Hi friends, thank you so much for watching! As always, please let me know what topics you'd like me to cover in the future, and hit that subscribe button for more fun physics content. I really appreciate your support :)
I think it would be great to explain the contexts, the backgrounds, or the puzzles of nature they were trying to unlock, when great scientists like Maxwell, Galileo, Newton, Einstein, Heisenberg and others made their discoveries. I think that would complete the picture. Many books just start with the theory or concept directly, which makes it difficult to connect the dots...
Space Time Algebra. If you want to research it, there are Clifford Algebras. That gives you geometric algebras. They are the interesting area because scalars, complex numbers, quaternions, Pauli and Dirac algebras are just sub algebras. Stokes' theorem, gauss's law all subsumed too. So a STA is a 3 dimensional space with an extra time dimension. The basis vectors for distances, square to -1. The time squares to 1. [you can swap]. For Maxwell, they interesting bit is when you take two vectors and multiply them using the geometric product you get two bits to the answer. a b where a and b as vectors becomes a.b [standard dot product] and a wedge b where the a wedge b is an oriented area. A lot of tensors, differental forms etc, also get subsumed. The bit that I think is very interesting is that what's going on is not abstract, it comes across as a far more physical representation of the world, and because its so simple, its even more beautiful. @@bjornfeuerbacher5514
Parth.. you're awesome Brother. As a physics teacher, I show your videos to my students. You explanations are visual, clear and simplified. Kudos to you as well as gratitude from me and my students. 😊
Parth, thank you for a great and easily understood explanation! Your addition of 3 to all of the numbers reminded me of a gauge invariance analogy I've used a couple of times: When you are paddling a boat at the surface of a lake it doesn't matter whether the lake is 10 meters deep or 1000 meters deep - that is, your boat paddling is “gauge invariant” for the depth of the lake. As long as your wave activity remains confined to near the surface the depth of the lake doesn't matter. Yet that depth is real in terms of the energy it contains, e.g., if the lake is drained to a lower level. Such a deep lake storing lots of energy corresponds to a high electric field and energizes an entire region of space in which smaller-scale electromagnetic activity is occurring.
@@ParthGChannel thank you, and you are most welcome. But seriously, I think it was more your analogy when you added an equal electrical potential to all points across the surface. All I did was translate that description into the classic water-level analogy of electric potential. :)
@@ParthGChannelalso, thanks for bringing this one up. As with your Dirac delta function video a few years back, this video made me question my analogy more carefully. The question is this: Is it _really_ correct to say that lake depth is like a mathematical gauge invariance since it's always only approximate? Obviously, if the paddle is big enough and moved quickly enough, the analogy can break down in shallow water due to interactions of the paddle waves with the ocean bottom. But that's also where it gets interesting regarding the _physics_ meaning of gauge invariance, which should always be distinguished from the overly simplified assumptions of formula-only gauge invariance. Take electric potential: You can raise it arbitrarily high within a hollow metal sphere, and as with motion in special relativity, there are no internal tests you can do to prove that the potential is there. That is truly amazing and one of the deep features of physics, one just as profound as special relativity, even if less widely known. But here's the catch: _You cannot make such a sphere infinitely large,_ and thus can never create an electrostatic gauge invariance that is any more "perfect" than the lake example. For example, suppose someone inside a large, charged sphere creates a sufficiently powerful electromagnetic wave. In that case, that wave will impact the sphere surface just as reliably as a large enough paddle wave can impact the bottom of the lake. Significantly, it also takes more and more energy to create the region inside the sphere as the sphere gets larger. This is comparable to the need to use energy to accelerate an object to high velocity. The physics _within_ the object is absolutely invariant, but its acceleration history is _not_ relativistic because it involves a historically irreversible transfer of energy. So again, thanks. As usual, you inspire me to look more closely and critically at my assumptions. This insight on the need for energy-aware, finite-scope gauge maths to replace overly simplified assumptions about how reality works is closely akin to what I'm working on now for special relativity, which has fascinatingly similar problems. (More bluntly: _Every_ mention of x'y'z't' in Einstein's 1905 papers is mathematically incorrect because it assumes infinitely fast, infinitely low-energy-cost creation of a meaningful coordinates system that, in reality, usually never comes into existence. Therein lies the real resolution of the twin paradox.)
Hi, Parth: I've published this dialog as an Apabistia Note dated December 21, 2023. Although I switched some time ago to a far more powerful and less paradox-prone finite-scope, local-only interpretation of Einstein's severely oversimplified x'y'z't' approximation of how new coordinate systems form, it wasn't until seeing your video that I realized that this new model is a gauge symmetry of momentum energy. That's well worth capturing as a Note. I'll try putting a full reference with a link in reply to this one, but that may or may not work, depending on your settings.
Wait, so this video is about Hermann Weyl's contribution or just plain ordinary explanation of E and B field and its corresponding scalar and vector potential
The Moment you started to do your little plug for subscribing to the channel, I realized how valuable you had made those 4 min for me already. I clicked all the things, you deserve it! The way you explained curl and gradient instantly made it click for me, thanks man!
