Hey everyone, thanks for checking out the video! :) Timestamps: 0:00 Intro - "Why is Electromagnetism a Thing?" 14:24 Dirac Zero-Momentum Eigenstates 39:10 Local Phase Symmetry 52:07 A Curious Lagrangian 1:11:43 Bringing A to Life, in Six Ways 1:27:40 The Homogeneous Maxwell's Equations 1:39:25 The Faraday Tensor 1:47:49 F_munuF^munu 1:53:05 The Lagrangian of Quantum Electrodynamics 1:58:14 Inhomogeneous Maxwell's Equations, Part 1 2:11:07 ... Part 2, Solving Euler-Lagrange 2:31:10 ... Part 3, Unpacking the Inhomogeneous Maxwell's Equation(s) 2:37:55 Local Charge Conservation 2:42:20 Deriving the Lorentz Force Law 3:01:25 Miscellaneous Stuff & Mysteries
Very well explained. I always wanted to have a better understanding of SU(1), and I had a vague idea about the complex phase spinning around, but I could never put the fragments together. Now, thanks to your explanation, I have a better understanding of what is going on. I find it very satisfying that one can derive the electromagnetic field right out of pure mathematical reasoning about the Lagrangian density of the Dirac field. That part was pure magic. Thank you once again.
Hi Richard, this is all very interesting but highly theoretical. I was wondering if you can show theory vs experimental data in the most simple and boring of the chemical reactions, maybe one involving hydrogen. So is it possible to plug reactants into these theories and get the chemical products as an output? How is calculated all the process?
33:01 only half hr in but I will be back, life calls ya know My dragon is yawning and turtle is moving her rocks about looking for food. She is making noises from her tank hence need to feed them. Love you work so far though. I’ll be back. Oh though I was Not watching just listening yet I was imagining my cube to follow along well not mine but the one I made. Amazingly enough it helped with the visualisation as you got to the flags I was already at the horizontal on a 3d plain I wondered as we all do How did I do that 😂 What cube I hear you all ask? Drill out the dots on a dice I made in from some hard wood a fallen piece from my possum tree 8cm x 8cm x 8cm Not all lines line up yet one can see how to join 3 vectors in unison with out a break or connection with in the massless of mass of the whole with in and with out of the holes to visualise all the Spin up or spin down and visualise your numbers of squiggles and invisible lines 😂 🙋🏻♂️👉🏼👁👁👈🏼 easy to see Oh place a marble in 1 and shine a light in the centre of 3 and 5 in the dark to make a projection of ? Well you see 😂 🙏🏼👍🏼
Hey Chris, thanks for stopping by! :) For those who don’t know, this is the legendary eigenchris, who made the Spinors for Beginners video series. Check out his channel!
What would really rattle your gauges is knowing how non-zero vacuum expectation value kind of negates the idea of a "big-bang".. Aka *_"How'd you like them Apples?"_* 🍏🍌😉
I was going to say. Richard's logical presentation was very easy to follow and I'd recommend it to anyone interested in understanding electromagnetism and gauge theory.
I would like a definition of Gauge in Gauge field theories which is general. Field invariance, Local phase invariance, Electrostatic potential additive constants and Magnetic vector potential additive gradients without physical significance are good, but seem varied and suggest a general definition.
Our modern technology gives us great potential for teaching each other. Video is like a blackboard that can come to life, and the great part is, once the video is done and uploaded, it takes of a life of its own and can teach people even when I’m doing other things. I love it, and I hope my videos can be a positive example for others to follow. I can’t take credit for the methodology though, 3Blue1Brown is the OG! His videos are what inspired me.
I feel like this video is a triumph for humanity. You’re making this topic accessible for way more people than could previously grasp it. And it’s so beautiful!
When I was newer to gauge theory and first heard that "U(1) symmetry gives rise to E&M", it took me many painful hours to get to the bottom of it. This video does an amazing job organizing the story, and the visuals give me something to grab a hold of.
@@ゾカリクゾIn the case of E&M yes. There are other gauge theories whose symmetry is described by some other Lie group. For example, Yang Mills theories have SU(n) (special unitary group) symmetry.
You make a student feel smart whilst they are learning, which is a truly uncommon and empowering feeling. With this topic you've changed my world view in 3 hours, I shall never be the same! Thank you!
Having made a 2 hour video on theoretical physics with stock video/photos I paid for and text that Powerpoint animated as I recorded live in a sitting, I know for certain that what you achieved here is far beyond anything my patience is ready to produce. This is just absolutely fantastic. If anyone wants clarity on sections I covered regarding electromagnetism, this is the video I will send them to from now on. There's no question about it. This is the best current summary I know of on TH-cam.
Thanks, I’m glad you enjoyed the video! :) Yeah, honestly this one took a lot of effort to make 😅 It turned out to be way more work than I was expecting (I thought this would just be like an hour). But that’s ok, it was a very satisfying project.
This answered a LOT of questions for me even though I don't have the mathematical background to follow 90% of it. It really just helps put things in order while contemplating the nature of reality. Thank you sir!
What this guy is basically saying ' for the laymen ' is that 1x1=2. =D Kidding aside, I grew up in a low income home. I wasn't able to go to college. Being 48, that doesn't mean I cant [try] to understand this. It is beautiful. 99% of what was said was over my head. But I'm a history nut, and love Newton, Durack, Feynman, Krauss, there are just to many to list. I love the way you explain things....which makes it sounds like I understood what you said in this video lol, but it's very unique to come across someone that teaches the way you do. I person can go to school and get a major, that DOES not mean they are good at explaining or teach said topic. I'm a guitar teacher and guitarist of over 34 years. So sir, I didn't understand pretty much any of this. BUT I want to learn. And you have a great way of talking / teaching. I know this video took you a long time to put together. Your right, we live in a time where a person like me can learn this stuff because of the resources we are able to obtain that you couldn't get back in the 90's unless you went to a university. Thank you.
I stumbled across your video on spinors a few months back, leading me to watch your full series on quantum physics. After doing some more research and developing a better intuition, I came back to your spinors video and suddenly everything just clicked. This has reinvigorated a curiosity for physics that I haven't felt in years! Thank you for creating that pedagogical masterpiece. Now I'll have to take notes on this one for the next couple days as well.
I am honestly out of words, the amount of effort that was obviously put into the production, length of video and putting it out on the internet for free, just out of words
Thanks, I’m glad you appreciate the video! :) It was a lot of work, but it’s great to see that people are enjoying it and learning from it. All this positive feedback is very rewarding. And I do get a bit of revenue from ads and patron, not a huge amount but it’s a nice bonus.
I think I make this comment on just about every one of your videos, but I want to continue to express my thanks that someone is making videos that lean into the technical/math aspects of these topics.
Thanks for saying that! :) I’m glad there are people out there who appreciate the technical details. Even though it takes more work to learn the details, that’s where a lot of the beauty can be found.
THANK YOU! By far the best 3 learning hours I spent in a long while. As an electrical engineer I has always been curious about the deeper meaning of the quantum origins of electromagnetism. In the EM classes I had, the A vector was just a cryptic, obscure element no one could explain properly, but they always said it was very important and profound. From the mathematical perspecive, it made sense, but it seemed to me back then, it was just a variable trick. Your video is absolutely enligthening, clarifying the origin of A: it's the seed for EM itself.
