09. HOW MUCH IS THE FISH?
LISTEN ON
What do you think of when you hear the word ‘quantum’? What even is quantum physics? What does it tell us about our world and universe, and what can it offer us in the future? In this episode, John and Eva meet up with executive producer Mundi in a London pub, and get sent on a special mission to discover as much as they can about the weird and wild world(s) of quantum science.
Professor James Binney is a British astrophysicist. He is a professor of physics at the University of Oxford and former head of the Sub-Department of Theoretical Physics as well as an Emeritus Fellow of Merton College.
Mundi Vondi is an artist, fashion designer and co-founder and CEO of Klang Games. He is the executive producer of The Life Cycle podcast.
LINKS
Eva Kelley: If you’re anything like me, any talk of quantum mechanics or quantum computing is dizzying. Essentially, what happens to me when someone starts talking about quantum, is that my brain powers down, goes into battery-saving mode, and my mind trails off to scenes of sandy beaches and waves crashing into my feet. I can't help it. It’s not that I think it’s boring, it’s just that the subject is so dense and opaque to me, that it’s as though I’m looking at a brick wall, and behind that brick wall, there is all this stuff going on, but I can’t see it, so, I start looking around at things that I can actually perceive. In other words, I don't get it.
EK: I know some of the buzzwords: waves, particles, light speed, I think? Imperceptible to the eye, I also know it’s somehow really important, I know it has to do with observing tiny particles. I think it has to do with perception. And also, I kind of know that nobody really knows what it is. Which sort of makes me feel better. But really, I have no idea. So when Klang’s CEO Mundi arrived in London with John on a business trip and they met up with me and we sat down in a pub in De Beauvoir for lunch, and Mundi said: I think you guys should do an episode on quantum physics this season, you can imagine my horror.
John Holten: This is episode 9 of the second season of the Life Cycle Podcast: How Much is the Quantum?
[“How much is the fish?” by Scooter]
[Intro: The Life Cycle, a podcast about the future of humanity]
EK: Hey John.
JH: Hey Eva. Dreading this?
EK: Oh, you betcha. I don't know what it is, I have this blockage when it comes to quantum mechanics! And so, here is the first thing that I want to clear up, the terms quantum physics and quantum mechanics: Quantum physics is a branch of science that focuses on quantum mechanics and quantum mechanics is a set of principles used to explain the behavior of matter and energy. So, it’s like kind of the same thing, but quantum mechanics falls under the umbrella of quantum physics I guess you could say. I found that really confusing.
JH: Okay, yeah gotcha.
EK: And now I have to make a confession which is that I actually started crying in the course of writing this episode.
JH: That doesn’t sound good.
EK: No. Because, when I was in school I had a really hard time with subjects like math and physics and chemistry.
JH: Me too.
EK: Yeah and I would just sit there in class and the teacher would be talking and I would just be like, what is happening? If somebody would explain it to me one on one I would get it, but in this broad explanation way that happens in schools, I just couldn’t translate it basically. And at the end of the day what that meant is that I would sit in the classroom feeling really dumb. You know that feeling? Where you just feel stupid because you don’t get it?
JH: Yeah
EK: And here I’ve been walking around planet Earth for the past 15 years, ever since I got out of school, feeling kind of smart. I can have stimulating conversations. I guess once you’re out of school…
JH: Yeah you avoid the subjects you don’t like.
EK: Yeah you surround yourself with the things that you’re interested in, which you naturally enjoy talking about and learning more about. So I hadn’t had that feeling in such a long time and I was listening back to interviews I had done about quantum physics with the experts that we talked with for this episode. And it just made me so sad because I felt so dumb suddenly, and I hadn’t had that feeling in such a long time. And suddenly I was 14 sitting in my chemistry class just like, I don’t get it.
JH: Let’s blame our executive producer.
EK: Yeah.
JH: But I do know what you mean. And to be honest with you though, to make you feel better, I am in the same boat, but also I think the people that actually work with quantum physics would agree with you. I don’t think they totally get it either.
EK: No and I think that’s actually a fact. You know, what its like? You know that Russell Crowe movie where he plays that famous physicist?
