What is Quantum Mechanical Spin? 

we need more metal musician teaching science

One step closer to understanding quantum mechanics. Seven billion more steps to go. :-)

Uhm, yeah. Could you repeat the part where you said the things about the stuff?

The best teachers don't make their students feel like they're being talked down to, regardless of how basic or advanced their subject matter might be, and Professor Morello's definitely that kind of teacher.

Can't say it enough: Absolutely amazing.. So clear.. Prof. Morello's ability to take a subject so non-intuitive and making everyone somewhat understand the laying foundations of it, is a true gift IMO... Great presentation, more of him, PLEASE! :)

0:59 When I hear "purely quantum mechanical" I associate "Noone knows what it is, but that's just the way it is... accept it"

This is the best laymans explanation of quantum spin I've heard, and I've heard many. I finally can grasp it. Thanks!

Double-pendulum = entangled state. Great analogy. Prof. Morello explains stuff better than any teacher I've ever had. I love this!

I very much enjoy professor morello. His explanations are fantastic, and being interested in mechanical engineering and quantum mechanical processes, I enjoy his discussions. I'd love to hear more from him. Thanks!

Quantum computers gives you the answer to life, universe and everything, but only when your not observing it :D

Good job. Some of the stuff you guys go over is way over my head, but I love it. Thank you.

My left ear enjoyed that scientists accent

the fourth configuration is where their movement state interchanges between them, they have their own phases that do not overlap.

I really think that this video is a good one! Especially because it tries to give a way to understand (or interpret) the spins. Also, this channel is becoming my favourite over Ve1, just because the acedemic level is higher. More quantum mechanics!

One more comment I should have included with my the previous comment. When you start with one pendulum swinging then, when it returns to full amplitude, it is 180 degrees out of phase. Another full cycle is required to return to the original phase. This is the Dirac "Belt Trick". It requires TWO full cycles to return to the original phase.

You're right that the components of a wavefunction aren't generally discrete. However, you can approximate them discretely, e.g. with floating point numbers. Quantum computer efforts actually suffer from more daunting challenges than classical analogue computers, partly related to precision, and partly due to thermal/other noise. I haven't covered the topics yet, but I've started a RU-vid series teaching how to solve the Schrödinger equation with basic math, and I'll get to QC eventually. :)

If you're interested in learning more, I've started a RU-vid series teaching how to solve the Schrödinger equation without needing to know any advanced math ahead of time; it's all explained as I go through it. I haven't gotten to QC yet, but I'm heading in that direction, because that's what my research is in. :)

Who else thinks we need a channel just for Prof. Morello?

Inside a quantum computer, the wavefunction components don't need to be discretized. I think Prof. Morello was just using 2^n as a rough ballpark of the number of classical bits needed, to give people an idea. There are 2^n classical states that can be occupied by n qubits, so you'd certainly need >= 1 bit each to try to directly represent a wavefunction. It turns out that a quantum system *can* be simulated classically with polynomial space; it just takes exponential time, so far as we know.

They have color which means they interact strongly with the strong force, but they also have charge - down type quarks have -1/3 e and up type quarks have +2/3 e

Besides this professor being able to explain this really well, the interviewer does a great job too: asking the correct question at the right time Now: we are 7 years later, How long is that guys hair by now?

The spin of Quantum Mechanics is not like the spin of an object in our everyday life. I think of it more as a spin in the process that forms future uncertainty. Like the bits of a computer the zeros and ones are all you need to run a computer. The up and down spin is what we need for the future uncertainty in the process we call time. By the way this is an invitation to see an artist theory on the physics of ‘time’ as a physical process!

AHA! pay attention starting around 2:04 where he explains 'lowest energy' because that is what entropy and the model of an atom are both related to also. minimum entropy vs. maximum entropy the new improved model of the atom suggests the Bohr model shells become 'energy levels'. the lowest energy level is found in the center - the REST stop photons must be released to allow electrons to drop down energy levels in the periodic table of elements ... the universe is REST and MOTION

Thank you. This video was enlightning.

I get lost when he started talking about the pendulum model, i thought there's no up,down and down,up, it's a superposition. They are entangled, you can only infer one after the other, but what was the "pendulum both swinging on the same direction" part, where does that fit on the entanglement? and what is the up up / down down state? are they not entangled? How do they decide which ones are entangled? why am i doing this to me?