I am a second year engineering student who's looking to specialize in physics. Your videos on Schrodinger's equation ignited my interest in quantum physics, and since then I have been spending much of my free time trying to teach myself. Now, just as I've finished Griffith's Introduction to ED and have been searching for a good follow up to learn about gauge theories, you release this. Moments of serendipity like this never cease to amaze me.
Laying out exactly how you get the E and B fields from the potential/ E-M field tensor, whilst seemingly obvious just minutes after you laid it out, was really impressive - which i think is the sign of a great teacher. Also im annoyed at how i think i will forever remember the way of the 6. Very clear and elucidating all around. Great video so far, thanks for the awesome content.
This channel is easily one of the best educational channels I've seen. The quality is off the charts, seriously. There are channels with 100x as many subs that put out worse content. Thank you for this feast
Within the first 3 minutes you completely blew my mind about the concept of a "field". I've never really thought about it. I now understand space-time and gravity a bit better as well! Thank you!!
As someone who has a bachelor's in physics and math but didn't go further, this video is perfect for me. It makes a complex graduate topic that is tough to self study a lot more accessible. Thanks for the effort you make to create these videos. There is something truly beautiful about this topic.
02:36:50 - it's beautiful. The longest lecture I've ever had, but interesting enough to keep me viewing to the end. I paused the video on each statement wich I have to checkout. And the part with derivatives is the easiest part. Man, this video is a lot of work.
Your videos continue to impress! Not being a math guy, this all goes way over my head. What I enjoy is reading the comments from others and am heartened to know there are so many curious and intelligent thinkers out there.
Once again, Mr. Behiel, you've absolutely knocked it out of the park. I am consistently stunned and blown away by the sheer quality and care of your presentation. I say this as someone who has passionately studied physics on my own for all of my life: This video, and all of your other works, are utterly invaluable. I have been studying the topic of "the U(1) gauge theory of electromagnetism" for at least 4 years now, even to the point that I am currently diving deep into connections on principal bundles and covariant derivatives on vector bundles just so I can finally wrap my head around "just how all of this machinery really fits together", so it really says something that this video still actually taught me a lot. It's given me a lot to think about and ponder. I love the way you give intuition-focused breakdowns for the different "moving parts" in both the equations, and the physical situations. The animations are incredible too. The way you blend the rigorous, algebraic expressions, with reference back to the "what is really going on in the physical universe, what does this mean", is truly invaluable for really extracting insight from these often opaque, yet inherently beautiful processes. The way you illustrate the journey... the usual narrative from "demanding local phase invariance of the Dirac field", to "well, local phase transformations result in the addition of a spurious term to the Lagrangian", to "what if we added something that canceled that out?", and so on... this journey is one that has been presented many times before by great educators, but you show the path in its entirety, in a very lucid and well-composed way, and I am deeply grateful for that. More amazingly insightful to me, is how you showed the way that the four-potential is "brought to life" by, apparently, the fact that that antisymmetric quantity (the Faraday tensor) is apparently "immune to" or "untouched by" local phase transformations. And thus, these "wigglings" are allowed to "scrunch up freely". I don't believe I have ever actually thought about it that way before. It will be very interesting for me to investigate later how this figures into my understanding of F as the curvature 2-form of the connection 1-form A on the principal U(1) bundle. In short, this video is nothing short of a masterpiece. I wish I could go part-by-part and really get into just exactly what I love about it. For now, it will suffice to say that this video is an invaluable resource for people like me. Your lucid, detailed-yet very well-paced and friendly-leadings-through of these physical and mathematical notions, vividly exposing the beauty inherent in the "mathematical machinery" of physics, are truly a gift. Thank you for this kindness. Your work is helping people. I hope you have a wonderful night and/or day.
Wow, thanks for the amazing comment! :) I’m very glad to hear all that, and I really appreciate your kind words, that’s very encouraging. I’m glad you enjoyed the video, and I can tell that you’re someone who has studied this topic in depth, so that really means a lot.
@@RichBehiel Absolutely! I've always been fascinated by electromagnetism as long as I can remember. I feel very lucky that I've been able to slowly work my way up to "the real stuff", above the mere classical "vector calculus" formulation. This is part of that! I am deeply grateful for the part you've played in my never-ending quest for deeper insight. ^^
Wow, this is amazing. I’m a pure math guy, and there’s a reason I skipped E&M but took classical, quantum, and statistical mechanics at university. This was an excellent derivation, thank you. The one thing I still have to wrap my head around is the fact that the “coupling” of fields seems to be asymmetrical when we minimize the action? I hope that this was a presentation choice for the video rather than a mathematical choice. Meaning if you look at the full QED Lagrangian without a priori knowing what psi is, but having the same initial condition, then one can first solve for psi as an electron and then solve for the photon field with psi fixed as was done in the video. Edit: I am definitely being dumb. I see the derivation is independent of psi and the dependence is the current J. It is hard to be locked in for 3 hours straight! Again, this was amazing. Thank you!
Probably the most anticipated/happiest youtube upload of my life, I have been researching all about EM as a gauge theory since the spinor video (I was even reading about it yesterday night!). Can't wait to watch this 3 times! Your content is invaluable, thank you so much
Rich. Thank you for this! The tale of how electromagnetism emerges naturally from the local phase symmetry of Dirac’s equation has to strike awe in one’s sensibility. The magic can only be told using the language of mathematics. You have done a magnificent job.
Coming here as a rising senior studying Electrical Engineering, I was not expecting to be out of my depth within the first 10 minutes 😂 Much love! I can’t wait to revisit this after reading up on that textbook you mentioned and watching your other videos!
Lol, coming here as a 2nd year electrical apprentice who last touched physics in any rigorous way in AP physics like 15 years ago, but also having a huge ego, I didn't listen when he told me I'd be out of my depth in first 30 seconds. I've given it half an hour of what largely sounds like a foreign language before throwing in the towel, ordering that textbook, and consigning myself to relearning calculus, among many other things. Ouch.
When I took a QFT class we derived F in class and then got deriving the maxwell equations as homework. It felt really weird. At this point in a physics degree euler lagrange and index raising are second nature. So you do the symbolic manipulation dance you're so used to, not really thinking about anything and pop! there is your entire theory of classical electromagnetism. It's like magic! There are 2 distinct other moments I remember as feeling the same: 1 - When you first do rot rot B and see a wave pop out 2 - Taking dirac or klein-gordon in rindler or schwarzschild metric, expanding to get the form of a schrödinger equation and finding + m*g*h + O(1/c2) at the end of the potential. Btw this video was amazing! I didn't expect to stay for the full 3h, but you've really managed to make this fun even for people who are reliving rather than experiencing the intense joy of seeing all of this play out. My only comment would be that it'd be nice if you wrote out the metric tensor and sums explicitly. I think a lot of "magic" regarding the co and contravariant things has happened here that make being very comfortable with SR a requirement here where more explicit notation would probably make things easier for people who only have some familiarity rather than full immersion in SR. Also, writing out the gs explicitly makes it much easier to see how gravity will end up effecting things. The sum symbol has less of a pedagogical justification and is just something I've seen many people get confused by where a simple symbol would clear things up.
