Spin in Quantum Mechanics: What Is It and Why Are Electrons Spin 1/2? Physics Basics

[@ParthGChannel]

Hi friends! Thanks so much for watching this video. I'd like to thank the sponsor, Skillshare - check out Skillshare Premium for free at this link: skl.sh/parthg11201 Also, if you enjoyed this discussion of spin then feel free to subscribe to my channel for more fun physics content. As always, thank you for your wonderful support!

[@itsbk6192]

Dude. This was awesome. Keep it up

[@sharma_anuj00]

I guess you are an Indian?

[@swarnenduroy668]

Hi Parth, awesome videos. I had some questions regarding your video on diffraction. Is there any way to address you personally? thanx heaps

[@akashsunil7464]

mr. parth can u make a new video its already been one week

[@akashsunil7464]

i mean i wanna learn something new

[@PrettyMuchPhysics]

The way I like to think about spin is that it's just some inherent property of a particle, like mass. But unlike mass, which is a scalar, spin is a vector quantity (i.e. 3 components), which obey the same maths as angular momenta do!

[@DrDeuteron]

that works for integer spins.

[@spikkelkip8128]

Mass isn't an inherent property of particles though.

[@blinded6502]

@@spikkelkip8128 Mass is internal momentum

[@AdrienLegendre]

For the simplest non-trivial representation, spin 1/2, spin is a spinor.

[@ArvinAsh]

Nice explanation. Well done!

[@ParthGChannel]

Thanks Arvin, love your videos! :D

[@weaversinstitutebydeveshji730]

And i love both of your videos.. A big Thank you and love from India.

[@dhanashrikulkarni5878]

Hey Arvin! Love your vidoes!❤

[@VeddMishra]

Llove you Arvin

[@शिवोहम-श2व]

Two finest physicist 🤩

[@wayneyadams]

These are the most useful videos I have seen anywhere. They use simple direct explanations and examples, and also discuss possible misconceptions. Even though I am retired after teaching Physics for 33 years, I still like to see how other people teach these concepts, and as I said, these are the best I have seen. Anyone who wants to gain a solid education in the basics of physics can do so with these videos.

[@tejasgowdakr4700]

Thank you so much You gave me hope!

[@nadinesereda-sass158]

I read your description and you seem like the worlds most unlikable and close minded person.

[@cyto3338]

I tried a lot of spin explainer videos and sites, this here is the best one on internet (it is amazing that you uploaded the video right when I was having problem with the topic)

[@kA-dc6zq]

I'm an English teacher but I read philosophy on my own. I also read about quantum to make a deeper view of the universe. Now, I'm reading Beyond Weird by Philip Ball. When I don't understand some difficult parts like spin, I watch these suggestive videos. They are amazing for us beginners. Thanks a lot.

[@jimjohn8581]

You explain physics better than anyone else on KZbin. Point blank

[@EpziWasHere]

Ive watched this and your video on "Why Spin Matters" and now understand Spin more thoroughly than from any other source Ive found in *years* of trying to understand this thing!

[@Internetlo]

I’m reading The Amazing Story of Quantum Mechanics by James kakalios & I found this concept so interesting & came across your channel. Thank you for explaining this 🙏🏼 I’m a nurse but I wanna go back to school for physics now 😤All of this is so fascinating

[@georgedoran9299]

It definitely possible, one of my friends in my year at uni did a full medical degree and worked as a doctor for 2 years then switched to physics

[@genericusername1243]

first time yt algo recommended a vid thats 10mins from its upload rather than 10 yrs and im not even sub to this channel yet. anyways good video here 👏

[@ashokb9456]

The best thing about your videos is that you explain even the tiniest things in a very detailed manner which is really helpful .Thanks a lot😊

[@Jas3nM]

That disallowed spin 0 photon NEEDS its own explanation!

[@DrDeuteron]

gauge invariance gobbles it up.

[@Sujay.Vaidya]

This is the most easiest and effective explanation of spin. Well done Parth!

