Spin in Quantum Mechanics: What Is It and Why Are Electrons Spin 1/2? Physics Basics
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- เผยแพร่เมื่อ 4 มิ.ย. 2024
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Hey everyone, I'm back with a new video! In this episode of "Quantum Mechanics, But Quickly", we're looking at the basics of Spin!
Spin is a very interesting topic that is not studied in detail until you choose to undertake a degree in physics. And yet, spin is commonly described at high school or even earlier, and we're often just told to accept that it exists. Instead of accepting it, I thought we'd take a look at what spin actually is.
Scientists noticed that some particles behaved as if they had angular momentum. For those of you familiar with angular momentum, it's just like linear momentum (p = mv), except an object gains angular momentum when it moves along an angular path (e.g. orbiting around a planet, spinning like a top, etc.).
The trouble was, the particles that seemed to have this angular momentum were showing no evidence of having any angular motion. The particles just seemed to inherently have this angular momentum, as if they were spinning like a top on their axis. Additionally, these particles would only be "spinning" with particular speeds - no faster, and no slower. This suggested that Spin was quantized - it could only take specific values. The particles could, however, spin in opposite directions. This mysterious particle property was called "spin".
(It's worth noting that particles could also gain additional angular momentum by the conventional classical means - moving along a curved path for example. But this angular momentum was added on top of the inherent Spin angular momentum the particle already had).
When Dirac came up with his famous equation, spin seemed to fall out naturally from the mathematics. Particles following the Dirac Equation needed to have this inherent angular momentum, that was not caused by any particular spinning or orbiting or anything like that. And Dirac's math suggested the Spins were also quantized just the right way (remember they could only "spin" at certain speeds, as observed experimentally).
The Dirac equation actually took into consideration Special Relativity as well as Quantum Mechanics. This suggests that Spin is a Special Relativistic effect, but this is not quite true - particles do not need to be moving at relatively high velocities in order to have Spin.
You may have heard particles being described as "Spin-1/2" (e.g. electrons) or "Spin-1", e.g. photons. In this video, we discuss what that means. We see how we can find the number of possible Spin measurement results each particle has, depending on its Spin number. We also see how we can find the exact angular momentum each particle has in each of its Spin states.
Lastly, we see that particles with half-integer spin are known as fermions, and particles with integer spin are known as bosons. These two classes of particle behave very differently to each other!
If you're unsure about how particles behave when multiple spin measurements are made on it in different directions, then I'd suggest reading up about wave function collapse and the Heisenberg Uncertainty Principle.
Thanks very much for watching - I hope this discussion of Spin in Quantum Physics was useful!
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0:00 - Intro
0:30 - What is Spin? Angular Momentum Discussions!
1:16 - Spin as Inherent Angular Momentum - Particles just kinda... have it?!
1:51 - Where does Spin come from? Special Relativity and the Dirac Equation... ish
2:35 - The Spin of an Electron: Spin Up and Spin Down
3:33 - Big thanks to our sponsor, Skillshare - free trial at the link in the description!
4:30 - How do we know electrons are "spinning" but not really? Stern Gerlach Experiment!
4:56 - Measuring the spin of an electron, Heisenberg Uncertainty Principle, Wave Function Collapse
6:21 - Spin Is Quantized! It can only take specific values :O
7:26 - Spin 1/2 and Spin 1 particles - what does this mean?
7:56 - How Spin Number gives all the spin states of the particle - with Reduced Planck Constant
8:13 - Finding all the Spin states of an Electron (Spin-1/2)0
9:16 - Finding all the Spin states of a Photon (Spin-1)
10:06 - Finding all the Spin states of a generic Spin-3/2 particle
10:34 - Fermions (half-integer spin) and Bosons (integer spin) - classes of particle!
11:08 - Thanks for watching! Check out my socials :)
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!
Dude. This was awesome. Keep it up
I guess you are an Indian?
Hi Parth, awesome videos. I had some questions regarding your video on diffraction. Is there any way to address you personally? thanx heaps
mr. parth can u make a new video its already been one week
i mean i wanna learn something new
Nice explanation. Well done!
Thanks Arvin, love your videos! :D
And i love both of your videos.. A big Thank you and love from India.
Hey Arvin!
Love your vidoes!❤
Llove you Arvin
Two finest physicist 🤩
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!
that works for integer spins.
Mass isn't an inherent property of particles though.
@@spikkelkip8128 Mass is internal momentum
For the simplest non-trivial representation, spin 1/2, spin is a spinor.
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.
Thank you so much
You gave me hope!
I read your description and you seem like the worlds most unlikable and close minded person.
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)
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😊
This is the most easiest and effective explanation of spin. Well done Parth!
Awesome Editing man ... Much Better than Previous videos. Well Done!!!
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.
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
That disallowed spin 0 photon NEEDS its own explanation!
gauge invariance gobbles it up.
Thanks Parth. You've always been a good physics teacher to me. Thanks for giving this free info to teens like me.
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 👏
Me: "gonna learn today what spin is "
Someone : "what is spin?"
Me: 🤷
Also every physicist : 🤷♂️🤷♂️
Everyone - 🤷♂️🤷♂️🤷♂️
Great Explanation, not a lot of other physics video's explain things nearly as well as you do.
Omg..the evolution of ur hairstyles is funny man😂..
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 TH-cam.
@@tmhood 😂
You explain physics better than anyone else on TH-cam. Point blank
Amazing. Love your explanations .
Thank you so much. This really help me understand better especially electron spin 👍😀
Your videos are as informative as they are fascinating. Thank you for sharing your knowledge and illustration skills!
Ooohh!! Looking forward to be watching more of your stuff!
Thank you, very clear and deep description.
