What is Spin? | Quantum Mechanics
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- Опубликовано: 29 июл 2015
- Follow up video: • Is Spin Angular Moment...
Research assignment: Teach me about spin.
Below there are suggested questions, recommended sources and my social media accounts:
QUESTIONS:
Questions that require less research:
1. This is our first real example of quantization, the phenomena that gives quantum mechanics it’s name. Here’s what it means. In the classical case of magnets going through a Stern Gerlach machine, the magnets can end up any where in the range. But in quantum mechanics, its can only be exactly up or down, these discrete values rather than a continuous range in between. This sort of quantization really bothered physicists. Can you understand why? And is there any classical physics phenomenon that also has sort of quantization?
2. Do you think that eventually all quantities in physics can be explained in terms of deeper physics? Are there any examples of quantities that later on did get explained through a more encompassing theory?
3. How can you use the Stern-Gerlach machine to measure spin in the ‘forward-backward’ direction?
4. Why do half the particles go left, half right at 4:24?
Questions that (probably) require research:
5. What are bosons and fermions? What’s spin got to do with it? If you really want to get into it, read ch 4, volume 3 of The Feynman Lectures: www.feynmanlectures.caltech.ed...
6. Electrons are so-called spin 1/2 particles. Are there any other spin types? What determines what spin a particle will have?
7. How does spin relate to the Pauli exclusion principle?
8. Explain how the Stern-Gerlach machine works
9. Is light polarization a type of spin? What are arguments for and against this? What spin does a photon have (spin 1/2, spin 1 etc)?
10. Why is it that charged particles moving causes magnetic fields- according to Einstein? (Look up relativity and electromagnetism)
11. What’s wrong with saying the electron is infinitely small? What experiments measure the electrons size? Are protons also infinitely small?
12. Find other reasons we don’t believe electrons are actually spinning. (An interesting one is about rotating a spin particle 360 degrees, and not getting back the exact same wavefunction.)
13. a) What is the Bloch Sphere, and why can we use it to represent spin? How do you visualise the spin left state on it? how about spin forward? (comp.uark.edu/~jgeabana/blocha... , note that a 2-level system is any particle that only has two options when measured (eg only up or down). |0) and |1) are the generic labels we’ll put on these options)
b) Also, How do you write spin forward in terms of up and down (i.e. |forward)=a|up)+b|down))? You will probably need to look this up, so it’s useful to know the spin “up/down”ness is usually called spin in the z direction, spin “left/right”ness is spin in the x direction, and spin “forward/backward” is spin in the y direction. You can figure this out by looking at the Bloch sphere.
14. Magnetic Resonance Imaginging (MRI) is an important clinical technic that completely relies on manipulating spin. Explain it! www.scholarpedia.org/article/M...
15. What happens to the electrons if you put them into the Stern-Gerlach machine and then slowly rotated from up and down to side and side, do some of the electrons switch places? (Thank you Majoofi)
16. Why aren't there magnetic monopoles? (Thanks Culwin)
17. What is isospin? Why is it that, even though it hasn't got the units of angular momentum, it still 'formally acts like spin?' according to Wiki? (Thanks Hythloday71)
RECOMMENDED SOURCES ON SPIN
The Feynman lectures, Volume 3: www.feynmanlectures.caltech.ed...
Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particle Physics- Eisberg and Resnick, the chapters of angular momentum and spin. This is a good one if you already know basic classical electromagnetism. Don't buy it, just visit your local university library and just read it there.
Sneaking a Look at God's Cards - Ghirardi. This is one of my favourite quantum books. It talks about the Stern-Gerlach experiment.
Wikipedia or Scholarpedia. These are always a good place to start- though sometimes they can throw you into the maths. Don't panic if you don't get all of it. Just try to glean the main idea, and that's more than enough to report here. Hopefully then others can help with any details that were confusing.
The Story of Spin. Thank you Michael Sommers for the recommendation. I haven't read it, but it seems good! Hard to find though.
/ 1. .
A Veritasium and Minute Physics video about electromagnetism! Thanks EnellGmz for reminding me about it. • How Special Relativity...
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I asked my chem mate what is spin i think he gave me the best answer: "imagine a ball spinning except it's not a ball and it's not spinning"
holy shit, base on the video, this is exactly how it is
Also, needs to spin twice to present the same side...
Totally makes sense dosent it...?
@@antoniomaglione4101 I tried to imagine a > 3 dimensional situation where that would happen but failed. Does that actually seem to be the case somewhere?
@@avrenna Beside the graviton (which can't be relativistically renormalised) many nuclei and atoms have j = 2. Thereis no 3D considerations, but refers to the eigenvalues of jz which is the projection of the spin.
"What is energy? What is Charge? It seems like we define these things by how we measure them". And this is how we detect a good scientist
Years back genes were just called as factors
it seems like
we define these things
and
What is energy
7:37 "Feeling like we understand something stops us from asking what it is." Perfectly put.
how does spinning work on a one dimensional axis?
Although that seems to be like arriving at a desired destination , then driving all the way back just to find out how you got there in the first place . Maybe I am missing something , I am open to learn from others perspective , especially if I am wrong in mine. Thank you for taking time to read my response
"It seems that we define … things by how we measure them."
There's a lot of wisdom in those words.
There really is... We just put manmade labels on things and then call it fact. I'm here because I'm trying to figure out why we assume magnetic field "vectors" have direction. It seems we just _chose_ to *define* that they move from "north" to "south" without any actual evidence for this.
The best evidence offered is that the little red part of the needle on a compass points to one end.... uhhh, and we simply ignore that the other side points to the opposite. A vector can't run in two directions. No no, it's the right hand rule. But again, there is an equal and opposite reaction. All these labels and definitions that attempt to explain these forces, I suspect, are highly misleading and cause people to not see reality for what it is. Highly dubious and damaging to the inquisitive child-like nature of the mind. All our manmade models of the fundamental forces of nature are to be wholly and categorically ignored and dismissed. Take the data. Ignore the model.
