What is Feynman: Definition and 646 Discussions

Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist, known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, as well as his work in particle physics for which he proposed the parton model. For contributions to the development of quantum electrodynamics, Feynman received the Nobel Prize in Physics in 1965 jointly with Julian Schwinger and Shin'ichirō Tomonaga.
Feynman developed a widely used pictorial representation scheme for the mathematical expressions describing the behavior of subatomic particles, which later became known as Feynman diagrams. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World, he was ranked the seventh greatest physicist of all time.He assisted in the development of the atomic bomb during World War II and became known to a wide public in the 1980s as a member of the Rogers Commission, the panel that investigated the Space Shuttle Challenger disaster. Along with his work in theoretical physics, Feynman has been credited with pioneering the field of quantum computing and introducing the concept of nanotechnology. He held the Richard C. Tolman professorship in theoretical physics at the California Institute of Technology.
Feynman was a keen popularizer of physics through both books and lectures, including a 1959 talk on top-down nanotechnology called There's Plenty of Room at the Bottom and the three-volume publication of his undergraduate lectures, The Feynman Lectures on Physics. Feynman also became known through his semi-autobiographical books Surely You're Joking, Mr. Feynman! and What Do You Care What Other People Think?, and books written about him such as Tuva or Bust! by Ralph Leighton and the biography Genius: The Life and Science of Richard Feynman by James Gleick.

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  1. bryanso

    Understanding the Laws of Thermodynamics as described by Feynman

    Hi, there is no other topics in my adventure in Feynman Lectures that makes me so loss in thoughts (https://www.feynmanlectures.caltech.edu/I_44.html). I seem to understand every sentence. But the whole thing is completely unintelligible. Let me start by asking one fundamental question. I am...
  2. E

    A Feynman solution for the radial wave function of the hydrogen atom

    Reading the classical Feynman lectures, I encounter the formula(19.53) that gives the radial component of the wave function: $$ F_{n,l}(\rho)=\frac{e^{-\alpha\rho}}{\rho}\sum_{k=l+1}^n a_k \rho^k $$ that, for ##n=l+1## becomes $$ F_{n,l}=\frac{e^{-\rho/n}}{\rho}a_n\rho^n $$ To find ##a_n## I...
  3. JD_PM

    Feynman Rules on ##\phi^3, \phi^4## theory

    Let us first take the S-matrix expansion (i.e. Dyson's formula) \begin{align*} S_{fi}&=\langle f | T \left\{ \exp\left( i\frac{\lambda_3}{3!}\int d^4 x :\phi \phi \phi (x) : + i\frac{\lambda_4}{4!}\int d^4 x :\phi \phi \phi \phi (x) : \right) \right\}| i \rangle \\ &= \langle f | i...
  4. JD_PM

    I Feynman rules on a ##\phi^3, \phi^4## theory

    The weakly coupled theory is given by the Lagrange density$$\mathcal{L}=\mathcal{L}_0 + \mathcal{L}_I=\frac 1 2 \partial_{\mu} \phi \partial^{\mu} \phi - \frac{m^2}{2} \phi^2 - \frac{\lambda_3}{3!} \phi^3 - \frac{\lambda_4}{4!} \phi^4 \tag{1}$$ Where \begin{equation*} \mathcal{L}_0 = \frac...
  5. John Greger

    A What are some example Feynman diagrams in Yang-Mills theory?

    Hi! So I have just been studying Yang-Mills theory advanced quantum field theory. In chapter 72 of Srednicki's book Quantum Field Theory they list the Feynman rules for non-abelian gauge theory. I was asked if I could show some sample allowed diagrams but I could not.. In standard particle...
  6. AndreasC

    I Pros and cons of Heisenberg and Schrodinger (and Feynman) pictures?

    So there's this professor who insists that the Heisenberg picture is all the rage and much superior in most ways to the Schrodinger picture. He compares it to how you don't use the Hamilton-Jacobi formulation of classical mechanics as much as the Hamiltonian one. Alright, I can buy it. I...
  7. J

    I Born rule in classical Ising model: Feynman -> Boltzmann ensemble?

