Feynman Definition and 617 Threads

Feynman very clearly presented QED in his book The strange theory of light and matter. He tried also with quantum gravity calculations. But, how to clearly present, why his calculations did not lead to quantum gravity.

I'm working on a "draw all possible Feynman diagrams up to order 2" problem for a scalar field that obeys the Klein-Gordon equation, and I'm wondering about a few things. When I did a course on particle physics and was first introduced to Feynman diagrams in the context of QED (but not QED...

I'm probably missing something small but I haven't been able to figure this out. In the Feynman rules (for a scalar field that obeys the Klein-Gordon equation), you write a propagator for internal lines as \frac{i}{k^2 - m^2 + i \epsilon}. The propagator integrand is originally...

Say you want to evaluate this integral: \int^{\infty}_{-\infty} \frac{dx}{x^2-A} Since the bottom factors into \frac{1}{(x-\sqrt{A})(x+\sqrt{A})} , using the theorem of residues, the integral is \pm 2\pi i (\frac{1}{2\sqrt{A}}) (where \pm is + if Im \{\sqrt{A} \}>0 and - otherwise, but...

Vincent Rivasseau and four others just posted "July3150" (I mean 1007.3150, just easier to remember that way for some reason) where they made the observation in effect that spinfoams are the Feynman diagrams of GFT. It's not a new thing to point out, but it is very helpful to mention...

I have been studying how to apply the Feynman rules for QED to various simple first order process (as prescribed by Griffiths' 'Introduction to Elementary Particles'). So far, all is well. I can follow the rules, and develop the results, and it all looks very clever. My problem is that so...

hey, i want to find the lowest order strong interaction feynman diagram for the following process: \Sigma^{++}_c \rightarrow \Lambda^+_c \pi^+ the quark composition is: \Sigma^{++}_c = (c u u) \ \Lambda^+_c = (c u d). \pi^+ =( \bar{d} u ) an image of a correct process is attached...

Can anyone explain what Feynman means when he is talking of a reversible machine in the chapter four of his lectures? What exactly is a reversible machine? Please explain this paragraph : "If when we have lifted and lowered a lot of weights and restored the machine back to its original...

Whenever I see examples of the diagram for the Coulomb interaction it always seems to be two electrons interacting via an electron and being repulsed. The diagram looks intuitive in terms of momentum conservation. I was wondering how (for example) a proton - electron interaction, and...

Hello, I have read the probability chapter in Feynman's lectures on physics. And got fascinated by the random walk. There is a statement, that in a game where either a vertical distance of +1 or -1 can be walked each move, the expected value of the absolute distance (lets call it <D>) from...

I found this passage interesting and illuminating: (from Feynman's book 'QED') ".. In this example, complex numbers were multiplied and then added to produce a final amplitude for the event, whose square is the probability of the event. It is to be emphasized that no matter how many...

So I bought myself the Feynman lectures and was reading up on his discussion on Statistical Mechanics and Thermodynamics (in volume I). The following is regarding Thermodynamics. So he defined entropy (at least the change in it from a to b) as delta S = int(Q/T) over a reversible path from a...

I know I should know this, but I have a quick question. Let's say we have a diagram: 1-->----------2 | | <- "q" v | 3--<----------4 Lets assume: 1 = "quark" 3 = "antiquark" 2 = W boson 4 = photon q = same quark flavor as "3" Time...

Homework Statement At the Tevatron you observe the process u ̅u → τ+τ−. Draw the lowest order Feynman diagrams for the processes involved and state which interactions are responsible. Label all internal lines, external lines and vertices [u = up quark, τ = tau lepton] The Attempt at a...

Homework Statement I need to draw a series of Feynman diagrams to show some processes, but I'm unsure if I'm doing these correctly. I've put them together in this one post and detailed each below in turn, hopefully this is going to make sense. I know there's a few, but I want to make sure I'm...

I'm learning how to do Feynman diagrams for an exam coming up, and have come across diagrams in both position and momentum space. If I'm asked to draw a Feynman diagram without specifying which kind, is it generally assumed that it's in position space? If I label the the incoming and outgoing...

