What is Spin?

[@lastchance8142]

Great video, thank you! Now I understand why I dont understand spin.

[@qzamboni]

There is a developing classical intuition for spin nowadays. As well as all of the behaviours formerly thought of as "quantum"-only. Basically, the quantum wavefunction is (and always was) just the statistics of the state the particle is in, not a full description of the chaotic dynamical system which gives rise to that state. In particular for an intuition of spin, I've always liked the video "Spin lattices of walking droplets." p.s. - I'm a PhD student and don't really have time or patience to respond to youtube comments, but just putting it out there. For anyone who happens to come across this and is interested, I recommend looking up walking droplets (there are more amazing videos) and/or reading the 2020 review paper by Bush, 'Hydrodynamic quantum analogs'.

[@jaydenwilson9522]

water droplets and hail also don't follow f=mg or f=ma ..... kinda cool!

[@PrettyMuchPhysics]

Comparing "spin as intrinsic angular momentum" to "mass as intrinsic energy" was great! 👍

[@zapphysics]

Thanks!! Glad you liked it!

[@alexandertownsend3291]

I don't understand either so it didn't help me at all. This one thong you don't understand is just like this other you don't understand. I just have to nod my hand and acknowledge that he is probably right and pretend to understand why. I feel like a 5 year old trying to understand calculus. I am so lost. The pictures are neat.

[@misterlau5246]

@@zapphysics I don't know my dear ZAP happy new year by the way 🖖 It's not clear what spin is. Because Rotation. Ok. Linear transformation. But people uses it as macro spinning. It's a property with 4pi period, that respond and aligns with magnetic fields.

[@enoyna1001]

​@@alexandertownsend3291Do you study anything related to natural sciences? If not, don't bother to understand it.

[@Cpt_John_Price]

@@zapphysics I still don't understand the analogy. I understand the whole mass=energy because you can interpret as matter being just energy condensed into a solid, or just all matter travelling in the exactly the speed of light through space-time no matter what (hence the c part). But I don't understand the angular momentum part. What's the "angular" about it when its just intrinsic and no angles? Can it be just "intrinsic momentum"? Can you give me formulas?

[@DrDeuteron]

one problem with understanding spin is thinking we already understand quantum momentum from classical physics. Momentum is that rate of change of phase w.r.t position, and as you mentioned: at zero momentum there is still intrinsic energy, or rate of change of phase w.r.t. time. Spin is rate of change of phase w.r.t to rotations. While that may admit no intuition, it does put E, p & S on equal quantum footing.

[@odiram]

Trying to think about this in other terms, sorry if this is a dumb question, but when we talk about spin or inherent angular momentum are we basically talking about how much a particular particle seems to have an inherent tendency to swerve in a particular direction? Like, we poke the particle to see where it moves, and instead of acting like a classical billiard ball that shoots in the direction of the summed forces, it swerves, and we analogize the tendency of the swerve to angular momentum though we know it can’t be spinning and isn’t orbiting anything. Is that kind of what we’re talking about, or is it some property unrelated to observations of motion?

[@joeriley8624]

I think you are correct about that but I’m not a physicist

[@lcarliner]

What would be extremely helpful would be some information and examples how spin is observed from the output of detectors used by particle accelerators!

[@ulrikof.2486]

Right! I was thinking about the same, this would be extremely helpful.

[@alexandertownsend3291]

I have so many questions: When you say a particle has a given amount of spin, how is that information being obtained? If you want to know how much time has elapsed you can use a clock. If you want to measure weight you use a scale. If you want to measure distance you use a ruler. What would you use to measure spin? You said that angular momentum as defined in classical physics requires motion around an axis. If the particle is not moving, how can it have angular momentum, intrinsic or otherwise? How is angular momentum defined in a quantum sense? There is something I am missing here. I could claim that there is a property called blurbis that all dogs have, an intrinsic property of dogs, but if I don't define blurbis or tell you anything about it, how would you fact check that? Maybe all dogs have the blurbis property, maybe they don't, but how would you know one way or the other? Since I don't have any knowledge of Quantum Mechanics, saying some particles have intrinsic angular momentum is like my blurbis claim in that I have no way to fact check you, given my lack of knowledge. Maybe if I knew more I could fact check you, but at the moment I have to take your word for it.

[@ButchNews]

YOU HAVE TO ACCEPT THAT ALL YOUR VALUES ARE RELATIVE TO SOMETHING. SINCE WE DON'T HAVE A SOMETHING WE CAN SEE, WE INVENTED THE QUANTUM UNIT... A POINT SOURCE. NOW YOU CAN, MATHEMATICALLY GIVE THAT POINT MEASUREMENTS AGAINST A RELATIVE TIME AND PLACE... WHERE YOU ARE RIGHT NOW. EVERYTHING IS RELATIVE. YOU LIVE IN A RELATIVE WORLD. ALL MOTION IS RELATIVE. NOTHING HAS EVER, EVER, EVER TRAVELED IN A TRUE CIRCLE UNLESS IT CAN EXCEED THE SPEED OF LIGHT SQUARED. YOU ARE MOVING ABOUT 7 BILLION KILOMETRES THROUGH SPACE EVERY YEAR... YOU ARE MOVING THROUGH SPACE IN HELICAL WAVES. CIRCULAR MOTION IS AN ILLUSION OF RELATIVITY. IN THE TIME IT TOOK YOU TO READ THIS YOU MOVED HUNDREDS OF THOUSANDS OF MILES THROUGH SPACE... BET YOU DIDN'T FEEL A THING.

