Hello. Thank you for coming out to bring scientist of all disciplines and then to interact directly with them and with those discoveries and here in brooklyn but speaker from new york science secret club north and and then right behind the new republic as always. And with rebecca and mary for helping us and also zach. And then fabulous libation of money and exhibit a. And you could get it at the bar to the left now is a good time to do it. And then to be back on decemberd with astronaut Catherine Sullivan a former nasa astronaut the first woman to walk in space but also because of an oaa very timely. So if you would like to find out in our Upcoming Events check out our website we have blogspot website and you can sign up for the mailing list they are. So tonight theoretical physicist has a new book out and in fact it came out today. It came out today. Physicist, mathematician, professor at Columbia University and director of the center for theoretical physics is also a playwright and sometimes an actor and a bestselling author of several science books including the elegant universe and fabric of the cosmos and he is hosted to any awardwinning pbs series based on his book and is also the founder of the gold old festival please welcome doctor brian greene. [applause] [cheering] thank you very much. The quantum cocktail so tonights focus is on Quantum Mechanics and as i think many of you know in a truly early years of the 20th century, we had a wonderful quite straightforward understanding of the universe. Classical physics. Beginning with the work of einstein themselves, its the paradigm change and now the best that we can do is the probability of what they will be like tomorrow. And that was not an easy transition for the physicists in that era to take on board. It was an emotional upheaval for many of them to make this transition but heres the thing. As sean will describe in detail, the wall of the Quantum Mechanics can be used to make predictions that agree with observations for fantastic accuracy. To nine or ten decimal places and the agreement between theory and experiment is so potent and powerful people begin to stop thinking about what its telling us about the nature of reality and begin to use it as a wonderful structure to make predictions about the world to begin to control to yield all of the wonderful technological gadgets that we walk away with all the time and infected is more than that. Its got to the point anyone as a physicist that wanted to about the meaning of Quantum Mechanics, but it was telling us about the world and how it wor works, they were looked at as someone that lost their way. It wasnt something we were supposed to do. There are a few people that say that trying to figure out in particular how we transition to the definition of th that we experience and many ideas were put forward. Shawn will talk about the most loyal of all the possibility that we are part of a multiverse, many worlds, parallel universes, the very strange idea but i will say this. Ever since the events of november 28, 2016, people have an easier time understanding the concept of parallel universe. And with that it gives me great pleasure to introduce tonights speaker you all of course know him from his many bestselling books on the nature of time, the particle, the nature of reality itself we know and love sean as one of the great pioneers in understanding caused algae and quantum physics tonight you have to treat to hear from one of the profound thinkers that are willing to push into the quantum physics to try to figure out what its telling us about the nature of reality so please give a warm welcome to my friend and colleague. [applause] thank you secret science club and all of you for figuring out this week for its. I dont know how that happens, but im happy that it does. When you become a physics professor they teach you that what you teach other people even if it is an abstract concept it is best to do demonstrations to bring it down. Im going to start by demonstrating. Im going to push a button on my phone which will send a signal over the internet to a laboratory in switzerland which will send a photon particle and hit and go either left or right with 5050 probability and then depending som, the signal will e back here and tell me whether i should go to the left or the right. Here we go. The photon is admitted. Thats the demonstration. Thank you. Why is it worth anything at all its because in my favorite version of the Quantum Mechanics, which i will tell you about come if predicts and i believe it is true that there is an entire reality where i hopped over there and am currently standing there to my left is a different version of me that did Something Different and like i said, i believe this is true what you should be saying is that kind of crazy person would believe this is true . But what we are here to figure out and let me see if i can do the technology. The reason we are talking about the things it is enormously successful. Particle physics and even my chairs and tables to collapse. But as my predecessor tells us i think i can safely say nobody understand Quantum Mechanics. I usually dont like to appeal to authority by bringing up others but the claim im making nobody understand something, its a Good Authority to say nobody else understands it anyway. How in the world can it be possible that even though he was Quantum Mechanics to make these predictions with enormous accuracy someone can say please see we dont understand if its because we can make predictions. They might say i dont know. The fact they would say i dont want to know i just wanted to make predictions, it is a typical attitude and they should be embarrassed with themselves. It wasnt always like this. No one would have said that this a hundred years ago. When they came on the scenes people were tempted to think the only reason we do physics is to make reductions and not to understand how nature works. Given that we dont understand the Quantum Mechanics, you would imagine since they are so important, the task of understanding would be the most important