I suspect in the future all our definitions will be thrown in the rubbish bin. Yesterdays ether is tomorrows quantum mechanics. I anticipate that we'll be going back to yesterdays model with what we've learnt from todays.
The girl in this video nailed it. Absolutely nailed it.
@@entertainme121 you're right, but terrible example. They do have a direction, fact is we made a choice about what we should call them and how we're going to put an arrow on it, but as long as you're consistent, if you make it go on the oposite direction of what you called + you'll probably get a different result. (exceptions on even functions? things? ya know? where f(-x) = f(x)
@@entertainme121 magnetic fields DO have direction. but forget about 'lines of force'. the magnetic field carries force between moving (technically, spinning or rotating) charges. steady currents can only flow in closed loops. there is also force between elements of parallel currents, but that's doing it wrong. ignoring the other half of the loop leads to erroneous conclusions.
i like the law of Biot and Savart for describing magnetic fields. for certain cases like circular loops of current or spinning electrons, the field is simple and no calculus is required. for other shapes of loops, the field at any point is given by adding the contributions of each element of current, which are vectors. the field of an element of current, at any point, is inverse-square in strength from that element, in a direction perpendicular to both the current and the radius to that point. so the field at any point is a vector sum, which is a vector. magnetic fields really carry 'electric angular momentum'. same particle that carries electric field, but spinning. the spin is magnetic field.
@@entertainme121 If you're so worried about choice of frame, why not just work over your favorite principal bundle like all the rest of the modern physicists?
It ain't profound
"Not knowing things isn't dumb, but pretending you do is"
So true. Thanks for a great video, I'll be sure to check out these questions and write a blog post.
Socrates said something similar, too, about 2500 years ago! He was too gentle to use a label like "dumb," so, he simply said: "there are many who think they know, so, they don't seem to know that they don't know. I alone know that I don't know. That's why they say I am the wisest in Athens."
Even though I mostly agree with the sentiment, I would like to point out that somebody who doesn't know that they don't know is not dumb.
When it comes to pretending, let's consider two cases:
1. The person feels strongly that they must have a strong opinion (two strongs!)
2. The person isn't aware that they have a strong opinion, but they do.
In either case, I can forgive them. I won't label them as dumb. That, after all, would be a dumb thing to do.. In fact, an error doesn't even require forgiveness. It needs correction. Hopefully, a gentle correction. Else, it would be an error, too.
One final note: there are dumb opinions and dumb acts. No dumb people. Even the infamous presidents around the world, not just in Africa and Asia and South America, but also Europe and North America!
How wise that the gentle and wise speaker of this video also labeled the act as dumb. The act of pretending.
Enough said. Maybe more than enough. This was the best video I saw on spin (and also metaphysics of QM). Thank you! I just subscribed.
@@BulentBasaran Very well said!
Bulent Basaran I disagree
Hey
@@BulentBasaran If you check - en.wikipedia.org/wiki/I_know_that_I_know_nothing#Etymology The evidence that Socrates does not actually claim to know nothing can be found at Apology 29b-c, where he claims twice to know something. See also Apology 29d, where Socrates indicates that he is so confident in his claim to knowledge at 29b-c that he is willing to die for it.
What Socrates actually said was - "... ἔοικα γοῦν τούτου γε σμικρῷ τινι αὐτῷ τούτῳ σοφώτερος εἶναι, ὅτι ἃ μὴ οἶδα οὐδὲ οἴομαι εἰδέναι.
"
... I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either. [from the Henry Cary literal translation of 1897]
So my point is he meant that he knows what his gaps in his knowledge are.
Now I do fully agree with you, it is not that the person is dumb rather it is the act of pretending that is dumb. If the person stops pretending, he can stop being stupid. This way of conceptualizing people allows them to grow and improve rather than internalize these tags.
Now I do agree that it is not stupid (dumb) to not know what we don't know. All of us have gaps in what we know and it is a certainty that we don't know the full list of these gaps. We can't know really.
Ok now coming to pretending, sure I can usually forgive them too. Lots of times they have their own reasons - they feel insecure about themselves, they don't want to hear me explain it, etc
But the two cases you presented do not seem to be dichotomous nor a useful way of dividing it into cases.
Often the need to hold a strong opinion on something isn't something most of us are "aware" of. So I can't think of many real cases of 1) while 2) is very common.
But I do think it is stupid to want to find a strong opinion. An opinion should only be strong if you have a correspondingly large collection of evidence supporting it. Wishing or needing for your opinion to be strong is irrational. But again I do understand that humans need certainty in their life and they prefer a wrong answer to no answer. But that just means we identify our flaws and we promote good thinking. We don't say it is ok to be irrational, we hold everyone to a high standard.
In the case of 2) we can just promote introspection, try to see when you get emotional, often it is because your core belief was challenged. It is too common for me to call those people stupid. But I think those who don't fall into 2) are talented, admirable individuals.
Ok finally when we say nothing belongs to X category you are basically saying the word is useless. We define words to have meaning. So it is a fact that people have different mental capacity. We grow at different rates for sure. I am not even sure if we all have the point where we hit diminishing returns near each other. For sure people have different talents, but it is not all fair in my opinion. Some people have a lot, some people have less. There are geniuses out there, there are people with learning disabilities. I do think there are dumb people out there. Mostly we can call actions dumb and behaviours dumb and try to disassociate it from the individual, but at some point, habits form, and values become a core part of who you are. Some people are practically beyond saving in specific areas. Like I think I am dumb in fashion, I am young and so maybe I can change but it is so unlikely and I have such bad aptitude for it that I think its an accurate way to describe me. But again this is all a Truthful look at humanity.