This was very well structured and equally well explained. Thanks for taking the time to make this! Although, the youtube algo's a little scary, LOL. Just started reading his Theory of Groups and QM a couple weeks back.
Last great universalist of the 19th century? Weyl's work on the invariants of groups appeared in the late 1930s. Since your statement appears at 0:25, it makes me reluctant to listen to this video. Please don't be so sloppy. It is not just that there is a date error: his work on Groups and Quantum Mechanics cannot appear in the late 19th century, because QM only developed in 1920s.
According to the auto-generated subtitles, he said, "Herman has been compared with the last great Universal mathematicians of the 19th century by his colleagues". To compare someone with someone else doesn't imply that they lived at the same time.
Very well made video, good content and explanation. My E&M professor kinda skipped over all that gauge stuff and left us scratching our heads at why we were allowed to do that so this is the first actual explanation of why I've seen. A note though: this is the first video of yours I've seen and i was strongly avoiding it due to the "clickbaity" nature of the title. Whenever i see things like "... changed physics forever" or "physics will never be the same" or something like that it turns me off cause there's just so many people out here trying to trick people who have no formal education into feeling like they received some profound knowledge that really doesn't mean anything and that the creator will just package up and ship out to them over and over again at least once a week. You're not that, but the title could've fooled me lmao. Had the title been something more addressed to the material like "Herman Weyl and Gauge Invariance" i would've clicked on it at light speed. You could even keep the flashy title and the information like, "The guy who made physics theories redundant - Herman Weyl and gauge invariance". To end, i understand. The algorithm is a fickle thing, and i really do appreciate you making this very good video, and i do understand I'm probably in the infinitesimal minority here. And i love you, and i hope you're doing well.
Also i really hope you read this. I've just looked back through your catalogue and i do think the vast majority of your titles are well done, catchy, interesting, and combined with the thumbnail usually convey the topic sufficiently for me to not feel bated. So don't take this as like "i hate every title, you're tricking people" or anything like that. I also realize I've seen q couple of your videos before and i really like your content. As someone who basically continually considers starting a channel just to help solidify concepts in my own head through producing videos on them, you're doing gods work. While i still do recommend putting more of the topic in the title so you'll come up in searches on the topic (i search lots of things for good explanations, i'd certainly watch one of yours if it showed up) , i guess in a way this catchy title has brought me back to you. It makes me sad that youtube cultivates this environment but makes me very happy I've found you again. Have subscribed. Love the content and the catalogue.
during the graduation i only found books with lenghty derivations without such a deep physical understanding.now i understand the meaning of these terms.thank you sir.
Oh this is so interesting. When I studied classical field theory gauge invariance took such a central spot, didnt know it was discovered only decades after SRT
I've always thought Maxwell's equations, leading to an absolute value for c independent of observer, were one of the main motivations for special relativity in the first place.
@KaiHenningsen This is true, Maxwell equations -> heaviside rewritten Maxwell equations -> Einsteins Special relativity -> Einstein general relativity -> Weyl's rewrite of Maxwell + Einstein
@@KaiHenningsenI don’t think maxwell said it would be invariant with respect to observer. Like if the observer were moving towards the wave perhaps Maxwell would have done usual Newtonian relative speeds.
extended electrodynamics has the arbitrary gauge transformations undone and now the equations have terms of and predict scalar waves, scalar long. waves, and curl free gradient driven current densities, they have experimentally verified it.
Soooo that's where potential difference comes from? I knew it's difference between two different points, but I didn't that it's difference between ANY two points of an electric field and is NOT fixed for the same electric field (my inference from the video). Learn something new every day. Well-articulated explanation & simple yet effective visual cues to the boot. You've you a rare gift of explaining this in easy to digest manner.
Hello sir, Plz make tha video on tensor more specifically covariant and contravariant, because is make confusion when use to covariant and when use the contravariant and when use both at one time. Plz make the video and also refer the book for learning the tensor calculus.
0:30 - Umm, contrary to a popular misconception, Einstein didn't arrive to his Special theory of relativity from Michelson-Morley experiment, but from considering electromagnetism. Just saying... Nice, clear little presentation.
So, the electric field is gauge-invariant to any potential field with all elements being equal, since the gradient is 0 everywhere for such a field. That's a fancier way of saying that the reference point in a potential field can be chosen arbitrarily.
To summarise "the gradient of the curl of a scalar field" ... Something like a temperature field would be a scalar field and because the temperature does not have a direction it does not rotate. So, rotation is always zero therefore the slope is always zero.
These light-weight physics info snippets take my fear away to go deeper into these topics. Compare the rather intimidating feeling you get when skimming over the Wikipedia article on Gauge theory compared to the intuitive, interested feeling you get here. That certainly makes it easier. And let's just acknowledge that at least for some, having a teacher being as stunningly handsome as Parth simply is, also doesn't hurt 😘.
Is the reason that the curl of the gradient of a scalar field always is zero that you take the cross product of nabla with itself, and a vector crossed with itself is always zero?
