Discovery of spin... but missed (Stern-Gerlach experiment, part 2)

[@jkzero]

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[@abhijithcpreej]

The pinnacle of pedagogy. This is physics taught at its finest!

[@jkzero]

Thanks. I am so delighted that viewers enjoy the content as much as I enjoy making it.

[@davidcarr2216]

It takes very special people with a unique combination of both brilliance and doggedness to figure this stuff out. Very smart people can perhaps follow the reasoning entirely but figuring this stuff out is something else. But are the greatest days in physics behind us now ? I guess we simply won't know unless somebody discovers something radically new, by accident or otherwise.

[@SAesir]

the constraints are evolving in a much more limiting way. there are many capable people but those constraints were also extremely limiting for those brilliant people in the photo. if they were alive, those constraints were still limiting them. renaissance of physics means, there are many to discover under the limiting constraints. we passed a renaissance. expect another of course, but it depends on the physical constraints of the reality. if it is inherently impossible to pass those constraints in reality, you wont ever able to get the answer. it is not because people are less smarter.

[@beamshooter]

different era, we are now in "big physics" where every experiment requires a team operating a particle collider.

[@gregorycareca228]

I absolutely appreciate your videos talking about experimental physics, it's sad how few good content there is in this essential part of physics

[@jkzero]

thanks, I am so delighted that viewers enjoy the content as much as I enjoy making it

[@lxiaspb]

Your videos are magnificent. Keep continuing with the great job

[@jkzero]

Glad you like them!

[@luudest]

0:01 Improved detection plate compared to the last video 😉

[@vadim32]

Reflecting on the Stern-Gerlach experiment, I thought that it is possible to perform its analogue with a magnet at home and get the same result. Imagine, we have a neodymium magnet on an articulated gimbal 3d suspension. The magnet easily changes orientation like a compass arrow rotating along magnetic field lines in 3D space. We have a screen in front of which we create a gradient magnetic field using two strong electromagnets. We put the magnets in front of the screen side by side, with a gap between them. Exactly in the middle, the magnetic field is zero. But as we approach from the centre of the gap to one of the magnets, the field increases upwards towards one magnet and downwards towards the other. We launch our magnet on a string towards the screen by hanging it from the string. The magnet goes through a zone of zero field. This is the zone of unstable equilibrium. Being in this zone, the magnet turns either up deflecting to one side or down deflecting to the other side. There will be no intermediate positions on the screen. It's just like the Stern-Gerlach experiment. What happens if we take a uniform magnetic field? What happens if we take a gradient magnetic field with zero at the centre?

[@jkzero]

What you are describing is a process in which the little magnets have enough time to reorient themselves, this is what Einstein and Ehrenfest calculated and showed that for the properties of the silver atoms, it would take more than 100 years (or a magnet more than 40 astronomical units long). It just does not work like the atoms in the Stern-Gerlach experiments.

[@mikedotexe]

Thanks!

[@jkzero]

Wow, I am speechless, thank you so much for you very generous support!

[@ivolol]

The math seems difficult, but also at the same time, somehow straight-foward. At least not as hard as some of the integration techniques and higher math I am aware of. Please leave as much of it in your lectures as you please :) It gives me an inkling to want to re-visit these videos again if/when I am studying it more thoroughly. Great series, I hope you are able to continue it.

[@jkzero]

I am glad that the viewers value the math components of my videos, I really enjoy including calculations and in the end they are crucial for really understanding what really happens in physics.

[@juansalvemini9270]

Balance perfecto entre teoría, matemáticas e historia. Da gusto ver tus videos

[@jkzero]

Se agradece, un gusto por mi parte tener una audiencia que valora el contenido.

[@AbhishekVerma-xw3lz]

At 7:17, the formula should be (1/2)*mv^2 = (3/2)kT instead of (1/2)*mv^2 = 3kT in the video. However, the correct formula is used in subsequent steps for Del z calculation at 7:30 which matches with Stern-Gerlach paper.

[@jkzero]

Oh rats! You are totally right, there is a factor 1/2 missing, it is just a typo, the rest of the calculation is correct, good catch. I added an erratum on the video description and credited you for catching this. Thanks for the constructive feedback!

