Your Daily Equation #21: Bell's Theorem and the Non-locality of the Universe
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- čas přidán 3. 05. 2020
- Episode 21 #YourDailyEquation: Albert Einstein and his colleagues Podolsky and Rosen proposed a simple way to rid quantum mechanics of its most disturbing feature--called non-locality--in which an action undertaken here can affect the result of a measurement undertaken there, even if here and there are far apart. John Bell came up with a way to test Einstein's vision of reality, ultimately showing that Einstein's vision was wrong.
Even if your math is a bit rusty, join Brian Greene for brief and breezy discussions of pivotal equations and exciting stories of nature and numbers that will allow you to see the universe in a new way.
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This video is just the best for someone like me, an amateur physics enthusiast, trying to understand the 2022 Nobel Prize. Thank you Professor Greene! I remember when I first saw The Elegant Universe on Nova in my bedroom as a kid in high school. You opened my mind to the beauty and wonder of the universe. It truly changed my life. I've also recently read The Hidden Reality. You are a treasure to humanity. I didn't expect to suddenly be gushing your praises, but you really have done so much for me when I think about it. So, thank you very much!
I've seen lots of attempts to explain this with fancy graphics but it never really clicked for me. Then this guy comes along and calmly explains it from his living room without any whizbang graphical aids and it all falls into place. Bravo, professor!
Professor, I just wanted to say how much I enjoy your presentations. I'm not a student or physicist, I'm just a retired automotive tech who has read all your books plus those of Lisa Randall, Leonard Susskind and Stephan Hawking and others. I can't do the math but it's a wonderful thing to listen, read and ponder the world around me. Especially these days. Thanks very much professor.
Awesome
It doesn't matter what you did to put food on the table, what matters is you have an inquisitive and seeking mind!
You might be interested in Leonard Susskind’s lectures if you haven’t seen them yet. If you’re interested in learning math/physics and have a basic knowledge of calculus, his lectures are perfect. He covers many of the important equations and describes the mathematical techniques that are essential for understanding physics (bra-ket vectors, tensors, etc.). It doesn’t take the place of taking university courses in physics, but it’s more like Feynman’s lectures where it’s entertaining and informative at the same time. It’s worth looking into if you’re curious.
Stanford University CZcams channel has a set of Leonard Susskind video courses (check out their playlists for Susskind courses) to match a 4 book series and a website on "Physics The Theoretical Minimum" required to understand
1) Classical Mechanics,
2) Quantum Mechanics,
3) Special Relativity and the upcoming 4) General Relativity.
These courses are specifically meant for curious adults like yourself who couldn't pursue their interest in Physics "cos life got in the way".
The 3 books + 1 upcoming book teach the basic minimum Math and Physics required to understand Physics.
Wow thanks professor Greene, this is the first time ever that I have heard an explanation of this subject that I could get my head around. Have not missed one episode so far. Your Daily Equation is the best thing to have come out of this corona crisis for sure!
Yeah, it's really good. I think Sabina hoffstader could benefit from this. She is claiming there is no spooky action at distance and the state at start is simply not known, ie a hidden variable. In other words she assert EPR.
Yet Bells Inequality refutes EPR notion.
"Fine" example of MODERN PHYSICS: You have to BELIEVE guys like him. Running this experiment??? WHERE was it done, mate? And by WHOM? Jesus (if he existed) convinced a couple of dumb fisthermen to spread his strange ideas, nowaday physicists do the same on CZcams. There too many theoretical physicists! But still they can't explain the magnetic moment of a proton. Physics is going down the drain!
Came here to make this comment. I have read and seen so many explanations but this is the first I have understood.
@@joeboxter3635 She doesn't say so if you watch the video more carefully.
@@joeboxter3635 i am stopping at 29 minutes in case he loses me can you say coward.
Sabina seems angr these days lol
honestly the truly tagic part is i get her anger and have it too. we dont need a biger lhc
Professor Greene that was amazing! I have never seen or read a better explanation of Bell's Theorem than you have just given. Very clear, very passionate. It is a joy to share your joy of physics.