    Quantum mechanics is often said to be equivalent with Feynman path ensemble, which "after Wick rotation" becomes Boltzmann path ensemble, also called euclidean path integrals (popular for numerical calculations), or random walk/diffusion MERW (maximal entropy random walk). But Boltzmann path...
  8. phinds

    RIP Joan Feynman: A Woman Scientist Ahead of Her Time

    Two months late, but I just found out she died back in July. First two paragraphs from the Economist obit which just appeared this week (I'd copy the whole thing but I don't want to do that w/ a copyrighted article) And after she had studied them for a while in adulthood, the statement "no...
  9. Quarkman1

    Greetings from a 'late learner' and physics fan

    Hello! I am a 'mature' learner and am fascinated by all kinds of physics and math ideas. Learning is the key to enjoying science and keeping an open mind. I must admit, I am not very sharp on my physics skills and my calculus is pretty rusty now (I don't work in the science field, per se) so I...
  10. ShayanJ

    A Developing the Feynman diagram expansion

    I'm reading "introduction to many body physics" by Piers Coleman. In section 7.2 he's trying to introduce Feynman diagrams by expanding the generating functional. But first he transforms it into this pictorial form: Then he calculates the n=1, m=1 term like below: Which I understand. But I...
  11. tomdodd4598

    I QED - ordering of Feynman diagram rules

    Hey there, In QED, we often have Feynman diagrams involving various numbers of non-commuting components, such as for the one-loop vertex correction (Peskin & Schroeder, page 189): The diagram this integral corresponds to is: How do we choose which order to put the propagators and vertex...
  12. saadhusayn

    A Two loop Feynman diagram with quartic vertex

    I am trying to calculate the effective potential of two D0 branes scattering in Matrix theory and verify the coefficients in this paper: K. Becker and M. Becker, "A two-loop test of M(atrix) theory", Nucl. Phys. B 506 (1997) 48-60, arXiv:hep-th/9705091. The fields are expanded about a constant...
  13. S

    Books for the Mathematics of Feynman Diagrams

    Summary:: What is (are) the best book(s) to understand the mathematics of Feynman diagram? Hello, Can anyone recommend some books for the mathematics of Feynman diagram? (I don't mind if they also include the physics; in fact it may be better). Ideally I would need books that are very...
  14. C

    I No "i" in the Triple gluon vertex Feynman Rule

    This is probably a simple question but puzzled me a little when trying to explain something to somebody. In all resources online and in most books I've seen, the triple gluon vertex has no overall 'i' factor while e.g. the four gluon vertex always does. The photon and gluon propagators as well...
  15. M

    I How to determine Spinor in Feynman diagram

    Consider Moller scattering, that is $$e^-(\vec p_1, \alpha)+e^-(\vec p_2, \beta) \quad\longrightarrow\quad e^-(\vec q_1, \gamma)+e^-(\vec q_2, \delta),$$ where the ##\vec{p}_i,\vec q_i## label the momenta of the in and outgoing electrons and the greek letter the spin state. The two relevant...
  16. GREENMONKEY

    I Why is the speed of photons different?

    Hi, I read the Feynman's book about the quantum electrodynamics and I realized, that he was talking about the different speed of photons. I know, that the light travel's "slower" in a material, but he is also talking about the different speed of photons. I read on the web, that some photons...
  17. JD_PM

    I Rewriting Feynman amplitudes and the Dirac equation

    I was studying the photon polarization sum process (second edition QFT Mandl & Shaw,https://ia800108.us.archive.org/32/items/FranzMandlGrahamShawQuantumFieldTheoryWiley2010/Franz%20Mandl%2C%20Graham%20Shaw-Quantum%20Field%20Theory-Wiley%20%282010%29.pdf) and got stuck in how to get certain...
  18. B

    B What happens to the uncertainty principle if....

    I just read the Feynman Lectures about the electron gun experiment with two holes in the middle wall. It demonstrates that if we don't look at the electrons while they travel toward the detector there is an interference pattern in the probability curve of the electrons similarly to what happens...
  19. anuttarasammyak

    B Question about notation in the Feynman Lectures on Physics III 3-1

    I have a question on formula (3.1) and (3.2) in Feynman Lectures on Physics III 3-1, available online, https://www.feynmanlectures.caltech.edu/III_03.html <x|s> here can be interpreted also as inner product of bra <x| and ket |s>, following usual Dirac notation ? For example, ##<r_1|r_2>## in...
  20. M

    I Calculating 2nd Order Scattering Amplitude: Feynman Diagrams

    In the following I will try to deduce the scattering amplitude for a specific interaction. My question is at the bottom, the entire rest is my reasoning to explain how I came to the results I present. My working Let's assume I would like to calculate the second order scattering amplitude in ##...
  21. ronnie snooker

    B Does the Feynman diagram process actually exist, or is it just for computation?

    i want to known whether virtual particle exist or not , and does exchange of particle really happen in interaction.
  22. Physicsphysics

    Pion annihilation Feynman diagram

    π+ + π- → γ + γ How do you represent this in a Feynman diagram showing the individual quark? I am very confused please help! [Moderator's note: Moved from a technical forum and thus no template. Own effort below.]
  23. J