I have been looking for this video for a very long time… I didn’t know it existed, but the content you were covering here and how you’re explaining it is unlocking a lot of doors in my mind on these topics
Just before I woke up near the end of this video, I was having a frustrating dream about being "taught" advanced theoretical physics by a fast-talking professor who was oblivious to how lost the class was. I was the only one even bothering to TRY taking notes, but I just couldn't write fast enough. I kept trying to ask questions despite knowing that the answer wouldn't actually make me feel less clueless. But he wouldn't stop speed-lecturing, except for once or twice, when I could finally get a question in. But each time, he barely acknowledged me, and just kept going without answering! The one thing I understood was his in-depth explanation of scalars... except I already knew all of that! And even more maddening was that it was in response to another student's expression of confusion! He didn't even have to ask a question! Gonna go back and actually watch this for real. Maybe I'll have a shot at comprehension without the handicap of being unconscious. EDIT: Nope.
For those people that are thinking about watching this video but dont wanna commit because its 3 hours long. It is super worth it. Really great video, it doesnt even feel like 3 hours dont worry :)
I am about to get a Master's degree and am applying for a PhD in physics. I have studied QFT for a few years now. While none of the information here was new, of course, the explanation is tiptop. It seems like the perfect thing for someone getting a bachelor who is thinking of getting into QFT for their masters, a perfect balance of handwaving and rigorousness. 10/10 no comments
My word... As an amatuer AF math hobby enthusiast, this video was both thrilling to watch, and also made in such a way that my feeble brain was able to absorb it and gain great insights. Absolutely wonderful job good sir!
Love the relatable “you can do it” style of presentation and the amazing graphics. Doing the algebra in public is rare for TH-cam but combining it with the geometry from the graphics is just what students need to connect the dots and develop intuition. While you’re driving the station wagon through the Grand Canyon of U(1) gauge invariance, it might be nice to take a side jaunt into Diracs magnetic monopole solution, with Wilson Loops and homotopy classes. Another fun side jaunt might be an intro to the path integral formulation of QM ala Feynman’s QED the A Strange Theory of Light and matter. As with most summer vacations it’s hard to say if the station wagon will be roadworthy next year. Anyways, thanks for your content. 😊
Thanks for the kind comment :) I’d like to do a video on Dirac’s magnetic monopoles one of these days, as well as the other things you mentioned. There are so many fascinating ideas in physics.
This is an awesome video! If you're interested, you should experiment with using OKLCH instead of HSL when representing phase using hue. You might notice that on a computer screen, pure blue appears darker to the eye than pure green. This is because the "perceived lightness" of a color varies by hue in HSL. This is what makes spinors look as if they're flashing. In OKLCH, the "lightness" parameter corresponds to perceived lightness, so panning through hue in OKLCH will fix the flashing. The tradeoff is that colors will appear somewhat washed out because using exclusively pure colors doesn't work for perceptual uniformity.
I've been looking forward to this. Will save it for later, but this series has been very helpful in the technical side of my journey to understand QM/QFT.
This is an incredibly good video. I watched it start to finish. Sticking to plain vector calculus/Einstein summation notation made it so much more approachable, and I feel primed to jump into a textbook on the topic and not get so lost in notation. Thanks for this. 🙇
Thanks, I’m glad you enjoyed the video! :) I agree, the vector calculus perspective is more approachable. There are some slightly more elegant ways of formulating these concepts with fiber bundles and differential geometry, but it requires more esoteric math.
This is probably the best breakdown of this topic I've seen. I'd love to see you cover SU2 Electroweak theory someday, and how the weak force manifests from it. I always find things like neutrino scattering through the weak force a bit confusing, as well as what weak isospin and hypercharge actually DO
I've only just finished my undergraduate degree, so my experience with field theories and relativistic QM is absolutely minimal. Still I decided to watch the video and I must say my mind was completely blown by Bringing A to Life in Six Ways. Seeing the EM field come to life purely due to mathematics and the original assumption is crazy. I also found the derivation of Gauss's law for magnetism quite funny, because in my introductory course this equation was considered a postulate of sorts by recognizing that there are no monopoles (or something of that sort) and knowing that a divergence-less field can be written as the rotation of a vector potential A. Now I know where that actually comes from. Amazing video.
If there's such a thing a heaven, you're the first one getting into it. Thank you for you invaluable contribution to humanity! Your video shows there is no upper bound on the quality of educational content.
Halfway through this video and I have to stop it because my mind is blown. Omg. This is crazy. Reminds me of a really good prof who explained an entire confusing course to me in 2 hours and suddenly it all made sense. You have a gift for making complex things understandable. Please keep making videos! (I would love to see you cover the component concepts in more detail too as I bet it would greatly add to my intuitive understanding.) Can't thank you enough...for explaining the entire universe to me.
Having watched most of this now, I can say that this is a great introduction to many concepts. I think this is the first time I'm starting to understand what a Lagrangian is. Which I may not have tried to understand explicitly before, but whenever I was looking up other more specific topics, people would keep bringing it up without explaining what it is and it made things very difficult. Having this introduction here is very great and I feel like it's a bit of a primer for jumping into even more complex topics that use a lot of these concepts however (Lagrangian, gauge symmetries, vanishing nudge factors). Before this, QFT was this daunting topic that I really had no way of probing since I had no idea what the mathematics were (and there's really no quick way to look them up). This video isn't about QFT and yet on top of its actual topic, I feel like I finally have a path towards it since the vague interaction terms or mass terms that people bring up every now and then now make sense in the context of the Lagrangian. I still don't really know much more about QFT than I did before, but I know what I need to do to start getting there and that's applying second quantisation (however that works).
How is it possible to explain such complex content so understandably?? I’m an undergraduate student and you’re making me understand graduate level physics. This is bananas.
Easily the best youtube video I have ever seen! Thank you for this video. It was exactly what I was looking for. While I have seen nearly everything in various courses in University, that's the problem. No one ever showed how it all connects together. U(1) symmetry leading to EM sounds very complex, but you managed to show in an extraordinarily structured way how at heart it is (conceptually) very simple. Looking forward to future videos!
This is the first time I've given someone a Super Thanks, but for this video, a like simply wasn't enough. Thank you for spending countless hours creating this. I'm only 19 and have wanted to explore quantum mechanics beyond Schrödinger for a while now. This was incredibly insightful and "easy" to follow. Thanks a lot!
I'm rewatching your entire catalogue so I can fully contextualise this video. I'm a PhD student in physics. I can feel a level of intuition building with QM fundamentals because of your videos that I've only ever felt with classical and statistical physics until now. I'm HYPED!!!
Just wanted you to know your are getting through. I have limited aptitude and work as a programmer, musician, and entrepreneur. I respond well to effective teaching and not so well to the rest. This enriches my understanding of the world and rejuvenates my admiration for rigor and tradition in science. I have not made this comment to any other presenter. I am sure that I speak for others when I say that this channel is appreciated.
I would be grateful if you could make videos of this type that are really complete and wonderful and in terms of time, the person can communicate with the subject. It is a wonderful method. Such works are permanent.
Damn, and I thought that the ~1 hour spin video was long. You're making extremely hard concepts intuitive and understandable, and I firmly believe that this is the best resource on the internet for both graduate and undergraduate physicists to fit what they've learned into intuition. I hope these videos keep coming, honestly your channel has become one of the biggest sources of my physics learning for me. I'll go become a "patron" now, and I suggest anyone who benefits from these videos to do the same, because the audience for a 200-minute Gauge QFT video is pretty limited for Richard to self-finance from, I suppose.
