Hey Cedric, what’s up with your voice? It really sounds different.

You uploaded finally...!!! Also, just want to let you know that you have a very good series on the path integral approach to qft...However, it is my sincere request to you that you please collect all your videos on qft under a single playlist in a serial manner. It would be much appreciated.

Please put all the QFT videos into an arranged playlist. It's really hard to find and watch them in order.

@ 6:02 Think of this as a single-slit experiment, repeated over and over again at the end of each short path. HIs completeness relation is then a mathematical description of the physical process of diffraction. The messy part of the graph shows all kinds of interference processes.

I think no books have mentioned the fact at 2:42 only 4 vectors having no spin degree of freedom with commute with gamma matrices, it took me a while to wrap my mind. thanks!

Salute❤

1:24 I think yo meant to say where n(t_1) = n(t_2) = 0

Enjoyed the video! The whiteboard is out of focus. Also, why is A = D^(-1) ? (inverse propagator) and why does the Wilsonian effective action have a negative sign? Don't the i on both sides cancel ?

While this is a great course, unfortunately there is no playlist/order for the single lectures so here is an index: 1.0 Intro 2.0 Causality (non-relativistic) 2.1 Causality problem - relativistic 3.0 Canonical vs. many paths 3.1 Many-path QM 3.2 Classical limit 4.0 Lorentz transformations (Scalar Fields) 5.0 Scalar fields Lagrangian 5.1 QM from QFT 5.2 Scalar fields - many paths 5.3 Sources 6.0 Recap 6.1 Classical scalar fields 6.2 Klein-Gordon 7.0 Free scalar fields 7.1 Free propagator 7.2 particles 7.3 Particle properties 8.0 residue theorem 8.1 residue theorem - application 9.0 Interactions between sources (Vector Fields) 10.0 Recap 10.1 Spin 10.2 Vector field Lagrangian 10.3 Maxwell equations 10.3.5 Polarisation 10.4 vector field propagator 11.0 recap 11.1 Coulomb 11.2 graviton 11.3 why we fall (Spinor Fields/Dirac Lagrangian) 12.0 Recap 12.1 Dirac 12.2 gamma matrices 12.3 spinor 12.5 Feymann notation 12.6 Dirac propagator 12.7 Dirac summary 13.0 Noether theorem 13.1 Massless scalar fields 13.2 global gauge invariance 13.3 space time translation 14.0 recap Noether 14.1 antiparticles 15.0 interactions 15.1 baby problem 15.2 teenager problem 15.3 adult problem 15.4 collisions 15.5 Feynman rules 15.6 Mandelstam variables 15.7 cross-sections 15.8 Lorentz invariant phase space 16.0 recap 1 16.1 Yukawa 16.2 QED Lagrangian 16.3 spinors 16.3.5 Ward Identity 16.4 QED Feynmann rules 16.5 electron scattering 16.6 electron scattering probability 16.7 trace gamma matrices 16.8 QED summary 17.0 global gauge invariance 17.1 local gauge invariance 17.2 gauge covariant derivative 17.3 gauge field 18.0 Recap 18.1 SSB (spontaneous symmetry breaking) 18.2 Chiral symmetry 19.0 recap 19.1 Higgs mechanism 19.2 summary (Canonical quantization) 20.0 recap 20.1 commutators 20.2 Hamiltonian 20.3 particles 20.4 wave function 21.0 recap 21.1 Causality 21.2 Pauli 21.3 S-matrix 21.4 LSZ formula 21.5 Correlation functions 22.0 many-body systems 22.1 NR (non-relativistic) Lagrangian 22.2 quantisation 22.3 Hamiltonian 23.0 propagator 23.1 free propagator 23.2 Dyson 23.3 mean-field 24.0 chemical potential 24.1 SSB (spontaneous symmetry breaking) 24.2 Goldstone mode 24.3 dispersion relation 24.4 phase 24.5 vortices 25.0 summary 25.1 summary

Can I get this lectures serially?

short and sweet

Didi I will be very thankful to you for please letting me know if we can affirm Relativistic Causality to be true please 🙏🏻🙏🏻🌼🌼...It appears to me that Qft may violate Causality... There is some problem in defining particle - antiparticle pairs and their cancellation, if one measures scattering amplitude between points outside light cone I do not know if it is zero or not... If it is non zero there is some problem with Causality 🙏🏻🙏🏻🌼🌼... Also Didi I do not know if Commutator of 2 fields outside light cone is zero for any field theory and if it can be proven or if there is a hint or conjecture for it 🙂🙏🏻🙏🏻🌼🌼...

