59. I am 59 years old. Studied physics in high school and university. Read many many popular science books written by all the greats. And in 15 minutes you helped me understand something that never ever made sense to me. Thank you dear friend. You have a new subscriber.

I love your conversations with Einstein/Feynman etc. They really bring the concepts to life.

I love how he refers to experiments that "we" have done, referring to us, team humans, and he's so excited to be on that team!!! Go us!!!! We can do incredible things!!!!

I love this guy, I genuinely NEED to see a gold play button somewhere in the background somewhere in the near future.

This is a very good explanation. As an old physicist I can say, I wish we had these powers of visualization decades ago. It took me years to establish a mental model for electron spin, and you’ve done it in a few minutes! To be fair, there was a lot more mathematics involved but an intuitive model is super useful. Perhaps you can explore this further by talking about some of the experiments that established the existence of the electron and its spin and magnetic nature.

I was a practicing magnetic resonance spectroscopist in my career, and taught courses that focused on spin dynamics. So it's not an unfamitiar subject to me. Even so, Ifound your presentation insightful and pleasing. Good work.

This is an extremely well put and organized way to explain electron spin. I greatly appreciate the humor and the way of narrating through the whole story, and most importantly not omitting the smallest of details that fill in all the little gaps and ultimately form the full picture. Thank you so much for this video!

“Individual pieces of cell aren't alive” Mitochondria: 💀

This is the first time I have ever heard such a clear explanation that I, a layman, can understand. Thank You!

What a brilliant way to explain this concept. I'm an avid watcher of physics youtube videos and have seen many that "explain" that quantum spin isn't really spin but most just leave it at that even when that is subject of the video. This "conversation with a physicist" style where you ask the obvious questions that I as viewer would have was really refreshing and informative. I have seen much material already on this subject, I rarely learn anything new, I did today! Well done!

I had tried a lot to understand what the Spin really was before this, but had a hard time. This video has taken me the closest towards understanding it. Thank you. Now I think I can move from this reference point.

I love the way you laid the whole matter out in the form of a "conversation with the master." Very helpful for folks like me, who love to follow the subject but who've got no formal training ... and CERTAINLY don't have the mathematical ability!!! ... to engage the material directly. Thank you!

I clicked on this randomly and I'm glad I did. You've finally explained electron spin in a way that I can understand and even believe. And with a sense of humour too. I've read about this stuff for a long time and yours is the first explanation that has worked for me. I think you are the first to take the time to not just skim over the peculiar details that need to be understood to make any sense of what spin is. Thank you, and I'm subscribing (and sharing) by virtue of this, the first of your videos that I have seen.

Legit. Tons of other vids and classes here, yet you still taught me something new--without math and based on intuition. Grow your channel, dude. Standing behind you.

For me, studying quantum physics was like a religious experience: it is beyond what the human mind can comprehend. So we use analogies and rules-of-thumb. This is as close as we can come to understanding. Listen to Mahesh enthusiasm as he experiences this religious experience! Fun video!

I'm a chemistry student, and this is a topic I struggle a LOT to understand (my teachers just say "it makes sense when you apply general relativity"). So it's refreshing to see videos like this. Good job!

Think of electrons being politicians. They "Behave" as if they care about people, but really, they don't and they can't. 😂

You should try to explain how a non-spinning electron can (or cannot) generate light that carries spinning field vectors (is circularly polarized). All light can be constructed with circularly polarized photons, so it's a critical concept.

Great explanation, but I have to correct something: the individual particles in your basketball *are* spinning about their own centers as they move in a circular path around the center of the basketball. Here’s another way to think on it: someone standing on the equator will do a full flip head over heels over 24 hours. Someone standing on one of the polls will spin around once over 24 hours. Every point in a solid (rigid) spinning object has an angular velocity equal to the angular velocity of the object it belongs to. Put a coin on a spinning record, or a book on a spinning chair and watch it - it doesn’t “hold still” as it moves in a circular path, it spins too! At exactly the same angular velocity. While it’s hard to conceptually think of a true singular point (i.e., no consituent parts) spinning, explaining this by saying spin is an emergent property of a collection of non-spinning objects moving around a common axis is a bit wrong. A spinning object full of non-spinning consituents would experience a ton of tidal friction. But, the explanation of how we detect the spin of an electron by measuring it’s wobble in a magnetic field is great, so the lesson of the video is still mostly unchanged and really great.

The way that you walk through the concepts helps me to understand, and your enthusiasm is infectious! Thanks so much for your work on these videos!