You are my favorite youtuber. Even though ive only finished my first year of college ever and theres a lot of academic jargon i dont understand, i still find physics and your videos incredibly fascinating!! Thank you for being inspirational
Wow! A video tuned just right to my level. Really appreciate videos at this level. Most are too simple and just words or for advanced grad students in quantum general relativistic theory
I was at a dinner party yesterday for Canadian Thanksgiving and I was telling them about how if I leave my TH-cam on autoplay for more than an hour invariably I will find myself back at the video about electromagnetism as gauge theory..... And here we are again 😂
I'm not well learned on math or physics, so I'm REALLY struggling to understand this video series, but I'm enjoying them immensely. Thank you! And I hope some day to be able to understand them better.
Thank you very much, finally a video that goes into the actual meat of quantum mechanics in a non trivial way. Very refreshing compared to all of the other content on YT that just tries to popularize the subject and more often than not completely fails to convey anything useful.
Omgg let's goo! I'm soo exited to watch this video with my mom (she was also a science student and has done electrical engineering) right after my exams finishes! I know this will be a really great video! This man is literally the best person in the world❤️✨️✨️ Love your channel Sir 🤍
Incredible video. You gave an explanation that appealed to basic intuition but you were not afraid to get into the math. Thank you so much for making this.
Wow, amazing video. I learned so much from it that I've been struggling to grasp from less in depth explanations found elsewhere. Most of the math was way over my head, but I could still follow your explanations of the math, and the visualizations of the equations are extremely helpful. Thank you for making this wonderful resource and I can't wait to see your next chapter.
Thank you so much. I had sworn off trying to learn particle physics because I felt like I was getting nowhere. Finally this has opened the door to understanding what people are talking about when they refer to gauge symmetry. Your calculations are very easy to follow and deriving Maxwell’s equations is extremely satisfying. It’s still deeply mysterious to me why U(1) symmetry is a thing but I’m convinced it creates EM!
Having learned EM from Feynman's lectures on physics, I have been over this ground from early days, but you have added a level of detail that is both new to me and very satisfying as well. It was also delightful to see professor Dirac on video, whom I had the good fortune to meet in life. The impression I get from your presentation is that "requiring" local gauge symmetry directly(!) gives rise to how (Dirac) charged particles interact. By the way, I have always been inordinately fond of the Dirac delta function, and I notice that you repeatedly took advantage of the Kronecker delta function (without explicitly mentioning it). Very elegant how it crops up, nicht wahr? ~~~~Arthur Ogawa
Just watched it once, loved every minute of being reminded of grad school. Going to watch it again to take it all in better :D Really really amazing presentation of such beautiful concepts and mechanisms.
Awesome video, had to rewatch all the earlier videos to refresh my memory and I have to say it really helped me digest this 3 hour journey (or whatever I was able to internalize of it :D). One question that popped to my mind is how would magnetic monopoles change things? The way that Maxwell's homogenous equations were derived seemed to clearly rule out any possibility of magnetic monopoles, whereas in my studies, where Maxwell's equations are just given and not derived one could easily formulate them again to add the existance of magnetic monopoles if they were ever found. And Paul Dirac himself proved that if magnetic monopoles do exist, electric charge is quantized. But now it seems that Dirac's own equation rules out even the possibility of magnetic monopoles?
2:38:00 At this point I want to point out that we derived Dirac equations by kind of taking square root of wave equation. And out of Dirac equation fiddling for the Gauge invariance, we derived maxwell equations, which would lead to the wave equation. We have proven 0 = 0. I like this video.
I got my physics degree 55 years ago and have been an engineer ever since. This video is a real tour de force and I thank you for it. It got me thinking about Dirac's question about the fine structure constant. My intuition says that our next level of understanding will be something along the lines of m=q (up to a constant of course). I have no idea what this means :)
Incredible!!! Best 1.5 hours I ever spent!!! Watched at 2x but the lessons were very clear. Thank You, Thank You, Thank You. Amazing that E&M comes out of the Dirac.
![The most beautiful equation in math, explained visually [Euler’s Formula]](http://i.ytimg.com/vi/f8CXG7dS-D0/mqdefault.jpg)
Hey everyone, thanks for checking out the video! :)
Timestamps:
0:00 Intro - "Why is Electromagnetism a Thing?"
14:24 Dirac Zero-Momentum Eigenstates
39:10 Local Phase Symmetry
52:07 A Curious Lagrangian
1:11:43 Bringing A to Life, in Six Ways
1:27:40 The Homogeneous Maxwell's Equations
1:39:25 The Faraday Tensor
1:47:49 F_munuF^munu
1:53:05 The Lagrangian of Quantum Electrodynamics
1:58:14 Inhomogeneous Maxwell's Equations, Part 1
2:11:07 ... Part 2, Solving Euler-Lagrange
2:31:10 ... Part 3, Unpacking the Inhomogeneous Maxwell's Equation(s)
2:37:55 Local Charge Conservation
2:42:20 Deriving the Lorentz Force Law
3:01:25 Miscellaneous Stuff & Mysteries
What type of energy gives particles their endless spin.
Very well explained. I always wanted to have a better understanding of SU(1), and I had a vague idea about the complex phase spinning around, but I could never put the fragments together. Now, thanks to your explanation, I have a better understanding of what is going on. I find it very satisfying that one can derive the electromagnetic field right out of pure mathematical reasoning about the Lagrangian density of the Dirac field. That part was pure magic. Thank you once again.
Hi Richard, this is all very interesting but highly theoretical. I was wondering if you can show theory vs experimental data in the most simple and boring of the chemical reactions, maybe one involving hydrogen. So is it possible to plug reactants into these theories and get the chemical products as an output? How is calculated all the process?
33:01 only half hr in but I will be back, life calls ya know
My dragon is yawning and turtle is moving her rocks about looking for food. She is making noises from her tank hence need to feed them. Love you work so far though.
I’ll be back.
Oh though I was Not watching just listening yet I was imagining my cube to follow along well not mine but the one I made. Amazingly enough it helped with the visualisation as you got to the flags I was already at the horizontal on a 3d plain
I wondered as we all do
How did I do that 😂
What cube I hear you all ask?
Drill out the dots on a dice
I made in from some hard wood a fallen piece from my possum tree 8cm x 8cm x 8cm
Not all lines line up yet one can see how to join 3 vectors in unison with out a break or connection with in the massless of mass of the whole with in and with out of the holes to visualise all the
Spin up or spin down and visualise your numbers of squiggles and invisible lines 😂
🙋🏻♂️👉🏼👁👁👈🏼 easy to see
Oh place a marble in 1 and shine a light in the centre of 3 and 5 in the dark to make a projection of ?
Well you see 😂
🙏🏼👍🏼
Sir I badly need your hydrogen 3 on fine structure. The way you relate mysterious concepts demistify them.
"Sorry babe, I cant go to sleep right now Richard Behiel just uploaded a 3 hour video on electromagnetism"
😂
Duuuude, I just set my phone to charge and just made the "mistake" of opening TH-cam 😂😂
It’s true 1:19am here
Liar u dont have a babe
Yay, got work in 4 hours 😂
Came for the physics. Stayed for the "pew pew pew" noises.
Hey Chris, thanks for stopping by! :)
For those who don’t know, this is the legendary eigenchris, who made the Spinors for Beginners video series. Check out his channel!
Yes sir
@@RichBehielThanks for the videos! You should consider making a video for the 4th Summer of Math Exposition, run by 3B1B, in 2025!