Didi just a small Question - In Qft we see that 2 point correlation function is non zero for spacelike seperated points( so it appears to violate causality)... Didi probably it is because of Framework of Quantum Mechanics where we consider Operators and States in Hilbert Space... Didi probably Hilbert Space does not know about Causal Structure of Space-time coming from Special Relativity... Quantum Mechanics is about operators and their spectrum... Operators as we select them like Momentum operator has a non zero spectrum everywhere even outside light cone... Promoting Non Relativistic Momentum operator to Relativistic operator ( as is done in Special Relativity) does not imply that expectation value of operator is non zero outside light cone... Didi probably we should select operators in Relativistic theory that have a Causal Structure and so are consistent with Special Theory of Relativity, so expectation value of operator is zero outside light cone and it's definition reduces to definition we know in Non Relativistic limit... Didi will be very thankful to receive your valuable comments for same 🙂🙏🏻🙏🏻🌼🌼... Very Sorry for trouble Didi am I getting mistaken somewhere 🙏🏻🙏🏻🌼🌼...

Respectful Sir, It appears to me that as long as there is correlation between fields outside light cone Causality is violated 🙏🏻🙏🏻🌼🌼... Sir also I do not know what order of measurement means one can measure 2 point correlation function and find it is non zero 🙏🏻🙏🏻🌼🌼...

Sir how can I prove gamma to the power 5 is pseudoscaler?

if this was true physics, you would not need to delete my criticisms.

Your videos are great! You should really put them into playlists so people can find each subject a bit better.

Thanks for that explanation!

Could you please make playlists for the courses? Many thanks.

thank you so much for these videos - a stressed masters student

may i know how about global gauge invariance for maxwell or vector field?

Lots of respect for you from Rajasthan India 💐💐

Nice

8:37 The "kinetic energy" density in the Lagrangian density is meaningless, so is the "potential energy" density phi^2 by analogy with an oscillator. This is the first step to build Field's New Clothes.

Why does the action have to be the same in all reference frames? What you say sounds like "because it's a law of physics." But isn't the only law of physics necessary for the Lagrangian formalism that the true path is the path of least action?

