The EPR Paradox & Bell's inequality explained simply
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- Опубліковано 12 тра 2024
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This video is on Quantum entanglement, Bell’s inequality, EPR paradox, nonlocality, determinism vs nondeterminism and probability. Bohr and Einstein argued passionately about their views on the essence of reality. And for 30 years, both views were considered equally valid. Then in 1964, Irish physicist John Bell devised a way to prove whether Einstein’s view of a classical, deterministic view of reality was correct, and he put this in a simple elegant equation - called the Bell Inequality.
The weirdness of quantum mechanics can be demonstrated with a dice. If the dice was a quantum system, it would be in superposition. It would be a 1, 2, 3, 4, 5, and 6 all at the same time. It’s value can only be known once it is measured. Einstein, was bothered by this interpretation of quantum mechanics. Einstein along with Boris Podolsky and Nathan Rosen came up with what they thought disproved the Copenhagen interpretation. The crux of their argument rested on the idea of a phenomenon in quantum mechanics called entanglement. EPR argued that since nothing can travel faster than light according to special relativity, this should invalidate the Copenhagen interpretation. This was the EPR paradox.
in 1964, John bell proposed an equation to determine who was right. In a universe where local hidden variables are true, when the two particles are emitted, they know what their state is going to be in all three directions, Z, X, and Q from birth. And there are only 8 possibilities of spins that each particle could have.
what is the probability that Alice measures in the z direction, gets a positive spin, and Bob measures in the X direction and gets a positive spin? Well, if the above case is for Alice, there are 4 events where Z is positive. In order for Bob to get X positive, Alice would have to have measured X as negative. So these would be in event 3 and event 4. To get the probability we have to divide by the total number of events, 8.
Let’s do this for two more scenarios. What is the probability that Alice measures positive in the Z direction, and Bob measures positive in the Q direction? In this scenario, it would be event 2 and event 4. Again we divide by 8 to get the probability.
And the third case is: What is the probability that Alice measures positive in the Q direction, and Bob measures positive in the X direction? This would be event 3 and event 7, divided by 8 for probability.
P: Z+, X+ = E3 + E4/8
P: Z+, Q+ = E2 + E4/8
P: Q+, X+ = E3 + E7/8
So these are the three probabilities given the hidden variables theory. Now here is big insight that John Bell had:
If I take the total number of Events, and multiply that by the probability that Alice measures Z positive and Bob measures X positive, this has to be less than or equal to the total number of events times the probability that Alice measures Z positive, and bob measures Q positive, plus the probability that Alice measures Q positive, and bob measures X positive.
P:Z+,X+ less than or equal to P:Z+,Q+ + P:Q+,X+
I can prove this is true by doing simple math:
E3 + E4 is less than or equal to E3 + E4 + E2 + E7
This makes total sense, because E3 and E4 are on both sides of the equation. And E2 and E7 have to be positive. So this inequality absolutely HAS to be true for any hidden variables theory to be true.
But what happens in a universe where the laws of quantum mechanics are correct, and not hidden variables theory?
And that probability of Bob measuring Q to be positive, after Alice has measured Z to be positive, is given by the following equation:
P: Z+,Q+ = sin^2 of 45 degrees/2
This is the critical difference between quantum mechanics and hidden variables theory. The probability is not linear but looks like sine wave. When you plot this out, this is what the probabilities look like: So you can see from the graph that at 0, and multiples of 90 degrees, the two systems are in agreement. But in between, like at 45 degrees, the probability is 25% for hidden variables, and about 14.6% for quantum mechanics.
#bellsinequality
#eprparadox
#bellstheorem
But the proof is in the pudding, because in test after test, the sine function correlation has been confirmed. The particle does not behave linearly, and so the hidden variables theory cannot be correct.
So most theorist do not think special relativity is violated, because we can’t communicate using this seemingly faster than light phenomenon. - Наука та технологія
The understanding of this material doesn't really come from one video, it comes from watching a whole bunch of them, listening to all their perspectives, and then slowly merging together a coherent interpretation. It's very exciting! Thank you for producing your videos and adding perspective to this problem.