[@Engy_Wuck]

I like the math - enough to make the science, well, science (and not handwaving), bot broken down to the essentials and "follow-able". Please keep it at this level.

[@jkzero]

Thanks, I am glad you like the content and the presentation style.

[@artemmentiy7107]

I'm so glad that I found this channel, such clear explanations! And I'm studying quantum mechanics this semester, so please go all in. ❤

[@jkzero]

Thanks for your kind feedback, I am so delighted that viewers enjoy the content as much as I enjoy making it. I am covering content that is left out in most QM lectures and textbooks, I am interested in understanding what was known at the time and get an idea of how all this was discovered. It might not be the best way of approaching the topic for the first time but I hope the content serves as a complement of your lectures.

[@kamigoroshi9459]

Fantastic video! Could you explain the motivation behind (12:00) Heisenberg proposing half-integer angular momentum? I can understand Lande proposing it as he was studying anomalous Zeeman effect. Was it the same reason for Heisenberg?

[@jkzero]

For what I read, Heisenberg had the same ideas Landé when studying the anomalous Zeeman effect. Since Landé published first, Heisenberg focused on the mathematical aspects of the multiplets and their relation to the much-needed fourth quantum number.

[@JrgenMonkerud-go5lg]

Try this, then see if there is a small effect of first passing the beam through a uniform magnetic field such as to align the spins in a certain direction prior to the entery into the non uniforms field, if there is a difference in spread of the beam, depending on whether the orientation of the uniform field is perpendicular or parallel with the non uniform field, if the perpendicular case takes more time for the particles to align and start being deflected compared to the parallel case we should see a difference in the magnitude of the spread that is measurable. The magnitude of the difference should be related to the time scale of the process of shifting the orientation of the spins. The parallel uniform field case should also have a sharper splitting of the up and down spins.

[@SloppyDeck]

Fantastic follow up!

[@jkzero]

Glad you liked it!

[@John-bq1lp]

Great content as always!

[@classicalmechanic8914]

"We need more data" for Stern and Gerlach meant they needed more cigars.

[@jkzero]

Nice!

[@fabienleguen]

Amazing as always ! Thank you so much ! One aspect that bother me : With the Bohr-Sommerfeld model, did physicists of that time already know that if a subshell is full (like modern subshells labelled 1s, 2s, 2p and so on) then the net magnetic momentum of the electrons in each subshell cancel out ? It makes sense that they chose silver atom because it is experimentally convenient as you explained (boil at a low temperature while staying chimically pure and stable) but they probably worried about the influence of inner shells electrons on the net magnetic moment of the atom yet convinced themselves that only the outest electron would contribute to the net magnetic moment. Did they speak about that in their papers ?

[@jkzero]

Thanks so much for your generous support. I could not find any reference to shells in the early papers, which is what I would expect. The whole theory of orbitals and shells that clarified the periodic structure of chemical elements from a physics point of view was only achieve after modern quantum mechanics was developed between 1925-1926. They has no idea that the last unpaired electron on the last orbital was responsible for the magnetic properties of the atom that they selected for the experiment.

[@fabienleguen]

​@@jkzero I kept digging. They were indeed already talking about orbitals and "subshells" in 1922-1923 (they called them "groups") and explicitly saying that this was the explanation for the periodic structure of chemical elements (Amazing). See Bohr's publication in Nature titled "The Structure of the Atom" and published on July 7th 1923. About orbital magnetic momentum, there is a book written by Hendrik Kramers (assistant of Bohr in Copenhagen), titled "The atom and the Bohr Theory of its structure", published in 1923 where one can see beautiful figures representing electrons orbits in high-Z elements (as they were understood back then using the Bohr-Sommerfeld model). For Lithium (Z=3), the electron orbits of the two innermost electrons are said to be circular, of the same radius and separated by an angle (between their orbital planes) and the outermost electron orbit is elliptical and has a relatively bigger major axis. If orbital magnetic momentum was thought back then to be generated by the small current loops made by electron orbits, then the two innermost electrons of lithium should have contributed in their mind to the net orbital magnetic momentum of the lithium atom. Therefore, for the Stern and Gerlach experiment, I cannot believe they just "assumed" that only the outermost electron contributed to the net magnetic moment of the silver atom and that they just "ignored" the innermost electrons. There is a piece missing in the puzzle. I tried digging further reading Sommerfeld book title "Atombau und Spektrallinien" and published in 1922 but I cannot read German and using OCR and auto translate app on this 600+ pages book is not reasonable for me.