It's absolutely scandalous that Jon Bell didn't win a Noble prize for this 🤯🤯🤯
I agree with you. He may not have won it because he died too soon after the Aspect experiments were won. You can't win the Nobel post mortem. I think the window between the confirmation and his death simply passed by.
Finally understood Bell's inequality. Thank you.
"Fine" example of MODERN PHYSICS: You have to BELIEVE guys like him. @40:00 Running this experiment??? WHERE was it done, mate? And by WHOM? Jesus (if he existed) convinced a couple of dumb fisthermen to spread his strange ideas, nowaday physicists do the same on CZcams. There too many theoretical physicists! But still they can't explain the magnetic moment of a proton, after zillions and zillions of collisions at the LHC. Physics is going down the drain!
@@StellardroneMusic hahaha, science isn't based on trust.
BRAVO!!!!!!!!! To me, the layman that I am in your incredibly interesting field, you Professor Greene are an outstanding teacher enabling someone like me to understand in simple terms that which is complex and deeply non-intuitive. Thanks for doing this.
Dear Prof. Greene,
Thank you again for this wonderful series. Like the previous “commenter”, I have not missed a single episode. And I also think that Your Daily Equation is one of the best things that have come about since the start of the Corona virus pandemic.
I would also like to say that, although I am a Science graduate, unfortunately I have never been very good at Math(s). However, this last episode of Your Daily Equation (21), is the first time that I have ever managed to understand Bell’s Theorem. Thanks again!
One small point that I would like mention, is that - during the Quantum Mechanics episode of the NOVA series : The Fabric of the Cosmos; you equated the EPR Entanglement proposal as being more like a pair of gloves, set in advance as left & right, rather than the standard QM picture of “Fuzziness” until measured. I thought that the pair of gloves analogy was an excellent way of putting it. I am only surprised that you did not mention it in yesterday’s episode.
And I still maintain that The Fabric of the Cosmos episode on QM is one of the very best explanations & visualisations of aspects of Quantum Mechanics, from Probability Waves to the Entanglement pair of gloves.
I am going to re-watch episode 21 of Your Daily Equation, to make sure that I can still understand Bell’s Theorem.
Many thanks again Prof. Greene.
with best regards,
Paul C.
Prof Greene is the Einstein of Physics explanations. If 'understanding' is quantised, then Prof Greene includes all the quantum steps. Many others (especially, and notoriously, my physics lecturers) leave essential quantum steps out - and your like, "but why, though?".
Professor Greene with all due respect, my head almost EXPLODED !!!
Being able to bridge the abyss between the formulas and the easy to relate to observable reality is truly a gift, which often, as it did in this case, brings understanding and happiness to the audience. Even to, as in this case, someone with a PhD in elementary particle physics. Thank you!
Dr. Greene's ability to explain complex phenomena in simple, understandable terms is so powerful it's akin to having your cognitive ability grow exponentially in the space of one hour. Watching his videos in various forums including this one is a treat to be cherished. How fascinating life has become with scholars like Brian Greene filling the internet with truly interesting, meaningful, and mind expanding information. Thank you, thank you, thank you.
Your video, your explanation is the best! I finally understood what's really going on with EPR and QM and Bell's Inequality. Thank you so much. You needed every minute of this video to explain it well, and you did explain it well.
Thanks Professor Greene. I have tried to grapple with the Bell's inequality theorem for a long time. Your video was the first one that I've seen that explained everything so clearly. I'm down with Covid right now but I feel lucky to have used this opportunity to come across your video.
Great intuitive, yet rigorous, description, of a complex physical phenomena, or in simpler terms, great teaching! Thanks for your time and effort in putting these explanations out in public.
Hi Dr. Greene. What a great explanation. Your ability to communicate complex physics in a way that's so graspable to us lay people never ceases to amaze me. In a future video, do you think you could give us a primer on what a "light cone" is? Thanks so much for these videos.
So far I ve watched so much of videos & read about Bell's theorem ,but description given by you sir is remarkable,now fully understood where the Einstein & Bohr world was conflicted .