@@DrDeuteron No, he did not get a Nobel prize. He took a chair in mathematics at ETH in Zürich in 1912, at the time Einstein and Schrödinger held chairs there in theoretical physics. His reputation probably was the magnet that drew John von Neumann study under him in Zürich. Though his accomplishments would well have warranted a physics Nobel, it's probably because he was primarily a mathematician that he wasn't awarded one. Weyl would have deserved the Fields medal for mathematics, however when it was first awarded in 1936 he was well past 40 ― the cut off age for Fields laureates. He spent almost all of his working life in Zürich until his death there in 1955 at the age of 70.
@@DrDeuteron Understandable. Wigner was fellow (Hungarian) student of Leo Szilard and Janos von Neumann and also moved within and intersected with that erstwhile clique of central European physicists/mathematicians whose ilk operated in the Meccas, Medinas, Jerusalems, Antiochs and Constantinoples of the physics and maths world at the time: Göttingen, Zürich, Berlin, Copenhagen & Cambridge...
B is not the actual physical field. It is a pseudovector, not a vector. Maxwell's equations do not have "handedness" or are parity invariant. The use of curl is a convenience, but all physical consequences of choosing the "left hand rule" or the "right hand rule" in applying the curl or cross product are cancelled out. For example, the cross-product in the Lorentz force law that applies the magnetic field to get the force on a charge and the curl operator used to calculate that magnetic field, as long as both have the same handedness, the handedness doesn't matter. B = curl A is closer to the actual physical field. That's because the combination of vector and scalar potential is Lorentz invariant. These transform like a four-vector. On the other hand, the electric and magnetic field are in the antisymmetric Electromagnetic Tensor and are not Lorentz invariant. Electric and magnetic fields are a convenience used when formulating the constitutive relations of physical materials when relativistic considerations (for example, for materials in reference frames traveling near the speed of light) are not important, and so Lorentz invariance is not so important. This may seem like a pedantic consideration but it's actually quite important when you consider gauge invariance and the physical realization of calculated quantities.
As far as I know, you "simply" use the energy momentum tensor from electrodynamics and plug it into the right hand side of Einstein's equation of General Relativity.
Very interesting. For mathematical analysis, Robert Bartle, Elements of Real Analysis is brilliant - but please note 1st Edition only is best, 1964. That's where you learn the real maths, but note a lot of the work has to be done yourself, its a kind of unstated Moore Method.
Paul Dirac tried the same for describing the electron. But the need of mathematical tricks (renormalization) let him doubt the correctness of his QFT till the end of his life.
I cratered badly in my EM fields classes 40 years ago, and I think part of my difficulty was that the symbology was ALSO redundant. Really, what freaking genius decided to use the same symbol for gradient and curl, with only the cross product symbol to show what's going on?
Haha great point! I think it was because if you thought of del as a vector containing partial derivatives (d/dx, d/dy, d/dz), you could get grad by 'applying' del to a scalar, div by taking the dot product between del and a vector, and curl by taking the cross product. However you're totally right about this confusing when learning about it from a pure physics perspective!
Thank you very much for the video. A question about the reality of the potential. Does Aharonov-Bohm effect make magnetic potential "real"? How would you describe this effect?
The Aharonov-Bohm effect says that the only measurable thing is an integral of the magnetic vector potential along a close path - and that integral is _invariant_ under a gauge transformation. So no, this effect does not really make the potential "real".
Hey parth, would you be willing to make a video on how to know physics? Like is it memorization, is it application of facts , is it finding new frame of reference .How to study physics in short, what method do you use ?
I'm not sure why you included that warning there about the "Intuitive Description of Gauge Invariance" not capturing all the intricacies.... You just described a specific example ; all the intricacies relevant for that specific situation are covered, as far as I can tell. The general concept is a pretty simple generalization from here.
I was expecting more background about Hermann Weyl and his contributions. You could have contrasted the field and potential formulation of the Maxwell equations. Instead you focus on the vector differential operators. However this is too short for anyone not familiar with them and far too basic for anyone how is actually interested in the potentials formulation for the Maxwell equations. Also the Weyl gauge is not commonly used.
at 3:58/10:28 , you said that that "the curl of gradient of a scalar field is zero " has nothing to do with the original scalar field is problematic. If the curl of the gradient of a scalar field (∇φ) is zero, it means that the vector field formed by taking the gradient of the scalar field (∇φ) is irrotational or curl-free. However, this does not provide any information about the scalar field φ itself.
I'm way too old to understand the math, but as I understand it, gauge invariance played a big role in discovering the Higgs Boson, a "massive scalar boson" and currently the God particle.
Easy enough concept to grasp... And I get the idea is that it makes the maths easier, but... I'm still left at what's the point? Can you show us a simple example of this at work where its beneficial?
Did he make most physics theories redundant ChatGPT Hermann Weyl did not make most physics theories redundant. Instead, he contributed to the development and understanding of various theories, particularly in the field of quantum mechanics. Weyl's work focused on providing mathematical foundations for quantum mechanics, and he made significant contributions to the theory of groups and symmetry, which had applications in quantum physics. While Weyl's ideas were influential, they did not render existing physics theories redundant; rather, they enriched and deepened our understanding of fundamental principles in physics. The evolution of physics involves building upon and refining existing theories rather than completely discarding them.