+upvote
@ Lydell Aaron
Yep, THE HUMAN MIND tries to simplify things so it can run with it trying to convince other HUMAN MINDS in order to "conspire" again its CREATOR. The analogy to it would be a PC (HUMAN MIND) trying to outsmart a Quantum Computer (GOD - THE THING THAT CREATED THE HUMAN MIND FOR HIS PURPOSE) You need the PC and the QC - but it should be clear by now which one reigns supreme! Which one IS still without the other and which one cannot exist without the other!
so it is not just me😊
And everything is just theory. Not proven to be absolute truth even the proving that Neils was right. Thats not an absolute proof. It just supports the Likelihood that Einsten was wrong.
Also, entanglement implies info can travel faster than light. In fact, instantly in the absolute sense
Many videos talk about same things
The most outstanding thing about this video by Arvin Ash is throwing in the explanation of the Mathematics in a way for the Layman to understand ...no other big media company Science show has ventured into this realm..not even the BBC .Congratulations!
And he doesn’t need big words to make himself sound smart, his knowledge and intelligence is obvious.
Tbh I didn't understand the maths. I wish Arvin could dumb it down more for peons like me :/
@@Sid-69 it was as dumbed down as it could get. I suggest you watch the math part again. And really focus on what he is trying to explain. I know you'll get it.
The Layman lmfao the nicest way you can call somebody dumbo
@k1w1 I maybe late man but I ain't no layman.
continually stunned at his ability to take incredibly complex concepts and topics and make them accessible in a conversational and layman-friendly way. truly setting the standard for content in these genres.
You understand that he is taking other peoples note and books and none of these texts are his? And disgracefully he doesn’t cite any of them!
But who gives a sh… in world where Trump becomes a president, Kardashians are know more than Tesla, why doesn’t this fake scientist be the hero of the day?
"The universe has rigged the game against me." I've known this all my life... SIGH.
Yeah, that certainly rings a bell.
🤣🤣
No it did not that's the whole point of the video
Lol
The universe is last to act.
good teachers make a huge difference, thank you!
Fans are neat
This is far and away the best explanation of Bell's inequality I have ever seen/read. Arvin has truly hit the nail on the head, not too hot, not too cold, just right. I actually think I understand exactly what Bell's inequality is all about. Thank you Arvin!!!
Omg I finally get it. The sin wave diagram did it for me. I’ve been trying to understand it for a couple of years!
Bravo to the actors playing Alice and Bob. It’s very difficult to stand motionless in front of a camera for a long period of time and not lose focus / concentration.
They are not real people, AI generated.
I can tell Arvin takes his role of teacher quite seriously. Loved this video and the subject matter is always edgy. That is Arvin explains current accepted science as simply as possible with mysterious difficult to comprehend topics.
I have seen many of these explanations but this is the best. You hit a few key points that are always overlooked and those key points made it very clear. The meat that most explanations don't explain is at 14:47. That was the missing part that you nailed! Good Job!!!!!
The general rule for science instruction (including computer science) is that the instructor's rate of progress through the material is directly proportional to its level of difficulty.
@@ernestmoney7252yep, the level of the audience.
Totally agree I’ve never seen that part before, now I get it.
Even after the Nobel announcement and all the videos that have come out recently, this is the only once I could find that actually mentions this part.
Agree, it is annoying when the instructor doesn't explain something very important (just watched another high ranked video)
I find it impressive to be able to explain things like this to a person like me.
I or course don't understand this theorem, but at least I now roughly understand the parts that makes up this puzzle.
I have no idea what he said but I enjoyed listening to him.
you make some of the best videos, i like the way you present info, you're an entertaining person to listen to! thanks for all these and keep up the great work!
I repeatedly ignored your videos in search results and recommendations, but from now on you will be among the first ones I click. Great job!
Best video about entanglement I've seen .
A really good video.
I liked Jimi Alkalili’s explanation on the episode Einstein’s Nightmare (obviously simplified similar reasoning).