JH: A Beautiful Mind? Yes.
EK: Yeah, and you know how when he’s figuring something out and the numbers and formulas light up and float off the blackboard? And you know that he just figured something out that’s really ground breaking, but to you, as the person watching the movie, it’s just a bunch of numbers floating around on your screen and a cool visual effect? THAT’s what this is like for me.
JH: Yeah. I must re-watch that movie, I haven’t seen it in years. In preparation for this episode, for this season in fact, I was reading this book about science in the 20th century, that is a mixture of fiction and history. It’s called ‘When We Cease to Understand the World’ by Benjamin Labatut, I don’t know how to pronounce his name exactly. He’s a Dutch writer who now lives in Chile and was nominated for the Booker International Prize. It’s a really great book, it’s a hard book to summarize what it is but I marked this passage and I’m going to read it to you because it kind of is reassuring for us.
JH: And I quote ‘...It’s not just regular folks; even scientists no longer comprehend the world. Take quantum mechanics, the crown jewel of our species, the most accurate, far-ranging and beautiful of all our physical theories. It lies behind the supremacy of smartphones, behind the Internet, behind the coming promise of godlike computing power. It has completely reshaped our world. We know how to use it, it works as if by some strange miracle, and yet there is not a human soul, alive or dead, who actually gets it. The mind cannot come to grips with its paradoxes and contradictions. It’s as if the theory has fallen to earth from another planet, and we simply scamper around it like apes, toying and playing with it, but with no true understanding.’
EK: Ok that makes me feel better. You know what though? I’m going to dismiss my negative attitude and make this happen for myself. I want to be the kind of person who doesn't think of that video with the spinning seal in the pool while someone is talking about the latest in quantum physics at a dinner party.
JH: Ask yourself though, is that the kind of dinner party you want to be at?
EK: It will be! And so, I googled the origin of the word quantum and it comes from Latin, where it means “amount” or “how much?” I already feel like that demystifies it a little.
JH: Yeah! It’s a question in itself. So in quantum physics, a quantum is the smallest unit of a phenomenon. So let’s also begin with that. A quantum of light, is a photon. And a quantum of electricity, is an electron.
EK: Ok that’s some good, bitesize info. So, back to when you came to London to have lunch with me.
JH: Yes, along with Mundi. It was super nice actually. I remember it being a very pleasant pub in Hackney near where you are in London. We had a few pints and a surprising pumpkin risotto, it was Halloween that time. And yeah Mundi announced this wonderful mission that we were to go on.
EK: Yes and disclaimer, this was recorded in a pub, so it was loud, you can hear glasses clinking and other people talking. But hopefully you will still be able to hear me prod Mundi with questions about why the hell he is so into quantum.
Mundi Vondi: At the heart of it quantum is just the world of the super small things. We’re always trying to dig deeper and deeper into what is the reality we’re in even made of. Which I find a very important question I would love to get more answers about. I don’t know how that actually, what the answer would actually look like, or why it matters to me. But I’m obsessed with it.
EK: What parts are you obsessed with?
MV: I think in general its the big questions. Like why everything basically. Why life and death and future and whatever. And when you look for answers, and a lot of people go to religion. I think that’s a bit of a cop out. Somebody kind of just tells you that’s the answer and you’re like, alright I’ll live with that, I’m fine with that. For the rest of us it’s a very important question: what is the meaning of life? And the world? And the universe? When you look for answers, and of course I believe that you can find them within and all of that crap, but in reality it’s in science. I want to try and understand the universe. And quantum is at the forefront of that research.
EK: Why is quantum at the forefront of the research? What is it doing that is so revolutionary?
MV: It’s where we have these very big unsolved mysteries that seem like magic, that look like magic.
EK: Like what? Like what is one of those unsolved mysteries?