    Feynman Diagrams for Decay of Δ++ & Ξ- Particles

    Δ ++ → p + π0 Ξ - → Λ0 + π-
  24. J

    A Looking Under the Hood of Feynman Diagrams

    I'm currently working my way through Griffith's Elementary Particles text, and I'm looking to understand what's going on with the underlying Hilbert space of a system described using a Feynman diagram. I'm fairly well acquainted with non relativistic QM, but not much with QFT. In particular, I'd...
  25. G

    Feynman diagram with TikZ-Feynman

    Hi, I'm learning how to draw Feynman diagrams in LaTeX using the TikZ-Feynman package, but in https://arxiv.org/ftp/arxiv/papers/1601/1601.05437.pdf I don't see if it's possible to draw loops in ##\lambda \phi^4## theory, how can I draw a loop that goes from one vertex to itself? Thanks
  26. R

    B Another doubt I had while reading Feynman Lectures

    "The “stage” on which the universe goes is the three-dimensional space of geometry, as described by Euclid, and things change in a medium called time." -Feynman Lectures Do the 1st two lines mean that the thing in which everything moves around is the 3 dimensional space...am i interpreting it...
  27. R

    Exploring the Physics of Attraction & Repulsion: A Feynman Lecture

    "Suppose we have another ther charge some distance away. Would it feel any attraction? It would feel practically none, because if the first two are equal in size, the attraction for the one and the repulsion for the other balance out.Therefore there is very little force at any appreciable...
  28. A

    Feynman problem 39-2: Calculations for an adiabatic process

    I'm not sure that this is an adiabatic process. As far as i can read, it is adiabatic if no HEAT or ENERGY is added. But pumping in molecules that are a non-zero temperature is an addition of energy, no? Anyway - my solution with the assumption of an adiabatic process. (skipping units for...
  29. R

    B Can someone tell me if I got this line from the Feynman lectures right?

    'Mass is found to increase with velocity, but appreciable increases require velocities near that of light. A true law is: if an object moves with a speed of less than one hundred miles a second the mass is constant to within one part in a million. ' What does 'constant to within one part in a...
  30. RicardoMP

    Feynman one-loop integral ##I_{21}##

    Starting from the general formula: $$I_{n,m}=\frac{1}{(4\pi)^2}\frac{\Gamma(m+2-\frac{\epsilon}{2})}{\Gamma(2-\frac{\epsilon}{2})\Gamma(n)}\frac{1}{\Delta^{n-m-2}}(\frac{4\pi M^2}{\Delta})^{\frac{\epsilon}{2}}\Gamma(n-m-2+\frac{\epsilon}{2})$$ I arrived to the following...
  31. R

    I Calculating a particular amplitude with Feynman diagrams

    So I’m trying to compute the probability amplitude of an electron with momentum p1 and a positron with momentum p2 annihilating into a photons with momenta q1 and q2. My question is how do you use Feynman diagrams to calculate the first and second order expansions (seen in the third image)? I...
  32. codelieb

    Intro Physics Feynman Lectures on Physics Photos posted online

    Hello, Everyone. I'm happy to announce that the entire collection of (3043) photos taken of Richard Feynman giving his famous 1961-64 introductory physics lectures at Caltech (including his blackboards - original source material for the book, The Feynman Lectures on Physics [FLP]) have been...
  33. A

    A Feynman diagrams strong process

    Hello everybody! I have to write the Feynman diagrams for the process ##\pi^- + p \rightarrow \Lambda_c^+ + D^-##. It is a strong process since all the quantum numbers are conserved. I have attached my attempt, is it correct? Thank you all in advance!
  34. S

    A Does Feynman's path integral ignore alternative histories?

    Summary: Does Richard Feynman's multiple histories ignore alternative histories? Did Richard Feynman's multiple histories (https://en.wikipedia.org/wiki/Multiple_histories) ignore the existence of other alternarive histories or paths? I ask this referring to this comment from this page...
  35. Archimedes777

    Intro Physics Several Physics Books to Choose From (Wolfson, Knight, Feynman)

    I have been lurking on PhysicsForums for more than a decade. I have been telling myself that I was going to learn physics for fifteen years, but I ended up studying computer science when I returned to school after having been an English teacher for several years. I am currently doing my master's...
  36. sponteous

    Carnot's Argument (Cryptic passage in Feynman Lectures v. 1)

    In chapter 44 of Feynman Lectures on Physics, Volume I, which covers thermodynamics, we find this passage: Does anyone know what this argument of Carnot's is? I'm not sure exactly what it is that he is supposed to have derived without using the first law. The efficiency of a reversible...
  37. D

    B What are Feynman Diagrams and how do they help explain Quantum Electrodynamics?