However I love this modern era we live in where we can get videos like these - offering clear explanations of the actual theory.
Very well made in my view.
Dear Arvin, i have seen so many videos on the topic but i must say that you have nailed the explanation at its best and not only in this video but in lots of other videos of yours. Thanks for putting your brilliant efforts to let us understand the topics that we are not much familiar with in our institutes.
Glad it was helpful! Thanks for your kind words.
I really loved this video. Your explanation was amazing and very easy to understand. The part I loved the most was the math and the way you simplified it so that Bell's inequality made sense. Please do more videos with maths like this. Keep up the good work👍
hi arvin, I just wanted to say that I really really appreciate your videos. they make me so happy and teach me a lot, keep up the great work ❤
Oh Oh, consider this an intervention.
There is danger in collecting fascinating interesting but ultimately useless information
If you collect a finite, but irrational, number of fascinating interesting but useless information -----
you will turn into a NERD.
Be warned. This condition, once attained, is irreversible.
You will spend your life boring people at parties, having people turn away from you
because they can't quite get what you are on about.
It is very sad.
So, next time you come to this channel be aware of the risk.
I forewarn you, so you don't spend your life like mine -- I, too, am a NERD.
@@whirledpeas3477 but also false
@@craigkdillon Hahaha Hahaha Hahaha 😆
@@vedantsridhar8378 You say that I am not a NERD??
So, you are defending me?
Or not??
I am confused.
@@craigkdillon Sorry, I thought nerd was an insult.
This is by far the best explanation of quantum entanglement
Lovely Arvin. It's a delight to hear you explain physics, real world, warped universe, Quantum world and the macrocosm. You not only fire my imagination, but also enlighten me to relate the magnificent forces of nature, their effects and affects. It is a chancy chancy universe or.... Keep it up!
Best video ever made about Bell's theory and the meaning of Epr-Kopenhag combat.
you are my favorite youtuber explaining quantum theories, cause you never use equations nor complicate, you always find ways to explain it to the everyday people out there. But this video wanst one of those :(
Thanks. This one required math to prove the inequality. I tried to make it as simple as possible. But Bell's inequality is one of the most difficult subjects to understand. Do have another look. It is less complicated than it might appear. It takes multiple viewings by everyone if you really want to get it.
This channel don't make me smash my head in wall like on other channels when it comes to science.
Your way of explaining is good.
Keep it up.
Avoiding a science concussion is a good thing buddy!
Another outstanding video and explanation. So plainly taught and easy to grasp. I am as anxious as you are to see this understood at a deeper level. Thank you again.
I've been binge watching these video's like it's nobody's business. Really enjoying the presentation and content, a lot. Good stuff
Nice! Welcome to the channel my friend!
A truly exceptional explanation of the maths behind Bell’s inequality without it being unnecessarily confusing and complicated well done 👍
Interesting and worthwhile video on Bell's Inequality.
Thanks for the Magellan tv recommendation, Professor. I just signed up...and thanx for another great video!
brilliant exposition on a very complex topic. Thanks, Arvin
My new favorite Science Channel.
This paradox has been giving me a lot of sleepless nights lately so thanks for this
best clear explanation of Bell's Inequality I have read or seen, thank you
One of your best ones yet, thank you!!
I've never seen a good explaination of this. This was clear, thank you.
Me too BBC , YT etc.
I thought I had half a clue until I watched this.
Arvin is so great. Love this channel
Superb video. Breathtakingly clear exposition. Will watch again, like a favourite story. Old UK duffer here :)
Thank you for this description of bell inequality 😊😍. It's so well explained, you are great teacher.
I love how he says , "Right now!"
This was REALLY(!) well explained.
The best explanation....in simple language and very good examples for such a hard topic....u r really awesome ARVIN
beautiful!! nice, elegant and succinct video on such a complex topic!
Found this video after Aspect, Clauser and Zellinger won the 2022 Nobel Prize in Physics demonstrating the potential to control entangled particles in practical uses of quantum computing and telecoms. But I wonder if in the process, the trio's works also involved explaining quantum entanglement phenomena just as you predicted at 17:38. Else, the quest for an explanation continues.