Fantastic video . I'm a 66 year old man with no physics qualifications at all but I've been reading quantum physics for the past 5 years just as a (unwinding) after work sort of thing I'm hooked on it I just can't get enough and I think your videos are just great thank you ( by the way I find the Richard Feynman lectures volume 1 2 and 3 a great read )

Great video! Ever since high school, any time electron spin was brought up in class, it was always accompanied by the phrase, "the electrons aren't really spinning, but...". So, I asked nearly every chemistry professor that I've ever had what exactly electron spin is, and never got any answers. This has finally put those nagging questions to rest. Thanks!

I am doing masters in physics and most of the time I encounter angular momentum of electrons and i always think why is it today i got the answer Thanks

Watched a few of your videos lately. You are really talented at explaining things: clear, methodical, enthusiastic in a genuine way, and most importantly, you lead logically from point to point guided by natural questions that would arise.

This seems to me like a strong clue that electrons are in fact *not* fundamental particles and that there is something deeper yet to be discovered. Thanks for the excellent video.

Thank you so much. I've been struggling to comprehend this for years. Your ability to explain complex topics in so simple manner is truly remarkable.

Excellent presentation. As you say, the issue with electron spin is that the electron has no breadth or if it does, it looks the same from all angles so there's no sense in which it can spin. Black holes have the same problem, but they can have angular momentum, too. The upshot is, angular momentum is more fundamental than we have been led to believe. It is possible to have angular momentum even if you have no breadth or you are devoid of features. It will manifest when you interact with your environment. Photons are another case in point. Planck's constant is effectively a chunk of angular momentum.

I love it when you finally hit on a video that explains clearly concepts you have been trying to understand for ages.

Mahesh we need QUANTUM MECHANICS from you ...more topics on QM please ❤🙏🛐

This was nicely done. I still don't feel I really understand electron "spin", but now I know precisely what I don't understand 😂. (40 years in electronics too!)

I love how you do your dialogues! It allows some pre-thinking and guessing, which makes it much more fun watching the video. Very creative!

KZfaq algorithm has finally understood me.

Incredibly well explained! Thanks for these nice physics tutorials, they are very understandable for “us” non physicists!

Great video. You are a talented teacher. Your entertaining and engaging method of explaining complex topics is fantastic.

Your explanations are fantastic! You're teaching the part of the curriculum that's left out of the books, e.g. the "big takeaway". Thank you so much. Keep it up!

Badass. Nice work. I’ve studied chemistry and quantum mechanics for 45 years and appreciate your approach!

Nicely done. I am a hobby physics student at age 47. When I first started QM few years back electron spin bothered me but I was able to overcome that by reading a lot from various sources including Feynman lectures. You have explained this nicely in a short video. I believe there is more to fundamental particles. I have intuition that even electron and other particles have structure and study of which will reveal more. I m sure your videos will encourage more guys to take interest in quantum mechanics. As more people will take interest in physics more Einstiens and Feynmans world will produce. So please keep up the good work and keep these videos rolling out.

I really enjoyed listening to you! Thanks so much for sharing a small piece of your mind with me. You communicated an important concept extremely well. I count myself fortunate to have lucked into finding your video here, today. I will definitely subscribe for more! Best wishes! By the way, I think that the wonderful readability of the Feynman Lecture series had more to do with those who surrounded Feynman during its development than with Feynman himself. I've listened to his lectures, not just those in the US but also to many of those done in Australia, and I consider all of them to be rather 'difficult' to access, in the moment. I'm not the only one. Freeman Dyson had to take nearly a year off and drive around with Feynman to grasp his ideas well enough to codify them in terms others could more readily follow and accept. Feynman was clearly a radical at the time. My absolute favorite book about Feynman is "The Beat of a Different Drum" by Jagdish Mehra. I cannot recommend it enough.

Guy, your videos are like the residual FAQ of every other physics video I've watched which didn't bother to explain either well enough or even at all this kind of fundamental topics. I'm binging against my will and available time, but no regrets. Thanks!

What a beautiful explanation! As an academic radiologist, I have always found it difficult to explain why protons precess in the magnetic field of an MRI. That is, how to reconcile the Newtonian concept of angular momentum with the quantum mechanical theory? Thank you, thank you!

