"To understand spin, imagine a ball which is spinning, except it's not spinning and it's not a ball."

The particles may not be actually spinning but my head certainly is.

I remember watching this video when it was released as a first year uni student. Now I work with quantum entanglement on a daily basis and this video was one of the things that piqued my interest in this field

I just sat down, listen intently to the contents of this video, and suddenly 9 minutes have passed without me knowing it and the video ends. What a brilliant presentation.

i am in a superposition of understanding this video and not understanding it at the same time...

I understood everything up to 00:01

I remember watching this video when it came out back when I had just finished primary school, I barely understood anything. Now rewatching it, as I'm in the midst of my Quantum Mechanics course in Uni, it's both nostalgic and satisfying finally being able to make sense of these concepts. Amazing video, thank you!

It's very complicated but I find this fascinating. It's one of those educational video's that you need to watch a couple of times before you start to understand.

He lost me when he said "They're not actually spinning of course, they just have angular momentum and direction".

"If you think you've understood quantum mechanics, then congratulations, you've not understood quantum mechanics" - Richard Feynman

I've always struggled to understand the experiments you mentioned regarding measuring entangled particles, and I found your visual representations to be very helpful.

Watching this video after the Nobel for Physics got announced. Gives me a basic idea of Quantum entanglement.

Heisenberg and Schrödinger get pulled over for speeding. The cop asks Heisenberg "Do you know how fast you were going?" Heisenberg replies, "No, but we know exactly where we are!" The officer looks at him confused and says "you were going 108 miles per hour!" Heisenberg throws his arms up and cries, "Great! Now we're lost!" The officer looks over the car and asks Schrödinger if the two men have anything in the trunk. "A cat," Schrödinger replies. The cop opens the trunk and yells "Hey! This cat is dead." Schrödinger angrily replies, "Well he is now."

I've watched this explained 50 times, 50 different ways, and I still only understand 50% of it. And for some reason, it's still interesting.

Thank You so much for the short but very clear explanation at the end about why faster than light communication is impossible using entanglement. I finally understand something I have been trying to understand for years.

This video is straight fuego 🔥. Veritasium always explains things so clearly and carefully. I'm so grateful for all these dope science educators on yt so I can keep learning even after graduating. Cheers!

In order to understand that we don't understand entanglement, we should first understand that we don't understand spin.

"Spooky spinning particles, send shivers down my spine." - Albert Einstein

I like the idea of living in a "probabilistic" universe that just gets concrete when things are measured. So, this entangled particles don't need to exchange any information. It's just the observer who, by measuring the spin of one of them, enters into a specific universe in which the other particle is (and always has been) consistent with the measured one.

INCREDIBLE VIDEO!!!!!!! I knew this was not going to be easy to understand. So I cleared my mind, sat back relaxed, and gave all my brain to understand this and also watched it 3 times, and I am really happy to totally understand what all you said. For me, It was my first video about the Quantum entanglement and you did a perfect job in keeping me enthusiastic about this SPOOKY topic ;D

"In order to understand it we must first understand spin. All fundamental particles have a property called spin. No, they're not actually spinning." You lost me. (0:41)

the spooky thing is, you're using yourself as a particle

i did a high school project about this exact thing last year, this video came to a better conclusion and was far more understandable than any of the reseach i did over a couple months. thanks for explaining the thing i was meant to explain myself some time ago, i finaly have at least some grasp of how this works now, because even after the project i was still completely clueless on the logic behind it all.

I was literally just watching Only Lovers Left Alive again yesterday and them talking about Entanglement Theory and Einstein’s Spooky Action at a Distance and was trying to look up information on it yesterday but every description I found went over my head. In sweeps Veritasium to save the day once again!! Lol You rule bro. Keep it up!!

Particleman... Particleman... does whatever a particle can. Spins around...up or down. Gets entangled. Traverses town...

I don't understand any of this, but since it's technically teaching me something, I don't feel bad about not starting my paper on Shakespeare.