[@wmstuckey]

This is a nice introduction to spin for the layperson. Let me provide the counterpart in quantum information theory where electron spin (spin-1/2) is a quantum bit of information called a qubit. We explain this in our book, "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" Oxford UP (2024) and I’ll summarize it here. The difference between a classical bit of information (like a computer bit being on or off) and a qubit is that, while both bits produce one of two outcomes when queried (measured), a classical bit has only one measurement possible while a qubit can be measured in many different ways (infinitely many, actually), each with two possible outcomes. Consider electron spin. When you pass an electron through an inhomogeneous magnetic field, the electron is either deflected towards the North magnetic pole ("up") or towards the South magnetic pole ("down"). You can orient the N-S magnetic field in any direction you like (continuously) and the electrons will still give one of those two outcomes, so electron spin is a qubit with two outcomes of spin "up" and spin "down" relative the the N-S magnetic field. Now suppose you pass electrons through a N-S magnetic field oriented vertically and then send those that were deflected "up" (literally up in this case) to a N-S magnetic field oriented horizontally. What do you expect to find? Well since the electrons have vertical spin up and spin is a vector (angular momentum as Parth showed), then you probably expect the electrons to pass straight through the horizontal magnetic field, i.e., they won't be deflected left or right at all ("up" or "down" relative to the horizontal N-S field). That's because the electron's spin vector (arrow) points up which means it doesn't point side-to-side (left of right) at all, so your horizontal spin measurement of a vertical spin up electron should seemingly yield a result of zero horizontal spin. But what you find instead is that 50% of the vertical spin up electrons are deflected left ("up" towards North pole) and 50% are deflected right ("down" towards South pole). True, 50% left plus 50% right *averages* to zero, but that's not what you expect from the measurement of a vector quantity like angular momentum in ordinary classical mechanics. This is quantum superposition, a vertical spin up electron is a quantum superposition of 50% horizontal spin left and 50% horizontal spin right and we write that as |V+> = |H+> + |H-> (divided by root 2 for normalization, but I don't need that to make my point). The point here is the horizontal spin measurement of the quantum state |V+> produces each of its two "up"-"down" (left-right) results in 50-50 fashion. This is exactly what you hear people say about Schrodinger's Cat, i.e., you open the box and find the cat is dead with 50% probability or find the cat is alive with 50% probability. With that information alone, Schrodinger's Cat could be a classical bit or a qubit. If Schrodinger's Cat is a qubit, then there must be a measurement of the cat-box system like the vertical spin measurement of the state |V+> that produces |V+>, i.e., |H+> + |H->, with 100% certainty. We know the measurement "open the box" producing "Live Cat"-"Dead Cat" results in 50-50 fashion is analogous to the horizontal spin measurement of |V+>, so what is the measurement of the cat-box system corresponding to |Live Cat> + |Dead Cat> with 100% certainty in analogy with the vertical spin measurement of the state |V+> that produces |V+> with 100% certainty? And what does its outcome mean physically? If you can't articulate that measurement and outcome of the cat-box system, and every possible measurement between that measurement and the "open the box" measurement, then the cat-box system is just a classical bit ... like opening a box to find a ball or no ball. No quantum superposition there 🙂

[@Jonathan-rr9ed]

holy grale what a yt cannel feels great to have found u!!!

[@nevermindnever8363]

1.Why is it that we subtract the spin by 1? 2.Why can't we go further with the subtraction after reaching the -ve value of n? 3.How do we know the initial spin number? 4.Why are they either whole numbers or integral multiples of half?

[@rensoraulvisbalacevedo5755]

Dude, this isn't physics, this is SCIENCE!!! Thank you very much for the content.

[@larrystone654]

5:44 I wish you would write a book. Your explanations are clearer and more intuitive than any of the popular physics books I’ve read. Please consider it!

[@gaurvsinha]

I'm trying to learn Quantum Computation. I'm using your video to understand the concept of Quantum Mechanics and how these concepts are using in Quantum Computer. Thanks you such a quality video.

[@Skeletone56]

WE ACHIEVING THE GOLDEN RATIO WITH THIS ONE 🗣🗣🗣🗣🗣🗣🗣🔥🔥🔥🔥🔥🔥💯💯💯💯💯💯💯

[@olijacobs3347]

Please do the Dirac equation

[@mudkip_btw]

Yes please!