[@jkzero]

Thanks for sharing, I was not aware of this. For what I have read, the periodic structure was there but the full understanding only came after Pauli{s exclusion principle. I mentioned Kramers in the video about Compton scattering and he will reappear soon.

[@donnerflieger3770]

Thank you for your nice video! A question to your second coincidence, the magnetic moment has an anomalous factor of ~2. While googling to understand I kinda get the reason why it's deviating from exactly 2 (possible short lasting transformations into other particles in a loop), It's hard to wrap my head around the twospinor/bispinor concept of the Pauli- Dirac- and Klein-Gordon equations. Did I understand it right that it is a consequence of a possible negative state for the electron to exist in, like a hole, which is to be found out being the positron?

[@jkzero]

This is a tricky business, it requires understanding the Dirac equation and its solutions. In a nutshell, Dirac discovered that his equation describing the electron predicts four solutions: one describes a spin-up electron, another describes a spin-down electron, and the other two are for the positron.

[@valentin_5564]

Thank you for your videos! High quality

[@faisalsheikh7846]

Awesome as always ❤

[@jkzero]

Thanks. I thought for a moment that Ed Witten had stopped by.

[@lanimulrepus]

Excellent historical review...

[@jkzero]

Thanks, I am glad you like the video.

[@luudest]

9:50 Is the orbital magnetic moment a wrong prediction of Bohr-Sommerfeld model or does it exist but can only be shown by other expriments?

[@jkzero]

The orbital magnetic moment a correct prediction of Bohr-Sommerfeld-Debye model but it requires the angular momentum quantum number (denoted l) to be greater than zero; otherwise, the physical effects vanishes, as in the case with silver, which has l=0.

[@luudest]

@@jkzero thank you!

[@ivolol]

@@jkzero I assume at some point later someone managed to do an experiment differentiating atoms with I = 0 and != 0?

[@jkzero]

@@ivolol goo question, I assume this is the case because we have a good understanding of spin and orbital angular momentum today, but I would need to search for a reference.

[@roshan0405]

Just more mathematical equation and you are 3b1b of physics which i was wishing for❤

[@jkzero]

Wow, thanks!

[@physicsbutawesome]

Great addition to the first vid. I find this era of the "alte Quantenmechanik" really fascinating - they were already on the right track in many ways, but a lot of the interpretations were still off (unavoidably). History of science is often told somewhat in hindsight ("Stern-Gerlach discovered spin"), so it's good to have such a detailed look into what they actually did and actually believed they had measured.

[@jkzero]

Glad you enjoyed it. I am following the discovery path, I really want to learn what was known at the time and building up the whole picture of quantum mechanics. I am somehow building the intro to quantum mechanics course that I wish I had taken before getting into Hilbert spaces, QM postulates, and eigenvalue problems.

[@physicsbutawesome]

@@jkzero i get what you’re saying. To play devil‘s advocate, though, I think learning the historical meanderings of how stuff really was discovered is better done AFTER you’ve learned a field. I think it introduces more confusion than benefit to people who don’t have yet a grasp of the big picture.

[@jkzero]

You have a good point, maybe this is why I am doing it now, away from my past-life as academic, now I have free time to read whatever I want, think, read more, and write. These videos are a condensed version of my learning notes.

[@ralffig3297]

Man your videos just rock. Looking forward to the next one. Now I'm curious to know what happened with the 3 magnet experiment!

[@jkzero]

Thanks, great to get viewers excited with the content.

[@malabikasaha2452]

How to predict the outcome of the experiment in an alternating magnetic field?