thing in all of physics. We have several of the worlds leaders in understanding the foundations of Quantum Mechanics. These people could be millionaires living in an apartment that they are not. They are great people and they are underpaid and undervalued and so it isnt only that we dont understand but that we havent even tried. I want to highlight the degree of embarrassment a physicist would have and say of the fable the fox sees some grea grapes ad hops over but they are too high so he says i didnt want them anyway they are probably sour. In case it isnt perfectly clear the fog present the understanding of Quantum Mechanics. We used to try but we could do it. Starting tonight everyone is going to understand Quantum Mechanics so im going to do a tour of why we came up with in the first place and why it led us to these crazy suppositions that are not a particularly historically accurate torpid history is messy and we dont have time for that so i will tell you the story that gets us there in a relatively brief period of time. 100 years ago or a little bit more scientists are putting together the picture of the at atom. Theres a nucleus at the center and today we know it is made of protons and neutrons. Orbiting around like the planets orbit the sun are these electrons that are successful for various reasons and it also cannot possibly be right. Remember also before Quantum Mechanics came along we had a theory called classical mechanics that had been given by isaac newton and his followers and it makes the prediction when you take an electron, a charged particle and send it around in circles were up and down it emits radio or infrared electromagnetic wave. All that you are seeing comes from an electron so here you have them zooming around being accelerated. They should lose energy and what they should do indisputably with classical mechanics is spiral into the sector of the nucleus. The chair you are sitting on, everything in the world, it should collapse. It has zero extent it should collapse into a black hole but it apparently doesnt. Scientists have a good theory it was conceptually inadequate and we need to do better. It was hard to do better. There are steps that im skipping that they came up with the following ibm maybe it isnt a particle. Maybe the way to think about it is as waves and not particles. There was a debate about whether it is so someone eventually said that the electron we call it the way that it represents the electron one of the least romantic names of the concept of all of the physics but that is what we call it. It spreads out around the nucleus for this concentrated in the middle and then it fades away and basically you can do the math problem to say what are the different ways that an electron could settle down into an athome and even though the way that it is all energetic and so forth there are certain discrete shapes that it can have where it has a specific energy to sit there and not change. So the electron settle into this. This is data, this is a picture of an electron around the helium where it is located. Its not in the sob simple orbit, it is spread out around what we call the wave function. They are not actually moving. I hope everyone is happy with this but the greek letter represents an electron and on the left you have a question that is asked mainly how much energy has been used and on the right, you have an answer which says how fast are you moving so there will be various different parts of the different energies and it simply says high energy cards change rapidly and lowenergy prudes change slowly and that is basically the whole story. What matters is that there is an equation. Physicists love the questions. Some of them dont love them as much but it is full employment both of the scientists in for the students doing homework though he creations as now that i know not just what its doing that in any circumstance comes up short in the equation is where it is. The scientists got the ability to say how it evolves with time. Everything was looking good except for one obvious and huge dramatic wall that says when you look at electrons if you are not hightech and this is a recent picture for the reconstruction based on very delicate stuff, usually when you look at electrons, they dont look like waves, they look like particles. So this is a little chunk of uranium admitting particles in the Cloud Chamber that we leaves a little string of bubbles behind and its the result of a charged particle being admitted by the radioactive uranium. What i want you to learn from this picture is the prediction from some radioactivity it is admitted in a spherical. That isnt what you see when you look at it you see a particle moving. They have to hope that when he solved the patient he would find that it looks like a particle. Then people did actually solve the equation and it spreads out all over the place. There is a dramatic mismatch that says the way they spread out and the observation that says that it looks particle like so people invented the following terrible, awful, no good idea which is that they can be spread out, but when you look at them, they collapse. They are shy. [laughter] so, you think im kidding. This is what we teach our students. Theres the function all by itself and on the right it says when you measure and say where is the electron you dont see that cloud, you see is located in some particular location. Theres something that happens when you look at the function. This is what was figured out and this is what people told themselves in 1926, 27 and 28. This came to be codified as luckless mom as the copenhagen Quantum Mechanics and this is what we teach our students today. If you open up a textbook in the Quantum Mechanics you will find if you ask it to the functions do, there are two sets of rules. They do one kind of thing when you are not looking at them, they obey the equation and if they do another kind of thing when somebody looks at them, they collapse in a particular value and the probability of getting any particular outcome. So it just means the probability of measuring