[@kevinmccarthy8746]

I am newly introduced to Quantum physics, particle physics and I like to review all the incredible aspects of Quantum Mechanics like the first time I read about the Double Slit Experiments, the Quantum Entanglement experiments, I ,was just amazed. So amazed in fact I instantly regretted ever having played sports. So I love to review say SPIN or ANGULAR MOMENTUM and go through a lot of different video`s on that subject to see the different ways they present their information. Which is more comprehensive for me than just one presentation of the subject matter. Then I can take a brake and review some video`s on Quantum Chromodynamics for instance. Very fun and relaxed at my own speed so to speak.

[@dalirkosimov4623]

3:08 using the right hand rule, shouldn't up be counterclockwise while down be clockwise?

[@josephtraverso2700]

This is applying to electrons with a negative charge so we use the “left hand rule”. It essentially reverses the outcomes of the right hand rule used for positive particles

[@RussellSubedi]

@@josephtraverso2700 Shouldn't angular momentum be independent of charge?

[@josephtraverso2700]

@@RussellSubedi angular momentum is a a vector quantity. Charge is a scalar that is applied to it. Thus, changing the sign of the charge would flip the vector around making the RHR backwards

[@RussellSubedi]

@@josephtraverso2700 But doesn't that make the magnetic dipole moment of the electron positive for positive angular momentum, but that and the angular momentum must have opposite sign? I'm having problems phrasing it, but I hope you get my question.

[@nirbhaykumarchaubey8777]

@@josephtraverso2700 thanks buddy

[@yilizhang790]

Firstly, thanks a ton for the detailed discussion on this topic! It all makes sense except at 10:18: Why not stop at -1/2 h since you have already hit negative here?

[@yilizhang790]

Oh, I think I get it! By negative limit, you mean the negative counterpart of the maximum positive momentum, right?

[@BRUH-pv9rb]

@@yilizhang790 i have the same doubt and i think u r right bro 👍

[@Saralcfc]

I had the same question

[@judemetcalf4265]

Such a great video on such a complex and misunderstood phenomenon. I have always had trouble understanding spin, and have read, watched and heard so many conflicting and unhelpful explanations, but this truly was useful. Love your videos

[@crimsoncanvas51]

I came to your channel last 10days and now I see your explanation of topic in simple ways. Wish my school teacher, college professor taught physics in such intuitive ways. Great explanation of each topic. Can you make separate video on quantum states? N, l, m and s, electonic configuration etc.

[@dylenweerasekara9533]

Thanks Parth. You've always been a good physics teacher to me. Thanks for giving this free info to teens like me.

[@damnboi972]

Me: "gonna learn today what spin is " Someone : "what is spin?" Me: 🤷

[@shayanmoosavi9139]

Also every physicist : 🤷‍♂️🤷‍♂️

[@Reddit_database]

Everyone - 🤷‍♂️🤷‍♂️🤷‍♂️

[@icyy-_-warrior1650]

You are amazing! People use the word magnetic and that can get in the way of learning. Thank you!

[@nemesiswes426]

Great Explanation, not a lot of other physics video's explain things nearly as well as you do.

[@danjbundrick]

Your videos are as informative as they are fascinating. Thank you for sharing your knowledge and illustration skills!

[@SWBarua]

It was really helpful. Please make a video on isospin.

[@nishatiwari9212]

Angular momentum

[@jeffeejenson707]

Omg..the evolution of ur hairstyles is funny man😂..

[@tmhood]

I suspect that Parth's hair is a quantum system. It exists in a superposition of states, only collapsing into a particular style when observed on KZbin.

[@jeffeejenson707]

@@tmhood 😂

[@abhishekprasad6350]

Nice video. Fun fact-Nothing in the universe rotates on its axis even the earth,if u think hard u would get that as earth is made up of atoms,molecules and compound they revolves together in a particular direction making it look like rotation on axis on a macroscpic level🙃

[@FD-rt3rv]

you just explained clearly in a 12 mins video something my well paid professor cannot explain in a full semester. something seems to be wrong with the system

[@waynelast1685]

Nice overview for someone new to spin

[@wayneyadams]

3:16 Curl the fingers of your right hand in the direction of the spin and your thumb gives the direction of the spin vector.