[@sethlawson8544]

What kind of experimental setup, regardless of whether it would actually be feasible/possible, could elegantly exemplify quantum spin and the different behavior of the fermions and bosons? I like the analogy of two particles being either red or blue and asking whether they are rb/br/rr/bb and eliminating two of those choices for fermions, but could we describe a similar thought experiment but in a more literal way? I'm imagining a scenario of firing two identical particles down a T track and having them encounter a magnet prior to being measured at either side of the T and running the experiment a million times and asking whether there's a different distribution of results when firing photons vs electrons, something like that. I hope my question makes sense. This video and the "what are fermions and bosons" are really insightful!

[@SplendidKunoichi]

i saw a cop chase on the news earlier that ended with an SUV leaving the road at speed in a rollover crash, but they didn't show the moment it came to rest. given nobody was hurt and the driver was able to exit on his own through the door, did his car ever actually roll? exactly how many turns must it have gone through for you to be certain it was a rollover?

[@gcewing]

@@SplendidKunoichi It depends on whether the SUV is bosonic or fermionic. If it's bosonic, it could have rolled any integer number of times, so you can't tell. If it's fermionic, it will have rolled a half-integer number of times and landed on its roof, so in that case you can be sure it rolled.

[@SplendidKunoichi]

@@gcewing precisely. may serve to stress here that we understand all SUVs to be fermionic but full points regardless

[@narfwhals7843]

Hi Zap! Hope you're doing well. Interesting video! I had no idea the spin statistics theorem followed from special relativity. I honestly was under the assumption it was, well, an assumption. Or an observation. I tried to relate the spin 1/2 rotation symmetry it to the anti-symmetry of fermion wave functions but I realized that I was actually pretty confused what exactly _has_ the 720° rotational symmetry for a spin 1/2 particle. Is it the sign of the spin? The wave function? The entire system?

[@ovidiulupascu]

at 09:30 you will have your answer to what has a 720 degrees rotational symmetry kzbin.info/www/bejne/pojPnGSdgdB5aLs

[@zapphysics]

@Narf Whals Yes, the fact that causality is the connection between spin and statistics is quite surprising, isn't it? To answer your question, when we say that we rotate the particle in quantum mechanics, what we really mean is that we are rotating the wave function. This means that, if we have a single-particle wavefunction and we act with a 360° rotation on said wavefunction, this whole wavefunction will get an overall minus sign. This, of course, is unobservable since any probabilities/expectation values involve essentially squaring the wavefunction. However, if we have a many-fermion system and only rotate, say a single fermion state, we will get a _relative_ minus sign, which can have observable effects. But we should at least somewhat expect this to be the case since we really only see fermionic behavior, e.g. the Pauli exclusion principle, when there is more than one fermion around.

[@Trizzer89]

The earth doesnt actually have angular momentum from orbit. spacetime is warped, so earth is moving in a straight line

[@SkyRiderJavelin]

Brilliant explanation you must really know your stuff to explain this concept in logical steps . I don't pretend to understand everything in this video but at least I am starting to appreciate the fundamental nature of the quantum property compared to other video's I have seen on this subject which gloss over the intrinsic quantum component. Thanks for posting .....

[@pkuvincentsu]

Great explanation! I've watched several vidoes on spin, and yours is the only one that conveyed the concept with clarity.

[@ominollo]

Yet another great explanation! I would be great if you good give some references (e.g textbooks) for self study 🙂

[@AressaKeter]

I just posted a pretty good JoJo reference in the comments. hope that helps! :3

[@gabrol7442]

Check out these lists (search these terms since I can't post links) "Sheafification The Fast Track" "The Portal Wiki Read" Landau series is a good one.

[@ominollo]

@@gabrol7442 these are wonderful references! Thanks!

[@MCLooyverse]

I'm a big fan of Geometric Algebra, and the representation of Angular Momentum (and the magnetic field) as a bi-vector (and bi-vector field), rather than a pseudo-vector (and pseudo-vector field) (although, in Geometric Algebra, "pseudo-vector" actually means "bi-vector", in 3D). All this talk about Angular Momentum based on the axis of rotation hurts.

[@StevenG22]

Awesome stuff! I really admire your videos. There’s a really nice visual proof of the spin-statistics theorem that I’ll try to share in words. Consider a process where two electron-positron pairs are created at t=0, and two electron-positron pairs are annihilated some time later. This can happen in two ways: the electrons can annihilate with the positrons they were created with, or they can switch and each annihilate with the other positron. Now, if you simply accept (from Special Relativity) that in a space-time diagram, you can treat a positron worldline as an electron worldline moving “backwards in time,” you can consider the first process as two separate “loops” of electron worldline, and the second process as one big “loop” connected like a figure 8. Focus on the second process. Viewing it in terms of electrons and positrons, you note that two fermions switched places, giving an overall phase factor of -1. Viewing it as one electron going through a “loop” forwards and backwards in time, you can convince yourself (take a loop of ribbon and make a figure 8 out of it) that the electron rotates by 2π during its trip. What spin must it have to explain the -1 phase factor? A half integer.

[@msergejev]

I would love to see this in an animation.

