many...

Hi, I just need someone to check if I am on the right track here Below is a mutual Coulomb potential energy between the electron and proton in a hydrogen atom which is the perturbed system: ##V(x) = \begin{cases} - \frac{e^{2}}{4\pi\epsilon_{0}}\frac{b}{r^{2}} \text{for } 0<r \leq 0 \\ -...

I am revising perturbation theory from Griffiths introduction to quantum mechanics. Griffiths uses power series to represent the perturbation in the system due to small change in the Hamiltonian. But I see no justification for it! Other than the fact that it works. I searched on the internet a...

Hi everyone, I'm struggling with the proof for the second order energy correction for perturbation theory when substituting in the first order wavefunction. I have attached an image of my current proof for it below, but I'm not sure whether this is the correct approach for it (the H's in the...

Thanks in advance for any insight! Following Pathria's discussion of phase transitions, I'm getting tripped up on the discussion of Landau's theory. Pathria begins with a zero-field free energy ##\psi = A/NkT## where ##A## is the Helmholtz free energy. He proceeds to characterize the...

Hello, After reading a few vulgarisation books, I'm looking into familiarising myself with the more mathematical aspects of quantum physics so I've started reading Quantum Theory for Mathematicians by Brian C. Hall. I'm only 9 pages in but I've already spotted what I think is a typo. I checked...

Having read many times that there is no theory of quantum gravity, yet physicists at Physics Forums must have some ideas of what a theory of quantum gravity will contain. Is it allowed to discuss these questions at Physics Forums? Wikipedia does allow some current theoretical work to be...

Looking at. <psi|AB|theta>, under what conditions would this be equal to <psi|A|theta> * <psi|B|theta> I’m just getting into perturbation theory and am running into confusing notation. Thanks john

[Moderator: moved from a homework forum. This does not sound like homework.]Homework Statement:: Why is it the case that when the low-frequency response is to the right of the M = 1 line that the 'speed of response is slow'? Relevant Equations:: M-cirlces Hi, Hope you are doing well and...

Hi, The following is an excerpt from Avogadro's biography. "Obviously, Avogadro could not accept the rule of simplicity adopted by Dalton. And thus he challenged the composition attributed by Dalton to ammonia, water, and the oxides of sulfur and phosphorus. As for the weights of ammonia and...

Hello everyone. =) In honor of Pi Day I'm going to be explaining the very beginning of set theory (which I consider the beginning of university math) live on Twitch in about two hours (1 PM GMT). For those who do not know Twitch, it's a completely free streaming platform - you can come in and...

Summary:: What are the relevant mathematics/ mathematical physics courses for studying quantum field theory and statistical field theory? I'm a physics undergraduate currently in my junior(third) year, thanks.

Hey guys. I have offers to do summer research at both Brown University and University of Chicago this summer, and I was wondering which school has a stronger department in regards to condensed matter theory. Personally, I think it's University of Chicago, but I'm not too sure and I'd appreciate...

Hi When calculating the superficial degree of divergence do you only do it for diagrams with closed loops? Many thanks :)

According to https://plato.stanford.edu/entries/zermelo-set-theory/ , Zermelo (translated) said: I don't know if that quote is part of his formal presentation. It does raise the question of whether set theory must formally assume that there exists an equivalence relation on "elements" of...

Dark forest is the title of the second book of Three Body Problem, IMHO, a masterpiece of science fiction. Dark Forest theory is a really scary answer to the Fermi paradoxon. Cixin Liu's book has the following axioms: - life grows exponentially, but there is limited amount of matter in the...

What is kutta juokowski theory for lift of aerofoil? (As people say that pressure difference theory of lift is just for basics but main lift is generated by Kutta J, Theorem) No formulae please. If someone can explain like what happens there literally? I tried searching animation or such kind of...

three sub algebra of Unitary group (6) as 1. U(5) . 2. SU(3) 3. O(6) here the three chains in attachment is attached. I want to know how these chains are understands in group theory.

Given a Structure , is the Set of True Sentences (which I think is called the full theory generated by the Structure) with, say, countable symbols. Is there always a bijection between the true sentences (Semantic ) vs the Theorems (Syntactic)? I believe this depends on the existence of a model...