[@Lucky10279]

4:44 They _aren't_ actually spinning. They're doing _something_ that's sort of analogous to spinning, hence the name, but not actually spinning. We know that because if they were spinning they'd having to be doing so thousands of time faster than the speed of light.

[@mostafaabdelhamid8653]

MAZING THANKS REALLY, WONDERFJL EXPLANATION

[@asifalamgir5135]

Awesome Editing man ... Much Better than Previous videos. Well Done!!!

[@arekkazmierowski9657]

Great vid as always. But puzzled about so much advertising. While I understand why it is there, I have a problem with it paying for YT Premium every month to get rid of ads and still support creators...

[@asnbman]

Wow! This video was awesome! Thank you. Can you teach our teachers how to teach?

[@dhanashrikulkarni5878]

I absolutely love your videos Parth! Just to tell you, I am 12 and I just adore your videos!

[@hk3676]

Im 12 and think u dumb

[@beyondhumanrange6196]

u know what quantum physics is ?

[@greensombrero3641]

Imagine it's a ball and it's spinning - except it's not a ball and it isn't spinning

[@johnpaulbounce3708]

It's just like attending to my college quantum class, but more juicier and spicier. Thanks. Wonderfully explained.

[@anuragkashyap9888]

Excellent explanation .

[@ninadgadre3934]

KZbin threw this channel at me and I am thankful! Awesome stuff, Parth, looking forward to consuming all your vids!

[@laranjajefessor]

Very cool! I was thinking about the spin of an electron and how it makes it change its path in the presence of a magnetic field. And that's exactly what happened on tube TVs!

[@davidianmusic4869]

Thank you, very clear and deep description.

[@alhasan586]

Hey, I like your videos. I want to one thing and that is, " Rutherford model big mistake was Maxwell law which says if electron spin constantly it will lose power and fall inside nuclease" I want to know the deep of these theory

[@vulpecula182]

.. Interested

[@captainshipman7377]

That’s saying if electrons orbit the nucleus, they would lose energy as radiation and “fall” into the nucleus. That’s how we know electrons don’t orbit atoms. But quantum spin is different. That’s why De Broigle thought that electrons were standing “waves” instead. Like photons, electrons are also subject to wavelike behavior.

[@aarohanyt7374]

Underrated video💙

[@zeio-nara]

Thank you a lot for a clear explanation. Don't know any place where the electron spin is explained more accessible.

[@bernardolozano7429]

Underrated video and channel, good job

[@krishnaraoragavendran7592]

Bengali's are doing good science. Impressed with this Bengali culture, I did my post doc in theoretical physics at saha institute of nuclear physics, Calcutta.

[@arekkrolak6320]

Very good and informative video, I will surely check more!

[@cofa4011]

Amazing content man ! :D Thanks you very much for sharing ! I'm a total noob didnt even graduate but i'm wondering is the spin actually "carrying" the energy of the particule or is it only a way to describe a behaviour of a particule that fits both quantum mechanics and special relativity ? I hope my question makes some sense ^^'

[@yasmincheani4633]

Thank you so much. This really help me understand better especially electron spin 👍😀

[@saisuneeth8168]

can we consider that diffraction also happens due to heisenberg uncertainty principle. cause we can also think that photons angular momentum changes (bends) due to decrease in distance in double slit experiment. can it happen like that? this is a question from your diffraction video.

[@vitorgracia5113]

partly yes, i believe, constraining spin in light is polarization, and as far as i remember from a feynman lecture the diffraction event can be explained in the double slit experiment by HUP. As you constrain the possible positions the particle can take, by tightening the slit, and as (∆h/4π ≤ ∆x.∆p) , then a sufficiently small gap requires a larger momentum variance in order to mantain the equation true, so its direction increases in spread.

