For everything airing over the next 48 hours. Check the program guide. We kick off the weekend with a look at Quantum Mechanics. Good evening everyone. Welcome. Thank you for coming out to the secret Science Source north. We are a series that brings science test of all the disciplines out to public sages where they can be part of the cultural life of the city where people like you can come in and interact directly with them. And be informed at the same time. Our regular hangout is at the bell house in brooklyn. The secret science club north we are were back here tonight it is our kick off of our many season here are fit many season of secret science club north. Were also happy to be helping to kick off the new season i think we are just right behind the new republic as always. We want to thank all of the staff of the symphony space. They are the best. A very special thanks they have created our fabulous libation of the night. It has in it bourbon, maple syrup in a smoky ginger ale topped with lemon. Very delicious. You can get at the bar which is out to the left there. If youre bored by me nows a good time to go do it. We want to give a heads up we will be back on december 3 she is a former nasas or not. You may have read the thoughts like this in the paper. If you would like to know more about the secret science club and the Upcoming Events you can visit our website at secret science club. Dot blogspot. Net. Onto tonights event. We want to say a wonderful night. Sean carroll has a new book out. And in fact it came out today. And that may be why you need to have a cocktail. Its a book party. Its a lovely folks at books on call nyc. They are at book sellers tonight. They will be signing copies after the talk. We are pretty excited to have sean carroll with us tonight. Were also pretty excited to have a very special guest here to introduce sean carroll. Brain gearing is a physicist. A professor at Columbia University in director of the center for theoretical physics. Hes also a playwright sometimes an actor. And the bestselling author of several science books. He has hosted two Emmy Award Winning miniseries. Please welcome dr. Brian greene. Thank you. The quantum cocktail. I was shocked that dorian did not follow it up by saying you can get it at the h bar. Youve been even a great audience. Tonights focus with sean carroll is on Quantum Mechanics. And i said think many of you know we have a wonderful quite straightforward understanding of the universe. You tell me how things are today and i use the equations of newtons or the equation of einstein. That all changed. In the early decades of the 20th century beginning with the work of einstein itself the paradigm change and now the new way of thinking about the world is the best we can do is predict that probability of what they will be like tomorrow. That was not an easy transition for physicists in that era to take on board. It was an emotional upheaval for many of them. But here is the thing. As sean no doubt will describe for you in more details the laws of Quantum Mechanics even though they are probabilistic. Can be used to make decimal point onward to nine or ten decimal places in the agreement between theory and experiment is so potent and powerful that people began to stop thinking about what the theory actually means. Whats actually telling us about the nature of reality and begins to just use it as a wonderful structure to make predictions about the world to begin to control the micro world. To yield all of the wonderful technological gadgets that we walk around with all the time. I got to a point where anybody who really is a physicist wanted to think about the meaning of Quantum Mechanics what but it was really telling us about how the world works they were looked on as someone who had lost their way. It wasnt something that we were supposed to do. They are a few people that say that how we transition from the description of the world to the deaf not reality that we all experience. And many ideas were put forward. The most wild of all of those ideas. The possibility that we are part of a multi verse. Many worlds. Parallel universes. A very strange idea. I will say this. Ever since the events at least i had found in talking about these people have a much easier time understanding the concept of parallel universes. And with that it gives me great pleasure to introduce tonight speaker you know him the bestselling books on the nature of time. We physicists know and love sean as one of the great leaders and pioneers in understanding quantum physics. Tonight you will have a great treat here from one of the profound thinkers who are willing to keep pushing through. Give a warm welcome to my friend and colleague sean carroll. [applause]. Thank you brian. Who do i need to think. Symphony space. All of you folks for figuring out the secrets. Im happy that it does. When you become as best to do demonstrations to bring it down to earth. Im in a start by doing a demonstration. I will do push a button on my iphone. It will send a photon down the tube and then it will hit a beam splitter and go left or right with 5050 probability. And then depending on if its observed to go left or right the signal will come back here and it will tell me other i should happen to the left or to the right. Quantum event. I should happen left. Ready is the demonstration. Why is it worth anything at all. It predicts actually believe its true. There is an entire other reality where i hopped over there and am currently standing right there gesturing to my left. There is a different version of me that did something different. I actually believe this is true. What you should be same as what kind of a crazy person would believe that this is true. The reason why we are talking about these things is because Quantum Mechanics is enormously successful we need it to understand lasers in transistors. Even white chairs and tables dont collapse. As my predecessor says i think i can safely say that nobody understands Quantum Mechanics i usually dont like to appeal to authority by bringing up other physics. When the claim is that nobody