If you want to teach and help people, its fine to believe no human is dumb and everyone has infinite potential etc. Lots of myths are powerful and useful when we hold them collectively.
"Not knowing things isn't dumb, but pretending you do is."
This was one of my single favorite lines of yours so far, and so very, very true.
Not knowing things is dumb.
Pretending to know things is stupid
One of my favorite lines from any video lol
What If you don’t know something but think you do so you act like you do know something. Are you still dumb?
Klingons are stupid, but they can still use this stuff to build their disruptor pistols.
Well, she presented the best explanation I've ever seen yet for quantum 'spin': you cannot define it except operationally: 'spin is the property of a particle that makes it do _this_ in a Stern-Gerlach apparatus' .
This explanation satisfies a key component of our puzzlement: "What part of quantum 'spin' justifies its retention of the idea of spinning-ness?". Well, because of her preamble on an electron going around in a circle (revolving, which is kinda-like... rotating). When the e goes around in a circle it displays a connection with magnetism. And when a non-revolving electron goes through a magnetically salient apparatus, it _still_ betrays an affinity for magnetic behavior, albeit mysteriously aberrant.
This tells us further that quantum spin isn't simply a (dynamic) _geometric_ phenomenon, and that naïve expectation isn't normally addressed by most 'explanations', those latter leave us a with a subconscious unease that something has been ignored in the profusion of verbiage on 'spinors', 'intrinsic angular momentum', and the like.
My only criticism was the intervening material on quantum notation and eigenstates, which came out of a clear blue sky and over most people's heads. It might have been left for a later treatment.
I’m reading Ohanian (1986), “What is spin?” It suggests spin is not just a quantum property, but more generally a wave property. Not internal or intrinsic (to e.g. an electron), but a field property. So I was impressed by the humility and openness in your video
I love how she doesn't just ignore the math like other science youtubers. Keep it up, thanks.
Wow at last someone has the courage to honestly explain that we don't understand spin instead of saying we wouldn't understand. Thanks..
David R well since quantum mechanics tend to be pretty difficult to impossible to imagine so math really is the only way to go.
Getting the right prediction is after all the goal and being able to imagine it is only a bonus.
Getting the right prediction is only one of the goals. Another is trying to make sense of fundamental reality.
TROUBLE with the ELECTRON SPIN:
ruclips.net/video/eqyi9oX9olA/видео.html
My quantum teacher was obsessed with the Stern-Gerlach experiment. There's a whole chapter on it in my grad quantum book: "A Modern Approach to Quantum Mechanics" by John S Townsend. It might be worth checking out... just beware. The book doesn't use SI units (very few quantum books do), so don't get hung up on units for formulas.
"Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particle Physics" by Eisberg & Resnick was a good suggestion in the video description. Unfortunately, it doesn't do a whole lot of bra-ket notation. They mostly stick to integrals to appeal to a wider audience.
As for my personal thoughts on spin, I don't think anyone really understands why it's there. I find it interesting that particles can have inherent angular momentum, but not inherent linear momentum. It makes angular momentum seem more fundamental. This kind of makes sense if you've seen the "A Character of Physical Law" lectures by Feynman (from 1964). In one (or the seven lectures in the series), he explains how you can get linear momentum by measuring angular momentum from really far away. If you haven't seen them, you should check them out... although, they're each an hour so it's huge time commitment. It's one of those things where you watch one lecture a day. When I watched them, I took notes :-)
Looking Glass Universe P.S. Almost forgot. Tumblr was originally supposed to be a blog (I think), but it mainly gets used for posting animated gifs and short text posts (like a sentence of a paragraph). It took me a while to figure it out, but I did. You're never too old for new things... it just takes a little longer. I literally just got an Instagram last week.
There are two things I love about Tumblr:
1) There's a queue for your own posts, so you don't have to worry about posting every day. I usually just like things whenever I'm on... then, on some idle Sunday, I'll spend an hour or so going through all my likes and filling up my queue. It has settings for how often it will post for you (I usually choose once or twice per day). The only time I post or "reblog" something immediately is when it's time-sensitive like current events or something.
2) There's an "ask box." Basically, if you turn the feature on, followers can ask you questions directly. They sit in your ask box until you get around to answering them. When you do answer them, the question along with your answer becomes one of your public posts (unless you specifically choose to answer it "privately").
***** Thank you !!!
I think people thought I was joking when I said I didn't know how to use it. I'll try use this queue feature and ask box :) Thanks helps!
***** Thanks for the book recommendation! Trying to find a copy now. I just saw that the contents starts with the S-G experiment. I really like when books do that, like Sakurai.
Yeah, those lectures are wonderful :) I hadn't really considered the idea that angular momentum is more fundamental, but I see your point. Really interesting idea... hmmm
Looking Glass Universe You're welcome :-)
This may sound stupid but I'm a young person who doesn't know what to study and btw my first language isn't English but what did you study or what are you studying? And why?
I ran into this video again years after seeing it, and shortly after seeing SpaceTime's "What is Energy". Despite holding an electrical engineering degree I found the definition of energy "disorienting" because for the first time really I thought about what it meant. Condensing his 10 minute video to the one phrase he used, energy is "an accounting trick". Deeply disturbing in my opinion because it didn't answer the question at all. And watching this video after that, even though I appreciated it the first time I saw it, I came away with the same sort of resignation that we don't really understand reality. We can measure it, we can predict it, we can characterize it, but we don't *KNOW* what is actually going on underneath.
As I've said on SpaceTime's video, I've been prone to saying we're just "energy", for years now. We say we're matter but we go down and we get to our molecular DNA and what are they? Collections of atoms. And you go down further and what are they? Collections of nucleic particles. And you go down further and what are they? Quarks! And what are they? Bundles of energy! And what is that? "An accounting trick!"
