The Stern-Gerlach Experiment (ESI College Physics Film Program 1967) 

For you young folks out there (I do hope there are some young people watching this video), think for a moment how the plotting machine works. It uses all Analog electronics, which in the days of the making of this film was a relative breeze since they had the transistor available to them. Now think back to the days of Stern and Gerlach, coils of wire, mirrors and a stopwatch if they were lucky. Those guys really must have had their sh*t together, hey.

How much more fascinating is analog tech to your brain than digital, there’s something about seeing every piece instead of imagining it

There is a quality of better understanding when you see things done practicaly .

Back to the days when introductions were blessedly short and backstories did not exist. Fantastic the way he got into it.

Let's see if I'm not completely off. The temp of caesium gas is 400K, which gives an average speed of √(2RT/M) = √(2·8.315·400/133) = 22.4 10³ cm/s That gives a flight time within the mag field t = L/ = 12cm/22.4·10³ = 536μs. The transverse force in the mag field is F = μ gradient(B), therefore the transverse acceleration is μ gradB / m, and the transverse velocity at the exit of the field is v⟂ = acc × t The transverse deviation on the screen is then L*v⟂/ The peaks are separated by 3.7mm, so the deviation is half of that: 0.185cm Therefore v⟂ = 82.9 cm/s The acceleration = 155 10³ cm/s² (a posteriori we verify the small parabolic deviation within the mag field is 1/2 acc × t² = 0.022cm, which is negligible) Finally the magnetic momentum of the caesium atoms is acc×m/grad(B) = 155 10³×(133/6.022 10²³)/10000 = 3.4 10⁻²¹ erg/gauss. Close enough to the Bohr magneton 9.27 10⁻²¹ erg/gauss? (all calculations in CGS, because the year is 1967)

The "old timers" really knew their stuff. I was very fortunate to have learned from them.

What a gorgeous demonstration! Sheer physicality of apparatus. Convincing experimental controls so we know what we’re seeing and what we’re not seeing. Modelling of the physics with coils and gyro/magnet gadgets. Transparency about doing the films in two halves filmed in opposite order. And use of CGS units! You could almost feel the excitement Stern and Gerlach must have felt as they watched their detector and saw the unfolding emergence of their original results. Beautiful!

Amazing I don’t understand everything but I find it fascinating.

This film reminds me of the atmosphere in which I entered the Philips NatLab (physical research institute) in Eindhoven, the Netherlands, in 1989. We obviously used state-of-the-art equipment from the 1980's, but we also used analogue measurement devices, like box-car and lock-in amplifiers, in order to detect small signals from measurements. And, I clearly remember how my mentor taught me to handle analogue displacement registration, so that I could conduct beam measurements of our laser-diodes by using a potentiometer at the axis of an arm, on which a phototransistor was mounted. I knew these things already from my amateur-background, but applying several techniques like that for professional research, was quite intriguing. The computer power was furnished by our HP 9000 system, on which we used a Pascal operating system. I used it to calculate the Zernike polynomic coefficients from my measurements of the laser-beams. Furthermore, we used HP small computers with BASIC programs to operate some conditions on the experimental table. Nowadays, all of this seems from an old world, but we made the best out of it.

Fascinating!!! I was born 50 years too late. Love this old stuff that holds true today. Analog and drafting tables for me.

Brilliant! Better than any other demonstration/explanation I've ever seen

This is great presentation. It is amazing what people could do in years past with limited technology.

Professor Jerrold R. Zacharias has such a wonderful and casual way of explaining.

For several years I have on and off searched for a replication of the SGE, and finally, hit gold when finding this video! Thank you for posting it.

You made my day with the demonstration of the precession of the bar magnet on the air bearing, starting at 19:06 and particularly 20:32. This is a fantastic film and I wish I was shown these things when I learned about atomic spin and NMR the first time.

One day, this will become a Television.

Thank you for sharing this amazing video. Its good to see the clever mechanisms and techniques employed back then in action, before the widespread use of electrical automation and detective sensors in our modern era.