[@jkzero]

This is the type of experiment that Frisch and Segrè did in the early 1930s. For modeling this you need to solve the time-dependent Schrödinger equation with spin. Here is an open-access paper with the details iopscience.iop.org/article/10.1088/1361-6455/acef83

[@5eurosenelsuelo]

You mentioned that were lucky to be using silver because of its electrical configuration. I thought it meant it wouldn't work with other elements. However, later you mentioned the experiment was repeated with many different elements. I thought you might be referring to elements within the same column in the periodic table since they supposed to share a similar chemical behavior due to having the same electrons in the last orbit but cesium, the one from MIT, isn't in the same column. I'm lost. By the way, I'm no physicist nor chemist so please correct anything possible mistakes in what I said.

[@jkzero]

No, I didn't mean that the experiment would not work with other elements. I called the use of silver an accidental choice that leads to no observable effects coming from orbital angular momentum; therefore, revealing the spin of the electron (although this was missed because they didn't know that the theory was incomplete). The splitting will definitely work with other elements too. In fact, most of the images at 17:41 are with silver, but some are with hydrogen and others with potassium.

[@5eurosenelsuelo]

@@jkzero Thank you for the clarification!

[@AE-cc1yl]

Your videos are a bliss

[@Higgsinophysics]

Really interesting to learn more about the history and the struggles of the experiment :D Awesome video! And no I don't know where "this is". But I'm intrigued

[@jkzero]

Thanks, glad you liked it. And I can see that you made it until the end, the combination of the cat and "measurement problem" is probably enough to infer where this is.

[@no-one_no1406]

The numbers matching up for orbital magnetic momentum vs. spin interpretations is intriguing to say the least! Never bumped into this in any physics lectures. Very interesting to see what has led us to our current explanations. And what other types of models could also explain the experimental results. How do you even find information on all of this? Microfilmed documents in libraries? Or is there some physics book that compiles most of these groundbreaking experiments, that can then be used as a basis to look up more details with?

[@jkzero]

You are not alone, I never encountered most of the content that I have shared in this series. I feel that so much is left out during our studies that it is no surprise that there are also so many unclear concepts and misconceptions. Making these videos has also been a journey of discovery for me, reading the original papers by the masters is quite hard, we are used to learning from textbooks that condense decades of knowledge. In the old papers everything is all over the place and hard to follow but it is also quite refreshing to follow the reasoning of these people. As for the sources, I find that textbooks are useless in that sense because they only focus on the condensed successful results and I am interested in the mistakes and wild guesses that these people attempted. For this papers on History of Science are more useful, I then move to the original sources, I have been reading the original papers rather than the pre-digested (and usually wrong) narratives.

[@no-one_no1406]

@@jkzero Basically it is as much work to find all this as I would imagine! Very sad that this is current situation. Especially in theoretical physics, going though experiments and the analysis of results etc. should be how it's done. Very nice that you're doing this for everyone to see! Hopefully you continue making these for a long time! And ideally are able to get more people to help out to be able to make even more!

[@jkzero]

@@no-one_no1406 There are many stories to be shared, I have also learned way more than expected when reading the old papers and creating the stories, it has been great to get an audience interested in these topics

[@GeoffryGifari]

On the point of changing the slit shape (17:01) from circular to rectangular, is it possible that a mechanism similar to diffraction made the beam area wider? (I know the wave property of atoms is unlikely to be relevant for the experiment, but maybe a beam of solid particles going through a small hole is analogous to light passing through a pinhole)

[@jkzero]

Good question, I do not know. I assume you are thinking on treating the atomic beam as matter waves. I showed you the equations to estimate the speed of the silver atoms, their mass can be found online; therefore, you can calculate the de Broglie wavelength and compare the the width of the slit.

[@AmericanDiscord]

I would like to know if there is anyway to shoehorn a classical explanation in via precession decay occuring very quickly. Maybe radiation or change in internal configuration of the atom similar to a nonpermanent magnet. Interesting video of an important historical topic.

[@jkzero]

@@AmericanDiscord This is one of the options studied by Einstein and Ehrenfest, they found that precession decay would take more than 100 years; however, the atoms spent less than a millisecond in the magnetic field so they concluded that this could not explain the alignment.

[@AmericanDiscord]

@@jkzero Did they appropriately calculate the self-torque in response to the magnetic field? I've seen some doubt raised about those calculations. Maybe more robust assumptions lead to a massive reduction in the decay timescale.