Fantastically educational video! The electron behaves like it's a magnet (has a _magnetic moment_ ) and that it somehow "rotates" (has an _angular momentum_ we call _spin_ ) and that the _magnetic moment_ is proportional to the _angular momentum_ , as is the case with classical electrically charged bodies that rotate (as explained in the video). However, there is a fascinating difference between the classical rotation and the quantum spin: The ratio of the _magnetic moment_ and the _spin_ of the electron is TWICE the ratio of the _magnetic moment_ and the classical _angular momentum_ of the classical counterparts. Somehow, the quantum spin is TWICE as "powerful" as the classical rotation, as predicted by quantum mechanics and confirmed by experiments.

The reason table-tops are stable when spinning is centrifugal forces. Yes practically everyone knows that, but why specifically? Well the spinning top has some energy, or angular momentum, and we know that it'll spin until it loses its energy. That energy obviously comes from the rotation, but all the particles of the top would prefer to continue on their straight path ... except that they're bound not just by their gravity (like in a star system or a galaxy) but are also bound by the much stronger electromagnetic-forces. But the thing is they're still trying to fly away in straight paths despite being hold back by these forces. And having each particle of a symmetric object pull away at the same time straight-away from the axis of rotation makes that axis stable (though that axis isn't actual physical object - just the line of rotation stability). To be even more pedantic in order to change direction of that axis you have to introduce force in order to affect their momentum, but while Gravity pulls a spinning top directly down - ie on the same line as that axis it's not going to topple the top at least until it loses enough of its energy due to friction and air-resistance. I know that's super pedantic description, and a bit boring to read (for those that understand it), but I hope that it explains the gyroscopic effect to those that didn't know it. :)

Hi Mahesh, I love how you make all these concepts so accessible. Like I cannot state how simple your explanation is for me to understand (for twin paradox and other non intuitive concepts). I just wanted to mention that for a 3d body, spin is rotation around an axis (not a point) which passes through the body

Been trying to intuitiveley understand quantum spin for over half a decade, this 15 minute video finally got it through to me, great channel and I love the way you explain things, coming from the perspective of the people testing the ideas at the time, 10/10 vid and channel!

Hey sir, you have a talented presentation/ tutoring skills, I work in field of medical physics, your explanations for terms are refreshing ! That makes me recalled the teaching of my old fashioned physics teacher, Thank you :)

Electrons have angular momentum - quantized (Lz = +/-h/2) -, and yes, it is angular momentum of the same type as the angular momentum of the wheel of a spinning bicycle, and changing the orientation of the spin requires the same type of effort as turning the handlebars of the bicycle. It turns out that since they cannot explain the gyromagnetic ratio gs=2, then they say "it is not angular momentum"

Thanks for the wonderful explanation 😀I've always tried to wrap my head around this ("yes it has spin, but it doesn't spin" etc.). Now it seems much more clear to me

PBS Spacetime actually did post a video that shows a close approximation of the physical spin of electrons. And yes it is spinning.

This (and your others) is fantastic. You give good explanations without skipping steps. I watch a lot of.videos and sometimes its easy to.get lost in the weeds or get too HIGH of an overview. You have a great balance. Keep it up

Thank you. That helped a lot to gain some insight on this mind boggling quantum property. I’ve never heard such a good explanation of this topic. It amazes me that those European physicists back in the 1920s could envision this stuff!!

Finally, an explanation that focuses on the nature of reality instead of trying to overly analogize it. Thanks!

I was feeling lost… but then your explanation hit me like a brick wall in a split second of understanding the analogy. 🤯 thank you for these videos.

We are tantalysingly close to understanding this but still it evades our grasp. Great video. The answer is just around the corner. It's a simple answer, surely.

Been self learning QM for some time and this is by far the best explanation of spin. Thanks.

I'd heard before that the spin is an expression of torque or something along those lines but this is by far a much more complete explanation. Thanks!

sir, in brief history of time, Stephen hawking writes that spin is actually the number of times you need to rotate a particle so that it has the same orientation as we started with. for example- if we take an arrow, we need to rotate it 2 times (at 180*) so that we get same orientation as we started with, thus it has a spin 2. Similarly a particle with spin 1 is like a double headed arrow. but electrons behave differently, we need to rotate them 2 times(at 360*) so that it looks the same and it has spin 1/2. how do I reconcile this with u said? your explanation makes more sense to me.

I just found your channel and I am now bingeing on your excellent videos. I am sure many of us viewers would love to know more about your story -- how did you get started in science education, how did you join Khan academy, what inspired you when you were a kid?

Even more perplexing for me is to imagine a particle that consists of no other particle and yet is greater than a zero point. I mean, how can something that has size not be divisible? You see the left side of it, you see the right side of it, obviously you see something in the middle, but no, it's fundamentally not divisible? If it has size, it must have surface, and it must have inner volume, right? And there must be something that limits that particle in size. A truly uniform non-zero particle can only be of the size of the entire Universe - because its boundaries are not distinguishable from its inner volume. Which gently brings us to another concept by John Wheeler: a one-electron Universe postulate. Thank you for the great video.