[@saisuneeth8168]

@@vitorgracia5113 thanks

[@Freja-z6l]

is this correct? Spin is a quantum mechanical property of electrons, which can be compared to a kind of "rotation," but it is important to understand that this "rotation" is not like the rotation we are familiar with in everyday life. Electrons have two possible spin values, often referred to as "up" and "down" (commonly written as +1/2 and −1/2). Although we use the term "spin," it does not refer to an actual physical rotation but rather to an internal quantum mechanical property. Two electrons cannot have the same spin and be in the same orbital, which means that each orbital can hold a maximum of two electrons with opposite spins. You might wonder why there can be up to 8 electrons in some energy levels when only two electrons can occupy each orbital. This is because each energy level, also called a shell, consists of multiple orbitals. For example, in the first shell, called the K shell, there is only one orbital, so it can hold only 2 electrons. In the next shell, the L shell, there are four orbitals (one s-orbital and three p-orbitals), so it can accommodate up to 8 electrons. Orbitals are regions where it is probable to find electrons. You can think of them as small "rooms," and each room can contain two electrons, one with spin-up and one with spin-down. Btw im 15 so dont jugde

[@reznovvazileski3193]

Thank you, finally :') This is what a high school teacher, a chemschool teacher and 3 college professors couldn't manage to tell me really? :') I mean they probably told me the most of it but I always got the story of yeaa it's called spin but it's not really spinning and it's a magnetic constant of sorts. Which is all nice and stuff but the little detail that slipped there is that it's a result of this implicit angular momentum, that clears up the entire picture for me :')

[@nvmffs]

But it doesn't have angular momentum, just to clear any confusion

[@abeersingh8855]

Didn't understand that concept 10 minutes ago now i do, thanks

[@bhcontraction]

I come hete because I wanted yo understand more about the muon g-2 experiment and in order to understand that, have to understand "spin" first😂

[@priyapk1017]

Thanks Parth 💜

[@danielsayre3385]

Damn this video was helpful. Thank you for the immense number of references toward resources... subbed. Thank you, seriously thank you

[@mdsaddamhossain3565]

You are an awesome Explainer, Teacher. Thank you.

[@dinghanxue704]

Need to know why spin occurs

[@DrDeuteron]

b/c all fields (particles) transform as some representation of the Lorentz group (that's math). Physically, it means it's the geometric thing that is compatible with special relativity, i.e., has no rest frame and has the same physics, regardless of motion.

[@IdeasOfAjit]

Thank you Parth for the video.

[@gethnoble4316]

Semoga bnyk skses dgn channel ini!

[@hellboy_____2019]

Thank you 3000, for this topic you have selected

[@akshatgaur84]

Thank you , awesome video.

[@vedanglad1767]

I think you might have flipped the direction of the spin at 3:13, by the right hand rule

[@laughinggooner4271]

If you didn't mention that special relativity being compatible with quantum mechanics I would never have known. I am not surprised that fermions and bosons have this half spin difference. I came to this video thinking that spin is some way affects these two groups of particles. My hypothesis was leaning towards the effect of spin on mass.

[@afriedrich1452]

Yes, that is all well and good, but "what" exactly is spin? And why do electrons have to spin around twice in order to spin around once?

[@ajhcornwall]

I don’t think he knows. And I don’t think mainstream physics has a clue either. And it bugs me that people like this can’t be more honest that they don’t have the foggiest idea how everything fits together. They like to present themselves as know-it-all experts.

[@afriedrich1452]

@@ajhcornwall Oh, I think he knows. He just doesn't want to tell us because he thinks we can't handle the truth.

[@jabbariqra6097]

In a job interview ,sometimes it is asked to write three forms of Heisenberg uncertainty principle.I thought that they asked just to confuse the candidate🤭🤭.. I really did not know about its third form.. Thank u Mr

[@rishigautam6992]

we are waiting parth

[@sisyphus645]

I have a simple analogy that can easily explain this concept. Imagine a sphere. Now imagine the sphere turning. That is spin. Except, it's not a sphere and it is not turning

[@JAUNEtheLOCKE]

HAHAHHAHAHAHHAHAHAHAH

[@sisyphus645]

@@JAUNEtheLOCKE Hey, I took the liberty of going through your channel. I must say, you're very fucking talented it's unbelievable. How old are you????