Wonderful ! I love these none formal lessons where I understand everything
I am not sure whether you still read the comments, but I want to tell you that you are great!! I am a yoga teacher and I don't know much physics but I like to read and here and there read and saw videos about Bell's theorem but never understood what they are talking about. You made it so clear and simple, and showed how the ideas behind it are just mind blowing and wonderful. I loved it!!! And I want to thank you for taking time and explaining these beautiful things. I feel like adding, I cannot believe it, I cannot believe nonlocal causality, it is spooky :-). Thank you from Israel - I go through the daily equations one by one - really love it.
As long as you don't follow or believe Deepak Chopra and his misuse of quantum mechanics and all his other bs, you are on the right corner, yoga teachers tend to love that charlatan. All his followers (Deepak's) should listen to THIS video several times to deprogram their heads from his bs, he uses a lot fo "action at a distance" etc to confuse people.
Thank you, Brian. I am slowly working my way through these so that maybe I can understand them better. I very much appreciate your efforts.
A wonderful, non technical explanation of one of the profound insights of quantum world. Have been a great admirer of your clarity of thought ever since I read The Elegant Universe and The Fabric of Cosmos. Thie admiration only grows after watching such videos. Keep sharing.
This channel is the only one that I watch live, above working or parenting, because I simply can't wait a few hours and watch it later.
It's a shame that John Bell wasn't awarded the 2022 Nobel prize in physics posthumously, because if it wasn't for him, Aspect, Zeilinger and Klauser would never have tested this idea in the first place.
gotta love this guy. i feel like i gained a lot of progress in my understanding of bells theorem although i still don't have the math figured out but that takes time. even still, it was a fascinating watch and i love his enthusiasm
The best presentation/lecture I have ever seen. And great graphics.
Your Daily Equation is the best thing to have come out of this corona crisis for sure.
Best video of the series. Your passion, enthusiasm, and intellect ooze in this one.
This is the best episode till now...
Can you make an episode on quantum eraser problem too!! Please 🤩🤩
Thanks Brian, definitely the best explanation and animation I've seen of the test of Bell's inequality. But I think at the end of the video where you committed to a conclusion that the universe is non-local, missed an important concept that you seemed to allude to throughout your video, that being that the observers have free will and the experiments are random. Superdeterminism also still seems to be a clean solution to the entire problem, that being the randomness of the experiments and the free will of the experimenters might not exist. I would love to see a video with your thoughts on Superdeterminism. Thanks again for the great video :)
The nobelist Zeilinger and his team used the frequency of photons from distant stars to adjust the measuring devices ( 2017), and another subsequent experiment used distant quasars.
So, the "free will loophole" is totally implausible. Moreover, local theories cannot explain the correlations in the experimental results ( that agree with standard QM ) without invoking contrived, infinitely fine tuned initial conditions. That's why most physicists do not take seriously superdeterminism.
Thank you for making this subject clear it brings metaphysics to mind for me
Thank you very much Dr. Green, I am absolutely delighted hearing you (indeed listening this more than one time)
Good series. Really enjoy them. When is the classes available?
Thank you, Dr. Green, for such wonderful series. We are all grateful for your hard work.
The implications of quantum non-locality are still being debated by physicists. Some believe that it means that information can travel faster than the speed of light, while others believe that it means that the universe is fundamentally interconnected.
Yes, that was bullshit. ;-)
1. I think the topic is easier for most people to understand using light passing through polarizing filters than using spin, since it's cheap and easy for laymen to perform experiments with polarized light.
2. The yellow thread connecting the entangled particles ought to be in the graphics (that start around 14:45) even before the state of a particle is measured, since Brian earlier said the thread continually connects entangled particles.
3. Brian neglected to emphasize an important logical point, which has been misunderstood by many physicists: although the Bell Test experiments have shown that Einstein was wrong about locality, they haven't shown that Bohr was right and Einstein wrong about whether quantum mechanics is a complete description of reality... for example there could be nonlocal hidden properties that both Bohr and Einstein denied, and if nonlocal hidden properties exist then qm is incomplete. For another example, if Many Worlds is true then qm is incomplete.
4. In a different sense, quantum mechanics is incomplete. As Brian noted near the end, the "measurement problem" isn't explained by qm.
Dear Prof. please continue your daily equation for eternity , we are all definitely enjoying it.
Need more series like this ❤️
THANK YOU , Pro Green Great fun you cleared up the entanglement, I did not know that the particles were in flux between spinning up or spinning down .