Hi bro 👋 , Thank for your as most best explanation to us ❤. As I am science student I understood it clearly. And because of your awesome explanation 😊❤. I request ❤ you bro to make the videos in another language like Hindi. Because it helps lot of us and specially who are not belongs to science field ❤. I hope you make the videos soon in Hindi 😊😊😊😊😊. Thank you for reading my comment 🙏🙏🙏. If you agree ❤❤ for my request give like 👍👍👍 to my comment 👇👇👇.
I thought it was dirac that combined special relativity with electroweak (electromagnetism + weak nuclear) theory.. I find the history uninteresting, but the theories themselves fascinating. I guess I am biased to forget.
I would call myself some waht intelligent, but with those abstract mathematics in a second language I just understand 30% of it! 🤯 My strength is more in causal coherences, not in algebra! 😅 Still very interesting! 👍
You shouldn't say that combining maxwells and Einsteins theory was his biggest contribution... Because it wasn't... He tried it and failed because experimental data wasn't agreeing with his model... He was a brilliant mathematician... But there is a reason why we are unable to combine all four forces
ever since oliver heaviside, in the 1890s, we don't talk about 'nabla' unless talking about the symbol itself. this is the 'del' operator in physics and math. en.wikipedia.org/wiki/Nabla_symbol en.wikipedia.org/wiki/Del It's hard enough for physics students to keep up with the sheer amount of concepts and operators in their studies, they don't need you to pile on more naming confusion. please fix @2:13 otherwise, great video.
I like your channel which is the only reason I’m giving you a negative critique. I really like your channel And I gave you a thumbs up for the attempt. I also like that you started with a review of gradient and curl. Now comes the bad stuff. Sorry. I suspect that for somebody who already knew this information, this was a great review. But you condensed way too much information and talked way too fast for it to be comprehended. Also, you should’ve started with something people know like that voltage example, and worked out from there instead of starting with something people didn’t know and worked back to what they know. I called that PhD’s who forgot what it was like to learn.
WHat is "Curl"? You don't know? We'll deal with it later, in the meantime let me explain a whole bunch of stuff using this "curl" that is an unknown to you. Just be patient and somehow magically follow along while maintaining interest for no reason at all. THIS. This is why I always hated math.
I’ve got a couple Cree “smart” bulbs that trigger functions with some jiggery-pokery on the switch. They routinely fuck up, reset themselves, and start in cool blinding 6500k blinking patterns. Cree has really fallen from grace. Utter garbage 🗑️
Hi friends, thank you so much for watching! As always, please let me know what topics you'd like me to cover in the future, and hit that subscribe button for more fun physics content. I really appreciate your support :)
The STA version of this is far more elegant. We're still hampered by the Gibbs version of vectors.
I watched until you mentioned Einstein, the biggest scientific fraud in history.
I think it would be great to explain the contexts, the backgrounds, or the puzzles of nature they were trying to unlock, when great scientists like Maxwell, Galileo, Newton, Einstein, Heisenberg and others made their discoveries. I think that would complete the picture. Many books just start with the theory or concept directly, which makes it difficult to connect the dots...
@@adenwellsmith6908 What does STA mean?
Space Time Algebra.
If you want to research it, there are Clifford Algebras. That gives you geometric algebras. They are the interesting area because scalars, complex numbers, quaternions, Pauli and Dirac algebras are just sub algebras. Stokes' theorem, gauss's law all subsumed too.
So a STA is a 3 dimensional space with an extra time dimension.
The basis vectors for distances, square to -1. The time squares to 1. [you can swap].
For Maxwell, they interesting bit is when you take two vectors and multiply them using the geometric product you get two bits to the answer. a b where a and b as vectors becomes
a.b [standard dot product] and a wedge b where the a wedge b is an oriented area.
A lot of tensors, differental forms etc, also get subsumed.
The bit that I think is very interesting is that what's going on is not abstract, it comes across as a far more physical representation of the world, and because its so simple, its even more beautiful.
@@bjornfeuerbacher5514
Either I am getting smarter, or you are getting better at explaining things... This is one of my favorite channels.
You're definitely getting smarter :D
both hopefully
Why not both?
Both.
@@ParthGChanneldid you go to OxBridge? I’m new to your channel but you’re brilliant!
Parth.. you're awesome Brother. As a physics teacher, I show your videos to my students. You explanations are visual, clear and simplified. Kudos to you as well as gratitude from me and my students. 😊
Thank you, that's very kind!
Parth, thank you for a great and easily understood explanation!
Your addition of 3 to all of the numbers reminded me of a gauge invariance analogy I've used a couple of times: When you are paddling a boat at the surface of a lake it doesn't matter whether the lake is 10 meters deep or 1000 meters deep - that is, your boat paddling is “gauge invariant” for the depth of the lake. As long as your wave activity remains confined to near the surface the depth of the lake doesn't matter.