Eigenchris, Rich Behiel. We just need 3B1B in the collab and we have the holy grail of physics Videos
lol
Best 3h spent this year. Thanks for the shout-out, Richard. The most digestible introduction to Abelian gauge theory I've seen.
Thanks Curt, that means a lot coming from you! I’m glad you enjoyed the video :)
What would really rattle your gauges is knowing how non-zero vacuum expectation value kind of negates the idea of a "big-bang"..
Aka *_"How'd you like them Apples?"_*
🍏🍌😉
I was going to say. Richard's logical presentation was very easy to follow and I'd recommend it to anyone interested in understanding electromagnetism and gauge theory.
Love it when my fav physics TH-camrs support each other 🤩
I would like a definition of Gauge in Gauge field theories which is general. Field invariance, Local phase invariance, Electrostatic potential additive constants and Magnetic vector potential additive gradients without physical significance are good, but seem varied and suggest a general definition.
Do you know what you're doing? You are taking education to a whole new level, you are making a breakthrough in the methodology of education
Our modern technology gives us great potential for teaching each other. Video is like a blackboard that can come to life, and the great part is, once the video is done and uploaded, it takes of a life of its own and can teach people even when I’m doing other things. I love it, and I hope my videos can be a positive example for others to follow. I can’t take credit for the methodology though, 3Blue1Brown is the OG! His videos are what inspired me.
@@RichBehiel yea, I will follow you. You are doing really inspiring stuff
Usuallyy when I'm this excited for a 3 hour youtube video it's an unhinged video essay about a game I've never played.
I’m so pumped. I ❤ these videos. Learning is the new black 😂
have you seen down the rabbit holes 5 hour disambiguation of Eve Online
Such as?? Don't leave me hanging!
@starrmont4981 mandalore gaming and patrician tv.
I feel like this video is a triumph for humanity. You’re making this topic accessible for way more people than could previously grasp it. And it’s so beautiful!
Thanks for the kind comment, and I’m glad you enjoyed the video! :)
@@RichBehielThanks for sharing. Do you have plenty of time to travel.and for vacation in your job? Thanks very much.
When I was newer to gauge theory and first heard that "U(1) symmetry gives rise to E&M", it took me many painful hours to get to the bottom of it. This video does an amazing job organizing the story, and the visuals give me something to grab a hold of.
Thanks, that’s exactly the kind of comment I was hoping for! :) And yeah, I feel your pain 😅 I hope this video makes the topic a bit more accessible.
I kinda forgot many things about this topic/still a newb too... is gauge symmetry the same as U(1) symmetry?
@@ゾカリクゾIn the case of E&M yes. There are other gauge theories whose symmetry is described by some other Lie group. For example, Yang Mills theories have SU(n) (special unitary group) symmetry.
@@michaelmerkle297 oh, cool! thanks. i hope to be the one answering these questions one day
You make a student feel smart whilst they are learning, which is a truly uncommon and empowering feeling. With this topic you've changed my world view in 3 hours, I shall never be the same! Thank you!
Thanks for the kind comment, I’m very glad to hear that! :)
Having made a 2 hour video on theoretical physics with stock video/photos I paid for and text that Powerpoint animated as I recorded live in a sitting, I know for certain that what you achieved here is far beyond anything my patience is ready to produce. This is just absolutely fantastic.
If anyone wants clarity on sections I covered regarding electromagnetism, this is the video I will send them to from now on. There's no question about it. This is the best current summary I know of on TH-cam.
Thanks, I’m glad you enjoyed the video! :)
Yeah, honestly this one took a lot of effort to make 😅 It turned out to be way more work than I was expecting (I thought this would just be like an hour). But that’s ok, it was a very satisfying project.
The “words of encouragement” section at 13:49 actually made me cry. I didn’t realize how much I needed to hear that. Thank you 💗
why do you drop this the same day i finish my electrodynamics course😭😭😭😭
This answered a LOT of questions for me even though I don't have the mathematical background to follow 90% of it. It really just helps put things in order while contemplating the nature of reality. Thank you sir!
Thanks, I’m glad you found the video helpful! :)
Legend is back with straight 3 hours quality essay .... GREAT MATE
fell asleep with autoplay on. woke up with a nightmare about some major equation thing.
What this guy is basically saying ' for the laymen ' is that 1x1=2. =D Kidding aside, I grew up in a low income home. I wasn't able to go to college. Being 48, that doesn't mean I cant [try] to understand this. It is beautiful. 99% of what was said was over my head. But I'm a history nut, and love Newton, Durack, Feynman, Krauss, there are just to many to list. I love the way you explain things....which makes it sounds like I understood what you said in this video lol, but it's very unique to come across someone that teaches the way you do. I person can go to school and get a major, that DOES not mean they are good at explaining or teach said topic. I'm a guitar teacher and guitarist of over 34 years. So sir, I didn't understand pretty much any of this. BUT I want to learn. And you have a great way of talking / teaching. I know this video took you a long time to put together. Your right, we live in a time where a person like me can learn this stuff because of the resources we are able to obtain that you couldn't get back in the 90's unless you went to a university. Thank you.
I stumbled across your video on spinors a few months back, leading me to watch your full series on quantum physics. After doing some more research and developing a better intuition, I came back to your spinors video and suddenly everything just clicked. This has reinvigorated a curiosity for physics that I haven't felt in years! Thank you for creating that pedagogical masterpiece. Now I'll have to take notes on this one for the next couple days as well.
All I did over 4th of July weekend was sit inside by myself and try to unpack these equations. Best summer holiday. Thank you RB
I am honestly out of words, the amount of effort that was obviously put into the production, length of video and putting it out on the internet for free, just out of words
Thanks, I’m glad you appreciate the video! :) It was a lot of work, but it’s great to see that people are enjoying it and learning from it. All this positive feedback is very rewarding. And I do get a bit of revenue from ads and patron, not a huge amount but it’s a nice bonus.
Amazing!!!!!!!
I think I make this comment on just about every one of your videos, but I want to continue to express my thanks that someone is making videos that lean into the technical/math aspects of these topics.
Thanks for saying that! :) I’m glad there are people out there who appreciate the technical details. Even though it takes more work to learn the details, that’s where a lot of the beauty can be found.
@@RichBehiel I just finished Sean Carroll's recent book on QFT that is also trying to fill a gap in this space as well. Keep it up, Richard.
THANK YOU!
By far the best 3 learning hours I spent in a long while. As an electrical engineer I has always been curious about the deeper meaning of the quantum origins of electromagnetism. In the EM classes I had, the A vector was just a cryptic, obscure element no one could explain properly, but they always said it was very important and profound. From the mathematical perspecive, it made sense, but it seemed to me back then, it was just a variable trick. Your video is absolutely enligthening, clarifying the origin of A: it's the seed for EM itself.
I am a second year engineering student who's looking to specialize in physics. Your videos on Schrodinger's equation ignited my interest in quantum physics, and since then I have been spending much of my free time trying to teach myself. Now, just as I've finished Griffith's Introduction to ED and have been searching for a good follow up to learn about gauge theories, you release this. Moments of serendipity like this never cease to amaze me.
That’s great! Perfect timing :)
Laying out exactly how you get the E and B fields from the potential/ E-M field tensor, whilst seemingly obvious just minutes after you laid it out, was really impressive - which i think is the sign of a great teacher. Also im annoyed at how i think i will forever remember the way of the 6. Very clear and elucidating all around.