I'm an accounting trick?
Disturbing.
Matter is a manifestation of energy.. just like everything else
@@Birginio420 And like this video, according to Matt Dowd/PBS SpaceTime, energy is an accounting method. It's not the final resting place of our understanding. It's just an entry in an equation. A cell in a spreadsheet. If you understand what I'm saying you'll find that deeply disturbing.
@@darioinfini I would like to agree with you but I don´t know how. Energy is accounting for how much work you need to do things. Like how much work you need to detach an electron from its atom. But it also tells you how much work you need in order to put a satellite in orbit at certain speed. Then you may ask how many electron detachments are equivalent to the work needed to put in orbit that satellite. It is a coherent way to relate the work done by different processes at different scales. No mystery there at all.
@@DJVARAO But you can't use electrons as part of the definition of the phenomenon that results in electrons existing. All you're doing is defining a measurement of energy, not defining energy.
@@shaftahoy That's how it works in physics. Einstein's definition of time?: what a clock measures.
One thing I love about RUclips being a mature platform is I can find awesome content from years ago!
Wow, thank you so much to everyone who's participated! It's been really fun to read and think about your comments. It was my birthday yesterday so I was doing things yesterday and will be doing things all of today. But after that, I'll finally get around to answering everyone.
Looking Glass Universe Happy birthday.
Looking Glass Universe Happy Belated Birthday!
Haapy wonderfull birthday
Looking Glass Universe Happy belated birthday!
+Looking Glass Universe thanks for the video! It was really helpful in understanding spin.
*『I N F I N I T E S P I N』*
Johnny ! Lesson 5 !... yeah, I'm sure that's what we're on right now.
Arigato. Gyro...
This is the last place i expected to see a refference but im loving it
@Johnny Joestar damn its the boy
@@usakenvi buon giorno!! I see another man of culture aswell
Towards the end of the video where you say that you don't understand fully physics terms like energy and charge because we usually define them as how we measure them, I really started to get what you mean. That really hits home considering when you look up the definition of charge most will say that's it's just a property of a particle. Saying what you did was really down-to-earth and I think that brings our thought processes together. Nice touch on that account, great video.
Beginning of the video: I'll tell u what is spin.
End of the video: no I can't do that!
Literally the very beginning in the video:
"I'll explain why we can't define it"
"If I knew I would tell you"
Basically Gyro
@@forkrolls well yes, but no.
Lmao
she's being a schrodingers cat, she can explain and can't explain at the same time
A very good video! While it definitely helps to imagine the Stern-Gerlach experiment being performed with free electrons, doing so would unfortunately make the experiment impossible. Magnetic fields interact with charged particles through the Lorentz force, which would cause an electron to be deflected out the sides of the apparatus. The original experiment used silver atoms, which have one outer electron in an s-shell (which has no orbit angular momentum), revealing that the lone valence electron must have had an intrinsic dipole moment.
"Not knowing things isn't dumb. But pretending you do... is!" So simple... yet so true! Thank you so much for giving me a motto for life!
"Lesson 1, Johnny."
Pizza mozarela🎵🎵
Thank you for this video. I've been reading David Albert's book on Quantum Mechanics after taking a one-semester QM course. This is, by far, one of the best videos I've found to use in conjunction with studying the Stern-Gerlach experiment. It doesn't just describe the experiment. It provides the intuition from classical physics and why this experiment "broke' our expectations. Thank you so much for this!
As a high school science teacher I am required to teach these concepts without advanced mathematics and I find myself committing gaffes all of the time. Your videos have given me some great ideas.
Great video!
Eugene Khutoryansky Thank you :D
Physics Videos by Eugene Khutoryansky I love your channel, hi
I love your channel too!
your channel is awesome too
Wow top 10 anime crossovers
It's what you're gonna need to master if we're gonna win this race, Johnny
K 👉🏻👌🤟🏻🤓🤪👉🏻
Arigato, Gyro…
This is the first physics video, that is honest, that I've seen on YT. Thank you for your honesty.
This makes sense, which is great. The best part for a layman like me was this: 7:35 (which was also great because it voiced how I feel about every science textbook "this is how it is, now stop asking about it") where you plainly say "spin is what makes a particle like a magnet". If someone had said that to me a long time ago, I feel like I would have understood sooner. It would have made more sense to me if they called it "bearing" like on a compass. Calling it a verb like "spin" would be like calling energy "shock" or "burn".
I'm glad that resonated with you too. When I was making this video I'd spent weeks and weeks going 'what is spin? But what *is* spin?" and it was only when I realised this that I could be less frustrated about it.
I like your analogy of calling energy "shock" or "burn", that's a good way to put it!
Looking Glass Universe Thanks!
How can metal move without moving it 🤫🤓🤟🏻🧲🔀♾
Finally! Thank you so much for this. As an extreme lay person, I've tried very hard to find a clear explanation of spin. It's usually just hand waved away (often with, what seems like, the insinuation that it is beyond the lay person to grasp). Thank you for owing up to the simple fact that we just don't know - and then following up with a very clear, breakdown of how to understand the basics of what we do know. This was super helpful!
I've been bingeing videos that explain spin to the non-physicist, and this is the best. Very well done.
Thank you. This is very useful. I love how you leave an open question at the end. It makes me want to discover more.
Excellent video, at least someone explains what we really know about spin in an honest way ! I also liked a lot the advise given at the end of the clip in order to explore and not be afraid of being wrong, that's absolutely great, those are concepts that in my view are even more important that whatever we may or may not understand about a specific topic, they outline the right attitude toward science. Congrats, just discover this channel and I am liking it a lot. Already subscribed. Thanks a lot.