[@narfwhals7843]

So here you are identifying the exchange anti-symmetry with the 360° rotation anti-symmetry? So the symmetry is in the phase of the wave function in both cases? This is a question I've been struggling with recently.

[@StevenG22]

@@narfwhals7843 Yes, exactly. The wave function picks up a phase of -1 during that process, and it can be understood as either the exchange of two fermions or the 360° rotation of a single fermion as it goes through a loop forward and backward in time.

[@narfwhals7843]

@@StevenG22 thank you!

[@zapphysics]

@Steven G @Narf Whals, I think this is definitely a very pretty way of picturing the spin-statistics theorem, and I had never actually heard it before, so thank you for sharing! I don't think I fully understand all aspects of the argument (e.g. where the exchange symmetry comes into play and why the loop must be a figure-8 instead of just one large loop), but I think that is just due to the limitations of the medium of KZbin comments. I will suggest to be a little bit wary about necessarily calling this a "proof" of the spin-statistics theorem, though. In particular, if you are truly trying to say that the electrons/positrons are physical particles, then their annihilation must come through some interaction (in the case of electrons/positrons, this will typically be via the electromagnetic interaction). However, the spin-statistics theorem is perfectly valid for free, non-interacting fields. If we want to view these instead as vacuum bubbles where we treat the electrons/positrons as virtual, unphysical particles, then we run into the issue that virtual particles do *not* have to satisfy the spin-statistics theorem. In fact, it is a very common technique to introduce unphysical particles into a theory which are spin-zero particles that are anti-symmetric under exchange, called "Faddeev-Popov ghosts". Since these only appear on the "insides" of Feynman diagrams, we aren't worried about the violation of the spin-statistics theorem since they can never be actual, observable particles (they are more of a math trick than saying anything about the physics). Nevertheless, I do think it is quite nice and want to thank you for bringing it to my attention!

[@En_theo]

@9:32 I don't get it, if m can only have integer values, how can it have a value that's not entirely equal to 1 due to uncertainty as you said earlier in the video ? I know that you said that it's actually "l" that has the "uncertain" value but when we measure it, what happens ? If we can't see any integer value for m in practice, then how can the spin be quantized ?

[@sakesaurus]

csn molecules change from fermion to boson or does it have to recieve a specific interaction with another mollecule?

[@halnineooo136]

I feel like using common language words like rotation, spin, wave, particle, to describe phenomena alien to our sensible experience only adds confusion. I would rather coin complete new specific names that are as much possible rooted in maths without the macro world confusing imagery.

[@aydencook03]

Fantastic video. I like it when a single video makes a lot of connections to other areas that we can research for ourselves.

[@شعرکوتاه-ع7ظ]

Very good. Thank you. It was informative

[@HeheHom]

I absolutely love particle physics. Quantum field theory to be precise.

[@brahimek9937]

Please make a course about classical electromagnetism

[@lexer_]

This explanation to me seems like it requires you to already understand spin in order to grasp the tools used to explain spin.

[@Vrooten]

Would have been helpful for me to see some examples of how spin actually manifests itself irl!

[@mrchangcooler]

Is this momentum a fraction of the mass of the particle? Does it constitute a part of a particle's energy?

[@enoyna1001]

As photons are bosons and are massless, the qm spin does not contribute to a particle's mass (which is rather a consequence of the Higgs mechanism).

[@mrchangcooler]

​@@enoyna1001rest mass perhaps, but I mean relativistic mass.

[@enoyna1001]

​@@mrchangcoolerPhotons also don't have relativistic mass and still possess a spin. Your question(s) should be answered.

[@mrchangcooler]

@@enoyna1001 Yes, thank you.

[@mrchangcooler]

@@enoyna1001 I have further researched it and found that gluons, despite being massless, account for mass inside the nucleus. How do you reconcile this if massless particles can add to mass of a composite particle

[@Tomyb15]

How does the fact that the spin of an electron is 1/2 with the fact that an observable for the spin of an electron along a given axis (talking about Pauli operators) have eigenvalues ±1? Also, if spin is constant for a given particle and we can only measure spin along a given axis a time even though its spin could be pointing in any 3d direction which also means that meausring spin changes it to be pointing in the direction of measurement, then how can all this be simultaneously true if a projection is always smaller than the original vector (when the projection axis is different to the vector's axis)?

[@misterlau5246]

Because we renormalise. The thing is having eigenstuff. And anyways we have h constant there in spin. Because if we were to use coulombs, that 1 is basically magnitude of electron U (1)charge . And we don't use particles at minimum energy. At least double or triple is the baseline. Spin is a property that is pointing wherever, we use up down left right in out. 6 detectors. What happens is we put strong magnetic fields there, and that property aligns with them, you can measure the interaction with the magnetic field and the detectors configured and placed as calculated will get each of those in the direction we FORCE them to be. So it's just an up state and a down state are same phase angle but go in opposite directions, ≈180º And standard method is aligning to Z axis. All of it (almost, cause he Isenberg) is there, max and min L values

[@μ-π-δ8β]

Hello!thank you for this amazing video! I have a question: at 7:59 where you correlate the max value of Jz with the total J, how is it that when Jz is maximum it is (almost) equal to the total magnitude of J?what about the other two components? Does this also mean that if for example Jy was max, then Jz and Jx would be close to zero? Thank you in advance!