Einstein was a real OG, I can't wait for a Zweistein

I had studied physics and did not receive such a good explanation during studies. In particular the bell experiment and why there are hidden constants. In the video it is a bit fast (should watch 75% speed 2 times and pause and ponder) but still extremely good. It is not easy, but essential, and the explanation is to the point.

When the words "the opposite random" entered my brain, it exploded.

I really wish there was a good video explanation of what a particle spin is....ive never understood it.

Thank you! I’ve watched countless videos trying to understand why we can’t just assume they spin opposite from the get go, and finally I understand.

this is the first time ive been able to understand why this doesnt allow for faster than light communication, good job man!

I understood 50% of this, and didn't understand 100% of it, so now I too can claim I know a thing or two about quantum mechanics.

It's confusing no matter how you spin it.

Once again, you've explained it better than anyone 😁 Thanks 👍

Finally a good explanation of why there's no hidden information. This question bothered me for quite some time, now it makes perfect sense, thank you

I have no idea what this guy is saying. This must be how my mom feels when I try to explain how her iPhone works.

This is the best explanation I've seen of Bell's theorem, excellent video

Many thanks for your explanation of Bells theorem regarding quantum theory as it leaves me finally understanding what's really going on.

Wow, that is a very smart experience, making use of the both quantum physics and probability... Thanks for sharing!

Now I just need a video explaining this video

Thank you to those trying to make sense of this! For clarification: 1. We know the entangled particles must have undefined spins before we measure them because if they didn't they would sometimes give the same spin when measured in a direction perpendicular to their well-defined spins (and they never do). 2. We know the entangled particles can't have hidden information all along about which spin they will give in different directions because if they did we would measure different results at the two detectors >5/9ths of the time and we don't - we only get different results 50% of the time. 3. We can't use this behaviour to communicate faster than light because we can only pick the direction to measure in, we can't force the spin to be up or down - and it will be random with 50/50 probability. When the two detectors pick the same direction to measure in the results at one detector will be random but the opposite random of those measured at the other detector, which is a bit spooky.

This is the best explanation of spin I've ever seen. Thank you!

An explanation of 'spin' I've never heard before. Enlightening and creative. I still can't say I fully understand, but at least I can go to bed with something to ponder.

The fact that there's a viable market for this video means I'm dumber than I'd hoped

Best explanation I have seen so far without over simplifying it. Thank you.

Wonderful ( even if I get lost sometimes.) Especially notable is when there is an actual painstaking, heart-stopping and ultimately VERIFIABLE demonstration, as in the OTHER Varitasium UKpostss --- "A Physics Prof Bet Me $10,000 I'm Wrong"--- and--- "Risking My Life To Settle A Physics Debate"---. MY Hats off !

Who's here after the announcement of nobel prize winners

Quantum mechanics is spooky and often feels like sci-fi. That's why it's so interesting.

I thought I was the only one who had trouble following this...after reading the comments....*whew* I feel better

The acoustics in that room you are in at the beginning was quite the vibe.

If we're all indeed living in a simulation, programming quantum entanglement into our counterfeit universe was quite an impressive feat!

you just wanted a excuse to wear the spandex

“If you can't explain it to a six year old, you don't understand it yourself.” - Albert Einstein

Thank you for your excellent videos! My students so enjoy them. As you look for new video ideas, you might consider doing a follow up on how Bell'st experiment does not rule out hidden variables if Statistical Independence is violated in the case of superdeterminism, which Einstein's block universe perhaps suggests. Basically, the actual measurement taken causes the particles to have been created in a definite way, with hidden variables. Nobel Laurent Sir Roger Penrose suggested in a presentation last year that he didn't think the resulting retro-causality would lead to paradox, if carefully thought through, but I can't seem to wrap my head around it.

The spin down sound makes me understand how Dennis felt when he got a wrong answer on Family Fight.

I feel like I need to watch this video 1000 times to understand it.

The most understandable video I've ever seen about Bell's Inequality. Which is quite a complicated thing. Well Done Derek !