the electron is relatively large and the probability of measuring it out there is relatively small. Like i said i am not making this up. I want to say this is Utter Nonsense but let me be client to be the kind this is unacceptable as a theory to nature. This clearly cannot be the right answer this is why people tell us that we dont understand but Quantum Mechanics because nobody in their right mind think that this is the ultimate way to the reality works. I will highlight two of the problems with this cookbook that we are given. One is what we might call the oncology problem, philosophical, philosophers use the word oncology to talk about what is real, the study of being. What is the world just what do you observe that even when you are not observing it so you notice that we kind of slid around on the western and we were being introduced to the copenhagen. There is a function, but what reality is that . Is a onetoone representation of a complete story of reality were only part of reality a bit of function and other things as well maybe theres particle as well. Or the word has nothing to do with reality. Maybe it is just a Little Black Box that we can use to make predictions about experimental outcomes. There are people who believe all these things and who do not agree about what reality is according to the Quantum Mechanics and slightly more publicized is what we call the measurement problem which is even more obvious. What do you mean look at. Come on, looking at things changes them. Do i have to look at it lacks what about something nonliving like a photograph or video camera backs but if i just look at it if i squint and dont forget very carefully doesnt imply that somehow my agency of consciousness and my disembodied mind has something to do with the fundamental recipe of reality . Again there are people who believe all these things, i dont want to discount them but at least we dont agree on the answer, so there is a problem. What are we going to do a . I have ideas, thats why we are here. There is a very wellestablished position highlighting how mysterious and weird and spooky everything is and never telling you how to get it right. When finally there to tell you my favorite version of how to get it right. A graduate student in 1957 basically acted as a quantum therapist. What he said was look, you have been working too hard. Chill out a little bit. You have some goodlooking rules for what is going on. There are functions clearly, they obey the equation a lot of the time, clearly, then the simplest most straightforward thing is that the function is everything. Theres nothing else and what it does is obey the equation over time does nothing else. Right away he published the pieces and try to convince other people what he thought was interesting and he said no its not. So, there is the interpretation of Quantum Mechanics. There is one the set of rules applies all the time, no matter what is happening and it is exactly parallel to every other theory of physics and every other theory of physics, electromagnetism, general relativity, there are states, positions and momentum were fields and those states are all according to an equation. All this stuff about measurement and nonsense, just erase it, get rid of it, you dont need it. Okay it sounds like it is going to be good if it works that stuff about measurement was invented for a good reason. We saw the picture with the particles. We dont seem to see the functions, so how in the world could this simple lean and mean austere version of the Quantum Mechanics possibly match the data in our experience . The secret is a little feature of Quantum Mechanics called entanglement which you may have heard of. By putting it into the modern terms as brian mentioned by also wrote a book about. I wouldnt be hurt if you took out your phone right now and ordered a book thats okay if you did that. But if is on the will be particle that weve ever detected that has zero spin. A quality that elementary particles can have. Its very much similar in spirit to the ordinary spin of a spinning top of the earth, but it comes with a discrete amount. So the spin is zero isnt spinning at all and it can decay in various ways. It can go to two electrons actually an electron and antielectron. They do have a spin. They spin one half, but it goes into to particles angular momentum is one example, so it must be the case that this benefit to cancel out from each other because it has to add up to zero before, so we talk about this they can either go up or down those are the two choices and electron number one could be up or down. Electron number two could be spin up or spin down, but they must be opposite. That is what we know. If any momentum is to be conserved. So, the way that that happened in the Quantum Mechanics is that it decays into what we call a superposition. There are two possibilities. Either electron number one is up or down or electron one is up and down but its not that we dont know. Its just like the one in electron with it its function spread out, thats what the function is. We are taking the point of view that its everything now. So, what this means is that it decays into the function that is both possibilities at once so we say that they are entangled with each other. We dont know if it is going to beat up or down. We dont know if it is going to be up or down but if we measure the spin of electron number one afterwards, we know that it will be the office said that they have to cancel each other out, so they are related in some way. They are not separate from each other. The lesson here is that in quantum can ask their are not separate states for the individual parts of nature. There are not separate functions for each particle. Theres only one function called the universal wave function of the universe and it is described as the probability of measuring everything in the world all at once. So, you might think if you were trained on the newtonian classical physics, you might think there is a state for particle number one which is up and down and the state for particle number two is a plus dow