I'm here for the same reason. Yet I still don't understand Bell's inequality. He lost me at Sin^2 blah blah. I guess I need to go back and understand spin in QM.
@@GizmoMaltese you're not alone, my friend.
Well done Arvin. Best explanation of Bell's inequality I've seen. Thank you.
Another awesome video. Love your optimism about the mystery of quantum mechanics. One day soon!
One of your best videos Arvin. Thanks
@Arvin Ash Do you do any presentations using three pieces of polarized film? The demonstration where inserting a film with axis at 45 degrees between from two crossed films at 90 degrees from each other _increases_ the transmission sounds similar to this discussion. It's at least similar to the extent that its theoretical explanation depends on the measurement probabilities of photon spins that are non-linear.
I’ve never had a clearer “you earned my subscribe” moment on UA-cam. What a well put together, amazing video.
I have to do a presentation about quantum entanglement and i had some troubles trying to understand what bell was trying to prove. This video is amazing now it all makes sense. im still shocked about this incredible theory. Thank you for explaining this complex concept in an accessible way. Thank you a lot
Watching again and again. Slowly understanding. THX!
Congratulations! You have explained a very delicate concept in a simple and easy to understand manner. What do you think about Pilot Wave theory? Does it offer any hope of resolving non-locality paradox of QM?
I see it only as a consolation to those insisting on a deterministic description. In my opinion, it is a messy mixture of quantum and classical concepts. But I will be covering it in a future video.
This is a role model for how to strive towards being a true educator. Thank you for your meaningful work.
That Magellan looks perfect for my current obsession. Thanks dude!
THANK YOU!
I was discussing with someone who held the position of a dichotomy, between [local hidden variable] or [random values + superluminal communication].
Like you, I believe it possible that Bell's theorem describes a "local hidden wave-function" model, replacing the fixed variables with more complex behavior; it need not be random.
Another possibility which could be considered is that the entangled pairs could be perpetually connected by some property that can't be detected within 3D spacetime.
this was a phoenomenal explanation! Hats off to you, subscribed. I've just started taking QM in my astronomy major, seems fascinating to say the least!
Great videos sir your videos just amazing💕😍
Really, really, fantastic video. the best one out there in my opinion. You earned my sub.
How can a particle have a Q+ spin and a - spin for X and Z, when X and Z are components of the vector Q?
Dan Davison that's my question as well: In theory you could have infinite variables if you take all the possible angles between Z and X, would that mean you would have to account hidden variables for all of them? Doesn't seem to make sense!
Indeed I also have a problem with, is the fact that all cases Z, X and Q have the same probability and are totally independent. I would assume that when Z and X are positive, Q is positive as well and can not be negative.
You have to remember that those vectors he draw for the spins are not in real space, but in complex vector space. So the 45 and 90 degree angles don’t behave the same way as for real vectors.
@@TheTck90 Isn't that the point that the 2 previous guys are making? (LKRaider and Willem Vriezen) If that is the case (i dont know if it is or is not, i am just trying to clarify) then would a measurement at 89 degrees also be independent of the measurement at 90 degrees?
Here is what happens: regardless of what Alice measures, if Bob measures in the direction Q+, the result can only be Q+ or Q-. There is no intermediary state possible. It has to be aligned to the direction of measurement. But, depending on the measurement that Alice makes, it affects the probability of Bob registering one Q+ or Q-.
Since Alice measured Z+, Bobs electron would want to be Z-. But since it can only be Q+/- and since Q+ is further apart from Z- than Q-, it has a much lower probability (only 15%) of happening, because it would have to "change" it's momentum a lot more than for Q-.
what a beautiful explanation for us lay persons.
Perfect recommendation youtube, I have a project on this next year
You explain this simply and beautifully
Thanks 👍 for your effort
You are doing great work keep it up
"local hidden variables" sounds like computer coding
Yeah. You have to first make it public otherwise it is hidden.