Thanks, Dr. Green! Great video...beautiful explanation of this surprising aspect of science!
Beautiful description of more complex ideas in simple words. Thanks professor
these are solid gold, love these videos so much
My head is ringing like a bell now (pun intended). I'm going to calm down now and ponder. Professor Greene, this is wonderful ! Thank You.
I learned so much more about the EPR paradox from your description, than I did from studying the math. I say that grudgingly, but as a compliment. How did you get to the end without playing the super determinism card?
Seems he just ignored it
superdeterminism is even spookier than "spooky action at a distance" - maybe the last straw Calvinists are clutching at 🤭
I was looking at nearly 10 videos to understand this concept and learnt 50% from those videos...
With this one video I understood the whole concept and so amazing and gifted Brian greene...
I dont mean I understand quantum mechanics which is always strange but the problem associated with EPR and Bell
Please continue to make such videos as others only make talks but you talk in mathematical , descriptive and imagery explanations and it is mind bogglingly simple
None could have thought that quantum mechanics could be so simply explainable
Complete, simple, understandable, amazing explanation of the Bell’s article.
professor you just nailed this.
you are an awesome educator.
looking forward to have something on quantum eraser experiment.
Professor greene thank u for explaining such a wonderful topic. U made my day. Thank u sir.
Hi Professor. Thanks for the great video, but I couldn't get why quantum version of reality would give 50% probability of opposite spin observation on your set of detectors. The set of measurements on same axis such as {(1,1), (2,2), (3,3)} would always give opposite spins so thats 3 and the rest 6 would have equal probability of opposite spins come up, i.e. 3/6. So, net avg probability for entire measurement set from {(1,1)...(3,3)} would be 6/9 or 66.6% , which infact matches exactly with the Probability in Einstein's assumption. (Quick math - 5/9*75% + 9/9*25%).
Can someone please help me out here, where am I going wrong, because definitely Bell's inequality isn't
The key is that quantum mechanics predicts that if you don't measure on the same axis, you only have a 25% chance of getting the same result, instead of 33%. But I think it's been swept under the rug in the video because it really isn't that easy to explain.
But it isn't that important, actually, because the problem is how you explain that you always get the same result when you measure on the same axis : is it because the two particules have been sharing a certain property since they were separated, which is the straightforward explanation? The problem is that if this were the case, you'd expect that if you measure on a different axis, you should get the same result in at least 33% of cases. And experimental results show that you only get the same result in 25% of cases. Therefore the 100% success in the case were you measure on the same axis cannot be explained by the fact that both particles have been sharing some property from the beginning of the experiment, and there really has to be some non-local phenomenon. The fact that classical quantum mechanics accounts for the result is another (more technical) matter, but it's not necessary to understand it in order to understand the meaning of the result.
@@freyc1 " if you measure on a different axis, you should get the same result in at least 33% of cases".... that's an assumption that could be wrong as regards spin measurement. I can't help feeling that there is a massive flaw in this whole argument.
@@GravityBoy72 The assumption the inequality is meant to test is that there is something in the state of the two entangled particles at the beginning of the experiment which explains the ulterior measurement of their spins along each possible axis.
If it were the case (which is not true : that's the point), then we would have a situation that could be modelled by a story. Two people are going to be interrogated in two separate and very distant locations by interrogators who have had no contact with each other. But the ones being interrogated know in advance that each of them will be asked one question from a set of three questions (A, B and C). They can answer to each question either "yes" or "no". They can elaborate a strategy together before being interrogated. But there is one constraint (since we are"modelling" entangled particles) : if they are asked the same question, they must answer the same thing. So they have 2^3 possible strategies.
Then, each interrogator randomly asks to each person one and only one of the three questions. One time in three, they will ask the same question and get the same answer. We don't care about those cases. We only look at what happens when both interrogators happen to ask different question (the first one gets question A, the other one question B or C, for instance). What then is the probabiliy they will get the same answer anyway? If they have chosen to answer "yes" to each question, it's 100%. Same thing if they have chosen to answer "no" to every question. But if they have chosen to answer "yes" to 2 of the 3 questions (or the contrary), then there are two possibilities : either the first one answered "yes" (respectively "no") and the other one has a 1/2 probability of giving the same answer. That can happen for two different questions for the first one. Or the first one answers to the only question he had to answer "no" (respectivley "yes") to, and then the other one will always answer differently. In total, there is a 1/3 probabiliy that they will have the same answer to different questions (2x(1/2)+0)/3 if they have chosen to answer "yes" (or "no) to two questions out of three. Since it is 100% for the other strategy (answering "yes" to all questions or "no" to all questions), they will give the same answer when asked different questions at least 33% of the time.