understands something the person that understood understood the thing the best is a Good Authority how can it be possible. We can make predictions but if you ask what is going on what is the be at reality beneath that prediction i will say i dont know. Theyll say i dont want to know. I just want to make predictions. This is a terrible attitude. And my fellow physics should be embarrassed of themselves. Its only since Quantum Mechanics came on the scene. The people who specialize in this would be the superstars of fedex dash mike physics. These people should be millionaires living and pent House Apartments and theyre not. Its not that we dont understand that we havent even really tried. That is a whole different talk. Right now i just want to highlight the degree of embarrassment. The fable of the fox they look juicy and delicious. They are too high. They cant get them. I didnt want those grapes anyway they are probably a sour. The fox represents physicist. We used to try we couldnt do it. We never really wanted to understand Quantum Mechanics anyway. Everyone is going to understand Quantum Mechanics. And why it led us to these crazy propositions. Historically accurate to her. I will tell you a story that gets there in a relatively brief time. I hundred years ago or a little bit more. They were putting together of the adam everyone has seen this picture. There is a nuclears at new keyless at the center. Today we know they knew there was a new keyless. And orbiting around the new keyless like planets orbit the sun are the little particles called electrons. It also cannot possibly be right the reason my before Quantum Mechanics came along. We have a successful theory called classical mechanics. The classical mechanics makes up prediction. When you send it as aiming around is aiming around in circles. It admits late. And infrared electric waves. Here you have them zooming around being accelerated. What they should do they should spiral into the center and collapsed into collapse into the new keyless. The timescale for this to happen maybe it takes a long time. Less than a picosecond. Trust me, im a scientist. They should not be stable. They should just collapse. It apparently doesnt. Did a good theory. It was conceptually inadequate. It was hard to do better. There is a long set of steps that i am skipping. Maybe the electron is not a particle. May the way to think about electrons is as waves not as particles. Someone eventually said the electron which is being a particle. We call that the wave function. One of the dumbest and least significant names. There is a wave function that spreads out across the new keyless. It then fades away. You can do that math problem seen what are the different ways that the waves could settle down into an atom. And even though the weight itself was going back and forth. There was certain discrete positions that they could have. It could just sit there and not change. The electrons settle into this. This is data. This is a picture of an electron around the helium atom. It is spread out and what we in what we now call the wave function. Thats why they dont decay because theyre not actually moving its not just a little point going in a circle. It really is this function, this cloud and the waves could be absolutely static and unchanging. Thats progress. More progress came a couple years later. Who gave us an equation. I need to show you the details of the equation because of the quiz that we are having at the end. Conceptually its not that hard. The greek letter represents the wave function. You have a question that is asked of the wave function. On the right you have an answer which says how fast are you moving. A typical wave function well had various different parts to it. In the equation simply said that high energy parts change. Scientists love equations. An equation is full. Both for the scientist and student. The equation says now that i know not just what its doing in this particular circumstance i can figure out what they will do in any circumstance. So the equation gave so does the ability to say how it evolves with time. There is one obvious huge dramatic flaw. When you look at it electron. Usually when you look at electrons they dont look like waves. They look like particles. This is actually a little chunk of uranium. This is in a Cloud Chamber when the particle gets through it leaves a string of bubbles behind it. I should you mostly because of school. What i want you to learn from this picture is the prediction of the equation. Its not what you see when you look at it. What you see is a particle like thing. Thats why would come particles in the first place. The wave sort of bunches up and looks like a particle. They found thats not what happened. It spreads out all over the place. There is a dramatic mismatch between the formalism. In the observation which says it localizes and looks particle like. So people invented the awful no good idea which is that ways dash mike wave functions can be there. You think im kidding you this is what we teach our students. This is what i got taught. There is theres the wave function on by itself. And on the right it says when you measure when you say that. The word went out. It is the collapse of the wave function. Theres something that happens. The copenhagen and interpretation. And this is what we teach our students today. If you open up a textbook in Quantum Mechanics you will find what do they do their two sets of rules. Wave functions do one kind of thing when youre not looking at them they do another kind of thing when someone looks at them. When you have something spread out like that on the left that means the probability of measuring the electron is on. This is what we teach our students. See mike this is Utter Nonsense but let me be more kind. This is clearly unacceptable. It clearly cant be the right answer. Nobody in their right mind thinks that this is the ultimate way that reality works. I will highlight two of the problems with the cookbook that we are given. What is the world not what do you observe even when youre not observing it. We kind of slid around