[@AmericanDiscord]

I think tau = mu cross B + (mu dot grad) B for example.

[@johnkuehler2608]

Nice. we are always taught in hind sight as if the spin was the original motivation of the experiment.

[@jkzero]

Thanks, I am glad you liked the video. You are exactly right, from its presentation in textbooks this experiment appears to be designed to measure spin but in reality it had a different purpose but some lucky coincidences and misinterpretations canceled each other out in a remarkable manner.

[@dwinsemius]

Really interesting. I was taught in my organic chemistry lab course that space quantization was the basis of NMR technology circa 1970. Wondering if that was an error that propagated 50 years down the line?

[@jkzero]

yeah, there seems to be a misunderstanding there, I do not know where the reference to the 1970s comes from: the physics of NMR was established by I.I. Rabi in the late 1930s after extending the Stern-Gerlach apparatus using variable magnetic fields. The first NMR units were already available in the early 1950s.

[@dwinsemius]

@@jkzero 1970 comes from the approximate year I was taking the organic chem lab course and would date the technology that was typical of that era.

[@jkzero]

oh now I get, I misunderstood, I read it as "NMR was developed in the 1970s," my wrong.

[@nikhilsen9007]

I am slowly realizing that learning a subject from historical prospective gives a much deeper understanding as compared to state pf the art, sanitized and polished modern content.

[@jkzero]

I personally believe that many of the misconceptions on quantum mechanics or conceptual holes arise because people jump directly to modern quantum mechanics and its ad-hoc postulates without studying the early developments. Even though the old quantum physics was rapidly replaced by quantum mechanics, it is the old quantum physics that led to the conceptual developments by Heisenberg, Born, Schrödinger, Pauli, and the others. Here I attempt to share these unfairly forgotten early times of quantum physics.

[@nikhilsen9007]

I completely agree with you but I just wanted to add that learning from historical development is great way to learn almost everything. Also modern textbooks completely overlook details of experiments which makes the experiments look boring and therefore most people interested in physics dream of becoming a theoretical physicist. It's really cool that you don't overlook details of experiments and also include seemingly minor details such as experimental condition's impact on O-rings and vacuum. Anyone who has worked in physics labs as a researcher can attest that seemingly trivial problems can make or break an experiment and if you are lucky, might lead to profound discoveries. For young children, your videos are also a good glimps in the life of an experimental physicist

[@jkzero]

I am a theorist and I see way too much praise for the theorists that came up with great ideas but little about the experimentalists who discovered anomalous results as well as came up with equally brilliant experiments that confirmed theoretical ideas. Plus the experiments from early 1900s are a beauty of scientific ingenuity and simplicity.

[@nikhilsen9007]

And also huge engineering achievements

[@malabikasaha2452]

What accelerated neutral atoms towards the detector glass screen?

[@valentinmalinov8424]

The curiosity.

[@jkzero]

atoms were in the oven at 1,000°C, which had a little hole, so atoms would randomly escape the oven at a constant speed. No acceleration was used to push the atoms towards the detector plate.

[@valentinmalinov8424]

@@jkzero Thanks, I know that...but I am sure that you don't know to whom you are explaining Physics. - I am the author of the book - "Theory of Everything in Physics and The Universe"

[@ShopperPlug]

4:16 - Please explain about spin. I still don't know who is right about it's explanation.

[@ivolol]

It seems to me that Mr Diaz plans to expand upon spin, in a future video or videos

[@jkzero]

Yes, a video about spin will come soon.

[@JrgenMonkerud-go5lg]