[Only true programmers can understand]
@@fahimjunayed5894 Its possible in c++
Private
OK this is by far the best explanation of this phenomenon I've ever seen, great job my friend
can't thank you enough. Really appreciate your work. Keep making great vids
Awesome explanation for such a complex paradox!
After viewing for the second time, I understand the process and the math and I agree with Arvin on his conclusion. Never thought I would say that. Wave function rules. Particles are not particles until the wave function collapses. A photon has the potential of being a particle, but its essence is a wave.
Perfect!
not quite. the photon is always a particle, the wave says where it can be. the field is everywhere... but it can only be absorbed by 1 charge. so is it really everywhere? it may be that the particles are only emitted when they are also absorbed and don't go in other directions. that part is non falsifiable, but we always observe inverse square fields. arvin hash is 20 years behind western science as usual
+[John Carter]
This is sad news. Even more sad is that I am months too late to do anything about it.
Because I am afraid that Arvin's conclusion is utterly wrong. Or.... at the very least utterly unfounded. He shouldn't feel _too_ bad, though, as Bell's Inequalities form what is pretty much the most misunderstood and misappropriated thing in all of Physics.
You see, the so-called EPR Paradox consists of 2 parts. The central crux of the argument, and the "paradox". Contrary to popular belief _[and by "popular belief", I mean the beliefs of the adherents of Orthodox Quantum Mechanics, which is the modern form of the Copenhagen Interpretation]_ , the central crux was in no way disproven by Bell, nor by the experiments that prove his Inequalities were violated by Quantum Mechanics.
The central crux of the EPR argument, of course, was that considering Entangled particles exist, the preservation of Locality *requires* Hidden Variables. There is *NOTHING* in Bell's Inequalities that disproves it. Nor could it disprove it, because that argument is pure logic, with no assumptions or any other form of wiggle room to get out of it.
Now, what John Bell did prove was that there was no paradox. He did this by proving that even *_with_* Hidden Variables, Locality would *_still_* be violated.
But neither result can make any sense without the other. Because Hidden Variables either exist, or they do not exist, EPR + Bell *TOGETHER* prove that Locality *must* be violated by Entangled Quantum particles.
It also says precisely *nothing* about whether or not Hidden Variables exist.
As a side note, Pilot Wave Theory, aka Bohmian Mechanics, which of all Interpretations of Quantum Mechanics makes the non-Locality the most explicit, was the favoured Interpretation of Bell himself for precisely that reason.
@@AhsimNreiziev
I appreciate that at least _one_ commenter has refused to join the avalanche of praise that monotonously recapitulates every other youtube physics video commenting proclaiming the sheer pellucid genius, accuracy, and pedagogical simplicity of the creator's production.
That said, I see no reason to complete your thought with yet another sideline hollered call for Pilot Wave speculation which, like String Theory, seems to have forked into dozen sub-theories; because if a theory is sound, hey, why not have themes and variations. There should be one ready at hand fitted to plug any leak.
This is by far the best, i.e. clearest, explanation I've found so far. Great use of graphics. 👍😃👍
Very timely for me as I'm reading The Age of Entanglement by Louisa Gilder for the 2nd time.
Highly recommend the book.
Such a beautiful explanation, thank you!
Very simple and very clear. Thank you 😊
This blew my mind. I was convinced for a very long time that Bell was somehow mistaken or misinterpreting what was going on, but I was wrong. What in the world is going on with these wave functions? Could this somehow tie into the potential to discover CPT violation?
I believe bell is wrong. I actually think there is a fundamental property that we do not understand that causes these probabilities. Hidden variables is correct but what is actually happening is that certain ways of collapsing are more likely. Most probably in a way that looks completely random to us.
@@neilweber1749 It’s funny that this should pop up now of all times. Wasn’t the Nobel prize recently awarded to people who investigated this?
@@LeTtRrZ Yes this is why this video is here i imagine. there are some physicists who do not agree with the current accepted interpretation. Which is always good for new ideas. I wish I had more time to study indepth but i do not. I take my reasoning from the double slit experiment. There is something we do not understand fundamentally about the wave function. But in saying that our calculations seem to work as most computers etc need quantum calculations. As do newtons calculations if you get my meaning.