on the question. There is a wave function is the wave function. Is it a representation of a complete story of reality or its only part of reality. Maybe there is particles as well. Maybe it has nothing to do with reality. He was just a Little Black Box that we can use to make predictions. There are people who believe all of these things. We do not agree about what reality is according to Quantum Mechanics. What do you mean look at, looking at things changes them. Could a cat look at it. What about something non living. What if i just glance at it. Does it imply that somehow my agency and consciousness. Has something to do with the fundamental recipe of reality there are people that believe all of these things. At least we dont agree on the answer so there is a problem. See mac mike i have ideas thats why were here. Peruse perusal will still position of highlighting how weird and spooky everything is. I want to tell you my favorite version of how to get it right. They basically acted as a quantum therapist what he said was look, even working too hard. You have some good looking goodlooking rules for whats going on. Their functions clearly. The wave function is everything. Theres nothing else. That was his prescription. Naturally he left right away. He tried to convince other people that what he said was interesting. And here was the interpretation. There is one set of rules. It is parallel to every other theory of physics. There are states, they evolve according to an equation. And all that about measurements and other things. You dont need it. It sounds like it would be good if it worked. But the stuff was invented for a good reason. How in the world could this simple version of Quantum Mechanics possibly fit the data. The seeker is a little feature of Quantum Mechanics. Entanglement. Let me get it in modern terms. I also mentioned that i wrote a book about it. I would be hurt if you took the book out. Has zero spence. Its very much similar in spirit to just the ordinary the spin is zero. It can decay in various ways. Two electrons. We will just call those two electrons. They do have a spin. They had spin one half for historical reasons. But it is a spineless particle. Angular momentum. It is concerned. It must be the case that the spin of the two electrons canceled out and had to add to zero to give you the same spin they have before decayed. You can spin up or spin down. It could be spin up or spin down. But they must be opposite. Thats what we know. The way that that happens in Quantum Mechanics is that they decay into super position. Either electron one as is spin up or spin down. It is everything now. What this means is that it decays into a quantum wave function. The two electrons were entangled with each other. We dont know whether it will be spin up or spin down. We know of the spin of electron to will be opposite. They will have to cancel each other out. Theyre related in they are related in some way. In the lesson here is in Quantum Mechanics. There is not separate states. There are separate wave functions. There is only one wave function. These days we call it the wave function of the universe. There is a state for particle one which is a plus down. But thats not right. He put the cat up in the box. The uranium that you found before. That probability that it clicks. And when it does. It will open the box. And in the original telling. It is poison gas. I think my father just didnt like that. Thats really true. I didnt make that one up either. The point of it though. Apparently. Didnt like any of this. That they squared and got the probability of something. Thats when the on equation was for. According to my equation. If the wave function of the radioactive source was a super position of having decayed or not. The wave function of the box is in a super the super position and having not. Lets use this to realize the difference in reasoning. I will introduce notation. There is a fact of the matter. At the cat is awake or asleep. It says no know theres a whole other set of possibilities. Whether you are taught. This case. But there is classical observers. They just observe things and gets answers. They have definite value. Have you ever been in the superposition. You think that you can do that. The godfather of Quantum Mechanics. The text version is you would open the and either you would have it awake. I tell you this because i want to contrast it with the ever ready many world version of this. There is no collapse. Only one wave function. There is no dividing line. You are part of the wave function of the universe. The experiment starts with the cast being the superposition. In an observer is played by hugh everett. And then they opened the box. It is not anything mystical. Opening the box just means i solved the equation. And have a physical interaction with what is outside the box obeying the equation at all time. What does it predict. When i open the box. Heres what we know. If we opened the box. And it was entirely awake he would see in a week text. If it was entirely asleep you would see it and that has all the information you need to know exactly what you would observe. Namely the world and involves a superposition of the cat was awake. Literally nobody in the world disagrees with the fact that this is the prediction of the equation. They might disagree it you should be using that. But thats the prediction. This is why no one believed. If you seem to follow that. It sounds like and i observed quantum things before. I think like everything. He didnt really had any right to get it right. It stems from the same philosophy. There is only one wave function. We did not include the entire universe here. We have a cat and we have an observer. What about the rest of the universe. Technically we should put it in. You might think that doesnt matter. But you would be mistaken. We call the rest of the universe. The technical term we use. We are not keeping track of everything that happens. Were any room here with light coming. I dont know the position i would not even know if they changed a little bit. The environment is both inside and outsid