Yet that depth is real in terms of the energy it contains, e.g., if the lake is drained to a lower level. Such a deep lake storing lots of energy corresponds to a high electric field and energizes an entire region of space in which smaller-scale electromagnetic activity is occurring.
Hey Terry! This is a really nice analogy that I think I might have to steal (with credit of course) in the future :)
@@ParthGChannel thank you, and you are most welcome. But seriously, I think it was more your analogy when you added an equal electrical potential to all points across the surface. All I did was translate that description into the classic water-level analogy of electric potential. :)
@@ParthGChannelalso, thanks for bringing this one up. As with your Dirac delta function video a few years back, this video made me question my analogy more carefully. The question is this: Is it _really_ correct to say that lake depth is like a mathematical gauge invariance since it's always only approximate? Obviously, if the paddle is big enough and moved quickly enough, the analogy can break down in shallow water due to interactions of the paddle waves with the ocean bottom.
But that's also where it gets interesting regarding the _physics_ meaning of gauge invariance, which should always be distinguished from the overly simplified assumptions of formula-only gauge invariance. Take electric potential: You can raise it arbitrarily high within a hollow metal sphere, and as with motion in special relativity, there are no internal tests you can do to prove that the potential is there. That is truly amazing and one of the deep features of physics, one just as profound as special relativity, even if less widely known.
But here's the catch: _You cannot make such a sphere infinitely large,_ and thus can never create an electrostatic gauge invariance that is any more "perfect" than the lake example. For example, suppose someone inside a large, charged sphere creates a sufficiently powerful electromagnetic wave. In that case, that wave will impact the sphere surface just as reliably as a large enough paddle wave can impact the bottom of the lake. Significantly, it also takes more and more energy to create the region inside the sphere as the sphere gets larger. This is comparable to the need to use energy to accelerate an object to high velocity. The physics _within_ the object is absolutely invariant, but its acceleration history is _not_ relativistic because it involves a historically irreversible transfer of energy.
So again, thanks. As usual, you inspire me to look more closely and critically at my assumptions. This insight on the need for energy-aware, finite-scope gauge maths to replace overly simplified assumptions about how reality works is closely akin to what I'm working on now for special relativity, which has fascinatingly similar problems.
(More bluntly: _Every_ mention of x'y'z't' in Einstein's 1905 papers is mathematically incorrect because it assumes infinitely fast, infinitely low-energy-cost creation of a meaningful coordinates system that, in reality, usually never comes into existence. Therein lies the real resolution of the twin paradox.)
Hi, Parth: I've published this dialog as an Apabistia Note dated December 21, 2023. Although I switched some time ago to a far more powerful and less paradox-prone finite-scope, local-only interpretation of Einstein's severely oversimplified x'y'z't' approximation of how new coordinate systems form, it wasn't until seeing your video that I realized that this new model is a gauge symmetry of momentum energy. That's well worth capturing as a Note. I'll try putting a full reference with a link in reply to this one, but that may or may not work, depending on your settings.
T. Bollinger, “Special Relativity as a Non-Relative Localized Gauge Theory,” Apabistia Notes *2023* 12211059 (Dec 21, 2023). sarxiv.org/apa.2023-12-21.1059.pdf
Thanks
which currency bro?
.ro
Wait, so this video is about Hermann Weyl's contribution or just plain ordinary explanation of E and B field and its corresponding scalar and vector potential
THANKS!! Very interesting, and nice to see you again on TH-cam
🖖😊
Excellent video, Parth, as always. Very interesting, informative and worthwhile video.
The Moment you started to do your little plug for subscribing to the channel, I realized how valuable you had made those 4 min for me already. I clicked all the things, you deserve it! The way you explained curl and gradient instantly made it click for me, thanks man!
- As a fellow teacher, I appreciate your clear/concise/insightful presentation.
- Keep up the great content...
Really love video's like these. Thank you for highlighting an important part of physics that's often glossed over.
This was very well structured and equally well explained. Thanks for taking the time to make this!
Although, the youtube algo's a little scary, LOL. Just started reading his Theory of Groups and QM a couple weeks back.
Excellent, lucid explanation. I'll be watching more of your videos. Thanks 👍
you really help ed with my understanding of the Vector Potential. thanks.
Last great universalist of the 19th century? Weyl's work on the invariants of groups appeared in the late 1930s. Since your statement appears at 0:25, it makes me reluctant to listen to this video. Please don't be so sloppy. It is not just that there is a date error: his work on Groups and Quantum Mechanics cannot appear in the late 19th century, because QM only developed in 1920s.
According to the auto-generated subtitles, he said, "Herman has been compared with the last great Universal mathematicians of the 19th century by his colleagues". To compare someone with someone else doesn't imply that they lived at the same time.
That's not what he said. Listen carefully
Very well made video, good content and explanation. My E&M professor kinda skipped over all that gauge stuff and left us scratching our heads at why we were allowed to do that so this is the first actual explanation of why I've seen.