Quite possibly my fave physics exposition channel. Kudos

After watching several of your videos I grew to need them as much as your microphone needs a pop filter

You’re such an honest teacher, it truly blows me away. There is no ego whatsoever in the way you explain things to the layman. I hope you realize how good of a teacher you are!!

You have a very pleasant voice as a speaker. More relevantly, i appreciate your enthusiasm and pace. This was very interesting.

Where have you been all my life? When asked to explain what spin is, most physicists would just say “it’s complicated”, but you actually managed to make sense of it. I love the imaginary conversations with Feynman!

I like your videos and your way of talking/explaining. Keep It up! BTW, this video should be titled "the quantum duck" (or elephant)... "If It looks like a duck, It behaves like a duck, It quacks like a duck, it's NOT a duck, in QM"

⁠@Mahesh_Shenoy Great video. Do you happen to have links to any talks/lectures where Feynman discusses spin? Or maybe the book(s) where he mentions this? I am curious now on his full reasoning for why electrons can not be spinning.

I think it will be an honor to be able to participate as an audience in Richard Feynman's lectures. I am not fully convinced that electrons are fundamental particles. Look at what we thought about atoms decades ago. Just because we couldn't detect the true stuff that make up electrons because of limitations of current technology, doesn't imply they don't exist. You have ability of putting forth complex scientific concepts, then break them down to bite-size chunks so normal folks like us could at least attempt to understand. Thank you.

This fellow has a gift for explaining this science.

I really liked your last lines that "we have no intuition for that quantum world" But it would be really great if we could go to the quantum world and maybe see the world with our own eyes 👀

Could you please mention the research paper on that experiment ?

From the opening 25 seconds alone, I know I will give the video thumbs-up. Whether it is left-thumb or right-thumb is kinda in superposition, always forget which one.

That was simple, and therefore huge! Thank you, man. And I appreciate this enthusiasm of yours.

A very nice presentation of the topic. Well done! From here, when we look at how much angular momentuum the electron has it gets even wilder. Electrons have spin 1/2 (in Planck constant units). A particle with spin 1 has a symmetry of 1 - that means that if you rotate "it" (meaning its wave function) a full circle it returns to the original state. A particle with spin 2 means that the wave function looks like itself twice in a full turn (think of a rod). A particle with spin 3 repeats itself 3 times in a full turn (e.g., a perfect triangle). This means that in order for the electron with spin 1/2 to return to its original state you have to turn it TWO full circles... this one fried my brain. 😵‍💫

3:10 But what if we found out the electron is still made up of smaller particles in the future. 😂

OMFG! Absolutely the best explanation I’ve heard! I’ve been spinning my wheels in vain trying to understand spin. I’m not technically trained or educated but have been interested conceptually for years. And I’ve read and viewed a lot over the years. Great, great explanation!!

I just finished watching your video on JJ Thompson & Ernest Rutherford, I loved it. This is another hit explainer. They the best thing to do with knowledge is to pass it on, so thank you. Keep giving us more!!

Great video. Another interesting observation is that the electric charge of an electron is 3 times the smallest unit of charge found in nature (charge equal to 3 down quarks). That, combined with their observed angular momentum and magnetic field, is pretty compelling evidence that electrons may consist of more elementary particles not yet observed.

Bravo!

The end felt like the biggest literal mic drop ever :D I studied physics and was working with magnetism on my master thesis. So I knew all of this. Whenever you were slowly going the next step in the video, I was like 'they precess', 'magnets', 'Larmor frequency'. In germany we would say "du hast bei deinen Erklärungen einen sehr guten roten Faden." which means something like "it is super easy to follow your explanations as you have got something like a continuous thread marking the right path through the maze."

You explained well in simple terms a very complex unintuitive concept, I loved your story-tellling approach. Wonderful!

Mahesh craking social cues and debunking pseudoscience with science

Bro, this explained nothing, wth

I like the style of these videos, the contrarian start-point from an interviewer perspective with the greats.