I have a two point Green's Function with a phi^4 interacting Hamiltonian and am considering the second order of pertubation, and must work out the following: T[\phi(x_1) \phi(x_2) \phi(y_1)^4 \phi(y_2)^4] = T[\phi(x_1) \phi(x_2) \phi(y_1) \phi(y_1) \phi(y_1) \phi(y_1) \phi(y_2) \phi(y_2)...

I have spent a while trying to get to grips with the building blocks used for constructing feynman diagrams, below is my attempt at a set of reactions, how am I doing so far? I don't think e^{+}e^{-}\rightarrow\mu^{+}\mu^{-} can happen since a gluon only interacts on particles with a...

Does the math of the Feynman path integral dictate particles taking many paths or is that just an english language gloss-over? Thanks, Jake

I ran a search for gyroscopes looking for a definitive solution to the "What causes Precession?" and found no good clear answers. I think the Feynman lectures come close to the solution and followed that thought process, all the pieces point to the solution, I had to put my theory to the test on...

Hi, Could u advise me please some references where the Feynman rules for graviton are derived I mean graviton-scalar graviton-graviton scattering ... in general graviton vertecies ... Thank you

Hi all! Does anyone know the position space representation of the Feynman propagator on the cylinder? The momentum space representation is the same as in Minkowski 2D space, but the position space representation is different because the integrals over momenta are now sums. Or could someone...

Hi, I just ordered the Exercises for The Feynman Lectures on Physics and although the exercises in them appear to be very interesting, most of them come without answer. I'm just wondering if there is someone with answers to all of them or if there is a book or website which has them. Thanks

Hi all, This is just wild shot, since my memory is not what it used to be ... I remembered reading about Feynman pointing out an interesting fact, that the integration of the gaussian function \int_-\infty^\infty e^(-x x) dx = \sqrt[\pi] has to do with Pi. He then went on to show...

Does anyone know where I can download Richard Feynman lectures free?

I need help - Higgs for idiots: So, how a particle which have no mass without higgs (so it travels at c, and on feynman diagram we would draw its worldline at 45deg) can slow down or even be at rest when Higgs is switched on? Could anyone draw a feynman diagram?

Greetings, In Feynman's lectures - vol. 2 either chap 19, 21 or 23 - I think 23 (I'm at work and don't have the lectures here), Feynman shows in a capacitor that a changing E-Field induces a B-field, then he shows that the B-field induces a new E-Field (he calculates the E-field) and then...

I'm watching a youtube video () of an interview with Feynman. He says, "...there are a number of paradoxes with this quark picture...we've done some experiments at very high energy, hitting a proton with an electron...that can only be interpreted by supposing that the number of particles inside...

I'm not making any statements here, only asking questions. When I take two permanent magnets and I feel the repulsive force between them, Feynman QED says it is the momentum of the virtual photons "pushing" the magnets apart? Experiments have been done, forcing some of these virtual...

Lets say we have a process where: Particle B(P) -> v(p2) + k some particle effectively goes to an antifermion and a photon, with momentums P, p2, and k. And the diagram is just straightforward, in arrow to vertex, out photon and out antifermion from vertex. Now the arrow on the...

Consider the functional: (1) \mbox{ }e^{iW[J]} = \int d \hat{\phi} \mbox{ }e^{i\int d^4x \mbox{ } \mathcal L(\hat{\phi})+J\hat{\phi}} Define a Legendre transformation to get a functional in \phi(x) instead of J(x): (2) \mbox{ }\Gamma[\phi]=W[J(\phi)]- \int d^4x \mbox{ } J(\phi) \phi...

I wonder... Would it be something like that?

Hi, Does anyone know where I can find the audio version of the "Feynman Lectures"?? I know not all of them are taped, but most are, I can't seem to find them anywhere. Help! Thanks.

As I state my questions, there are likely to be errors that I would appreciate being corrected. Beyond that, however, if the gist of the questions can be salvaged after correcting these errors, I would also like answers to your version of the questions. Both Feynman's summation over histories...