A note though: this is the first video of yours I've seen and i was strongly avoiding it due to the "clickbaity" nature of the title. Whenever i see things like "... changed physics forever" or "physics will never be the same" or something like that it turns me off cause there's just so many people out here trying to trick people who have no formal education into feeling like they received some profound knowledge that really doesn't mean anything and that the creator will just package up and ship out to them over and over again at least once a week.
You're not that, but the title could've fooled me lmao. Had the title been something more addressed to the material like "Herman Weyl and Gauge Invariance" i would've clicked on it at light speed. You could even keep the flashy title and the information like, "The guy who made physics theories redundant - Herman Weyl and gauge invariance".
To end, i understand. The algorithm is a fickle thing, and i really do appreciate you making this very good video, and i do understand I'm probably in the infinitesimal minority here. And i love you, and i hope you're doing well.
Also i really hope you read this. I've just looked back through your catalogue and i do think the vast majority of your titles are well done, catchy, interesting, and combined with the thumbnail usually convey the topic sufficiently for me to not feel bated. So don't take this as like "i hate every title, you're tricking people" or anything like that.
I also realize I've seen q couple of your videos before and i really like your content. As someone who basically continually considers starting a channel just to help solidify concepts in my own head through producing videos on them, you're doing gods work.
While i still do recommend putting more of the topic in the title so you'll come up in searches on the topic (i search lots of things for good explanations, i'd certainly watch one of yours if it showed up) , i guess in a way this catchy title has brought me back to you. It makes me sad that youtube cultivates this environment but makes me very happy I've found you again. Have subscribed. Love the content and the catalogue.
Maybe if people were using his name instead calling him "a guy" would help with recognition.
Although, I know about Gauge Invariance before, still the way he describes get you thr new insights of this same topic.
Guage invariance in the calculation of price indexes.
Great explanation! But I was waiting for Weyl’s relation of electromagnetism to Relativity. 🤔
during the graduation i only found books with lenghty derivations without such a deep physical understanding.now i understand the meaning of these terms.thank you sir.
Oh this is so interesting. When I studied classical field theory gauge invariance took such a central spot, didnt know it was discovered only decades after SRT
I'm gonna need like 5 sequels to this
I've always thought General Relativity looked *very* similar to Maxwell's Equations, since self learning it. Thanks for teaching on this topic!!
I've always thought Maxwell's equations, leading to an absolute value for c independent of observer, were one of the main motivations for special relativity in the first place.
@KaiHenningsen This is true, Maxwell equations -> heaviside rewritten Maxwell equations -> Einsteins Special relativity -> Einstein general relativity -> Weyl's rewrite of Maxwell + Einstein
@@KaiHenningsenI don’t think maxwell said it would be invariant with respect to observer. Like if the observer were moving towards the wave perhaps Maxwell would have done usual Newtonian relative speeds.
@@patinho5589 yep thats the point, Einstein did very little maths on all this, the important part was to interpret it.
Nice :-) You might want to add a negative sign as in E = - Del Phi.
Nice explanation
extended electrodynamics has the arbitrary gauge transformations undone and now the equations have terms of and predict scalar waves, scalar long. waves, and curl free gradient driven current densities, they have experimentally verified it.
Soooo that's where potential difference comes from? I knew it's difference between two different points, but I didn't that it's difference between ANY two points of an electric field and is NOT fixed for the same electric field (my inference from the video).
Learn something new every day. Well-articulated explanation & simple yet effective visual cues to the boot. You've you a rare gift of explaining this in easy to digest manner.
Hello sir,
Plz make tha video on tensor more specifically covariant and contravariant, because is make confusion when use to covariant and when use the contravariant and when use both at one time.
Plz make the video and also refer the book for learning the tensor calculus.
First time I watch a video of yours, but know that if you keep the same quality for each video I will become a regular viewer no doubt
0:30 - Umm, contrary to a popular misconception, Einstein didn't arrive to his Special theory of relativity from Michelson-Morley experiment, but from considering electromagnetism. Just saying...
Nice, clear little presentation.
Parth, I’m very grateful!
So, the electric field is gauge-invariant to any potential field with all elements being equal, since the gradient is 0 everywhere for such a field. That's a fancier way of saying that the reference point in a potential field can be chosen arbitrarily.
is there a follow up with time dependence? iiirc curl(E) ~ dB/dt = curl(dA/dt) means E = -grad(phi) + dA/dt while B=curl(A) holds....
To summarise "the gradient of the curl of a scalar field" ...
Something like a temperature field would be a scalar field and because the temperature does not have a direction it does not rotate. So, rotation is always zero therefore the slope is always zero.
You didn’t really describe how general relativity and electromagnetism are related.
These light-weight physics info snippets take my fear away to go deeper into these topics. Compare the rather intimidating feeling you get when skimming over the Wikipedia article on Gauge theory compared to the intuitive, interested feeling you get here. That certainly makes it easier. And let's just acknowledge that at least for some, having a teacher being as stunningly handsome as Parth simply is, also doesn't hurt 😘.
Ok..?
Toujours aussi passionnant. Bravo
Merci beaucoup!
Could you please include some actual citations to the relevant scientific papers by Weyl in the description?
I cant belive ive only just found this channel
I think you could elaborate a bit more on the applications of Gauge Theory. Besides that, lovely video.