[@yenyelinito]

Love from Puerto Rico!

[@jimmypk1353]

The BEST explanation I've found so far. Succint, precise, no fancy effects/graphics. Brevity is the soul of wit!

[@jefsof117]

motion itself is the fundamental quanta - all forces and matter are made of it, tightly bound little spinning spheres of pure motion force

[@bigbtripathi]

Regardless how many Quantum videos I am seeing, I am not able to understand a thing..Still I feel interested in watching more such videos because it forces me exercise my grey cells.

[@prashantlale4976]

Boy you are amazing physics guy ♥️

[@jaybhambure5969]

@3:15 In your video. the angular momentum vector for the cricket ball is incorrect and does not follow the rules of a vector product or so called “right hand rule”.

[@sunithasomalingam2668]

Lots of Love❤️

[@bobshea6523]

5:40 why not? What keeps us from measuring more than one aspect of spin simultaneously? Is it equipment limitations or has no one tried?

[@chrisstargazer5866]

Amazing. Love your explanations .

[@narutouzumakix9201]

Quite bold of you to address a topic like this lol

[@ajhcornwall]

Thanks for the video, but although you say a few times “but the particle is not actually spinning, it just behaves as if it’s spinning”, you don’t answer the very obvious question which is “why are you so insistent that the particle is not actually spinning?”, I would really appreciate if you could answer this.

[@kidzbop38isstraightfire92]

So theres two reasons I've heard, with the second making the most sense: 1) its a point particle, meaning that there is no surface/volume to do the spinning; 2) one "revolution" of spin does NOT return it to its original position. It actually takes two revolutions, and they call this a Spinor. There is a video by PBS Spacetime on Spin and spinors thats really good, I suggest watching it

[@ajhcornwall]

@@kidzbop38isstraightfire92 thanks. I think I watched that PBS video. But whilst I appreciate the spin 1/2 characteristic rules out something simple like a spinning top, I don’t see why it necessitates making the leap to thinking of spin as an abstract property that has no physical meaning, I.e there is not something going around and around with a twist

[@kidzbop38isstraightfire92]

@@ajhcornwall agreed on why it doesn't rule out a physical spin...I actually think there is a physical spin (granted, I'm a casual physics follower so I dont know what I'm talking about), but I guess the point is that it doesnt follow conventional spin rules, according to most physicists.

[@michaelfox6831]

Wolfgang Pauli said regarding quantum mechanics, "the best that most of us can hope to achieve in physics is simply to misunderstand at a deeper level"

[@xephyr417]

​@@ajhcornwallI had the same thought. It seems as tho someone made a calculation a long time ago and said "if it were spinning, the surface has to be moving faster than the speed of light" so it can't be. But they assumed it was a sphere for that calculation. As far as I have found there are no other reasons to say spin isn't actually rotation, but I could just be wrong.

[@draasim007]

Super thanks , I will pray for you In Sha ALLAH.

[@jakelyle5663]

Great video!

[@ricardodelzealandia6290]

Nice, and not too dumbed down.

[@jeromemanceau4263]

Ooohh!! Looking forward to be watching more of your stuff!

[@rakazki01]

Thanks parth sir it helped me to answer why e spin is 1/2 in my inorganic lecture 😅

[@rmawn2816]

Thank you so much

[@karthikk4831]

i am waiting long time parth thank you

[@mahamayaz8380]

Please add video about maxwells fourth equation..waiting for so long

[@bigbtripathi]

Sometimes I feel we are overthinking topics like quantum theory and general relativity. String theory, quantum gravity etc are at another level.

[@joegonzalez6241]

So during the singularity. The energy became so compressed it collapse within it self. Creating a pull . Then Exploding faster than the speed of light until it cooled . trapping itself within itself.

[@joegonzalez6241]

Reminds me of vacuum tube for those old television sets.

[@abdulrahmanalhamali1707]

Great video, thanks!

[@STONECOLDET944]

I like how no one knows actually what spin is, but just makes loose analogies, no body knows what it is, its just an abstract concept given the name spin.