. I JUST LOVE HOW EVEN COMPLEX EXPERIMENTS OFTEN LOOK LIKE THEY WERE COBBLED TOGETHER IN SOMEONE'S GARAGE .

Thank you for this. I have seen many a slick animated illustrations of the Stern-Gerlach experiment on YT, the real thing is SO much better! I swear i did not blink during the whole 26 minutes of this. Thank YOU!

Best explanation so far. This was fascinating.

this movie was the first time someone decided that zooming and blurring were good things sometimes

Thank you very much for sharing this video. These are fantastic learning/teaching aids!

Neat. This is some real deal stuff fight here. A good old film like you'd see in science class. Remember those anyone?

Wow. This makes me want to design lab experiments and apparatus!

Classic old school presentation, watch and learn modern teachers who wish to engage with their pupils.

Good old, hard science. Thank you for sharing.

Good old, hard science. Thank you for sharing.. Best explanation so far. This was fascinating..

I wish my life was back in these days so much. Seems like such a great time to be alive. Nobody has any idea what a social media influencer is, and experiments are all analog and the results get plotted on an etch-a-sketch. What could be better?

Its always amazing, how much more clear and logical old videos are.

Never heard of this experiment, but it's old-timey and science so I'll let it surprise me.

Americans that know what millimetres, centimetres and degrees kelvin are in 1967. Refreshing.

What an amazing video. Thank you for sharing !

Very good, there should be more of these videos with other experiments. Why don't they have quality in modern times?

Please continue sharing those films, you're doing God's work

Very high quality video - simple explanation for non-physicist like me and they even added some numerical data (field strenght) for mote advanced audience.

I remember well the PSSC books. Extremely well made for teaching.

Thanks for sharing this! Great demo

The audio is pretty clean despite the video getting pretty dirty at times. Since the audio on film is read optically, it's surprising that the audio isn't clicking and popping when the video is full of artifacts.

Who calibrated that plotter, 1 sq = 1.35mm, scaled to the source. , good Y range, no clipping. The machine at 1:10 might have been my first view of a TV screen, I think ive felt a desire to create one ever since. and i did make a ring motor with helmolts coils just recently , and videoed it. That machine is so, lets do it 2023. Pulley driven vacuum pump, , diff stack , speed frame angle plate structure, and all the beautiful ones on top, That is an astounding instrument, at any time. Physics is such a beautiful science.

Glad to see in the comments that I'm not the only one gawking at the needle mysteriously going up and down and finding that particular analog-driven invention equally interesting as the cesium atoms ablating somewhere and passing through a split, through a magnetic field and hitting a not further explained detector to make said needle move. It's just voltages and resistances fed into an amplifier, being driven by natural unseen forces that make meticulously set up matter function like an analog graph maker even more enigmatic in its function until one looks at the graphs and takes a few semesters in College/University to even know which courses to take to learn more about it. Our ancestors gave us the tools we took for granted.

"All the bugs that always beset every experiment" lol.

They are using magnets to manipulate inside apparatus, electric wires with current to heat the metal and detect the beam - I don't see how this arrangement could cause any interference with the experiment 😉

I see that this was a important discovery that lead to the Cesium Atomic clock!

Just everyday home DIY experiments for kids playing in the garage with Dad's Physics gear from work.

Very cool! I have not seen this experiment in a long time. To be more exact, I only saw it once in an undergrad experimental physics class and that was almost half a century ago. Having said that, I have done lots of nuclear magnetic resonance as a student, which is kind of equivalent, except that it's being done in the time domain.

It's wonderful to see that the US had embraced SI units by the 1960s. No doubt full national metric conversion soon followed?

Thank you so much for this video

20:57 this must be the behavior that MRI machines look for when they are imaging

Half way through I understood the point of the experiment and shifted to the right in my seat.

A closer look into what cannot be seen with the naked eye.