I have been struggling to understand this for many years from Prof. Leonard Suskinds lectures but I couldn't. But today, this video has demystified it for me. Thanks a bunch.
Best explanation I heard so far 👏🏽
this is even more simplified and intelligible than Prof. Khalili's game with the demon analogy in his atom series .. great job!
Could be some fundamental law of physics we dont get, where there is a deeper reality that everything is localized at one point. Like the holographic universe idea or the info on the surface of a black hole. But instead of reality being 2d flat surface, its 1d.
Or the entangled pair only look to be far apart, but really the space between them is folded in a way we cant tell and they are really right next to us like some type of worm hole when they fold a piece of paper, in all the science fiction movies to explain worm holes.
Was wondering if there was a way to tell when someone on the other side of the universe has measured the entangled pair? Could something be used to detect that he has measured it? but only after the person on the other end has measured it?
That way you can have multiple boxes with an entangled pair, that you do not measure, but the person on the other end, measures only certain boxes. then dependent on your end, the ones that he measured signal to you a certain combination, therefore communicating something. ?
I would imagine this has already been proposed. Perhaps go do some research and let us know what you find?
@@brookefoxie9610 Ive tried in the past, in the idea of knowing when the other person on the other side checks it. I Am not good at researching and understanding. Arvin Ash is a great explainer. Thats why I asked him to confirm.
From what I understood, there is no way to tell if the person on the other side of the universe checked the spin and taking the particles out of super position.
Its like you cant detect what happening in the box without taking it out of super position.
But I am also asking the question to see if someone with more expertise can think of something using this concept.
6:00 this is what happens when two Great scientists Argue both win , and rule changed.
because
QP says , superposition and entanglement should exist !
Which exists.
CPhy says , Nothing can't travel faster than C.
It's also True .
So.. quantum physics and Classical physics Are in superposition both working at same time in same universe.
So if qp and cp work in superposition in the same universe then it implies that at the very end qp wins
@@sheikmohamedamanulaa3898 if you talking about singularity then yes
Finally explained this in a way I understand. Thanks!
CONGRATULATIONS FOR THIS OUTSTANDING EXPLANATION OF BELL`S INEQUALITY....FROM BRAZIL.
Dam wish I saw this video back in modern physics.Would’ve made my lab reports legendary.
I prefer these longer videos, even though the maths make my eyes glaze over.
Fabulous video and expertly narrated.
Out of all the physics videos online yours are def. The best
"Truth is, the game was rigged from the start."
This video really got me thinking......maybe I should quit smoking so much weed
Or perhaps you aren’t smoking enough
I started watching these videos and learning because of weed and acid and I retain everything I learn i want a artificial intelligence and robotics major drugs dont get in the way of life if u are smart and committed
Nah dawg i think your not smoking enough. If this is true, imagine the internet we can get with this and quantum computers 😁
Same with me except it's heroin
DjMacgumby Stop ruining your life
Awesome explanation, thank you.
Excellent presentation... Simple and direct...
Thanks for putting on such an awesome channel! You stole me away from Vsauce!
Haha...Thanks my friend. But I'm not trying to steal anyone's audience. The ocean of knowledge is big enough to accommodate all boats.
Vsauce just teaches you generic stuff, but for advanced physics there are only few channels such as PBS Space Time, Arvin Ash and Fermilab
17:13 "...and since the colapse is random, it can't be use to communicate in this way" Why?. Great chanel thanks!
Great question! I did not get into this in detail, but here is the simple explanation. Since the result that Alice gets from measuring particle 1 is completely random, and the result that Bob gets, from his perspective, is also completely random. And since the two can not communicate each others' results to each other faster than light, no communication of information can happen faster than light. Also, the randomness of the results precludes one from somehow manipulating the result to communicate instantaneously to the other.
if you could control the direction of the collapse, you could send a message. but since this is impossible and the direction is random, the outcome at the other end is also random, so no information is transmitted.