It seams easier to switch up and down with black and white and would a superposition be grey it probably doesn't make sense but that's how I try and understand it

that professor is awesome!

Does he have a Hungarian accent?

that smirk at 4:37 XD

Why is there even any spin? Or, since there is spin, why aren't all of them spinning the same way? What prevents or causes them to spin in a particular direction?

I got to share this on facebook!!!

It confuses me that the electron could be both a negative particle and a dipole magnet. Far instance in the presence of negative electric foretold, a negative particle would be repelled, but a magnetic dipole would just flip around.

At 8:30 wooooow . Hear at full volume using hand free

I still don't get it though. So the superposition is a linear combination of binary states with complex coefficients. In practice, are these coefficients discrete, too, though? Or do they have arbitrary precision? How is it then possible to store a quantum state with a set number of classical bits at all? And doesn't this then suffer from all the problems of classical analogue computers? I'm confused.

So when they are entangled on a quantum level, their direction is never known; it is only known that they are opposite of each other? yes?

lemme see if i understood it a classic bit has its own independent value, so they only hold 1 bit of information and are independent of each other. a Qbit however does not hold a value on its own, but instead has a relationship with every single other Qbit that it is together with it. and that's where the information is. so a N Qbits will be equivalent of a NxN matrix of real bits? EDIT: ops i mean N-1xN-1 matrix

Why is there spin in the first place, or for that matter, at all ?

Yes, get rid of that ending loud sound and please hold your camera more steadily, you are shooting as if it was a sting operation.

So, where did he say what spin IS?

I'm not going to lie: even though all this probably explains and proves Pauli exclusion principle, the up-up and down-down orientation sounds odd. I wish I could understand even half of this :D:D

the 1/sqrt2 is a 'normalization' meaning that the probability of finding the electron in any state at all must be one. So that factor is there because otherwise you'd have a 200% chance of finding an electron in any state at all. The +/- signs he discusses are associated with having electrons in the same phase or opposite phase - the best analogy is the double pendulum.

thanks for the heart attack at 8:27

This is great, brilliant in fact. I just have one question... what?

Unfortunately, the act of talking about or lecturing on quantum mechanics changes the description of quantum mechanics. Which is why it's so hard to understand.

This guy is sooooooo good but that doesn't keep my brains from blowing up into pieces and splattering everywhere in my dorm after the pendulum energy model.

I will subscribe to see more of this guy, he was amazingly precise and interesting

yes, please get rid of loud sound at 8:27 Veritasium for future videos. Great video, but people listen with headphones...

haha, ok, point taken. I think the trouble may be the rest of the interview is too quiet but I'll try to get the balance right.

The pendulum thing blew my mind. I guess it's clearer to me when you transpose it to the more intuitive newtonian mechanics.

This blew my mind. And at the end it blew my eardrums

The most clear, concise, and understandable explanation of spin I've heard. I wish I had this guy as my quantum mechanics professor 25 years ago.

4:30 I love his face here, like "Pretty badass, right?"

That heavy thick accent, awesome

So we're jus going to ignore that perfect circle he drew...yea sure

I can tell he knows quantum mechanics very well because I still have no idea what the hell QM spin is. (inside joke between me and Mr. Feynman)

Normal Person : What is a quantum spin? Physicist : Slaps him hard on the face Normal Person : What ?! why !? My head is now spinning Physicist : Can you now explain what you mean by your head spinning ? Normal person : I now understood completely. Thank you !

I just keep rewinding 2:03 - 2:05 because he's like a cat, and something just caught his eye and he lost his attention. Or maybe he heard someone talking shit either one lol

4:30 - 4:38 I love that little "k?" at the end of the explanation, as if what he said wasn't super counter-intuitive.

Dracula does physics.

Holy shit! 6:49! Yin & Yang! Ancient Aliens confirmed!

This guy is AMAZING to listen listen to. The way he explains things is just delicious.

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{φez･(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.

I'm going to have to make a double pendulum.

I liked how you use Newtonian to show quantum works. Thanks

A really good explaination for a really controintuitive subject! Excellent work!!