I'll do another video on it in the future :)
Many thanks for your video! 😊
Is the reason that the curl of the gradient of a scalar field always is zero that you take the cross product of nabla with itself, and a vector crossed with itself is always zero?
Would be nice to know more about Weyl's personal biography. How was his work received?
He got a. Nobel prize
@@DrDeuteron No, he did not get a Nobel prize.
He took a chair in mathematics at ETH in Zürich in 1912, at the time Einstein and Schrödinger held chairs there in theoretical physics. His reputation probably was the magnet that drew John von Neumann study under him in Zürich. Though his accomplishments would well have warranted a physics Nobel, it's probably because he was primarily a mathematician that he wasn't awarded one. Weyl would have deserved the Fields medal for mathematics, however when it was first awarded in 1936 he was well past 40 ― the cut off age for Fields laureates.
He spent almost all of his working life in Zürich until his death there in 1955 at the age of 70.
@@benedictdesilva6677 oh, I was thinking the king of symmetry, Wigner
@@DrDeuteron Understandable. Wigner was fellow (Hungarian) student of Leo Szilard and Janos von Neumann and also moved within and intersected with that erstwhile clique of central European physicists/mathematicians whose ilk operated in the Meccas, Medinas, Jerusalems, Antiochs and Constantinoples of the physics and maths world at the time: Göttingen, Zürich, Berlin, Copenhagen & Cambridge...
@@benedictdesilva6677 Also I use Wigner's math at work, but only read about Weyl's stuff.
Nicely explained.
Very well explained.
B is not the actual physical field. It is a pseudovector, not a vector. Maxwell's equations do not have "handedness" or are parity invariant. The use of curl is a convenience, but all physical consequences of choosing the "left hand rule" or the "right hand rule" in applying the curl or cross product are cancelled out. For example, the cross-product in the Lorentz force law that applies the magnetic field to get the force on a charge and the curl operator used to calculate that magnetic field, as long as both have the same handedness, the handedness doesn't matter.
B = curl A is closer to the actual physical field. That's because the combination of vector and scalar potential is Lorentz invariant. These transform like a four-vector. On the other hand, the electric and magnetic field are in the antisymmetric Electromagnetic Tensor and are not Lorentz invariant. Electric and magnetic fields are a convenience used when formulating the constitutive relations of physical materials when relativistic considerations (for example, for materials in reference frames traveling near the speed of light) are not important, and so Lorentz invariance is not so important.
This may seem like a pedantic consideration but it's actually quite important when you consider gauge invariance and the physical realization of calculated quantities.
You ended it without actually talking about anything more than 1st year electromagnetism. Title is completely misleading
We need a video about combining the electromagnetic theory with general theory of relativity
Would love to make one - as soon as I understand it well enough myself haha
Dang that's quite the request.
As far as I know, you "simply" use the energy momentum tensor from electrodynamics and plug it into the right hand side of Einstein's equation of General Relativity.
Thanks, very insightful.
Very interesting. For mathematical analysis, Robert Bartle, Elements of Real Analysis is brilliant - but please note 1st Edition only is best, 1964. That's where you learn the real maths, but note a lot of the work has to be done yourself, its a kind of unstated Moore Method.
Paul Dirac tried the same for describing the electron. But the need of mathematical tricks (renormalization) let him doubt the correctness of his QFT till the end of his life.
I cratered badly in my EM fields classes 40 years ago, and I think part of my difficulty was that the symbology was ALSO redundant. Really, what freaking genius decided to use the same symbol for gradient and curl, with only the cross product symbol to show what's going on?
Haha great point! I think it was because if you thought of del as a vector containing partial derivatives (d/dx, d/dy, d/dz), you could get grad by 'applying' del to a scalar, div by taking the dot product between del and a vector, and curl by taking the cross product. However you're totally right about this confusing when learning about it from a pure physics perspective!
I think you left out a negative sign in electric field at 8:29
geometric algebra and calculus takes this even further
Thank you very much for the video. A question about the reality of the potential. Does Aharonov-Bohm effect make magnetic potential "real"? How would you describe this effect?
It’s been described as a “non integrable phase”. But, yes: the 4 vector potential might be what is real.
The Aharonov-Bohm effect says that the only measurable thing is an integral of the magnetic vector potential along a close path - and that integral is _invariant_ under a gauge transformation. So no, this effect does not really make the potential "real".
Hey parth, would you be willing to make a video on how to know physics? Like is it memorization, is it application of facts , is it finding new frame of reference .How to study physics in short, what method do you use ?
If you have to ask, you will never know.
Bless your soul @@coreyleander7911
I'm not sure why you included that warning there about the "Intuitive Description of Gauge Invariance" not capturing all the intricacies.... You just described a specific example ; all the intricacies relevant for that specific situation are covered, as far as I can tell. The general concept is a pretty simple generalization from here.