[@jossarian]

There is no "total J". For the 3 spin nxn matrices (j¹, j²,j³) = J we have to compute the scalar product J•J wich turns out to be l(l+1)E, l is maximal eigenvalue of all of these 3 nxn spin matrices and E is the nxn unity matrix. For n =2 we have for J the three spin matrices 1/2( σ(x).σ(y),σ(z)) and J▪︎J = (1/4)(E+E+E) = (3/4)E = (1/2)(1/2 + 1)E. In case n = 3 we have spin 1, n = 4 for l = 3/2, and so on. l = (n-1)/2. So J•J is an observable with exspectation value l(l+1). ###### We "observe" (ψ|J•J|ψ) = l(l+1) and |ψ) is a normalized n-tupel Hilbert space vector.

[@BiswajitBhattacharjee-up8vv]

When you take any "m" value between 0and 1and multiply with "hand write down it using zero and decimal we will reach very two value of classical continuum. And fraction is always an incomplete state What is then expected symmetry??? But question is what is intrinsic. What is the critical set up for intrinsic and extrinsic???

[@alexandreocadiz9967]

Spin is a country between Frnce and Portugl

[@barrypickford1443]

Can’t I intuit this by looking at a particle collision image from cern? Or more so those old cloud chamber black and white images of the particles colliding and curving off into spirals?

[@stevechrollo8074]

Physics has so many great Jojo references!

[@cristianmarinescu3053]

Just wondering: if it were no spin property at quantum level, would the 3-D macro space we leave in not exhibit the rotation property and the symmetry under rotations? Anyway, kudos to an amazing video!

[@dimashus]

Arigato...Gyro

[@critikasalihmeylani]

Tust, Act 4..

[@jakublizon6375]

Does spin affect linear momemtum as well?

[@jossarian]

In contrast to electrons nucleons have "extensions", like atoms. But unlike atoms they have only spin 1/2, like pointlike electrons. "small balls" exist with only "intinsic" spin. ###### In classical mechanics a physical system is a point in phasespace and moves along certain curves in this phasespace and angualar momentum may be conserved and abitrary, ... , why not 1/2 x h. In Quantum Mechanics a state is an element of the - unique - Hilbert space and these states may be developed as eigenstates of all representations of the rotation group, for instance (defining rep. of) SU(2), in case of the n.r. Pauli equation (spin 1/2) ######## We do'nt need a "Quantum Field Theory" or the Poincaré group for relativistic quantum mechanics.

[@swarog3]

spin is xyz vector written as xb complex number (x, y+jz)

[@robbie_]

Whenever I see a physics video with "what is" in the title, I laugh a little. "these are the observed regularities" is about the best you can say. "what is" I think is unanswerable. 😁

[@SapphireSpire]

If QM 'spin' isn't classical spin, then don't call it 'spin'. Call it torque.

[@TonyO8187]

Great video as always. I was hoping you could help me with a conundrum I've always had. I'm pretty convinced that there is no such thing as "energy". By that I'm not disputing any established physics, but always saw energy as a mathematical abstraction to help with conversions between motion, temperature, wave frequency, etc., not a literal thing that exists in reality. While useful to solve problems, I always wondered if energy is a red herring that has led to some stagnation in theoretical breakthroughs. By a similar line of logic, I have similar concerns about fields. Hopefully I explained this well, let me know if you'd like to discuss more!

[@zapphysics]

@tonyo8187 I think these are interesting questions and make for a wonderful philosophical discussion. I think it all sort of depends on what you mean by "real." Do we ever directly observe "energy?" No, we don't. We typically observe motion or currents or something along that line. In some sense, I think I agree that energy is a sort of book-keeping tool that is used to solve problems and get mathematical results, and its non-physicality I think is very much shown by the fact that we can shift it by a constant amount and not change our physics (at least for systems that conserve energy). However, I don't think that it is really a red herring since it doesn't exist independently from the actual physics: for a very basic example, one can arrive at an expression of energy simply from the relation of more "physical" quantities F=ma. In fact, the sole motivation for searching for the neutrino was to save conservation of energy. So it seems to me (again, this is all my opinion) that while energy itself may not be physical in that it is directly observable, the mathematical rules one gets from considering energy seem to describe our universe amazingly well so I don't think there is really an issue with treating it as a physical quantity. I think that the underlying philosophical debate to all of this is whether or not math (or perhaps said better, the logic that we describe through math) is physical. It seems that we can describe our physical universe remarkably well using math, but are the rules that we find "built-in" to our universe or are they just what have been convenient for us? Asked another way, if we met an alien species, would their system of math and physics look exactly the same as ours or would it be wildly different?

[@ipudisciple]

Energy is observable because it is equivalent to mass. If you put a load of energy in one place - for example by squeezing a load of electrons into a small space - it can get heavy enough to form a black hole. So gravity sees energy as a real thing, even if none of the other processes do.

[@ButchNews]

ENERGY IS THE ABILITY TO DO WORK. WHERE IT COMES FROM, I.M.O., IS THAT MATTER REQUIRES SPACE AND SPACE IS NOT EMPTY... I.E. THERE IS NO SUCH THING AS EMPTY SPACE, BUT ALL "MATTER" IS FIGHTING FOR IT... LIKE BEING ON THE BUS OR TRAIN AT RUSH HOUR. NO RESPECT FOR ANYONE AROUND YOU AND IT'S PUSH, PUSH, PUSH, PUSH, PUSH. GRAVITY IS PUSH, NOT PULL. IT ALL WORKS OUT THE SAME, JUST A DIFFERENT MIND SET ON WHAT REALITY IS.