Thank you for explaining this like a normal person 🙏 physics often neglects to get to the point about how we’ve actually detected things like spin and they just try to give us lame analogies. You’ve explained everything we know and nothing more! That is how it should be
The first time, I achieved a glimpse of understanding of the term spin.
Well explained.
First step to understand quantum mechanics is to let go the need of illustrations.
Quantum Mechanics works different. To accept that, is the first step.
I'm loving your videos! I was longing for some casual yet heavy physics videos and you are hitting just that spot! Thank you so much for your work and keep them comin' :)
Blimey! At last a vid on particle-spin that I could actually follow! YAAAAY!!!
It’s when you harness the energy of the ‘golden spiral’
Jojo reference
The golden ratio
Thanks for this nice video. I appreciate you breaking down how we measure spin, including the limitations of the means we have available.
Your effort is highly appreciated, someone had said that "If anyone knows quantum physics then he knows it, if he little bit knows it then he knows nothing."
I don't understand spin but I love your voice, that's something
patrice373 and accent, don't forget the accent ^-^
It doe's really spin, it is more like a charge orienting the electron. In theory if I understood it should spin to create elctro-magnetism, so that's why they call it spin.
@MrBadassheavymetal, South African , love it, clear and warm
Francois Morin From what I have read the electron can't be considered to be actually "spinning" to create it's magnetic field otherwise it would be spinning hundreds of times faster than the speed of light when calculated. IIRC, Pauli made a point of this when this idea was brought to his attention. It's considered an intrinsic property that is mathematically described as if it was spinning. Just one of the ways QM is a bit frustrating.
I won't argue against that. They call it spin and it is confusing because they talk more about the change of poles not really a spin. Thanks for pointing it again, because we do get caught up in terminology just like there was no Bang in Big Bang as there was no air so no sound to be heard.
I love cool channels that I find by accident. I can dig on this one for a WHILE.
'Gracias.
Wow, I have the feeling you covered most of my thoughts about my attitude to learning and teaching in absolutely short, easy and wise way. Thank you really much, your way of understanding this greatly helps me, "not knowing is not dumb, but pretending you do is"- I will save this cite in my heart, thank you for this great deal of wisdom, I hope I will use it;)
Love this, your clear explanations, clever graphics and marvelous sense of humor.
What is Spin ? I think the answer is phase shift (= shift in coordinate).
1. I think the de Broglie waves of multiple particles in one quantum state are connected in series, and the each wave shift msλ at the connecting point. (ms:spin quantum number, λ:wave length)Let us consider a case in which two electrons are in one quantum state [n,l,ml,ms=+1/2].
The de Broglie wave of 1st electron shifts +λ/2 in coordinate. And the de Broglie wave of 2nd electron shifts +λ/2+λ/2 in coordinate. Accordingly the two waves destructively interfere.
[the Pauli exclusion principle]
2. Suppose that two electrons are moving in a single orbit, and suppose that the de Broglie wave of one electron shifts +λ/2 in coordinate and the de Broglie wave of another electron shifts -λ/2 in coordinate.
The two waves have the shift of exactly one wavelength, which leads to a constructive interference of the wave, making it possible for the two particles to move in the same orbit.
[the 4th quantum number]
3. The variable of wave function Φ{φ･(r ×p)} in φ direction has angular momentum r ×p.
Accordingly, the shift in coordinate msλ change the angular momentum as follows: ml(h/2π)→ ml(h/2π)+ms(h/2π).
I'm sorry that I'm not good at English.
So why do moons/stars spin backwards creating an angular problem?
As an engineering student with acute shyness in advanced physics, I'd love to listen to you talking about everything else I need to learn. Like... forever. Will you consider?
Really enjoying the videos, thank you!
victortries Aww thank you! I might happen to explain some of the things in your course, but I don't really intend on making tutorial style videos... Sorry!
charge and energy were also my questions, i am so glade to know some one in the physics world shares the same, looks like spin is going to be added to the list now. Thank you so much, nice videos keep up the good work
Great exposition! I loved it! Thank you so much for sharing!
When thinking about the spin of a particle i'm rather visualizing it as spinning "inwards" or "outwards" in the sense that it still denotes a binary state of the particle, but with more emphasis on the kinetic interaction between that particle and an external event without having to refer to an external system of direction.
interesting, but if one considers the total angular momentum of an electron in a hydrogen atom, it would be equal to the sum of the angular momentum due to electron circulating around the proton and that due to the spin of the electron.
I think I just found my new favorite channel...I friggin love you!
You are an awesome teacher and your little drawings add so much to your video. ...I think I understood spin for the first time !! Thank You
8:52
Plot Twist: She just wants us to do her homework for her so she can chill
Plot twist: Particles don't actually spin.
Atoms of silver were used in Stern-Gerlach experiment due to their neutral charge. Electrons, or any charged particles, that move in magnetic field feel the Lorentz force. The non-linear path of silver atoms was another hint that spin is not assosiated with classical spinning/moving charge.
Atoms of Silver, the NBA commissioner?
this was an excellent video. i believe that when trying to illustrate a new concept, you should show the problem that brought about its creation. you did exactly that.
You are an amazing educator. How (the youtube nerd that I am) am I still learning about this channel is beyond me. thank you very much.
I'm going to try answer: 8. Explain how the Stern-Gerlach machine works,
since I still don't get it.
What is this :o
Looking Glass Universe What don't you get about it?
Here's a nice write-up: web.mit.edu/8.13/www/JLExperiments/JLExp18.pdf
Michael Sommers Thank you for the link! In particular, I don't understand why a magnetic dipole larmour prodesses. It's a very particular point about it that didn't make sense to me. But I've got a book that I think answers it, but I've leant it to a friend. Going to try get it back on Sunday.
Looking Glass Universe Ah. I can't help with that. I remember the phrase 'Larmor precession', but nothing else about it. Decades of disuse have caused me to forget most of what I ever knew about physics (and I don't think I ever knew as much as I thought I knew).