@@ArvinAsh
The paradox of information is supersymmetric.
In the same way as from inside a black hole, you cannot calculate or interpret if it has a spin, that is, if it turns on something ...
When we analyze a photon-higgs-graviton we can only calculate and interpret that they have mass and charge "0", but if they spin.
It is the same paradox of information, since they are the same on different fractal scales.
The paradox from inside to outside is supersymmetric to that from outside to inside.
In order to communicate you must send organized (i.e. non-random) signals; since the collapse is random (i.e. not organized) it can’t be used to transmit any information. Just think if you tried to send a text message your friend telling her where to meet you. You decide to write the message by rolling 5 dice over and over, adding up the total value shown on the dice each time, and using the result of each roll to decide what letter to type next. How would you ever be able to get the information to your friend?
*In case it isn’t clear, the letters of alphabet would be assigned a number 1-26, the numbers 27-30 could represent symbols like commas etc.
You guys look like you forgot that the fact that represents the action of the wave function collapsing in itself holds information, and it says that "Alice is trying to say something" so Bob would still know that Alice tried to say something, THAT still represents information.
Dear Arvin,
This is a really good 'simple' representation of the EPR paradox and Bell's inequality violated in QM. A few things remain unclear to me (very most likely due to my lack of thinking/ understanding). But first about my background:
I studied physics and was fascinated by QM the first time I learned about QM. I asked my professor at that time some more background info and he gave me the EPR paradox as an exercise. I concluded that the spin information travels faster than light, which I knew was in violation with special relativity. That was back in 1976. I left it for what it was, finished my studies, did a PhD in nuclear physics and almost the rest of my working career was on (satellite instrumentation for) remote sensing of atmospheric composition for which I was program leader at SRON Netherlands Institute for Space Research for almost 20 years.
Now, after my retirement I wanted to pick up where I left in 1976 and found your video on UA-cam.
My questions and remarks to your excellent video presentation:
- 1. The fundamental one in the EPR 'Gedankenexperiment': If you measure spin up (in any direction) for photon-1, then you know - preserving of total angular momentum - instantaneously that photon-2 must have the opposite spin (after all, the total angular momentum was 0). That is valid both in hidden variable theory (where the spin direction of the particles was known from their creation) and in QM (where both particles have all the spin direction simultaneously until you perform a measurement . So what is so special here?
- 2. The double slit experiment for the particle-wave duality of the photon: You actually mention the case of a single photon where you end up with one hit on the screen, which is nothing special. I think it would be better to explain it the following way: If a photon resolves to a point on the screen (that only applies to very low intensity sources so that you can indeed speak of single photons) the measurement is when the photon hits the screen. Thus, in QM, intensifying the photon beam the experiment should give different outcomes, i.e. the photons not necessarily always hit the screen at the same place. And indeed they don't. Slowly intensify the beam will result in hits on the screen forming the well known interference pattern of a wave.
- 3. Arithmetic in your example of Bell's inequality when comparing hidden variables theory (HVT) (linear) and QM (sinsqr): something is not right there: if angle (Z, Q) = 90 degrees, then you actually have angle (Z, X); and we have seen that in HVT P (Z+, X+) = 1/4 and not 0.5 what am I doing wrong?? In QM, story is correct: sin2(Z, Q)/2) = sin2(90)/2) = 0.5.
Looking forward to your explanation!
Kind regards,
Avri Selig, the Netherlands
The answer is that Bob can not know in which direction Alice the measurement of the spin has performed. The direction of the measurement is missing in the story!
That is the answer to question-1
Are you looking for a girlfriend? Sorry to say, but this is not a dating app. ;-)
absolutely love your videos . Thanks a lot
How do they know that the particles are measuring came from the other particle
This has always been my biggest question, and how can they take the particles so far apart for measurements without interfering with their properties in any known or unknown way
That was really interesting, and Alice is really cute.
And Bob 👀
finally............a detailed breakdown! THANKS
thankyou very much for clear explanation !
So say if I invite the universe to a casino with me, would that be considered cheating or would there be no consequences if I keep it on the down low?