As you can see, this is just logic. It has nothing to do with the particles we are dealing with or with spin. The fact that it doesn't work for measurement of spins of entangled particles along well-chosen axes simply chose that there can be nothing at the beginning of the experiment which may determine the result of the measurements.
Sorry for having answered too quickly the first time and then deleted the answer : I wasn't fully awake and wrote some stupid things!
@@freyc1 "The fact that it doesn't work for measurement of spins of entangled particles along well-chosen axes"... again, the assumption is that the same logic applies to spin.
What about degrees of spin?
What about "in between" spin?
Not easy to find a video where Bell's ideas are so easy to understand. Studrets of Physics should see this.Thanks a lot.
I'm still fairly confused Dr. Greene. I guess this isn't answered, but how does the data reveal opposite spin only 50% of the time? If we control the settings to the experiment with regard to axis, how does the data not reveal 55%? Is there any chance on live stream to go more in depth for this? Thanks again!
I have the exact same question Ryguy. If 5/9 is fixed like a ratio then it doesn't matter how many times you run the numbers you are always going to get some larger version of 5/9 or 55%. So why does the number become 50% just by running the experiment? Something else must happen. It would be great if Dr. Greene explained what that something else is. As it stands I agree with Ryguy this isn't fully answered. However I do agree with everyone else that this is a really good explanation of everything else. Or at least I followed it :) Very much appreciate and enjoy the videos Brian.
This is exactly where I lost the thread also (or I've missed something relevant before this point). If QM predicts 50% and that is what the experiment showed, but how is that? It would be useful to see the same step by step statistical explanation as for the EPR argument.
@@cottawalla When I consider all possibilities, I find the probability of detection of opposite spin is 48/72 (=67%) and the probability of detecting similar spin is 24/72 (=33%). This is the probability when the two detectors (left and right) can have only three angle (120 degrees apart). This analysis does not include the situation when the detectors are oriented in other random angles relative to each other. My guess is that may change these probabilities.
I find myself in the same place. What specifically are the conditions that we get 55% and what specific "change' in conditions resulted in 50%?
This was awesome. Thank you sm!
Regarding Pauli's comment about the dancing angels on the tip of a needle - the same applies to the Strong Copenhagen interpretation claiming that superposition is actual physical probability cloud, and that it really physically collapses instantaneous upon measurement.
Professor Greene, I really appreciate your video very much. It offers the best explanation for this phenomenon.
One of the best explanations of what I have never understood properly
QM, hidden variables , EPR paradox
I love them.
More mathematical one, but could you try to do something on the amazing theorem of quadratic reciprocity?
wonderfully explained Professor Greene! I had NDE a few years back, experiencing three flatlines in a twelve hour period, and since recovery, regularly experience the Pauli Effect, as well as much Jungian synchronicity…been a fan of Bell’s inequality ever since I read Fritjof Capra and the work of the Fundamental Fysiks Group, which has all helped me maintain a semblance of sanity since I awoke from the coma!
What an amazing science communicator Prof Green is. Thank you for sharing your insights into this fascinating intellectual discussion that has been ongoing since the last millennium.
A very lucid description of Bell's Theorem. Many thanks.
Thanks, Brian; you’ve just given me an idea how to emulate/simulate a 3-axis spin of my axiomatic virtual particles in my “gedanken simulation” of 3D digital color space… 👍
Thank's for a clear explanation about this issue! Very many youtubers and other physicists try to explain it, but Brian Greene had it pretty well done. Thank You!
Dear prof. Green your lecture is magnificent , it’s explains the most unintuitive result in such bright way we’re all just speechless. THANK YOU
Very appreciated, thank you. Clearest explanation I've seen yet.