Great video so far, thanks for the awesome content.
the fact information like this is freely accessible gives me hope in humanity
The only time i can be awakend from my eternal slumber is whenever this guy uploads.
Good morning! :)
This channel is easily one of the best educational channels I've seen. The quality is off the charts, seriously. There are channels with 100x as many subs that put out worse content.
Thank you for this feast
Thanks for the kind words, and I’m glad you enjoyed the video! :)
Within the first 3 minutes you completely blew my mind about the concept of a "field". I've never really thought about it. I now understand space-time and gravity a bit better as well!
Thank you!!
As someone who has a bachelor's in physics and math but didn't go further, this video is perfect for me. It makes a complex graduate topic that is tough to self study a lot more accessible.
Thanks for the effort you make to create these videos. There is something truly beautiful about this topic.
I’m glad to hear that you enjoyed the video! Physics is beautiful :)
02:36:50 - it's beautiful. The longest lecture I've ever had, but interesting enough to keep me viewing to the end. I paused the video on each statement wich I have to checkout. And the part with derivatives is the easiest part. Man, this video is a lot of work.
Your videos continue to impress! Not being a math guy, this all goes way over my head. What I enjoy is reading the comments from others and am heartened to know there are so many curious and intelligent thinkers out there.
Thanks Dad, that means a lot! :) It’s amazing how positive the comments always are. People are excited to learn!
During my studies of Electrical Engineering, I was never under the impression that Maxwell's equations have such deeper meaning! Excellent video!!
Once again, Mr. Behiel, you've absolutely knocked it out of the park.
I am consistently stunned and blown away by the sheer quality and care of your presentation. I say this as someone who has passionately studied physics on my own for all of my life: This video, and all of your other works, are utterly invaluable.
I have been studying the topic of "the U(1) gauge theory of electromagnetism" for at least 4 years now, even to the point that I am currently diving deep into connections on principal bundles and covariant derivatives on vector bundles just so I can finally wrap my head around "just how all of this machinery really fits together", so it really says something that this video still actually taught me a lot. It's given me a lot to think about and ponder.
I love the way you give intuition-focused breakdowns for the different "moving parts" in both the equations, and the physical situations. The animations are incredible too. The way you blend the rigorous, algebraic expressions, with reference back to the "what is really going on in the physical universe, what does this mean", is truly invaluable for really extracting insight from these often opaque, yet inherently beautiful processes.
The way you illustrate the journey... the usual narrative from "demanding local phase invariance of the Dirac field", to "well, local phase transformations result in the addition of a spurious term to the Lagrangian", to "what if we added something that canceled that out?", and so on... this journey is one that has been presented many times before by great educators, but you show the path in its entirety, in a very lucid and well-composed way, and I am deeply grateful for that.
More amazingly insightful to me, is how you showed the way that the four-potential is "brought to life" by, apparently, the fact that that antisymmetric quantity (the Faraday tensor) is apparently "immune to" or "untouched by" local phase transformations. And thus, these "wigglings" are allowed to "scrunch up freely". I don't believe I have ever actually thought about it that way before. It will be very interesting for me to investigate later how this figures into my understanding of F as the curvature 2-form of the connection 1-form A on the principal U(1) bundle.
In short, this video is nothing short of a masterpiece. I wish I could go part-by-part and really get into just exactly what I love about it. For now, it will suffice to say that this video is an invaluable resource for people like me. Your lucid, detailed-yet very well-paced and friendly-leadings-through of these physical and mathematical notions, vividly exposing the beauty inherent in the "mathematical machinery" of physics, are truly a gift.
Thank you for this kindness.
Your work is helping people.
I hope you have a wonderful night and/or day.
Wow, thanks for the amazing comment! :)
I’m very glad to hear all that, and I really appreciate your kind words, that’s very encouraging. I’m glad you enjoyed the video, and I can tell that you’re someone who has studied this topic in depth, so that really means a lot.
@@RichBehiel Absolutely! I've always been fascinated by electromagnetism as long as I can remember. I feel very lucky that I've been able to slowly work my way up to "the real stuff", above the mere classical "vector calculus" formulation. This is part of that!
I am deeply grateful for the part you've played in my never-ending quest for deeper insight. ^^
Wow, this is amazing. I’m a pure math guy, and there’s a reason I skipped E&M but took classical, quantum, and statistical mechanics at university. This was an excellent derivation, thank you.
The one thing I still have to wrap my head around is the fact that the “coupling” of fields seems to be asymmetrical when we minimize the action?
I hope that this was a presentation choice for the video rather than a mathematical choice. Meaning if you look at the full QED Lagrangian without a priori knowing what psi is, but having the same initial condition, then one can first solve for psi as an electron and then solve for the photon field with psi fixed as was done in the video.
Edit: I am definitely being dumb. I see the derivation is independent of psi and the dependence is the current J. It is hard to be locked in for 3 hours straight!
Again, this was amazing. Thank you!
Probably the most anticipated/happiest youtube upload of my life, I have been researching all about EM as a gauge theory since the spinor video (I was even reading about it yesterday night!). Can't wait to watch this 3 times! Your content is invaluable, thank you so much
I’m glad to hear that! Thanks for the kind comment :)
Literally about to write an essay on how gauge fields describe interactions - ABSOLUTE LEGEND 💯
Idk why but 1:07 the fact that the blue particles are positive and the red ones negative makes me uncomfortable
Rich. Thank you for this! The tale of how electromagnetism emerges naturally from the local phase symmetry of Dirac’s equation has to strike awe in one’s sensibility. The magic can only be told using the language of mathematics. You have done a magnificent job.
Thanks, I’m glad you enjoyed the video! :) I agree, the beauty of the math is awe-inspiring.
Coming here as a rising senior studying Electrical Engineering, I was not expecting to be out of my depth within the first 10 minutes 😂
Much love! I can’t wait to revisit this after reading up on that textbook you mentioned and watching your other videos!
Lol, coming here as a 2nd year electrical apprentice who last touched physics in any rigorous way in AP physics like 15 years ago, but also having a huge ego, I didn't listen when he told me I'd be out of my depth in first 30 seconds.
I've given it half an hour of what largely sounds like a foreign language before throwing in the towel, ordering that textbook, and consigning myself to relearning calculus, among many other things. Ouch.
When I took a QFT class we derived F in class and then got deriving the maxwell equations as homework. It felt really weird. At this point in a physics degree euler lagrange and index raising are second nature. So you do the symbolic manipulation dance you're so used to, not really thinking about anything and pop! there is your entire theory of classical electromagnetism. It's like magic!
There are 2 distinct other moments I remember as feeling the same:
1 - When you first do rot rot B and see a wave pop out
2 - Taking dirac or klein-gordon in rindler or schwarzschild metric, expanding to get the form of a schrödinger equation and finding + m*g*h + O(1/c2) at the end of the potential.
Btw this video was amazing! I didn't expect to stay for the full 3h, but you've really managed to make this fun even for people who are reliving rather than experiencing the intense joy of seeing all of this play out. My only comment would be that it'd be nice if you wrote out the metric tensor and sums explicitly. I think a lot of "magic" regarding the co and contravariant things has happened here that make being very comfortable with SR a requirement here where more explicit notation would probably make things easier for people who only have some familiarity rather than full immersion in SR. Also, writing out the gs explicitly makes it much easier to see how gravity will end up effecting things. The sum symbol has less of a pedagogical justification and is just something I've seen many people get confused by where a simple symbol would clear things up.