I have long suspected that the Universe doesn't play fair.
So in Avengers End Game, Tony Stark was using EPR paradox to reference a wrong phenomenon that led Scott Lang to appear in different stage of his life while trying to time travel. That's funny cuz End game took a dig at all the time travel movies for propagating wrong notion of time travel.
Yeah, I think the movie attempted to sound "scientific." This is perhaps better than most sci-fi movies (I'm looking at you Star Wars), that gloss over any semblance of science.
Your channel is one of the best youTube channels
Best presentation on this topic I’ve seen. Clear, concise, and very approachable. Thank you for the excellent work
I don't think you can give a true judgment on the double slit experiment because the Universe/Cosmos is the norm but earth's are the exception, has the double slit experiment ever been done in the Universe/Cosmos? I think there will be a different result if the double slit experiment is done in the Universe/Cosmos, Compared to being done here on earth.
I guess you think we are not part of the Universe.
@Donald Kasper Let me Finnish my dinner first, it's just an opinion, even billionaires would find it extremely difficult to PROVE IT, but we will prove it eventually and if I've got it wrong then I'll party like it's 2999.
@@FobbitMikeOh you caught me off guard I'm at a party, I've been studying the Universe/Cosmos/space since I first started school because I hated school, I predicted there was water, oxygen and others, all over the Universe/Cosmos/space at a very young age, I do not make predictions without giving it deep thought, now back to the party.
What is spin and locality?
Great questions! Spin has to do with the magnetic moment of particles. It is not a physical spin like a ball. "Spin" is really just a measurement. Exactly how "spin" occurs inside a particle is not known. Locality usually means that any influence that is imparted to an object or particle is due to a change in the particle's local vicinity. It can not be influenced by something that is far away in space. In other words, it is the opposite of action at a distance. My video on QFT (quantum field theory) talks about this.
Hey again, Arvin, I'm back! 😀..this time to discuss another pet peeve of mine with you: the double slit experiment. I absolutely LOVE this. I've watched so many related videos including the all of the quantum erasure ones as well. Here are my questions to you: 1) what are your thoughts on the Bohm / De Broglie pilot wave theory (a personal passion of mine), as it relates to the double slit experiment. What if there exists a wave for which light (and maybe even gravitons) ride on that we cannot yet detect, and 2) do you think that the manner in which we attempt to observe the particles travelling before OR after the barrier might have an effect on wave decohernece such that it makes it "appear" that simply observing the particle modified the wave - thus, eliminating the wave and influencing the potential interference pattern and reducing it to "tennis balls going through two slits"? Hoping for a reply. Thanks!
I am not a huge fan of pilot wave theory. I could be wrong, but overall it seems to me, to be an attempt to demystify a mysterious phenomenon so that it is more palatable for human logic. The universe has no obligation to be logical. I don't think the manner of our observation has any effect on the behavior of quantum particles.
Arvin, this is so beautifully explained! Really great job! I even learnt what quantum entanglement actually is, TED ED's video on it was not that accurate and it mislead into believing human teleportation is possible via entanglement. This video cleared up that misconception!
Just a question, what's the name of the music you played throughout the explanation of the Bell's Inequality or at 8:30? I like that music, it's so relaxing but also dark and chill.
Einstein is right :
When I was asleep at home during physics test at school , I got a call from my school , the school existed .
It was worth skipping the test .
According to neils Bohr
My school shouldn’t have existed cuz I was asleep ( not conscious) .
The school "shouldn't" have existed... inserts a moral dimension into the equation of existence. It appears to be saying : Don't do anything behind my back. And that is paradoxical in that all science tries to do is to figure out what has been done behind our backs.
So, in antiquity, electrons, protons and the like simply did not exist? Or they shouldn't have?
Ah, when science dips its toes into philosophy...
I think therefore the school am?
This confirms my theory that when i close or cover my eyes i become invisible
@@bonedog5130 How so? I will like your comment on what you said.
Are you guys all stuck on the "observer" thing? If so, you've really misunderstood what's going on.