I think that you have the ability to excellently explain meanings, clarify things and expose their taste and beauty. I appreciate life now that it gave birth to some one like you and like Feynman !❤😊🌹

Spin is what Joe Biden’s press secretary does at a news conference

A toy dog can behave (to some extent) like a live dog, but it is not alive. In quantum level, most probably there are some other forces involved that we are yet to comprehend. Great video by the way. 👍

Great video - I love the "conversations" with Feynman. You've captured his demeanor. I disagree with some of your interpretation, but it's a marvelous look at his analytical technique. A couple of things to consider: First, the Moon orbits the earth in such a way that the same side faces Earth all the time. If you have an Earth-centric point of view, you would say that the Moon does not spin. But if you look from a distance, you can observe that the Moon does in fact spin at the rate of one rotation per orbit of the Earth. The Moon spins at a very slow rate, even as it migrates through space. If it didn't, we would see different sides of it. In other words, it spins just enough to keep it synchronized with the Earth. I know you know that, but it's important for the second part. Second, electrons are not two dimensional. It has a surface. And if, for instance. you shined a light on one side of an electron, you would observe that the opposite side is dark. Spend some time thinking about that, and you see that a single fundamental particle, like an electron, COULD indeed spin and bring the dark side to face the light. Your grain of sand analogy indicates that it can spin because it is made up of many, many particles. But consider all of the particles within that grain of sand (particularly electrons). Even if they have no "spin" of their own (according to this theory), they would still complete rotations just like the moon does. Like it or not, rotation is spin. Picture that grain of sand spinning, and all the particles inside come along for the ride. Now make all the particles transparent, except for a single electron. Then shine a light on the grain of sand that illuminates the one opaque particle. As the grain of sand spins, a different portion of our electron would be illuminated by the light. And that means? Yep... the electron is spinning. It must be, in order to bring a different area of its surface toward the light. Keep going down that path and you have to ask, "Is there some minimum spin required for an object to experience/exhibit angular momentum? I suggest that the answer is no. The slower the spin rate, the more difficult it becomes to MEASURE - but it still exists.

After watching hundreds of videos on spin this is the first video that really explained what spin really is . Thank you kind sir you are a genius

Your "if you can't convince them, confuse them" expression reminds me of something I've heard a lot as a repair technician: "if you can't dazzle them with brilliance, baffle them with bullshit"

How is it possible that I haven't discovered your channel before?! This is so awesome. I finally understood spin. Thank you so much. Keep it going

Your cogent and enthusiastic explanation brings joy to my heart and even a bit of understanding to my brain. Thank you!

Fantastic explanation. I've watched a ton of videos on this topic and each one fills in little puzzle pieces. This was great.

my teacher failed to explain "spin" to me when i was in school, he just talk about "some particles have angular momentum that called spin". It's bugging me out until i found your video! Very well explanation!!

I've searched high and low for an explanation of quantum spin that actually made sense to me. This is honestly as close as I have found in as much as it at least clearly explains the logic as to why we say an indivisible particle has the property of spin. Thanks.

“What is well conceived is clearly said, and the words to say it flow with ease. “ That famous Nicholas Boileau quote clearly fits you Manish. Thank you man.

I don't remember the name, but there is also an experiment where you flip the spins of particles in a suspended chunk of matter, and then the chunk starts spinning, showing that spin and angular momentum are only conserved together.

I've come to think of quantum spin as a form of intrinsic angular momentum. Hardly anyone ever bothers to mention this when introducing the concept of quantum spin. They usually just go on and on about how we call it "spin" but nothing is actually spinning. Although the exact nature of the quantum spin property still eludes us, I don't have a problem with saying that quantum objects have intrinsic momentum. Some day we will learn how this intrinsic momentum arises, but for now we just accept that there is intrinsic momentum verified experimentally. I enjoy Mahesh's style of teaching very much, and I have a similar philosophy myself when it comes to my own students.

Angular momentum is rotation speed, and the video demonstrates how an electron has angular momentum. So It doesn’t « spin », but it rotates. I understand how we have to respect some old physicists weird definition of spinning that only applies to macroscopic scale, but in all practicality, rotating and spinning is basically the same thing. I think the term electron spin 100% works in this scenario if I’m basing myself off of the information in this video (there might be a gap in my knowledge of quantum physics, feel free to correct me).

Whoa… fantastic explanation. I always just wrote off electron spin as a fundamental property of electron that I just had to accept. I knew it wasn’t like a baseball spinning but couldn’t imagine beyond that. The function of resisting an external magnet makes sense. I’m going to save this video so I can rewatch it many times.

There is certain beauty in having clarity about a subject which is intuitively unclear … well done !

Alternative explanation: maybe electrons are made of smaller particles, we just don´t have the technology to detect them yet, hence they can have both spin and charge. Wonderfully clear explanation by the way!