Einstein and erenfest were right about classical electrodynamics not being up for it, but classical theories in general, I think not so. Just imagine this, an electron as a real physical spin in some sense, not a free body in space spinning like a flywheel, but some sort of structure with angular momentum. Imagine that it is driven and also dissipative, some current of torque flowing through it at all times and also to some degree energy. In free space with no magnetic field it just keeps spinning with no impetus to change its direction, but in a magnetic field, angular momentum can be removed at ant rates in its axis of spin and added in the direction of the magnetic field at any rate you want hypothetically, changing the orientation as quick as you want really in a classical model of your choice, which if these are realistic is another Matter, but classical electrodynamics is not the limitations on such dynamics that should concern you at all, any classical model that reproduces the results and can coexist with other results are fine. And if we just take a gyro as an example, it is possible to turn a flywheel in any direction you want as quickly as you want as long as you can introduce enough angular momentum to the system in a short time as is needed, it's just about the available tourqe in a magnetic field in a sense, and that torque does not have to be the same as what the classical magnetic potential would provide, it can be as fast acting as you want hypothetically as long as microscopic magnets are appropriately tourqed as a result of the new physics, and quantization of spin in magnetic fields is basically going to guarantee that as long as the basic quantum results are reproduced on a short timescale, as long as the effects are mostly just the emergence of quantization of spin.

[@philoso377]

Nice video and presentation. I wonder why the electrons uniquely spin up/down and not either left, right or compound of up, down, left, right.

[@jkzero]

The up or down is just a definition referring to either parallel or antiparallel to the magnetic field. If you want to measure left/right instead you need a Stern-Gerlach apparatus with a magnetic field along the left/right direction, this is exactly what Einstein and Heisenberg were wondering about. A complete story requires a complete theory of quantum mechanics and the uncertainty principle.

[@philoso377]

@@jkzero, Thanks for letting me thinking. That was a wrong question on my part. My thinking is this. If the electron do spin (as it seems) it will leave the source either spin randomly left or right at a spin axial tilt randomly in all angles between +/-90°. Electron happen to have B field perpendicular to the test B field it didn’t deviate horizontally but landed straight ahead at the center of screen. Contrary Electron with B field run between perpendicular to parallel wrt the test B field will deviate +/-90° from the test B field. The result is a continuous sweep on the screen as recorded in history and not only landed on two spots horizontally. My conclusion is that - spin axial tilt, angular velocity, direction are all random. I didn’t expecting electron to spin departed the source. Even if it spins with its point charge, and I don’t expect a spinning point charge can produce a B field. Unless the point charge has a helix trajectory leaving its source. (resembling charge streaming along a solenoid coil)

[@peterfireflylund]

@@philoso377have you ever played with polarizing filters? Take two and twist them so they block out almost all light (one is 90° to the other). Now take a third and put it in between the two and turn it. When it’s rotated 45°, you’ll be able to see through the whole stack (but darkly). When you rotate it more or less, you’ll see less light. The measurement (by each filter) changes the polarization of the light + blocks some of it. The magnets do the same with the spin: change its axis + deflect the electrons. Diaz is clearly building up to that for the next video.

[@philoso377]

@@peterfireflylund yes I’m aware of that in previous visit of YT channels. That suggests us we haven’t done enough homework in light polarization and the most popular version can’t explain that. Looking forward to see in depth explanations. Thanks

[@foobargorch]

Type 3 errors are the most fun

[@malabikasaha2452]

Was the data rationalised in terms of Maxwell Boltzmann distribution at 1000degC?

[@jkzero]

Yes, they were very careful on the speed estimate of the silver atoms. I only showed the proposal but in reality they justified modifications to the speed formula to account for possible bias. For instance, 3/2kT is the average thermal energy of the atoms inside the oven; however, the atoms leaving the oven could have different energies. They explain these details in the 1924 paper.

[@robertosutrisno8604]

​@@jkzerodo you any good source for translated pre-quantum era papers?

[@jkzero]

@@robertosutrisno8604 there are no official translations available for most of these old papers. Only the famous Stern-Gerlach paper was recently translated arxiv.org/abs/2301.11343

[@randomchannel-px6ho]

Diracs "The Evolution of the Physicist's Picture of Nature" should be required reading IMO

[@jkzero]

Thanks for sharing, I knew that this article existed but I have not read it. I just got a copy to check it out in detail.

[@markberardi109]

Has the Stern-Gerlach experiment ever been conducted using an electron beam, as opposed to a bean of silver atoms?