I'm only now realising how little physics I ever knew...
According to me e can expressed as a complex function where variables change by many factors some from itself some from others.that gives them different magnetic properties.and all I saidjust came in my mind after watching this video
As a pretty enthusiastic lay person, I've been waiting for this video for years. Thanks for clearing up that this isn't at all cleared up :)
Thanks for the video. It's really informative to me, even it's just video provided quick glimpse on spin.
Can you make a video about the planks constant?
Is like hamon but for the rebooted jojo universe with johnny and gyro.
You forgot Wekapipo
Wow I came here thinking this but... to see it outside my head
There really are JoJo references everywhere isn't there?
Physics baby up down left right 🤪👉🏻
@@AN-vs5pb wait till part 7 is animated. It is already scary how anything that has to do with spirals or spinning has jojo references.
OMG!!! those questions in the description made my head spin a lot faster than any spinning subatomic partical that iam aware of😵😵😵
"Thinking you understood something stops you from asking what it is" whoa!! Just subscribed
Ah, I read a little bit about this in A Brief History of Time. I still need to finish the book but I'll come back later with knowledge
Well, particles are irreducible and unitary representations of the Poincaré group. Given that the Lie algebra of this group is isomorphic to 2 copies of that of SU(2), spin is then the sum of the weights of each representations (the two can differ). Labeling the representations with half-integers makes the Casimir (an operator acting uniquely in each irreducible representation) eigenvalues nice. So spin (as half-integer multiples) is a needed number to describe particles if we want them to be translational, rotational and boost invariant quantum objects we cannot break further (irreducible).
Do physicists use "representation" for both the representation map and the vector space of group action?
Came to learn spin and instead of knowing it , I Iearned the truth and beautiful wisdom . Loved the video
Just discovered your videos and I do find them very good with information. Although I am lost but I am just starting to learn these things. Your videos are great and love your voice.
"whenever a charged particle moves, it creates a magnetic field"
Does relativity come into play there? could I get an electron to create a magnetic feild just by standing on a moving train, for example?
Yes! In fact, special relativity says that electric fields and magnetic fields are the same thing but from different reference frames.
@@tracyh5751 then how come I don't spout electric bolts/magnetize whenever a bird flies overhead?
Because being in the presence of an extremely weak magnetic field caused by the movement of charges in a mostly charge neutral object isn't expected to have any sort of noticeable effect.
@@benthomason3307 you know, if that bird is flying at 99.9999999% the speed of light, you are flat as pancake and nearly frozen in time....but you don't really notice what's going in its reference frame.
For an observer on the ground,yes a magnetic field is produced.
But with respect to you,the electron is not moving,so no magnetic field.
Yes, magnetic field is relative
Arigatou... Gyro
HxH community everywhere...
@@MonographicSingleheaded bruh
@@MonographicSingleheaded Yep. Definitely that
@@randomperson-vv5oq didnt you die in the election tho?
Aye sup
This was brilliant!!! Thanks so much for putting this out there!
Thanks! I got my degree in physics 30 years ago, and at that time, I didn't have a good handle on spin, except for how it comes out of the math. After all that time, I still can't really understand what it means. Then your video showed me that I was right all along. It doesn't make any sense! :-)
The infinitely small spin makes me think of curl. It’s literally the spin of an infinitesimal point, and is what determines magnetic fields per Maxwell’s equations. How accurate is this thought?
It's not spinning but rather Vibrating at different FREQUENCY the difference in Vibration at that point is the mass Energy EQUILIBRIUM and the additive is the Wave function.Delta represent the particles energy at point x Represent a Eigenvalues or a translational SYMMETRY of particles wave spin determine the INTERGER value of Spin as ELECTRIC magnetic and Isoelectric valies
Maybe it’s similar to the Fibonacci Sequence whee it spins in a path that gets smaller and smaller quicker and quicker, until it theoretically reaches an infinitely small point that spins at incredible speeds.
JOJO reference is what spin is
@Kur Ajing hating jojo,is a jojo reference
@Kur Ajing YOU FELL FOR IT YOU FOOL,I WAITING FOR YOU TO SAY FUNNY,FUNNY VALENTINE!
𝚆𝚑 𝚠𝚑 𝚠𝚑𝚊𝚝? 𝙻𝚘𝚕
OMG, I LOVE YOUR INSIGHTS INTO THIS THEME, IT'S SO HONEST AND IT MAKES US FEEL LESS IGNORANT. SPIN IS NOT A FULLY UNDERSTOOD PROPERTY OF PARTICLES EVEN BY PHYSICISTS.
Excellent video. I never get tired of thinking about things like 'spin', and what they might mean.
JoJo reference
*Tusk Act 4 has entered the chat*
Great video. I like the explicit focus on "how something works isn't the same as why something exists." I like leaving open areas for new scientists to ponder, perhaps a better solution... for what? for anything.
Professor Looking Glass!!!! I think I finally understand spin! Thank You!
I see - said the the blind man.
Who picked up his hammer and saw. ;)
Stevie Wonder Said that
k a k y o i n
To the deaf woman
I could hurt you without a slap Yano babe ♾🔀🤟🏻
I studied physics at uni (many years ago) and remember my tutor explaining an experiment in which elections are fired at a disk. The electrons are particles but had 'spin' in a particular direction.
After a short time, the disk would start to rotate (acquire angular momentum), this therefore demonstrates that the 'spin' of a particle (which does not mean it's spinning) gives the spinning motion to the disk.
I feel the urgent need to find a youtube channel that gives detailed videos of actual experiments in physics demonstrating these and other properties of nature to see for myself. This includes Youngs double slit experiment and others, to get a feel of what and how these phenomena are realised.
Any suggestions ?