I have been looking for this video for a very long time… I didn’t know it existed, but the content you were covering here and how you’re explaining it is unlocking a lot of doors in my mind on these topics
Great video. Dark background is a huge plus makes it easier to learn
You made and uploaded a 3h video, which is basically a full lecture. Just that shows how amazing this channel is (also your videos are amazing lol)
It's not a full lecture... It's half a course!!!!
Just before I woke up near the end of this video, I was having a frustrating dream about being "taught" advanced theoretical physics by a fast-talking professor who was oblivious to how lost the class was. I was the only one even bothering to TRY taking notes, but I just couldn't write fast enough. I kept trying to ask questions despite knowing that the answer wouldn't actually make me feel less clueless. But he wouldn't stop speed-lecturing, except for once or twice, when I could finally get a question in. But each time, he barely acknowledged me, and just kept going without answering!
The one thing I understood was his in-depth explanation of scalars... except I already knew all of that! And even more maddening was that it was in response to another student's expression of confusion! He didn't even have to ask a question!
Gonna go back and actually watch this for real. Maybe I'll have a shot at comprehension without the handicap of being unconscious.
EDIT: Nope.
For those people that are thinking about watching this video but dont wanna commit because its 3 hours long. It is super worth it. Really great video, it doesnt even feel like 3 hours dont worry :)
I am about to get a Master's degree and am applying for a PhD in physics. I have studied QFT for a few years now.
While none of the information here was new, of course, the explanation is tiptop. It seems like the perfect thing for someone getting a bachelor who is thinking of getting into QFT for their masters, a perfect balance of handwaving and rigorousness.
10/10 no comments
My word...
As an amatuer AF math hobby enthusiast, this video was both thrilling to watch, and also made in such a way that my feeble brain was able to absorb it and gain great insights.
Absolutely wonderful job good sir!
Thanks, I’m glad you enjoyed the video! :)
Imagine never hearing about electromagnetism and this is how you're introduced to it
Love the relatable “you can do it” style of presentation and the amazing graphics. Doing the algebra in public is rare for TH-cam but combining it with the geometry from the graphics is just what students need to connect the dots and develop intuition.
While you’re driving the station wagon through the Grand Canyon of U(1) gauge invariance, it might be nice to take a side jaunt into Diracs magnetic monopole solution, with Wilson Loops and homotopy classes. Another fun side jaunt might be an intro to the path integral formulation of QM ala Feynman’s QED the A Strange Theory of Light and matter. As with most summer vacations it’s hard to say if the station wagon will be roadworthy next year. Anyways, thanks for your content. 😊
Thanks for the kind comment :) I’d like to do a video on Dirac’s magnetic monopoles one of these days, as well as the other things you mentioned. There are so many fascinating ideas in physics.
"every pseudovector is secretly a plane" *geometric algebra foreshadowing!!!*
Even though I’ve just started my upper div courses, I understood a good chunk of this and I love it. This math is a thing of beauty.
This is an awesome video! If you're interested, you should experiment with using OKLCH instead of HSL when representing phase using hue. You might notice that on a computer screen, pure blue appears darker to the eye than pure green. This is because the "perceived lightness" of a color varies by hue in HSL. This is what makes spinors look as if they're flashing. In OKLCH, the "lightness" parameter corresponds to perceived lightness, so panning through hue in OKLCH will fix the flashing. The tradeoff is that colors will appear somewhat washed out because using exclusively pure colors doesn't work for perceptual uniformity.
this kind of stuff should be put in universities
I've been looking forward to this. Will save it for later, but this series has been very helpful in the technical side of my journey to understand QM/QFT.
Seated and ready! That you would educate us this deeply is amazing. Thank you.
Thanks for watching! :)
This is an incredibly good video. I watched it start to finish. Sticking to plain vector calculus/Einstein summation notation made it so much more approachable, and I feel primed to jump into a textbook on the topic and not get so lost in notation. Thanks for this. 🙇
Thanks, I’m glad you enjoyed the video! :) I agree, the vector calculus perspective is more approachable. There are some slightly more elegant ways of formulating these concepts with fiber bundles and differential geometry, but it requires more esoteric math.
This is probably the best breakdown of this topic I've seen.
I'd love to see you cover SU2 Electroweak theory someday, and how the weak force manifests from it. I always find things like neutrino scattering through the weak force a bit confusing, as well as what weak isospin and hypercharge actually DO
I've only just finished my undergraduate degree, so my experience with field theories and relativistic QM is absolutely minimal. Still I decided to watch the video and I must say my mind was completely blown by Bringing A to Life in Six Ways. Seeing the EM field come to life purely due to mathematics and the original assumption is crazy.
I also found the derivation of Gauss's law for magnetism quite funny, because in my introductory course this equation was considered a postulate of sorts by recognizing that there are no monopoles (or something of that sort) and knowing that a divergence-less field can be written as the rotation of a vector potential A. Now I know where that actually comes from.
Amazing video.
❤❤❤❤❤❤❤❤❤❤❤
If there's such a thing a heaven, you're the first one getting into it. Thank you for you invaluable contribution to humanity! Your video shows there is no upper bound on the quality of educational content.
A comprehensive and technical explanation of (relativity through) EMF Gauge Theory. We have our finger right on the button. Thank you Richard.
Halfway through this video and I have to stop it because my mind is blown. Omg. This is crazy. Reminds me of a really good prof who explained an entire confusing course to me in 2 hours and suddenly it all made sense. You have a gift for making complex things understandable. Please keep making videos! (I would love to see you cover the component concepts in more detail too as I bet it would greatly add to my intuitive understanding.) Can't thank you enough...for explaining the entire universe to me.
I'm absolutely in love with this video
Literally one of the only youtube videos I actually keep coming back to
Thanks, I’m glad you love the video! :)
Having watched most of this now, I can say that this is a great introduction to many concepts. I think this is the first time I'm starting to understand what a Lagrangian is. Which I may not have tried to understand explicitly before, but whenever I was looking up other more specific topics, people would keep bringing it up without explaining what it is and it made things very difficult. Having this introduction here is very great and I feel like it's a bit of a primer for jumping into even more complex topics that use a lot of these concepts however (Lagrangian, gauge symmetries, vanishing nudge factors).
Before this, QFT was this daunting topic that I really had no way of probing since I had no idea what the mathematics were (and there's really no quick way to look them up). This video isn't about QFT and yet on top of its actual topic, I feel like I finally have a path towards it since the vague interaction terms or mass terms that people bring up every now and then now make sense in the context of the Lagrangian. I still don't really know much more about QFT than I did before, but I know what I need to do to start getting there and that's applying second quantisation (however that works).
How is it possible to explain such complex content so understandably?? I’m an undergraduate student and you’re making me understand graduate level physics. This is bananas.
Easily the best youtube video I have ever seen! Thank you for this video. It was exactly what I was looking for.
While I have seen nearly everything in various courses in University, that's the problem. No one ever showed how it all connects together.
U(1) symmetry leading to EM sounds very complex, but you managed to show in an extraordinarily structured way how at heart it is (conceptually) very simple.
Looking forward to future videos!
This is the first time I've given someone a Super Thanks, but for this video, a like simply wasn't enough. Thank you for spending countless hours creating this. I'm only 19 and have wanted to explore quantum mechanics beyond Schrödinger for a while now. This was incredibly insightful and "easy" to follow. Thanks a lot!