I was expecting more background about Hermann Weyl and his contributions. You could have contrasted the field and potential formulation of the Maxwell equations. Instead you focus on the vector differential operators. However this is too short for anyone not familiar with them and far too basic for anyone how is actually interested in the potentials formulation for the Maxwell equations. Also the Weyl gauge is not commonly used.
at 3:58/10:28 , you said that that "the curl of gradient of a scalar field is zero " has nothing to do with the original scalar field is problematic. If the curl of the gradient of a scalar field (∇φ) is zero, it means that the vector field formed by taking the gradient of the scalar field (∇φ) is irrotational or curl-free. However, this does not provide any information about the scalar field φ itself.
*Elecrical Engineering flashbacks* 😵💫😵💫😵💫
Shout out to the conservation of energy and Newton’s second law at 4:00
I'm way too old to understand the math, but as I understand it, gauge invariance played a big role in discovering the Higgs Boson, a "massive scalar boson" and currently the God particle.
The term "God particle" is a really bad one. I don't think most physicists approve of it.
You are totally correct. I need to bone up on being facetious. @@omp199
He was a 9 incher.
Easy enough concept to grasp... And I get the idea is that it makes the maths easier, but... I'm still left at what's the point?
Can you show us a simple example of this at work where its beneficial?
Calling ground 0 volts is simple. But you need A to use Lagrangians, and you need it to generalize electrodynamics into chromodynamics.
You’re just scratching the surface!
as a maths grad not physics, this looks very similar to group invariance. do the gauges form a group?
Yes. The group of electromagnetic gauge invariance is isomorphic to U(1).
Did he make most physics theories redundant
ChatGPT
Hermann Weyl did not make most physics theories redundant. Instead, he contributed to the development and understanding of various theories, particularly in the field of quantum mechanics. Weyl's work focused on providing mathematical foundations for quantum mechanics, and he made significant contributions to the theory of groups and symmetry, which had applications in quantum physics.
While Weyl's ideas were influential, they did not render existing physics theories redundant; rather, they enriched and deepened our understanding of fundamental principles in physics. The evolution of physics involves building upon and refining existing theories rather than completely discarding them.
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Nice video
Good new look.
The last great conman
Your mustache is glorious
I thought it was dirac that combined special relativity with electroweak (electromagnetism + weak nuclear) theory.. I find the history uninteresting, but the theories themselves fascinating. I guess I am biased to forget.
Electroweak theory came long after Dirac, it was invented by (among others) Glashow, Salam and Weinberg.
Weyl gauge is so important in astronomy
How did he not solve unification?
Burnt toast and the butterfly effect lead Weyl to miss that in this universe. Just shows how important breakfast can be.
very cool
awesome mate
very good
I would call myself some waht intelligent, but with those abstract mathematics in a second language I just understand 30% of it! 🤯
My strength is more in causal coherences, not in algebra! 😅
Still very interesting! 👍
You shouldn't say that combining maxwells and Einsteins theory was his biggest contribution... Because it wasn't... He tried it and failed because experimental data wasn't agreeing with his model...
He was a brilliant mathematician... But there is a reason why we are unable to combine all four forces
@4:20 I did what you said and now my monitor is broken.
It's too bad SO(3,1) is not compact 😢
Redundancy ia good. M'kay? Redundancy is good.
ever since oliver heaviside, in the 1890s, we don't talk about 'nabla' unless talking about the symbol itself. this is the 'del' operator in physics and math.
en.wikipedia.org/wiki/Nabla_symbol
en.wikipedia.org/wiki/Del
It's hard enough for physics students to keep up with the sheer amount of concepts and operators in their studies, they don't need you to pile on more naming confusion. please fix @2:13
otherwise, great video.
I like your channel which is the only reason I’m giving you a negative critique. I really like your channel And I gave you a thumbs up for the attempt. I also like that you started with a review of gradient and curl. Now comes the bad stuff. Sorry. I suspect that for somebody who already knew this information, this was a great review. But you condensed way too much information and talked way too fast for it to be comprehended. Also, you should’ve started with something people know like that voltage example, and worked out from there instead of starting with something people didn’t know and worked back to what they know. I called that PhD’s who forgot what it was like to learn.
Amazing!!
Dumber cuz I'm just heating up.
"Why is this exactly fun for physicists?" 😅😅😅
Whats the song in the behinning?
It's my own music! I'd love to release it some day 😄
@@ParthGChannel I like the sound!
@@ParthGChannelpls do it
to say combined relativity and elmag feels rather misleading ...
badminton?
for the algo
Indian uncle moustache supremacy 🎉
WHat is "Curl"? You don't know? We'll deal with it later, in the meantime let me explain a whole bunch of stuff using this "curl" that is an unknown to you. Just be patient and somehow magically follow along while maintaining interest for no reason at all.
THIS. This is why I always hated math.
I’ve got a couple Cree “smart” bulbs that trigger functions with some jiggery-pokery on the switch. They routinely fuck up, reset themselves, and start in cool blinding 6500k blinking patterns. Cree has really fallen from grace. Utter garbage 🗑️
...what would happen... IF... you were not allowed the use of the word... INTUITIVE?...
Haven't got a clue what you are talking about.
This is just a starter... I hope...?
AI stole this idea