“Mass”/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent with/as what is BALANCED electromagnetic/GRAVITATIONAL force/ENERGY, as ELECTROMAGNETISM/energy is gravity ON BALANCE; as E=mc2 is F=ma ON BALANCE. Carefully consider what is THE MAN (AND THE EYE) who actually IS standing on what is THE EARTH/ground ON BALANCE. Great. BALANCED inertia/INERTIAL RESISTANCE is fundamental. E=mc2 is F=ma ON BALANCE, as this CLEARLY AND necessarily explains the fourth dimension AND the term c4 from Einstein's field equations, as ELECTROMAGNETISM/energy is CLEARLY AND necessarily proven to be gravity ON BALANCE. E=mc2 is F=ma ON BALANCE, as ELECTROMAGNETISM/energy is CLEARLY and necessarily proven to be gravity ON BALANCE. The equations are understood together in what is a linked and BALANCED fashion, as gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites; as ELECTROMAGNETISM/energy is gravity ON BALANCE. TIME dilation ULTIMATELY proves ON BALANCE that ELECTROMAGNETISM/energy is gravity ON BALANCE, as E=mc2 IS F=ma ON BALANCE. TIME is NECESSARILY possible/potential AND actual IN BALANCE ON BALANCE, AS ELECTROMAGNETISM/energy is gravity ON BALANCE; as E=mc2 IS F=ma ON BALANCE. The sky is blue, AND THE EARTH is ALSO BLUE. Very carefully consider what is THE EARTH/ground ON BALANCE. The stars AND PLANETS are POINTS in the night sky. Carefully consider what is the speed of light (c) ON BALANCE. E=mc2 is NECESSARILY AND CLEARLY F=ma ON BALANCE. Accordingly, ON BALANCE, the rotation of WHAT IS THE MOON matches it's revolution. Great. The orange Sun and the fully illuminated and setting Moon are the same size as what is THE EYE. E=mc2 IS F=ma. This NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE, AS ELECTROMAGNETISM/energy is gravity ON BALANCE. Gravity is CLEARLY AND necessarily proven to be ELECTROMAGNETISM/energy ON BALANCE. BALANCE AND completeness go hand in hand, as it ALL CLEARLY makes perfect sense ON BALANCE. ACCORDINGLY, F=ma AND E=MC2 are CLEARLY in balance; as ELECTROMAGNETISM/energy is gravity ON BALANCE. (Gravity is ELECTROMAGNETISM/energy ON BALANCE.) F=ma AND E=mc2 mean two things in balance: Inertia/INERTIAL RESISTANCE is proportional to (or BALANCED with/as) GRAVITATIONAL force/ENERGY, as this balances gravity AND inertia/INERTIAL RESISTANCE; AS E=MC2 is CLEARLY F=ma ON BALANCE; AS ELECTROMAGNETISM/energy is gravity. Gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites, as ELECTROMAGNETISM/energy is CLEARLY proven to be gravity ON BALANCE. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, as this balances gravity AND inertia/INERTIAL RESISTANCE; AS E=MC2 is CLEARLY F=ma ON BALANCE; AS ELECTROMAGNETISM/energy is gravity. Accordingly, ON BALANCE, the rotation of WHAT IS THE MOON matches it's revolution. Notice that the stars AND PLANETS are POINTS in the night sky. Now, carefully consider what is the Sun AND what is the speed of light (c) ON BALANCE. I have proven why THE PLANETS (including WHAT IS THE EARTH) move away very, very, very, slightly in relation to what is the Sun, as ELECTROMAGNETISM/energy is gravity ON BALANCE. TIME dilation ULTIMATELY proves ON BALANCE that ELECTROMAGNETISM/energy is gravity ON BALANCE. Great. I have explained the cosmological redshift AND the supergiant stars. ELECTROMAGNETISM/energy is gravity ON BALANCE. TIME is NECESSARILY possible/potential AND actual IN BALANCE, as E=mc2 IS F=ma ON BALANCE; as ELECTROMAGNETISM/energy is CLEARLY and necessarily proven to be gravity ON BALANCE. By Frank DiMeglio

Great work 👏 👍 👌 💪 🙌 😀

Thank you 😊

I'd suggest adding playlists to your channel, gathering videos of the same subject in the order in which they should be watched. Thanks.

In this video "special" means "spatial".

Some say that Feynman did QFT without QM ;-)

Using natural units in an educational environment would not be my choice.

what a load of nonsense. Where is the rational thinking and common sense?

Perfect video when you didn't spend enought time to do your homeworks for the tutorim tomorrow. Thank's a lot for the fast and clear explination!

Honest, but a bit disenchanting.

@ 0:20 The usual mistake, made by so many people! The particle is NOT moving along the curve, but moving along the x-axis. This is a 1D-situation!!!

@ 0:44 Haha, great animation!

In Quantum Mechanics the classical displacement of a wave function from its equilibrium-position is called a 'probability amplitude' and the classical amplitude (or maximum-displacement) is called a 'normalization-constant'. Scientists made these terms up for their own convenience, not for educational purposes.

@ 3:32 Because 'position' (x) is a continuous quantity we don't get a probability-distribution, but a probability-density distribution! Continuous means that there is an infinite amount of values of the observable available, each marginally different from each other. The probability of exactly hitting one of these very small positions is zero: P(x) = 1 / infinity = 0. Here, in this 1D-example, a probability-density is a probability per meter.

Conclusion: 6:25. See Video 21.1 for the QFT-solution.

Thanks a lot! After watching a lot of your videos I'm even more surprised that QFT can describe reality, or at least a part of it. P.S. I hope, for the sake of your students, that you talk a bit slower in real-time lectures ;-)

More "Quantum Physics": kzbin.info/www/bejne/bImuhKWeiKl1qq8

From Wikipedia: "Action is only of interest when the total energy of the system is conserved". en.wikipedia.org/wiki/Action_(physics)

I still think this is pretty amazing stuff. Chapeau, Cedric!

Merci. Just what I needed.

I think more people should watch this video

Exactly what I was looking for... Thanks

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