I think if you substitute the word synchronized for entanglement and the word possibility for superposition, it is much easier to understand.

Sir please make video on "Aspect, Clauser, Zeilinger" 's experiment

Now my head is spinning too!

Nothing exposes the inadequacies of the human mind like quantum mechanics.

Awesome video, but I got a few questions: How do we know how the two plans are distributed? In the experiment, we can't really tell which plan the particle obeys to until measurement. So let's assume the first plan occurred with probability a and the second with probability b, so a+b = 1. Now we solve the equation a+b*(5/9)=(1/2). All solutions of a and b give distributions of the plans that would result in a 50% chance to measure different spins for the particles... Second question: What exactly would it mean to measure two entangled particles in two different directions? Is the upwards spin result of the measurement measuring in direction 'up' the same as measuring 'up' sideways? What would we get if we measure the same particle in different directions? The background of this question is: is the measurement still entangled if we measure in two different directions?

Please make a new video because recently three people got noble prize for Quantum entanglement and it makes me think that is Einstein's theory really been proven wrong?

Too advanced for a 15 year old some one help explain?

"No they're not actually spinning, but they do have angular momentum" aaaaand I'm lost

The mainstream media seem to have an issue with Social Media. Watching YT has engaged me with science more than since school 40 years ago. Stuff like this video has re ignited my mind much more than hearing sound bite news bulletins of fear & misery on repeat every 15 minutes….

As someone who has a background in Physics, I always went along with the accepted point that the randomness within a quantum entangled system prevents FTL communications. I recently read a book 'Cracking the Cosmic Code' which actually shows that the randomness is not a restriction at all. It now opens up the distinct possibilities of FTL communications.

Watching at 75% speed is helpful

The universe is indeed, a fidget spinner.

My questions: 1. How can a particle not spin if it has angular momentum? Isn't angular moment the definition of spin? 2. The guy is spinning the same way every single time after he goes through the cardboard, how is the spin changing? The only thing changing here is his orientation. 3. According to your equation, the "spin" (orientation) should always be up in the vertical cardboard experiment, but you show that it can be down?

You could use this to sort of, kind of make it appear like you were communicating faster than light though, at least to a 3rd party: Like say it were a battle situation across the galaxy somehow and you wanted for some reason to be doing the opposite of whatever your allies back home are doing. you could have a pre-planned agreement to let the spins dictate behavior. of course this is not actual communication but it could look like coordination to an outside observer.

I am smarter now. Not sure how, but I am smarter.

Let's say we send a spaceship a lightyear away. On board, there's one particle and we program the spaceship to measure the spin at a specific time. If the spin is up, it destroys itself, if the spin is down, it keeps on flying. If we measure the spin of the other particle here on earth at the same time, we immediately know whether the spaceship just blew itself up or is still flying - hasn't then information been transmitted?

Now that the Nobel prize 🏆 has been given, relating to this subject, please make a video on the theory's progression.....

First, I must say that I really like your videos. Very informative and very well done. Thumbs up and I'm a subscriber. The simplest explanation for why we can't use the "spooky-action-at-a-distance" or FTL communication between entangled particles is that it doesn't exist. Two particles interact, move away from each other to distant detectors, and the results are correlated in a way that conforms to conservation law. This seems very much like what happens with, say, colliding billiard balls. Except that, prior to detection, what we're calling particles might be waves, i.e., disturbances in media of unknown substance and structure. So, let's suppose that. Let's further suppose that these waves are continually changing in form, and therefore really don't have any particular "spin" value while they're heading for the detectors. Nevertheless, they will still be related by conservation law. In experiments designed to produce opposite values for timestamp-correlated detections, isn't referring to a relationship due to mutual interaction and application of conservation law enough to obviate the need for them to be communicating in some FTL or spooky way? Relationships of this sort don't care about distance. I'm somewhat familiar with Bell's stuff. Violation of Bell inequalities can be used to indicate the presence of entanglement. I think it's a mistake to say that Bell has shown that hidden variables don't exist or that any deeper level of modelling quantum phenomena (i.e., hidden variable models) has been proven impossible. Since there's currently no way to know what's happening at the level of quantum phenomena, between emitters and detectors, and current models are somewhat inadequate, then (per Bell himself) maybe we just need to be more imaginative.