Just finished the video, engrossing! Can someone explain the whole third axis concept a bit more to me? Got a bit confused by the three arrows diagrams and what’s going on there, namely how we’re comparing them to one another?
I am fascinated with quantum physics and am loving your really well explained videos❤❤❤
38:00- A X-shaped matrix with each opposing pair being a mirror image of each other.
38:43- A tilted diamond spoon.
39:39- The center of a square.
Trying for weeks to get my head around Bell's inequality. This one finally did it for me.
Professor Greene is way better than I thought reading his books. Cool way to get things across!
Great talk, thanks. I always assumed that Einstein agreed that the two particles were in superposition, but that they were just shown to be in opposite states when finally measured. It’s interesting that Einstein believed they had definite properties from creation.
I think I finally(!), years and years too late, got it :). Thanks. A great presentation.
Hello sir. Would you please provide the links where we can read those papers you always show and allude to?
Thanks 🙏 I was looking for this explanation.
This goes straight through the head. Can't shake off what I've just learned.
Amazing explanation. Thank you professor Greene.
Totally brilliant presentation. I didn't expect to understand Bell (on any level) anytime soon. I was wrong!
I love your stuff so much Brian.
Thanks for your talk. I loved the explanation. Thank you
Brian is so good at this. Great popularization.
Excellent video, thank you. I finally understand the Bell's inequality! I've read there is another pre-requisite to validate the experiment: the selection of the axis between detectors must be truly independent of one another. What if they are not? Think of superdeterminism.
Thank you, Brian.
Brian, why isn’t the fuzzy to specific location issue like a photograph of a moving train. We can’t really know the position of a moving train when it’s moving (without any references) and when we take a photo, the fuzziness snaps the train into a specific location?
Wonderfully and patiently explained
I love you Prof. Greene for Spreading scientific knowledge in this Trumponian Dark Age. I'm a biology student and you showed me the wonderful world of physics!
this explanation is a gift to all of us, it's as brilliant as Bell's theorem!
That was a great lecture. Thank you. You’re an excellent teacher.
Wow!! Best explanation of Bell‘s Theorem and non locality I‘ve heard ever!
I am not qualified to say if this oversimplifies the essentials of this debate but it is at the very least a supreme example of how to communicate difficult scientific ideas. I think Prof Greene's students are very fortunate!
best explanation so far! finally i understood :D ...many thanks 👍👍👍
One of the Exellent explaination of Bell's inequalities on CZcams
Brilliant explanation ,Professor Greene.I did physics at Queen's University Belfast 71-78 and John Bell was not even mentioned...once. Now that is spooky action at a distance!
A very accessible explanation. Thank you.
Thank you so much Professor Greene! As a physician who was inspired to one day hopefully become a physicist by your books and others I can say that this series of yours came to fill a space not previously occupied. You are helping, brilliantly, people like me to do the leap between nonquantitative, nonmathematical physics books to the entire physics literature, I'm sure.
Easily the best description of Bell's Inequality. Many thanks Prof. Greene. Mind boggling implications. What however does choosing 4 axes or other numbers of odd or even axes say? Why are 3 axes the go to in this example? Just saying.
I followed the first 40 minutes OK and it is the clearest exposition I have seen so far. So thank you for that. However, I now cannot understand why it is that the experiment disproves the idea of the spin directions being set at the start but is OK with them being set at the end.
I also have a question about the three axes. Why three axes? How do things change if you pick two or four, say?
Thank you for such a clear explanation of this topic
I think you're great... every time I dont understand half of what you explain (but it his not on you, it is me) but I can never stop listening and watch the whole thing even if I got to come back to it later.
I'll never be a physicist but I love hearing you Greene and Sean Carroll speak... I love the concepts that I understand only half way, but I dislike the math in it, so I take you guys' word for it that all you say has been mathematically and experimentally verified.
Thank you for this wonderfully explained Qstory, in a way that I can understand the spooky implication. Thanks a lot!
Sir could you give lectures related to space relation with time and clear concept of light waves.
Thank you Sir
You r enriching the world of those who seek the knowledge … I can’t believe that I am lucky enough to learn physics from a genius like you…
🙏🙏🙏🙏🙏🙏
Love from India