Unfortunately, you may have to watch many videos or read many documents. But you may get pretty far by just watching a few videos or reading a few documents, depending on your selection criteria and your skills.
Read ton of books watched couple of videos but it was in your video, that I seek refuge inn. Thank❤❤ you
Love it. Reminds me of minutephysics. Also, the lack of certainty around the meaning/reason is refreshing, and I think a good counterpoint to the certainty and precision of what we've experimentally observed.
Spin may not be intuitive, but I think it helps to remember that magnetic fields are really just electric fields being "observed" by charged particles in relative motion. When one charged particle moves relative to a line charge, it "measures" the line charge as being length-contracted, and then experiences a push or pull as a result.
Glad this has come up, special relativity...
I understand how this happens in a current carrying wire, but how does this work in a permanent magnet? Does the electron movement or spin create the magnetic field through relativity?
ruclips.net/video/1TKSfAkWWN0/видео.html
7:55 oh few, a definition I can remember
I like how you stated that when we don’t fully understand something, we call it by how it is measured, for example, energy. That reminds me that when I look for a definition of time, I read things like that which we measure with clocks.
I have to say you have and awesome outlook on relearning what others have guessed at. Way to think out of the box!!!!
The Spin is simply the way my head feels after watching this video and feeling traumatized by a inner bombardment of questions springing from what seemed to be an answer to what Spin is so, we had a little talk me, myself and I came to the conclusion that Spin is simply confusion XD Thanks for the video !
PS : Also, thanks for ruining many sleep hours to come because I'll be trying to sooth my curiosity on the matter =] Enjoy !
Gyro zeppeli was here
This was fantastic! I love the presentation, how have I not seen this channel before?!
Thanks for a great video! This needs more views!
Lesson 3, Johnny! Repeat "There's no way that I can do this!" five times.
Maybe spin is rotation on the time axis rather than a spatial one.
Socks With Sandals …Great , but I think spin is a Rotation about the Axis of Nothingness , which is the Original Base of all creations……JagtarSinghAujla
I made this subject my area to do experimental physics in. Thank you for doing this!
Thanks for making this video! I hate taking things on faith, and spin, energy, and charge, are three of those things that have always bugged me!
Hontouni... Hontouni nante tooi mawari michi.
Arigato, Gyro.
Chronognosis YEAH
Stern-Gerlach's setup looks a bit suspicious to me. And, possibly I can answer to your Question 1.
That external magnetic field must had been enormous in comparison with magnetic moment of a single tiny electron and the external field's torque simply wrenched electrons to align themselves with field lines. If one threw a leaf into category 5 hurricane, than the original leaf's orientation would be obliterated.
Additionally, path through the magnetic field is billions of times longer than a diameter of a single electron. So there was plenty of time for external field to twist electron's arm into submission.
Practically, it seems that the outcome was coerced by a brute force, rather than subtly measured with care not to disturb the sample. Even if the electron spins were randomly distributed, the super-strong external field would be so overwhelming that all the electrons would end lining up into just two orientations, parallel to the field. Is there any inkling that the external magnetic field was of the similar strength of the electron's magnetic field?
At 2:20 you say that if small magnet is horizontal, than no up-down force is acting on it. But that's not true. First there would be a torque acting to first align magnet with field lines. Second, once torque did its work and magnet was fully aligned with field lines, small magnet will be pulled towards stronger pole (here triangular bar's pole).
+HitAndMissLab To my knowledge, all experiments to date are consistent with this notion. Two points to respond to your concerns:
1) Originally, the Stern-Gerlach experiment was set up with Silver atoms. Although still small, when moving at great speeds they certainly cannot be coerced as easily as electrons, since they are 200,000 times heavier.
2) The path length is independent if the original 'coersion' delays translational acceleration along the vertical axis by an amount related to the alignment time constant of the moments. (It takes time to torque) The landing spot for the atoms/electrons would simply be shifted according to their original orientations. However, we do not observe this, but instead there is a "precise" pinpoint location measured.
The theory of quantized states was actually furthered by this result by introducing the idea of spin at all - This is because if the deflection were left up to the orbital magnetic moment, the highest available orbital in Silver (d shell) would suppose that there could exist many different magnetic moments (especially because of the possible tri-valency of silver) which would respond to the magnetic field, and one of those should be with zero angular momentum (zero deflection) if it were the orbital moment that caused the deflection. Instead, there were only two, indicating that there was a binary nature to whatever the magnetic field was afflicting. This is now part of our EM theory, since we model ferromagnetic behavior as being a result of spin only.
+Dever Norman Thanks to the great explanation.
this answer is a bit verbose: "... 2) The path length is independent if the original 'coersion' delays
translational acceleration along the vertical axis by an amount related to the alignment time constant of the moments. (It takes time to torque)"
Are you trying to say that electrons/atoms fly too fast be affected along relatively short length of the instrument?
As well, if I may ask, do you know if different atomic particles can be entangled? Like can an electron be entangled with proton, or neutrino etc.?
As for the first, I mean not so much that they fly too fast, but rather that they each would have different experience along the way. Imagine you drive a car into a tunnel, and turn your steering wheel abruptly to the left every time at the entrance (you will crash, of course). But we would expect the steering wheel to be randomly oriented before you start. So sometimes you will crash rapidly into the wall, and sometimes you will take longer to turn the steering wheel because it started off all the way to the right, for instance, or in the middle. But you would end up with a bunch of randomly distributed car crashes along the wall. If, instead, you were to find that the car crashes only showed up in certain spots, you would surmise that the steering wheel is only allowed to start off in very specific orientations, rather than just at any place.