Having watched many videos on quantum entanglement, I can say that the explanation of john bell's experiment doesn't get better than this.

Dude my head started spinning after 2 mins of watching spin ups and spin downs.

I suppose the many worlds interpretation explains this pretty well. When you measure the particle in one of the three directions, you enter one of the two possible measurement outcomes in that direction (for a total of six possible cases). Whatever your choice, the other particle behaves in the way it has to in that version of the world: it yields an opposite spin in that direction. No faster-than-light action has occurred; you are in the world of a certain specific case, and when you eventually receive information from the measurement result of the other remote particle, it will be the information of that same world.

I love this video, every university professor should watch this.

Its incredible, unknowable things like this that make it fascinating to be alive! It's like, you want more of it, can't handle the reality of what is already out there , yet you yearn for more! Thank you sincerely!

04:10 You know things get real when the music kicks in.

most of this went through my head, have to rewatch it again

The best video so far in explaining quantum entanglement

"Spooky Action at a Distance" very scientific-sounding name

this is the first video that made me actually understand “spooky action at a distance” it didnt make as much sense before, thank you!

This is a great explanation! :) it is in deed fascinating science. It starts explaining the unexplainable and yet, the more we discover, the more we understand there is still more and more. The nature of Universe is a constant change and expansion and QM seems to present that. Well, I am not a scientist, but I love to explore the scientific point of view. What is interesting in science is that often it rejects something until it is finally proven by someone. The unseen is vast and miraculous and the more we explore, the more we are amazed. Why? Because it tricks our logical mind so much and force us to wider our perception or reality.

I heard this been explained multiple time and did not get it... But this video helped me a lot, thanks :D

Well of course! Wait, what the hell did you say?

my dreams tonight will be of spinning men in jumpsuits.

I’m thinking of your video regarding how we can’t measure the speed of light going in 1 direction, so there would be an extreme possibility that the light goes c/2 in one direction and instant in the other one. With this prospect in mind, do you think that the measuring device interacts with said particle at c/2 to find out it’s spin and the information instantly propagates to the other one?

This is the first time I hoped for a science video to end

Am I getting dumber or was this WAY harder to grasp than any other Veritasium episode? The video ended a few seconds ago and I have no idea what I just watched. Thumbs up either way for using your 2 million subscriber channel for something like this, rather than yelling over video games or whatever ;)

So what I gathered from this video is that quantum mechanics is really f**king confusing

Hm is it possible to transmit (loss less) energy with quantum entanglement? For example we change often the states of Elektrons on one side and produce heat on another and cook a good kofee?

The measurement of the position of the first particle affects the spin , because the other particle will have opposite spin in the same position but measured at a different position the spin can vary as the position of measurement of the first particle and the angle it creates with the position will cause the spin to change

There is a third interpretation : when you get the results of the second experiment, you are still measuring a quantum system (whose proper description depends on your results). This interpretation preserves locality, but is observer dependent. It is called relational quantum mechanics.

Bell's inequalities are brilliant and mindblowing, with implications that go deeper than most people realize. They tell us that either locality (things are only influenced by their immediate surroundings) is wrong, realism (the moon is there even when you're not looking at it) is wrong, or both. Their most important lesson is that the things you assume, the things which seem like common sense, must themselves be subject to question, because reality might not agree with your assumptions.

Very good explanation. Could also have mentioned supper determinism as another hypothesis without a need for the assumption on the independence of the observer. Also @ "7:30" its less confusing if u add the 1/3 + 1/4*2/3 to get the probability of different spin to be consistent with the hidden variable part.

I'm more confused than I was before the presentation. There are so many counter-intuitive issues raised and so many statements that need explaining, rather than just having to be accepted as self evident.