Your Daily Equation #21: Bell's Theorem and the Non-locality of the Universe

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.

The World Science Festival (WSF) is an innovative multi-media organization that produces original live and digital content straddling the arenas of science, technology, the arts, media, performance and education. With the goal of radically transforming public perceptions of science, WSF creates world-class programming, both live on stage and televised, featuring inspired collaborations, outstanding talent and novel production techniques that bring scientific discovery, insight and perspective to a broad general audience.

[moonymachine]

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!

[markdavich]

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.

[prydin]

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!

[martijn]

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!

[timjones]

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.

[privateerburrows]

FINALLY somebody explains Bell's Theorem in a way I can understand it! Thank you! Thank you! Thank you!!! Liked and subscribed.
EDIT:
By the way, the way I've resolved the question of locality, personally, just for my own satisfaction, is that perhaps locality is real but not primary. Locality being primary would mean that locality is immanent and fundamental to reality. It being non-primary would mean that locality is a consequence of deeper physical laws. If locality was immanent and primary, a particle would not have to "know" where it is, whether in absolute terms, or relative to another particle, as space would exercise its influence directly. If locality was not immanent, non primary, a particle would have to somehow "know" where it is in order to "obey the law" (of locality), just as a driver needs to have a speedometer and know what speed it is going at in order to obey max speed signs; the signs alone are not enough.
If locality is primary, it is as if in some town there were no max speed signs, but rather speed bumps or physical arrestors that directly limit your speed without you needing to read signs or look at the speedometer ... Without you needing to even have a speedometer at all.


Now, let's assume locality is non-primary, and model it as two drivers driving in opposite directions from a spot in a city or town. The drivers only know where they are by looking at the address plates on the doors of houses and stores. But if they are driving very fast, they cannot read the addresses, and so they base their location reckoning on the last address they saw, which happens to be the address they had at the starting point. Therefore they keep thinking that they are both at the same place even as they speed away from each other. If they use their warped reckoning of their own location as input to the task of obeying the rules of locality, they will fail miserably at behaving non-locally (independently), as they were supposed to ... behaving as if locally instead (entangled), thus making it appear that the universe is non-local. Like a driver with a broken speedometer driving at MACH-3 in a 50 zone.
So, to me, the question of locality is not a to be or not to be, but rather whether it is primary or secondary.

[paulc]

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.

[topredtv]

It's absolutely scandalous that Jon Bell didn't win a Noble prize for this 🤯🤯🤯

[bjornmossberg]

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!

[adamadiallo]

Finally understood Bell's inequality. Thank you.

[pranjalsomani]

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

[rickmorrisrigar]

Professor Greene with all due respect, my head almost EXPLODED !!!

[haimkohan]

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.

[DrJeeps]

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.

[ajoebo]

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.

[vaylx]

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?

[triqpham]

Dr. Greene, you set the bar so high for these educational videos that when I watch other YouTubers I inevitably scream at the screen stating, “Why can’t you explain it as clearly as Professor Greene’s video?” And I always come back to your channel. All I conclude is, you have a gift! Thank you for sharing it to the rest of the world!

[aubreylafrance]

Wonderful ! I love these none formal lessons where I understand everything

[brothermine]

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.

[ryguy]

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!