Thanks for the Super Thanks! :) I’m glad you enjoyed the video and found it insightful.
What does it mean if I fell asleep to Rhett and Link best moments for 1 hour, and woke up at 2:59:12 of this video
Awesome work! 🎉 Thank you 🙏 New people to the topic will never realise how hard it was to understand these concepts in the past.
I'm rewatching your entire catalogue so I can fully contextualise this video. I'm a PhD student in physics. I can feel a level of intuition building with QM fundamentals because of your videos that I've only ever felt with classical and statistical physics until now. I'm HYPED!!!
That’s great, I’m glad to hear that! :)
This video is absolutely incredible. After an undergraduate particle phys class this is an incredible explanation of what I’ve seen
Just wanted you to know your are getting through. I have limited aptitude and work as a programmer, musician, and entrepreneur. I respond well to effective teaching and not so well to the rest. This enriches my understanding of the world and rejuvenates my admiration for rigor and tradition in science. I have not made this comment to any other presenter. I am sure that I speak for others when I say that this channel is appreciated.
Thanks, that means a lot! :)
I would be grateful if you could make videos of this type that are really complete and wonderful and in terms of time, the person can communicate with the subject. It is a wonderful method. Such works are permanent.
Who else woke up to this in the middle of the night
Damn, and I thought that the ~1 hour spin video was long.
You're making extremely hard concepts intuitive and understandable, and I firmly believe that this is the best resource on the internet for both graduate and undergraduate physicists to fit what they've learned into intuition. I hope these videos keep coming, honestly your channel has become one of the biggest sources of my physics learning for me.
I'll go become a "patron" now, and I suggest anyone who benefits from these videos to do the same, because the audience for a 200-minute Gauge QFT video is pretty limited for Richard to self-finance from, I suppose.
Thanks, that means a lot! :) I’m glad you’re enjoying the videos.
You are my favorite youtuber. Even though ive only finished my first year of college ever and theres a lot of academic jargon i dont understand, i still find physics and your videos incredibly fascinating!! Thank you for being inspirational
Thanks for the kind comment! :) I’m glad you’re enjoying the videos.
Wow! A video tuned just right to my level. Really appreciate videos at this level. Most are too simple and just words or for advanced grad students in quantum general relativistic theory
I was at a dinner party yesterday for Canadian Thanksgiving and I was telling them about how if I leave my TH-cam on autoplay for more than an hour invariably I will find myself back at the video about electromagnetism as gauge theory..... And here we are again 😂
Welcome back! 😂
same here but it always lands on the "Fall of Civilizations" channel 🫤
it's a good channel and all but wth?
I'm not well learned on math or physics, so I'm REALLY struggling to understand this video series, but I'm enjoying them immensely. Thank you! And I hope some day to be able to understand them better.
Thank you very much, finally a video that goes into the actual meat of quantum mechanics in a non trivial way. Very refreshing compared to all of the other content on YT that just tries to popularize the subject and more often than not completely fails to convey anything useful.
Thanks for the kind comment, and I’m glad you enjoyed the video! :)
Omgg let's goo!
I'm soo exited to watch this video with my mom (she was also a science student and has done electrical engineering) right after my exams finishes!
I know this will be a really great video!
This man is literally the best person in the world❤️✨️✨️
Love your channel Sir 🤍
Thanks for the very kind comment! I hope you and your mom enjoy the video :)
Awesome job!
Makes me studying all of this again before deep diving into the QFT rabbithole
It's so weird how as I'm now getting interested with gauge theory, you upload this banger
Incredible video. You gave an explanation that appealed to basic intuition but you were not afraid to get into the math. Thank you so much for making this.
Thanks, I’m glad you enjoyed it! :)
Wow, amazing video. I learned so much from it that I've been struggling to grasp from less in depth explanations found elsewhere. Most of the math was way over my head, but I could still follow your explanations of the math, and the visualizations of the equations are extremely helpful. Thank you for making this wonderful resource and I can't wait to see your next chapter.
Thanks for the kind comment, and I’m glad you learned a lot from the video! :)
This is simply awesome. Finally, after years of looking for a complete dissertation, there it is! Love this
been preparing for this video by watching and re-watching all of your other quantum physics videos!
Thank you Richard. Great contribution! Also, love seeing your excitement for the math and the connections to our physical world
This came on while I slept and I dreamed it was someone explaining time travel.
Just watched it for the 2nd time and it just got better. Please, make a video like this for the arisal of strong force and QCD. It would be epic!
Thank you so much. I had sworn off trying to learn particle physics because I felt like I was getting nowhere. Finally this has opened the door to understanding what people are talking about when they refer to gauge symmetry. Your calculations are very easy to follow and deriving Maxwell’s equations is extremely satisfying.
It’s still deeply mysterious to me why U(1) symmetry is a thing but I’m convinced it creates EM!
Having learned EM from Feynman's lectures on physics, I have been over this ground from early days, but you have added a level of detail that is both new to me and very satisfying as well. It was also delightful to see professor Dirac on video, whom I had the good fortune to meet in life.
The impression I get from your presentation is that "requiring" local gauge symmetry directly(!) gives rise to how (Dirac) charged particles interact.
By the way, I have always been inordinately fond of the Dirac delta function, and I notice that you repeatedly took advantage of the Kronecker delta function (without explicitly mentioning it). Very elegant how it crops up, nicht wahr? ~~~~Arthur Ogawa
Just watched it once, loved every minute of being reminded of grad school. Going to watch it again to take it all in better :D Really really amazing presentation of such beautiful concepts and mechanisms.
Best way to start off the week. Bless you!
Awesome video, had to rewatch all the earlier videos to refresh my memory and I have to say it really helped me digest this 3 hour journey (or whatever I was able to internalize of it :D).
One question that popped to my mind is how would magnetic monopoles change things? The way that Maxwell's homogenous equations were derived seemed to clearly rule out any possibility of magnetic monopoles, whereas in my studies, where Maxwell's equations are just given and not derived one could easily formulate them again to add the existance of magnetic monopoles if they were ever found. And Paul Dirac himself proved that if magnetic monopoles do exist, electric charge is quantized. But now it seems that Dirac's own equation rules out even the possibility of magnetic monopoles?
2:38:00 At this point I want to point out that we derived Dirac equations by kind of taking square root of wave equation. And out of Dirac equation fiddling for the Gauge invariance, we derived maxwell equations, which would lead to the wave equation. We have proven 0 = 0. I like this video.
I got my physics degree 55 years ago and have been an engineer ever since. This video is a real tour de force and I thank you for it.
It got me thinking about Dirac's question about the fine structure constant. My intuition says that our next level of understanding will be something along the lines of m=q (up to a constant of course). I have no idea what this means :)
Incredible!!! Best 1.5 hours I ever spent!!! Watched at 2x but the lessons were very clear. Thank You, Thank You, Thank You. Amazing that E&M comes out of the Dirac.
That’s great, I’m very glad to hear that you enjoyed the video. Thanks for watching! :)
I'll be waiting for that future electroweak video, even tho I won't understand a thing about it!
The “Activity” is such a good word for the Lagrangian density! I totally support using it
I just woke up, it’s 3:37 am and see formulas I’ve never seen before and will be ☠️
Can’t wait for the quantum chromodynamics video😈