[@thomasolson7447]

I know absolutely nothing about Complex Octonions, zip, zero, ziltch. I'm not pretending in anyway. I just thought it kind of implied the picture on the left. That whole thing was constructed to make spinners, wasn't it?

[@fr3ddyfr3sh]

Though this is a interesting video, I totally miss the very helpful explanation of an MRT, which is unbelievable helpful to understand spin intuitively. 1. the vector/orientation of the spin is the same as the magnetic dipole of a proton. 2. When you apply a huge magnetic field slightly more than 50% of them, a line in the direction of the magnetic field, and the rest is exactly opposed to the magnetic field. 3. If you drop the magnetic field, they perform a calibration (like a spintop) 4. Because they seem to rotate, every proton emits an electromagnetic wave. Detailed explanation: kzbin.info/www/bejne/oH3RpoOBnbCLjK8si=Ker0qEX00XwbiiU7

[@solapowsj25]

Deviation results in sine wave; deflection, in spin or loop.

[@user-iksd0713]

The spin of quantum mechanics is affected by electromagnetic waves, and in superposition and entanglement, the entanglement is antimatter and the electric charge can be calculated. An example of seeing particle and wave nature at the same time is the blue glowing phenomenon of the fuel control rod. Western quantum mechanics is based on uncertainty. It is not the quantum mechanics of the invisible calculus like the principle, but the quantum mechanics that is visible starting from the eight trigrams of Eastern philosophy, where non-pole is taegeuk and taegeuk is non-geuk. It shows microscopic quantum mechanics and macroscopic atomic magnetic force. A quantum computer requires knowledge of elements and principles. Even a regular computer can produce the effect of a quantum computer. It is an error to explain the Earth's revolution and rotation in terms of angular motion. When the revolution is at perihelion, the amplitude is small. However, when it is at perihelion, the amplitude is large and numerous. This is why the four seasons are distinct. The rotation period is 230-400 million years, the amplitude is 17-8 years, and the rotation period is the same as the galaxy rotation period. This result is the absence of human science that has made it an unconditional feast of numbers with calculus equations that do not take into account the fact that the sun also orbits and the influence of the rotation of the galaxy on the sun and Earth.

[@regulus8518]

not to mention that its the basis of chemistry ... without it you could not form any kind of chemical bonds to form molecules ... the basis of biology

[@pyropulseIXXI]

Mass is an intrinsic property; charge is an intrinsic property; spin is an intrinsic property!

[@jussap3641]

NOICE!!. Can you relate electron spin to how electrons move in the atom

[@enoyna1001]

No, spin is a quantum number not responsible for the electron density distribution of atoms.

[@EverAfterMsp]

this helped a lot thank you !!

[@KipIngram]

I wouldn't say that EARTH has orbital angular momentum. The EARTH/SUN SYSTEM has that. Earth actually has rotational angular momentum, all by itself - no reference to other bodies required. But that's not so re: the orbital angular momentum. I mean, you can just arbitrarily associate the orbital part with "Earth," when you name it, but it's not really a good physical picture.

[@Amanpreetkaur-cp4fs]

Actually electron didn't spin it behaves like it.............

[@jackebinger5144]

What

[@Verlamian]

Unfortunately you've repeated rather than dispelled one common misconception about spin. It's *not* actually a "quantum thing", it's a "spacetime symmetry thing", and classic elementary / point particles have (or would have) intrinsic angular momentum too.

[@fiveshorts]

You SO don’t need the elevator music in the background. Makes it impossible to focus on what you’re saying. If you were teaching in a class, would you have music playing?

[@NovaWarrior77]

For the past couple of days, I was thinking about exactly this. And here you are!

[@stevewhitt9109]

You should refer to Spin a only being a 2D Vector and Dual Vectors

[@alejrandom6592]

Holy shit I feel like I'm finally understanding why all the weird chemistry stuff

[@AravJoshi-mi9nz]

Thankyou sir

[@tariq3erwa]

Simple and beautiful

[@deckuofm]

Why do we need spin?

[@helifynoe9930]

So, thinking in a classical manner, a particles spin axis can also extend across the dimension of time, rather than it being entirely a spatial axis. How much the axis extends across the time dimension, determines how many rotations are required before the particle is re-oriented back to its original orientation. Also, due to this being a 4D spin axis, there is motion back and forth across time. If in motion, this makes it impossible to determine the particles exact position. And, due to this appearing and disappearing relative to the present time, a moving electron for instance, can be located on one side of a thin wall one moment, but be on the other side of the wall by the time it again reappears in the present time. One could call this, a quantum leap.

[@jean-paul-niko]

In the brain, knowledge is encoded through the organization and relative density of neuronal infrastructure. Since I find your video to be more appealing and pedagogically valuable to me than other physics videos I have seen, I believe our brains must structure and retrieve information similarly. Simply put, we think alike! Thank you. 🫶

[@BBBrasil]

So why, why call it spin?? Guys, physicists just blew this. They could have called it blahblah for all the differences it has with the classical term.

[@HieuNguyen-qe5ix]

They should put the explain into the wikipeida

[@doctorvimalkatarmal4704]

Tough to understand and digest

[@Higgsinophysics]

breve to tackle this issue !!