Feynman Looking for A "Particle Version" of QFT Hey, I think I read somewhere (though can't find it now) that Feynman was looking for a 'particle' version of quantum field theory which he didn't find but this instead led to the path integral approach of quantum mechanics. Can anyone shed any...

I have some well ordered feyman diagrams which have an incoming neutrino interacting at a vertex with a w boson and emitting an electron. since a neutrino can pass through some 18 light years of led without interacting, I'm wandering how a single neutrino interacts at this vertex?

Is this right? To calculate a scattering amplitude for a certain scattering event, you take the term in the wick's expansion of the S-Matrix that suits your situation best. Then you draw a Feynman Diagram that corresponds to the term in the wick's expansion, then just use the Feynman Rules to...

https://www.youtube.com/watch?v=http://www.youtube.com/watch?v=QMRGYkfzgs0

I've been in a very history of physics mood lately and have been rediscovering Feynman. I was watching the Nova special from after his death and SJMF was typed out from audiotapes of Feynman telling the stories. Does anyone know if there is anyway to get a hand on the original version as read by...

Homework Statement I am trying to prove that \displaystyle{\not} a \displaystyle{\not} b + \displaystyle{\not} b \displaystyle{\not} a = 2a\cdot b using the relation \{\gamma^{\mu},\gamma^{\nu}\} = 2g^{\mu\nu} Homework Equations The Attempt at a Solution If I work backwards...

I'm having a problem calculating the Feynman amplitude for the scalar scattering process \chi^+ \chi^- \to \chi^+ \chi^- for an interaction Lagrangian which is: \mathcal{L} = - g \chi^\dagger \chi \Phi - \frac{\lambda}{4} (\chi^\dagger \chi)^2 So far I have the 2 Feynman Diagrams for...

Homework Statement Hello all, thanks for reading... I was assigned to calculate feynman rules for the scalar QED theory via functional methods. The fields are a scalar complex field \phi, \phi^* and gauge field A_\mu, and the lagrangean is \mathfrak{L} = (D_\mu \phi)^* (D^\mu \phi) - m^2...

Has anyone read the Feynman Lectures of Physics*? I've heard about them and they seem pretty nice. I'm thinking of looking into them but wanted some feedback from someone who has already read them. I already know some of the basics and so I mainly wanted these to better my understanding of...

Hey all, I am just wondering if one can directly calculate the Einstein coefficient in spontaneous emission of, say, two-level atoms through feynman diagrams? I searched for sources in google but could not find anything. Thanks a lot for an answer! Wit best regards, blue2script

I was reading the Feynman lectures, on the parts that deal with optics, and he explains diffraction in a very interesting way. He imagines a diffraction grating to be made up of a long line of infinitesimal dipole oscillators, all oscillating in phase. What I don't understand is, in which...

Not looking for much of a discussion, just a simple answer. Did Feynman smoke cigarettes?

I always wanted to ask (but was afraid to) about the borders on the famous Feynman diagrams. As I understand, Feynman diagrams have the same age as Copenhagen Interpretation. So at that time it looked very logical: quantum behavior inside, but classical world outside. Outgoing particles are the...

Hi everybody, I'm new. I'm approaching to QFT in these months and I have a couple of questions about Feynman rules. The most of the books I have read (or tried to) explain feynman rules telling what you have to do when you have an internal or external line in a graph, and when you have a...

http://research.microsoft.com/apps/tools/tuva/index.html" has a transcript, timeline, and other interesting features. (Silverlight required.) I learned this from Slashdot: http://science.slashdot.org/story/09/07/15/1635245/Bill-Gates-Puts-Classic-Feynman-Lectures-Online?art_pos=4"

Hi everybody! I'm a new Physics Forums user and hope someone could help me out with my minor dilemma. I'm a PhD student in mathematical/theoretical physics and I' working on the Boltzmann equation in QFT. Up to now, there was no major emphasis on Feynamn diagrams - the approach was rather more...