I had to comment because the video was at 666 comments

Tommy Wiseau?! Is that you?!

I love that pendulum experiment! That's so cool!

Wow. What a great teacher. This is the first time I understand spin. For some definition of understand ;-) He clearly loves what he does and loves sharing the knowledge. Thanks Professor.

Very nice video. I think that CIG Theory can be applied to spin and explain it in quantum terms of not necessarily classical angular momentum but in terms of new spatial quantities of the moving particle. Maybe not but it's worth a try.

Got confused pretty quickly.... But he explains this things better than anyone else I've heard. Post more videos with him please !

So then if the particles where spinning in opposing directions and constantly changed directions, what sorts of things could come of such an unnatural state could it be a type of perpetual motion that produces energy?

I'm amazed and inspired that you managed to explain spin so clearly in 8mins

Great video, but one thing: He said that a neutron has no charge but still has a magnetic dipole so therefore you can't think of the magnetic moment being due to an actual charge spinning on an axis, but as far as I understand, the neutron's properties come from its constituent quarks, which have their own spins/dipoles and charge. When the quarks are brought together, their charges cancel out but their magnetic moments don't, so doesn't this still allow for the idea of actual spinning of a charge since the constituent elements of the neutron have charge along with spin?

But why are the two spins coupled two each other? I mean they are electrons from different phosphor atoms, right? Could somebody please explain me that.

Spin is not the magnetic field of the electron or other particles. Spin is an intrinsic property of elementary particles. The magnetic spin moment is determined by the spin of the particle and it tells us how the particle will behave when introduced to a magnetic field... A neutron has spin because it is a hadron. Hadrons are composite particles made up of elementary particles. Neutrons are made of quarks which in turn have their own spins. This is where the neutron, and analogously the proton, gets its spin from.

So these qubits work because they're an entangled couple... but what if there are three of them?

The explanation with the pendulum was excellent

he has a charm...😍

I see said the blind man

People in the comments be like: E=mc² Me, an intellectual: *tHe ThUmbNaiL sAYs pEe PeE haHaHAhahAHAhAha*

Scared me at the end

I don't understand how a neutron not having a magnetic dipole means that that it doesnt spin in classical sense? I would suspect that if a neutron actually did spin, it wouldn't have a magnetic dipole (since its not charged), and that would be fine...?

Can I take quantum mechanics with him instead of with my professor? xD

i understood (i think) this video, but how do two particles become entangled in the first place? It seems like all of this only makes sense, and we can only be sure of the entangled particle, if we can somehow guarantee that a particle is entangled to one and only one other particle... now i'm confused again.

i find his explanations pretty easy to get

It's always classical, if you go to the bottom of it. We just haven't gone deep enough and found out what exactly's going on.

This stuff hurts my brain, but it's a good hurt. I'm afraid all I have in common with the prof. is the long hair.

This video is great, really appreciate your work!

4:20 is where I lost him. The 2 electrons have opposite directions, but no directions of their own. Doesn't make sense.

I like listening to Russian accent 😂 xD; D

we need more of this person. the accent, the articulation in layman, its on point.

I think the reason the neutron can have a spin but no charge is because it is not an elementary particle, but is made of quarks. The charges of the quarks cancel out but the spin of the quarks doesn't (I think)

I guess my wife and I are entangled because she always goes with the opposite of virtually anything I say.

hahahahahahahahaha. Yep...I suck at physics....hahahahahahaha

I still have barely any idea what he’s saying...but I could listen to him all day. Actually entertaining as a teacher

HOW WOULD YOU CONTROL A COMPUTER THAT'S SWITCHING FOREVER

4:36 I absolutely know your facial expression at this moment.

And why is 2 electrons better than 2 transistors ? They have booth 4 options ... Do you know some book where I can learn more about quantum mechanics and quantum bits / computers ?

The pendulum is only used to describe the states in which the electrons are entangled, so the up-down or down-up states. The first "unstable" configuration is used to describe why the electrons do not have a single stable spin state associated with them. The other two configurations are the stable configurations for the entangled electrons, either in phase or out of phase with each other. To sum up, the first configuration doesn't exist, the second and third are the observed configurations.