As for the second, I'm afraid I'm not very studied in the field of entanglement. If I understand properly, it is quite common for other (1/2 spin) particles to be entangled, in particular quarks or neutrinos, since they often are momentary or lasting decay products from single events. It is not so much an issue of the identity of the particle as much as the fact that all particles are simply waves, and when those waves mesh they must be entangled by what is called the "anti-symmetrization of their wavefunctions", the meaning of which is really fundamentally poorly understood, despite the fact that it has been mathematically correct and rigorous for almost a century. But I believe the larger the particle, the less likely entanglement will be.
Hope that helps.
+Dever Norman Thank you for dropping down to my level ;-) and creating such a phenomenal example with cars and tunnel.
I enormously appreciate your effort, but what would happen to the cars if along the left side of the tunnel you had ventilation ducts blasting horizontally a triple the hurricane strength winds (aka. here magnetic field)? I am guessing, all the cars would hit the right side wall of the tunnel, regardless of the orientation of the wheel? Its more a question of the relative strength of external magnetic field and single electron's magnetic moment. Ratio must be 1,000,000,000 to 1. So, in principle, orientation of the wheel doesn't matter, because wind (field) is so strong.
I am not really questioning existence of spin, MRI scanners work on spin and quantum computers work on spin. If I remember right spin enabled Dirac to discover anti-mater. So spin is here. Just can't see how Gerlach & Stern came to their conclusion.
Regarding the "anti-symmetrization of their wavefunctions" that sounds (possibly) like resonance in inductor & capacitor (LCR) circuits. Inductors & capacitors have symmetrically opposite ways of handling potential and kinetic energy. Since quantum particles have waves maybe entanglement is some kind of temporary resonance. That might explain why it is so easy to disturb it, same as macroscopic resonance can be stopped if one participant gets kicked out of the geometrical alignment.
I agree that a single free electron would have an awful time in such a "gust of wind". But it is not so terrible with atoms a large as silver. Would it not be possible to simply turn down the wind until you see the minimum response time? It's pretty easy to adjust the magnetic field and speed of the beam such that you can find a blurred region where torque on the moment does not overpower its trajectory.
As for wavefunctions, they're odd things, and although mathematically we have some very good clues about what can and cannot be, there is obviously an issue with our assumptions somewhere. I don't believe antisymmetrization is best compared to inductive or capacitive response, as waveforms of these two phenomena have very classical models that can describe their behavior using classical fields. Wavefunctions of particles cannot be described using classical field theory, and require some peculiar rules to work, and there isn't an easy analogy for how they operate. It isn't like anything we know at the macroscopic level. Macroscopically, I could flick a marble in a bowl and put a lid on it and you could give me a probability of where the marble is based on the bowl shape, and we could measure where it is by sound. Quantum phenomena are such that you wouldn't be giving a probability of where the "marble" is, because it can't mathematically exist at one single place while it's moving - and it has to move, or it violates all the rules. Instead, you'd be giving a waveform of where the particle is, and it happens to be such that if you measure the particle in some way, you'll see that same "marble" probability show up, even though it isn't possible for it to have been located at the one spot before you measured it. Weird? You're telling me.
I'm certainly not going to tell you you're wrong about the "temporary resonance". As a matter of fact, temporary resonance is what creates the identity of neutrino flavour, which is what this year's Nobel Prize was about. Who knows, maybe there is a hidden deterministic quality about particles that circumvents the mathematics we have thus far.
Its 2018 and this video is still so useful.
wow.. so much is in here. i really love the way you explain a lot of complicated ideas..
Trying to answer #6
Excerpt from "The Universe in a Nutshell" - Stephen Hawking.
"All particles have a property called spin, having to do with what a particle looks like from different directions. One can illustrate this with a pack of playing cards. Consider the Ace of Spades. In a full 360 degree revolution it looks the same only once. And hence is said to have spin 1.
The Queen of Hearts has two heads. It therefore looks the same under only half a revolution, 180 degrees. It is said to have spin 2.
Similarly one could imagine objects with spin 3 or higher that would look the same under smaller fractions of a revolution.
The higher the spin, the smaller fraction of a complete revolution necessary to have the particle look the same. But the remarkable fact is that there are particles that look the same only if you turn them through two complete revolutions Such particles are said to have spin 1/2."
Essentially spin is the number of times a particle looks the same in a full revolution
Vinay Kumar But is this source of spin, or a consequence of spin?
Seeing as we talk about quantum particles as being in two places at once ("I know it's no exactly that but bear with..."), couldn't we just apply that same reasoning to spin? So the particle could be spinning in one "direction" but also the other simultaneously. And that's why we can't measure it but still measure a magnetic field?
This probably makes no sense and I don't even understand what I'm saying but I just wanted to put my thoughts out there!
Love the videos!
flabberghast I guess imagining the particle "spining" both up and down at the same time is a good view. The real problem is with the interpretation of what really is spin. In the mathematics of Quantum mechanics, electrons are just points, and points can't spin, so the fact that the Dirac equations derive that they have something that looks a lot like a spin is shocking! What could be it?
The particle is spinning up and down at the same time. It is just that the experiment is kind of like a measuring device which collapse the superposition of the particle. The eigenvalues are the observational probability for each possible state.
Niiiice
Florbz yeah that is the case with quantum entanglement
Florbz I’m far from an expert but I think what you’re describing is similar to quantum superposition, the possibility of an object to be or do many multiple things and to be described as either a particle or a wave until observed, which is when the Heisenberg Uncertainty Principle takes affect collapsing all possible outcomes for the most likely.
Here to try and understand the energy in relationships , magnetism and chemistry between certain individuals and groups . Thank you, none the wiser but I am willing to try to work out the connection of what you present and how it relates to the human condition . I enjoy learning or at least attempting to intellectually expand
I have subscribed after watching this awesome explanation, finally understood the spin.
So what is fractional spin? Why is electron spin 1/2? Why do other bosons/fermions have different spin values?
How are we assigning these values?