[@zapphysics]

@Higgsino physics lol, I have been wrestling with the idea of doing it for a while and finally caved!

[@denzali]

If they don’t spin but have intrinsic a m, how the shit do we know? What does its non existent spin that it has do?

[@miloszforman6270]

The video does not even point out the Stern-Gerlach experiment. Another useless attempt to explain "spin" by someone who does not know what he is talking about.

[@denzali]

@@miloszforman6270 I’m starting to form a model in my head that looks like this: Math can map things There have been cases of “imaginative/unintuitive” math ideas that have described things beyond what our tools can observe/measure accurately We have started to map the unknown with imaginative math structures We are adrift in an infinite ocean of imaginematics. 🤷🏻‍♂️ Really cool tbh. We are now math artists conjuring models into existence to see if they match experience.

[@miloszforman6270]

@@denzali _"We are now math artists conjuring models into existence to see if they match experience."_ Would be glad if that was so. But what is this fckn "spin" all about? All I hear is what it is _not_ supposed to be. It's the math formula that we need. All that "classical physics analogy" comes to nothing but confusion.

[@drdca8263]

@@miloszforman6270 is your complaint that the video doesn’t trace out the full path between the math and the experimental results that justify it? I’m pretty sure that would be a long video.

[@miloszforman6270]

@@drdca8263 Yes, it would have been better to explain what are the physical effects which lead to introducing spin instead of a lengthy explanation what spin _is not._ It's quite useless in this context to compare it to the Earths rotation (2:10) and to explain classical angular momentum. Someone who doesn't even know what angular momentum is will certainly not be looking for videos about quantum spin. 4:55 _"Okay, so now that we have an idea of what spin is we can ask what values the spin can take."_ Actually, after this video we don't even have a slight hint of what spin really is. Such videos are an annoying waste of time for the viewer as they promise explanations which they can't give.

[@AressaKeter]

Fun math fact: If you multiply any spin by infinity, you get infinite spin, which is a JoJo reference! :D

[@Ohmagat69420]

Beyblade

[@zapphysics]

Let it rip!

[@markmathis5189]

Hi. Can you please describe what is meant by "exchange" and "exchange symmetry"?

[@zapphysics]

@Mark Mathis, yes definitely! This is just referring to what happens to the wavefunction which describes two identical particles when we switch the two particles. So, for example, if I have a wavefunction describing identical particles A and B, Psi(A,B), exchange just means that I look at Psi(B,A). The symmetry piece just refers to the fact that there are only two options: the symmetric one where Psi(A,B) = Psi(B,A) and the anti-symmetric one where Psi(A,B) = -Psi(B,A)

[@digitalsiler]

nothing is sitting still it would spinning(slowly of course) around the center of the galaxy, around the sun, and around the pole of the earth relatively speaking

[@savage22bolt32]

Constructive criticism: lose the background noise! The subject & your narration of it is great. The addition of distracting, monotonous & annoying music ruined the vid for me. I did not get past the 2 minute point.

[@WilliamDye-willdye]

I didn't follow the part about causality, um, "causing" the spin differences between fermions and bosons, but perhaps it's a topic for another time.

[@zapphysics]

@William Dye Yes, I intentionally didn't go into too many details on this because the proof is quite hairy mathematically. The important part is that we can essentially determine the form of a quantum field based off of how it transforms under rotations and therefore its spin properties. Then, we can simply require that physics in non-causally connected regions do not influence each other, which ends up giving us that particle wavefunctions are _either_ symmetric or anti-symmetric under exchange. But since we know the form of the fields (which we already determined based off of spin properties), we can build these states and just check which ones must be symmetric and which ones must be anti-symmetric. The result is that half-integer spins correspond to anti-symmetry and integer spins correspond to symmetry. I certainly don't expect this to be intuitively clear, but that is how it works out in practice.

[@RazorBaze]

If I had read that like week ago - I'd be lost in math as usual. But I started digging into Unification theories lately, and now may hope to translate your description in "intuitively clear" terms. So, field's excitations (i.e., particles, i.e. quanta) may actually have whatever energies they like: this is true (although extremely in general) not only for Spin, but for any other observable, like Momentum, Mass, Charge, etc. The only reason why we observe some patterns (like Standard model) more often than other (like virtual particles; although ZAP may willing to give more, contradictory even, mathematical precision to it) - is that _somehow_, via summing over current properties of all fields out there, the Standard model ones are merely more "preferable" (in terms of probabilities) than other. So, this "somehow" term, which I hoped to made intuitively clear - is merely the fact that some _certain_ values of observables (like integer, or half-integer spins) are, again, more "preferable" to go into pair with, again, _certain_ (not any!) values of other observables (like momentum, or charge). I.e., we can calculate probability for any infinitesimally arbitrary pair of observables - even if one of them has, say, Spin 1/2 (like in SM), and other Spin 1/22, or 7 (or let it be negative mass, or some ludicrous momentum, or charge - whatever "virtual particle" that is you need to fit to your very rare and specific Feynman diagram, and give it any extraordinary physical meaning): it's just that Standard model values of field excitation are *so outnumbered* by "virtual" ones, that one (and it's here where I'm hoping be correct) can assign the similar infinitesimally small probability to them, as if to say that they as well as not contributing to causality, or our observables at all. Except that I feel like they are - "they are just outnumbered", "infinitesimal", simply speaking, and I'm hoping that's what's can be seen in rigorous math proof as well (although I've seen such meaning only from very far, if it is right in a first place).