Am I just too slow for modern day, or was the pacing a lot better back then?

great lab experiment

Wonder if this is how Earl Strickland learn to spin a pool ball . . . Excellent series

Was für ein schönes Experiment.

I used to have that exact same ion gauge controller.

12:58 Bugs were already a thing in 1967.

Thanks to the detail explanation ❤❤

This is amazing thanks ☺️

There is an error in the narration at 25:18: "The oven temperature is about 400 DEGREES [sic] kelvin." The SI unit of temperature called the kelvin is not called a degree.

Thanks so much for the video!

Well MIT knew how to build stuff back then for sure.

Was that an HP pen plotter? I used a version made ten years later and found some unfortunate quirks of non linearity.

In those days, the video presenters did not ask the audience to like and subscribe by clicking on buttons 😁

purely electromechanical _badass_

I argue that that parallel/anti-parallel dipoles get pulled into "temporal-phase" with the relative "now" moment. Perpendicular dipoles are shifted temporally out-of-phase with the now moment. I.e. the magnetic field enforces dipole orientation via selective temporal phases.

Could these experiments/demonstrations be used to explain the reasons behind the earths magnetic pole movement?😮

Second part? Where they study only one side of the split beam? Can’t find the video anywhere online.

Terrific I learn a lot here. 👍

Need more videos

could have added a velocity selector fairly easily to sharpen the peaks...??

I don’t think there can be a conclusion made that spin is “quantum”. The rational given is that the axis or angular momentum will precess in the magnetic field and the angle of that will be based on the orientation when entering the magnetic field. The only issue with this is that the particle is charged. As the particle precesses, it should experience a force. Surely that force will eventually cause the particle to completely align with the magnetic field. This would also explain why measuring spin a second time from a different orientation will have a 50/50 chance of being spin aligned or anti-aligned.

19:07 how do you know they are randomly oriented? Theres a big magnet in the middle of the room for the experiment

Great hobby !

This would be great if the audio could be cleaned up

mass spectromety principe... awesome...

Bugs should get their Nobel prize too

Now do that using the dreaded double slit apparatus

So how expensive would it be to make magnetically sorted metals, and how could it be used? What metal might yield best quality permanent magnets I wonder...

18:54 The peaks don't get sharper as you turn up the magnetic field... How on earth could you conclude quantization of spin from this?

Groovy! Slick! Cool Beans!

🎵….Our whole universe was in a hot dense state and nearly 14,000,000,000 years ago….

Interesting. Is this the principle behind mass spectrometry?

What moves the magnet back into the centre after the single coil is switched off?

I thought I had an ant or something crawling in and out of my laptops bottom bezel at 2:51

2:37 Does a compass really point to "North" or "to a South"?

is this what I missed when i ditched physics in high-school? well now I don't feel so bad about wasting all that time in the bathroom smoking weed...

This was an excellent video. They presume we know nothing and walk us through the science. That's how science was back in 1967. Today science videos still presume you know nothing, and NEVER will, so they don't even both to do the deep explaining anymore.

Could somebody explain why the magnetic gyros would lead to a symmetric distribution if normal bar magnets would not? I didn't get it from the video.

Omg they didn't shield the oven...

I find it annoying that anything quantum has to be weird, strange or bizarre now. That just sounds like unrealistic expectations. No effort is required to make it interesting. It is what it is, nature.

Now imagine if they could measure this not in 2d but in 3d.

Some of this info is wrong these days or the guy needs to update his vocab

Are the atoms leaving the oven ionised?

walter gerlach? the one german who had the highest security clearance of all civilians in the third reich gerlach?! wow that is one interesting individual if you are into supressed technology.

Cool Vid 😎

Maybe, someday, in the distant future quantum mechanics will be accepted by the scientific elite.

" over half the atoms in the periodic table are as magnetic as Iron " Who knew that ?

Fantasyland vocabulary explains everything, where is mechanical model?

EVERYONE COMES FROM THE TESTED TUBES

Or just becouse of wery strong magnetic fileld , beam become so wide that atoms collide with magnets and they go reflected to two beams.