Hi Guys, Forgive me, as it has been quite sometime since I have done my spring theory. The problem I am having is the following: This is the current situation: - In a steel block I have a pocket depth of 15mm - I have a compression spring with the following information: Outside diameter is...

As in the summary: is the term "theory" only used for binary-valued logics? If not, how is it defined for multi-valued logics?

I have confusions about representation theory. In the following questions, I will try to express it as best as possible. For this thread say representation is given as ρ: L → GL(V) where L is the Lie group(or symmetry group for a physicist) GL(V) is the general linear...

I think these theory is made to match the experimental results because I watched videos from Khan academy, jg e.t.c all of them teaching in video is that how do we calculate hybridisation, sigma bonds, π bonds e.t.c and to me these these sources are best because most of the times they gives...

Summary:: Trying to find Rth but I do not get the same value as the one from the solution. [moderator: moved from a technical forum. No template.] I am trying to find Rth to solve this problem, however once I simplified it, I get a value of 700.745 Ω while in the solution, the answer is...

"The fact that the above eleven properties are satisfied is often expressed by saying that the real numbers form a field with respect to the usual addition and multiplication operations." -what do these lines mean? in particular the line "form a field with respect to"? is it something like...

Supposed a future theory of Quantum Gravity reconciles Quantum Mechanics with the Theory of General Relativity, is mathematically self-consistent and makes falsifiable predictions which are not testable though. Can we ever trust a scientific theory which is self-consistent but not testable...

This thread is inspired by the statement of @vanhees71 in https://www.physicsforums.com/threads/books-about-interpretation-and-philosophy-of-physics.983540/post-6290970 : "What a measurement is, is not defined by philosophers (not even by theoretical or mathematical physicists) but by the...

While studying Special Theory of Relativity I came across the formula for the energy of a particle. The total energy of a relativistic particle in STR contains the Rest Mass energy and the Kinetic energy. But, in Classical and Quantum Mechanics, we consider the total energy of the particle to be...

If anyone is familiar with the calculation of scattering amplitudes using momentum twistors. I am working through the book "Scattering Amplitudes in Gauge Theory and Gravity" by Elvang and Huang. I am completely stumped by one step that should be simple. My question is about Eq. (5.45). My...

Is there any version of string theory or cosmological inflation that allows the most fundamental laws and constants change between universes? String Theory and Cosmological Inflation are two theories or models that allow multiple universes to exist. Laws and constants of physics could change...

I created this thread for a separate discussion of apparent wind theory from the thread about sailboats providing their own wind, which is a bit mis-leading title, since the OP's question is about using a fan blowing against a sail to move the sailboat forwards. A quote of a post from that prior...

I'm looking for a book about the theory of measurement in quantum mechanics. A book that goes deep into understanding different kinds and ways. thank you

Reading old text about the limit of large N_c, there are some remarks telling that for finite N we have a colour tube and that it becomes a string in the limit. It sounds as the extra dimension of M-Theory, and I wonder if the math of both calculations are related somehow. Is the transition to...

I was studying mathematical logic and came across this statement of group theory I'm having a hard time in understanding it. I have concluded that ##G## is any set but not an empty one, ##\circ## is a function having input as two variables (both variables are from set...

Hello all, My name is Kyle. I am a physics student at Columbia. I do a lot of science for the public in the New York area and one of my projects involves helping out a group of high schoolers advance in there physics knowledge and self study. Currently I am teaching them the basics of QFT and...

Trying to better understand quantum field theory, I've read that particles are created when it becomes an exitation of its quantum field. Would it then be right to think of a particle as the manifested kinetic energy of its field?

1. For $(a,b) = 1$ and prime $p\ne 2$, prove that $\displaystyle \left(a+b, \frac{a^p+b^p}{a+b}\right) = 1$ or $p$.

While revising Yang-Mills theory, I have stumbled upon a certain problem, which I solved in a somewhat trivial way so I would like to check whether my reasoning is correct. Let's say we have a multicomponent matter field ##\{\phi^m(x)\}## which transforms according to some Lie group ##G## of...

In Kinetic theory of gases, what is the reason behind introducing a new kind of average known as root mean square velocity (##v_{rms}##)? I read the following: The molecules in a container are in constant random motion. So when we add all the velocity vectors to find the average it cancels out...

Are Type Theory and Category Theory alternatives to Set Theory?