[@karamashi520]

Sweet

[@shelburnjames7337]

Flight requires 4 processors by NASA and I think Space X uses 8.

[@ButchNews]

Objects move in helical waves through space and NOTHING sits still. Trying to make some sense of it all can melt your mind. Earth makes a helical wave of one cycle per year which has a (local... within the galactic frame of reference) wave length of about 7 billion kilometres long. Earth makes a helical wave about 7 billion Kilometres long within the Milky Way. What the motion is OUTSIDE of that, we're still working on that one. Never was a beginning, never will there be an end... it's just simple logic. You just can't know ALL the values... what, exactly causes inertia (hidden energy/motion) is not known... first cause, as it were. But... a 3D object has an option of turning/moving/spinning left, or right relative to an observer, and moving through space (wobble). Living upon the surface of an object without external references... light/stars... against blackness, one might not be aware of the object's motion in space, at all. The Earth's net motion through space, within our galaxy, is an extremely stretched out wave about 50 times longer than it is wide. Sticking (thinking) to/of a point source actually helps matters. Within a given framework of reality things do spin... but they are also moving constantly through space... using up their motion inertia... matter, of course, can also be turned into pure raw energy of various wave lengths. When all those folded up waves/folded space get to expand they go "BOOM". Ya gots yerself a pretty dirty but decent bomb. Those LONG wave lengths cause a LOT of destruction... longest is strongest. Remember that from your basic physics class? You can take a one mile length of string and crowd it into a pretty small package but, if it wants to become straight, again... get out of the way. Nothing may move in an absolute circle unless it can exceed the speed of light squared. Even then, it can still MOVE THROUGH SPACE (wobble). To remain stationary an "object" must have a total (physical/3D) spin of 4/3pi (speed of light/time existence of one second) cubed which is the formula for a sphere with a radius of the speed of light for one second of what we call time (a value determined by physical changes we observe about us). How fast is fast? How slow is slow? Size matters. Have fun with that. No circular motion/absolute motion... ever. Circular motion is an illusion of relativity... a kind of ratio of reality vs the speed of light vs the physical size of the observer. I'm guessing the speed of light is determined by an actual physical size/radius of the "point source". If you were living upon a Carbon atom, one second of our time would be a very, very, very long time, to you. I'm old... 79. Here are some final words from Butch, himself... 'Science is the belief in the ignorance of experts' argued Richard Feynman, one of the greatest scientists of the last fifty years. He wished to promote the idea that the best science respects no authority and is not a learnt set of facts, but a rigorous method of questioning in search of a better account.

[@daltanionwaves]

🤯

[@patrickguy8797]

Ce que l'on mesure c'est un moment magnétique jamais un spin. Le côté expérience est passé sous silence, c'est dommage. La physique c'est aussi et surtout des expériences ou des observations pas simplement des maths.

[@basoormb1]

Background music is irritating and makes the speaker unintelligible. Pls remove the background music and repost the video if possible.

[@T0NYD1CK]

If spin isn't spin why call it spin?

[@duaneburris7ate9]

Something you put "on it".

[@gonegahgah]

If it quacks like a duck… maybe we should start recognising that nothing exists as a point, not light, not an electron, not even a black hole 🙄

[@lucash8234]

It's when things go around in a circle. Duh.

[@andrewjarvis4074]

spin isn't a hard thing to grasp...... youre make it confusing..... it's the magnetic field that irradiates in and around a particle... the field spins on its axis thus creating angular momentum and spins helically with respect to x as in as it travels along x the field spins in a circle from up to down..... like the earth spinning creating day and night and the angular momentum creating seasons almost but spinnin up and down by a full half of the particle.... wave functions aren't hard to understand..... people just explain this stuff like assholes.....

[@danksta7103]

I wish my brain had nerd power

[@hingray6892]

im not seein enough jojo references in the comments

[@christophergame7977]

The spin angular momentum doesn't belong to the point particle. The spin isn't to be described by a vector. The spin angular momentum belongs to the field lines by which the particle is attached to the electromagnetic field. The spin is to be described by a bivector.

[@FunkyDexter]

1:22 This is incorrect because particles are not point-like. Otherwise, the electric field around the electron would be infinite. They are waves. 3:45 Behind E=mc^2 is the idea of bound energy. The bound energy is always some form of kinetic energy, like for example in the proton, most of the mass is due to the bound kinetic energy of the gluons and quarks. So no, you can't talk about "intrinsic energy". Furthermore, this is just sweeping under the carpet the simple fact that we just dont know what spin fundamentally is. The electron having no known substructure does not prevent it from having internal dynamics, which is unfortunately an extremely common misconception.

[@garysymons3930]

Not for beginners ,

[@dofingo2986]

Resisting the urge to say is this a jojo refrent

[@pelimies1818]

Is E*2=p *2c *2 + m *2c *4 Hamiltonian? Why it is written so funny? Why not E=pc+mc *2?

[@zapphysics]

This is not quite a Hamiltonian since the total energy is squared. However, if we take the square root of both sides, we do end up with the proper classical Hamiltonian of a free particle in special relativity. If you are asking about the quantum Hamiltonian operator, this gets a bit trickier because it is a bit complicated to take the square root of an operator. On top of that, the quantum theory allows for negative-energy states due to tunneling between the positive and negative roots, which adds in additional complications that need to be accounted for. It isn't written as E=pc + mc^2 because taking the square root of both sides does not yield this expression. In particular, sqrt(a^2 + b^2) =/= a + b (you can convince yourself by squaring both sides and expanding).