Thank you 3000, for this topic you have selected
Underrated video and channel, good job
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.
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
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
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!
Very good and informative video, I will surely check more!
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.
You’re amazing! 🙌🏼
holy grale what a yt cannel feels great to have found u!!!
3:08 using the right hand rule, shouldn't up be counterclockwise while down be clockwise?
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
@@josephtraverso2700 Shouldn't angular momentum be independent of charge?
@@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
@@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.
@@josephtraverso2700 thanks buddy
TH-cam threw this channel at me and I am thankful! Awesome stuff, Parth, looking forward to consuming all your vids!
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.
i am waiting long time parth thank you
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.
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.
@@vitorgracia5113 thanks
Thank you Parth for the video.
MAZING THANKS REALLY, WONDERFJL EXPLANATION
Please do the Dirac equation
Yes please!
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!
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 ^^'
Thank you , awesome video.
Great video, thanks!
Underrated video💙
Excellent explanation .
Great video!
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!
You are amazing! People use the word magnetic and that can get in the way of learning. Thank you!
Thank you a lot for a clear explanation. Don't know any place where the electron spin is explained more accessible.
Damn this video was helpful. Thank you for the immense number of references toward resources... subbed. Thank you, seriously thank you
You are an awesome Explainer, Teacher. Thank you.
This is my favorite explanation of this!!
Hi Parth, awesome videos. I had some questions regarding your video on diffraction. Is there any way to address you personally? thanx heaps
It's just like attending to my college quantum class, but more juicier and spicier.
Thanks. Wonderfully explained.
Lots of Love❤️
Didn't understand that concept 10 minutes ago now i do, thanks
Subscribed. Thanks
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?
Oh, I think I get it! By negative limit, you mean the negative counterpart of the maximum positive momentum, right?
@@yilizhang790 i have the same doubt and i think u r right bro 👍
I had the same question
love ur content thnx
Thank you so much
Wow! This video was awesome! Thank you. Can you teach our teachers how to teach?
Boy you are amazing physics guy ♥️
i need how many videos to understand this? damn i need to make a playlist and take notes. btw, do you teach in private?
How do you create your videos?.
I want to create the ones for CS.
Semoga bnyk skses dgn channel ini!
@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”.
Thanks Parth 💜
Thank you💚
Parth can you do a video on "tensors" in feild equations?? 💗💗
Nice overview for someone new to spin
Angular momentum
Love from Puerto Rico!
What do you think of Vivian Robinson’s particle model that describes spin?
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🙃
Nice, and not too dumbed down.
At 3:14 if I see in different direction then it would be anti clock wise. it's relative. So how we would differentiate up and down spin
Heeeyy parth !! Why is no further with -ve allowed for spin . And why did you subtracted one and not added one...?
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?
Question : to know weather an electron is spin up or down ie: spinning clockwise or anti clockwise dont you have to know which part of the electron is the top surely the direction of spin reverses if the observer stands on their head (so to speak)
Just a thought.
Can an electron possibly be a wave on a string describing half a wave on one complete loop of the string. Then measuring the spin at any one state would also give the anti-phase state of the wave(180 degrees). Hence the crest of the wave would be time dependent(I.e. phase).
I absolutely love your videos Parth!
Just to tell you, I am 12 and I just adore your videos!
Im 12 and think u dumb
u know what quantum physics is ?
Thanks!
Thank you very much!
SUBSCRIBED!😀
Please add video about maxwells fourth equation..waiting for so long
I have a question.
I understand the reasoning for the use of a ball model to represent particles. For your research do you still use the ball model? if not what do you use.
I enjoy your videos 👌
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.
You are the best:)
5:50 ...So are you saying that the Spin can be 'around' any chosen measurement axis?
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
.. Interested
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.
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😂
Bro but can we relate spin with shape of the object like in one book it is given that if spin is 1 then the object would look similar after one rotation if 2 then half rotation but how to deal it in the case of electron is there any shape with repeats itself after 2 complete turns
Thank you love your videos
can you please make a video about the water spin property?
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...
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?
I have a question in case of torque- can a single force generate torque or is there multiple forces needed to generate torque??
Please answer my question 🙏
I think you might have flipped the direction of the spin at 3:13, by the right hand rule
Does a stationary electron have spin? If so it should act like a magnet and have a dipole moment, and therefore if sitting in a B field, should be affected by it. However the Lorentz Force says that there is no such interaction if the electron is stationary, ie has zero velocity. Which one is right?
Actually figured this out. The electron will have forces on it, just no net force. As it is behaving like a magnetic dipole, it will have equal and opposite forces due to the B field on each Pole. This will mean it will have a Torque on it, but no resultant force and this is in keeping with the Lorentz Formula.
Great video! Could you please give an example of the superposition of a spin-3/2 particle, complete with all 4 of its probabilities (or probability amplitudes)? I'm hoping there is an example spin-3/2 particle where all of the probabilities are not equally likely - as they apparently must be for any spin-1/2 particles that are used in common examples. Or does the conservation of angular momentum require all four probabilities to be equal?
The probabilities for a spin half particle need not be equal! (assuming you’re referring to the probability of it being spin up or spin down).
Maybe in simple examples the probabilities are equal but that will only be for a single moment in time! The amplitudes evolve according to the Schrodinger equation and there is nothing in quantum mechanics to imply that they need to be stationary or equal to each other!
The same applies for a spin 3/2 particle (with the spin states 3/2, 1/2, -1/2, -3/2). If the amplitudes are equal this will only be for a moment in time. They will evolve again in time according to the Schrodinger equation (in particular the Hamiltonian, aka the “energy” of the system).
Please make a video about solitons.
Thanks parth sir it helped me to answer why e spin is 1/2 in my inorganic lecture 😅