    I'm new to QED, so I want to have a general grasp of what's going on. I just want to understand it conceptually. Can anyone explain it in a way so a layman can understand?
  38. R

    B Multiple Histories theory by Richard Feynman

    Summary: There is some thing i did not get about Multiple History theory Summary: There is some thing i did not get about Multiple History theory I am reading big answers to the big questions from Stephan Hawking. He has mentioned very little about Multiple History theory. I could not...
  39. Glenn Rowe

    A Feynman propagator for a simple harmonic oscillator

    I'm reading through Lancaster & Blundell's Quantum Field Theory for the Gifted Amateur and have got to Chapter 17 on calculating propagataors. In their equation 17.23 they derive the expression for the free Feynman propagator for a scalar field to be...
  40. R

    Feynman Lectures vol.1 Chapter 4 Topic 4-2GravitationalPotentialEnergy

    Could anyone explain me in simple words what is being said in this topic from this book (great book and author btw)... i don't understand after it starts talking about perpetual motion and lifting and lowering of weights.please explain in simple words. okay someone said to add more details to my...
  41. Wrichik Basu

    LaTeX Writing Feynman slash notation in LaTeX

    I started reading QFT recently. With respect to the Dirac spinors, I was introduced to Feynman's slash notation: OR There are sites which say how this can be inserted in LaTeX documents. I checked out the LaTeX guide of PF, but found that it is not listed there. Writing...
  42. E

    I About the Feynman Path Integral and Principle of Least Time

    I don't entirely get why we usually say that only the shortest path contributes in the path integral. If you calculate the volume of nth fresnel zones which is the locus where the path length is between n-1 and n wavelengths from the shortest path in 3 dimensions, they are the same I believe. So...
  43. codelieb

    Intro Physics Feynman's Notes for The Feynman Lectures on Physics

    611 pages of notes Richard Feynman made in 1961-64 to plan and prepare lectures for Caltech's two-year introductory physics course, later known as The Feynman Lectures on Physics, have been posted in deep-zoomable format at The Feynman Lecture Website. Photos of Feynman giving his...
  44. A

    Amplitude with Feynman diagrams and gluon propagators

    The term which is relevant for the calculus is: $$ \bar u(p) \gamma^\alpha \frac{1}{\displaystyle{\not}p+\not k} \gamma^\nu \frac{1}{\displaystyle{\not}p'-\not k} \gamma^\beta v(p') \frac{k_\alpha k_\beta}{k^2} $$ $$ \bar u(p) \displaystyle{\not}k \frac{1}{\displaystyle{\not}p+\not k}...
  45. astroman707

    Intro Physics Suggested outline/syllabus for Feynman lectures?

    I just finished the intro physics sequence at my college, and I wanted to work through the Feyman lecture Vol.1, with the workbook, over the summer. Does anyone know of any sample curriculum used for this book? Or perhaps, knows a good way to work through the book?
  46. binbagsss

    Did I Misinterpret the Change of Sign in the Feynman Propagator Integral?

    Homework Statement [/B] Hi in the first attachment I am stuck on the sign change argument used to get from line 2 to 3 , see below Homework Equationsabove The Attempt at a Solution [/B] Q1) please correct me if I'm wrong but : ##d^3 p \neq d\vec{p} ## since ##d^3 p = dp_x dp_y dp_z ## and...
  47. fluidistic

    Solid State A guide to Feynman diagrams in the many-body problem

    I'm trying to go through Mattuck's book "A guide to Feynman diagrams in the many-body problem", the Dover's 2nd edition book. I have read that apparently it has been criticized for being way too easy. I'm having an extremely hard time going through the 3rd chapter, let alone the 4th! I feel...
  48. Milsomonk

    I Feynman Diagrams: ψφ → ψφ | Tips & Advice

    Hi guys, And Happy new year :) I am revising for a module on relativistic quantum mechanics currently that I took some time ago. A large portion of the module, and hence the exam involves drawing Feynman diagrams and computing invariant amplitudes. The part I am a little rusty...
  49. F

    I Complete list of Feynman diagrams

    Is there an on-line list of all possible Feynman diagrams for all the known particles?
  50. Srihari05

    I Exploring Feynman's Theory on Reflection of Light from Glass Surfaces

    I recently started reading Feynmans book QED. There are a couple of questions I have regarding his theory on the percentage of light that is reflected of two surfaces of glass. My question is as follows, A piece of glass in fact has four surfaces. The front of the glass the back side of...
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