[@jkzero]

I believe that electrons have never been used in a SG experiment. There is a theoretical argument by Bohr and Pauli claiming that it is impossible because the orbital and spin angular momentum would always be coupled for single electrons; also they claim that the Lorentz force would wash out the effect. These claims have been challenged due to their semi-classical description but as far as I know, this experiment has not been conducted. Neutral atoms don't suffer of the Lorentz force problem and the orbital angular momentum can be eliminated for atoms with an unpaired electron in a s-orbital, like silver, which offer a clean access to the spin.

[@Engy_Wuck]

this is probably impossible, as you'd then get much larger effects from electromagnetic effects (electrons are charged particles, which react to magnetic fields). The Stern Gerlach experiment is interesting because it uses neutral atoms which _shouldn't_ be influenced by a magnetic field. But *if* it is possible, then with electrons. Protons and neutrons have much weaker magnetic moments.

[@drvanon]

What an absolute example Sommerfield was. How many of his students achieved success? This is hard to attribute to chance!

[@jkzero]

Totally agree, he was recognized as "the great teacher" and by the success and impact of his students we can confirm this title.

[@praveenb9048]

Maybe another video about Uhlenbeck and Goldsmith?

[@praveenb9048]

Goudschmit

[@jkzero]

yes, definitely! It is on my to-do list

[@luudest]

19:17 Out of couriosity: Is this short MRI sequence produced by AI?

[@jkzero]

No, it is an actual clip. I include credits of all the images and clips in the video description.

[@zachreyhelmberger894]

You're killing me! What is "the measurement problem"?

[@jkzero]

This is a good description of the measurement problem: kzbin.info/www/bejne/Y5zbnoVuZ7aAhJo

[@voidisyinyangvoidisyinyang885]

No wonder Ehrenfest offed himself - this stuff was too revolutionary but also the whole entropy problem. Roger Penrose understands that gravitational entropy is the opposite of the entropy of mass, hence our ecological crisis today.

[@Naomi_Boyd]

Dr. Jorge, can you help to settle a debate? A friend argues that light is a particle. For evidence of this, he says that an electron must absorb the energy of a photon in whole or not at all. The energy of the photon can not be divided, so it must be a fundamental particle. On another day, he uses Compton scattering as evidence. He says the photon acts like a billiard ball. It imparts a portion of its energy to the electron and then gets deflected with the remaining portion. Do you see the problem here? Why do physicists think they can have it both ways?

[@jkzero]

In a nutshell, light is not a particle but it is not a wave either, it is something completely different. In some phenomena light manifests properties that we associate to waves (refraction, polarization, diffraction), whereas in other phenomena light manifests properties that we associate to particles (photoelectric effect, Compton scattering). This wave-particle duality is precisely the topic of my next video.

[@Naomi_Boyd]

@@jkzero Thank you. I very much look forward to it.

[@068LAICEPS]

Beautiful

[@peterfireflylund]

18:34 missed a gemination (+ wrong diphthong). It sounds exactly like “and 1828”. You got the one just before right: “between 1927”. Not pronouncing the -d in “and” is also correct in continuous speech. Did the -d trick you?

[@jkzero]

Thanks for this; as you might have noticed, I avoided the use of "in 19xy" and found a way to add a word in between "in early 19xy," "in late 19xy," "in August19xy." Clearly I missed the case with "and 19xy," yes, I blame the missing "-d"

[@peterfireflylund]

@@jkzero but you got “between 1927” exactly right! Gemination and diphthong and everything! Don’t give up on “in” yet ;)

[@DrDeuteron]

Omg, Wigner would be like wtf bros?

[@christophergame7977]

Then shall the eyes of the blind be opened !

[@AlmarPostma]

🐈 Kreis 6, Zurich, Switzerland perhaps? ;)

[@jkzero]

I see that you now your way around Zurich

[@AlmarPostma]

@@jkzero mostly my way around the internet. I still haven't been to Zurich proper.

[@jkzero]

@@AlmarPostma I see. I have been to Zurich long ago, before I knew about the kitty at Schrödinger's house so I missed it.

[@Rolancito]

Experimental physics stalled once smoking was forbidden in the lab

[@jkzero]

That's an interesting hypothesis

[@christophergame7977]

Watching this with bated breath.