[@pelimies1818]

@@zapphysics Thanks for squaring things! I suck at math.. really bad.

[@slythekek]

IS THAT A MOTHAFUCKIN JOJO REFERENCE?!?!?!

[@trevoremery7111]

No mention of spin up and spin down, quarks etc. Pauli exclusions or Linus Pauling. I like to see a bit more experimental proof in these lectures, not just a mathematical formula

[@JamesAwokeKnowing]

I think u should have spent time describing the way spin changes behavior in the real world

[@user-qr4jf4tv2x]

Spin your nails in the golden ratio!... then you should have the ability to harness the power of infinity.

[@takyc7883]

went wayyyy too fast in the 2nd half of the video

[@mrslave41]

2:49 Terrible way of explaining science. Always start from demonstrating an experiment.😮

[@voluntasmortis]

Is this a JoJo reference?

[@enochbrown8178]

Listen, it doesn't make sense that intrinsic angular momentum does not involve something rotating around an axis or revolving around something. It's a totally nonsense idea. Who the hell came up with such a concept and what is the experimental evidence of its existence?

[@misterlau5246]

It's a rotation, a linear transformation. A rotation is not like revolving around like planets the sun. It's like a 3D game. You can turn the camera, but the thing there is the computer does that maths and rhe textures are ROTATING. And those quantum objects are nothing like the normal stuff in macro scale. Physics put terrible names ok. Now. This property is something like angular momentum, it conserves, but an electron spin property is only two states. The particles are oscillating waves. What is this spin, what experiments prove it is a thing? Spin has correlation with magnetic fields. If we put a magnetic one in one polarity, spin will align to that. Up or down, left or right, in or out. 6 possible results. But there's the interesting part. When you do this with metal behaving, particles, you get all spin aligned in a single direction and it will generate another magnetic field. So, that's the thing that happens here. When you put a charged particle, better electrons, smaller, it WILL measure that interaction with the magnetic field. It aligns and sums or subtracts from that external power. Then, you can use another magnetic field to align them to the opposite polarity, and same. Spin down, but now it's reversed. Now, it's like spinning? Not! It's a thing that aligns in presence of magnetism, but it rotates in only 2 steps, because it's not a macro typical object, is something that is not a particle or wave, really. That spin is comparable to one "full revolution" is 720º, not 360. The thing here is what is supposed to be quantised, well, it's the frequencies, the components of the wave, if it's certain frequency, and 2x,3x,4x, that's always a certain particle and not others. When you increment power to this, the particles "go to minimum" let's say from 5 to 10V, only maximum at 10, but not before and not until 15, again. The magnetic "angular momentum" jumps just like this. It's in one direction or the other. And it rotates from + to - 360º and then to + another 360,º So, of course that is nowhere near to the common meaning of spinning, it's just the name. It's this property that helps to keep the electrons coupled to those orbitals around the nucleus, but they are not revolving around it like planets. Still waves, or something similar to them with these properties that change according to our use of electricity and magnetism. Everything at this quantum level has discrete properties, they just jump from one to another, but periodically anyway, so that's another reason to call it spin.

[@enochbrown8178]

@@misterlau5246 If you can't explain it to a seven year old, then you don't know it...Richard Feynman

[@misterlau5246]

@@enochbrown8178 he also replaced equations with symbols and we can build interactions connecting those symbols. But the seventh years old tot won't be able to have a good grasp of this unless he's a genius and already studied many things.

[@Cpt_John_Price]

@@misterlau5246 "You can turn the camera, but the thing there is the computer does that maths and the textures are ROTATING" You basically explained why quantum spin is not spinning but the maths give the "impression" that is spinning.

[@misterlau5246]

@@Cpt_John_Price and the fact it is said spin changes immediately from up to down, but it's more a little trembling of it before you get it in the opposite polarity. A rotation in maths is not necessarily something that turns like a wheel, it's more like after doing operations, there's a symmetry, like you can put a twin of let's say a straight triangle and you "rotate" it by the hypotenuse, you get a rectangle.. No way of doing it on a 2D object because that means you are using a third dimension. But that doesn't mean you don't have the gimmick of doing it, it doesn't need to turn. It's not like a turn up - down because the vectors are perpendicular, not opposite. And it's 4pi, it won't turn, it will change polarity after one 2pi 360º turn, and after another of those, THEN you return to the initial polarity of spin 🤔

[@lowpressure5143]

Zap

[@CstriderNNS]

during the annihilation of a neutron , the turning of matter into energy, what happens to the energy of the partials spin ? and does it spin polarize the energy ?????

[@nicholasbohlsen8442]

I'm not entirely sure what process you are thinking of when you say annihilation of a neutron here. But if we consider electron-positron annihilation (a real process of interest) the spin of incoming fermions is important. Since angular momentum needs to be conserved it must be carried away in the helicity (which is the massless vector particle analog of spin, sort of) of the photons. This has interesting consequences like that a spin up electron cannot actually annihilate with a spin up positron to produce two photons. We would need three outgoing photons to produce a state with total spin quantum number 1. These are sometimes called spin polarisation effects and they can be very interesting in particle physics.