[@isbestlizard]

It must have been crazy to have been a physicist in the 1900-1920's like from going to thinking yeah we've pretty much cracked this the universe is classical and we know it all just a bit of mopping up to wtf even is this?? within a working lifetime is a serious attitude adjustment

[@jkzero]

Yeah, there is a great lecture by Hans Bethe describing his PhD years in Sommerfeld's group receiving an early copy of Schrödinger papers and he describes the period as very confusing because nothing worked but also very exciting

[@abrikos1100]

Soo... does space quantization of ground state exist irl like explained in previous video?

[@NemosYouTube]

That’s what I’d like to know too.

[@jkzero]

Space quantization (or quantization of orbital angular momentum, as we call it today) exist but it only produces observable signatures when the corresponding quantum number (we call it l) is greater than zero (l>0). In the system used by Stern and Gerlach, the silver atoms have l=0.

[@NemosYouTube]

@@jkzero so the general story you laid out in the previous video is still correct, namely that most of the physics community of the time did not actually believe the mathematical “tricks” to explain the data really implied something fundamental about how space is quantized. I thought that was something really profound and demonstrated how entrenched everyone was in the classical viewpoint. It is perfect example of how science can undergo a self-correction, and how hard that can be when the idea being challenged seems so foundational.

[@abrikos1100]

@@jkzero In previous video there is a strange thing: in old notation k is in 1..n and m is from -k to k while in new notation there is l is from 0 to n-1 and m is from -l to l, so m has less number of values (by 2) in new notation. Is it the source of a problem?

[@jkzero]

you are totally right!

[@Dismythed]

Individual particles cannot retain their individual spins if they all contribute to a group spin because of conservation of energy. The spin is due to electromagnetism. If every particle retained all its electromagnetic properties, they could not generate strengthened and combined features. It would be impossible because of conservation of energy. But now because their fields do enlarge, strengthen and combine spins, conservation of energy dictates that they cannot retain their fields individually. They must therefore move independently of their fields within the group field.

[@roberto.lineros]

first! 🙂

[@jkzero]

qué gustazo tenerte por acá

[@MatrixVectorPSI]

Nice presentation. This video seems to be pure classical quantum mechanics though, which is what I advocate for anyway, but I didn't have my nap today so.. Maybe I'm missing something? The spin orientation of an atom is not really a superposition. It's an "or" wave of spin up "or" spin down. Spin orientation and magnetic moments are classical phenomena, they can be described with quantum mechanics. But spin orientation is inherently classical. And whats this "measurement problem" you speak of? The observer effect has been thoroughly debunked if that's what you mean.. If you want to know the current state of a system, you don't absolutely have to make a measurement. You can just make an observation. Such as observing stars before they cross the cosmic event horizon. Or just make an observation of where it isn't and deduce the state from there.

[@jkzero]

I disagree with "spin is inherently classical," unless you refer to an actual spinning object (which is unrelated to the concept of spin in quantum mechanics).

[@MatrixVectorPSI]

​@@jkzero Fair enough. More directly, my point would be that spin is not an "and" wave of multiple objects manifesting itself into alternate dimensions as indicated by the "modern" interpretations and the "observer collapse" non-sense you see as the general consensus. Spin is an "or" wave. The object does not exist in multiple positions. It exists in one uncertain position. "Classical" is definitely a subjective misnomer. I should think up a better term.

[@MatrixVectorPSI]

​@@jkzero More to the point. "Alice and Bob's" correlations aren't above 2 as demonstrated by this experiment. The atom only exists in one instance and a correlation of above 2 can never be physically measured. The CHSH inequality violations are a mere mathematical abstractions that doesn't exist as real physical entities in a single instance of reality. I guess I'm talking to myself here. I think I'm ahead of my time. Or too late. No one knows wtf I'm talking about, lol.

[@alexandrekassiantchouk1632]

Are you familiar with Dr. Williamson, Robinson, ... real meaning of spin of electron: photon rotating in two plates/directions, when it makes 360° turn in one dimension, it makes only 180° degrees turn in other dimension. In other words, photon's circular orbit is half wavelength long.

[@jkzero]

I am not familiar with this.

[@alexandrekassiantchouk1632]

@@jkzero QC0021: Dr. Vivian Robinson: Photons, Particles, Matter, and Relativity