MV: I think there’s two opposing factions, that’s at least how I break it down. There’s the Copehnhagen people, the Copenhagen Interpretation that is on one side of the aisle I would say. And then there’s kind of the realists on the other, which is like Einstien and Lee Smolin, and those guys. You have like Sean Carroll over on the Copenhagen Interpretation. So both sides are completely insane. Sean Carroll believes that there are infinite universes where every version of anything you ever think of exists in some parallele universe. Where you and I may be sitting right here but the only difference is…
EK: You ordered the lamb?
MV: This piece of risotto was over here. Every single version of every atom placement and every variation creates an entirely new universe. That’s completely insane. 100% insane. On the other side, which is the realist, there’s another thing that sounds less insane but is very crazy, which is called non-locality. Very hard to explain. Basically it means that information travels through the universe faster than light speed. Which if we get into it, speed and time are very related. The faster we go the slower time moves. One of the weird laws of our universe.
JH: I didn’t know that.
MV: Well, time is relevant. And gravity bends time as well, so we have many things that interfere with time. And so, you can imagine the faster and faster you go, the slower and slower time goes for you, until you hit time zero, then you are at light speed. Then you are at maximum speed. That’s why light is the fastest moving thing. It’s because going faster would mean you would go backwards in time essentially. You could say that.
EK: Wow, okay.
MV: So like photons are very interesting. I’m falling down a rabbit hole here. Photons are very interesting because if they were wearing a wrist watch, the second arm would never move. They are stuck in time because they are always moving at light speed.
EK: Right okay. Because they’re moving at the same time as time.
MV: Yeah. That’s a weird way to put it but yeah.
EK: It’s like if you were on a plane and there was a runway next to the plane and the plane was going the same speed as…
MV: Time.
EK: Not a runway, you know one of those things that you stand on in the airport?
MV: Like a conveyor belt?
EK: A conveyor belt. And the conveyor belt and the plane are going at the same time. So you’re moving but it looks like you’re not moving. Is that what its like? Like it feels like you’re just actually moving but it looks like you’re not?
MV: It’s more like you’re inside the plane and you fly the plane around the universe at light speed. And inside the plane because you’re flying at light speed, time does not move for you. So you would experience the trip happening instantaneously. Let’s say you fly 1,000 years around the universe at light speed. It would feel like a split second, and then you’re back, but when you arrive everyone is dead that you know.
EK: Interstellar?
MV: Yeah that’s what Interstellar is yeah.
EK: To sum up Interstellar.
MV: Yes, just like Interstellar.
EK: Ok, let’s back up for a second! I think this is probably a good time to pause the audio. Mundi is obviously way ahead of us in terms of his knowledge and his through process on the topic. So we need to get back to basics.
JH: Yeah we need to catch up with his enthusiasm shall we say. I guess the main bits that stuck out to me here listening back to it, that I think we should look into are: Copenhagen interpretation vis-a-vis the Realist Approach, he mentioned Sean Carroll and Lee Smolin, Non-locality, Entanglement, what am I missing?
EK: My favorite part of this is when Mundi was talking about the photons wearing wristwatches.
JH: Oh yeah. That was quite an image.
EK: That was cute. Also, something that really resonates with me and sort of changes my perspective on this topic is how he compared understanding quantum mechanics to searching for the spiritual meaning of life, you know? Like, you can look at this like a magical, mysterious world that exists all around us but is imperceptible to us. I guess that echoes that passage you read from the book earlier. We haven't figured it out yet but we know it’s there. It surrounds us, and we are unaware of it somehow. It’s part of the fabric of life I guess. Like that joke with the fish in the water.
JH: What joke is that? You’re going to have to tell it to us.
EK: I mean it’s not really a joke I think. I heard it in this speech that David Foster Wallace gave at a university graduation once. It goes something like this: Two fish are swimming in the ocean. Another fish swims toward them and as he swims past, he asks the two fish “Hey fellas, how’s the water?” The two fish keep swimming and after a while one of them asks the other “What the hell is water?”
JH: Oh yeah, I like that. I like that.
EK: Alright, well, let’s get to it. Let’s focus on the basics. And then from there, we can spin off into magical spiritual quantum beliefs. But I want to get the foundations right. And I figured, there would be no better place for me to go than Oxford University. So I booked myself a train ticket and went to see Professor James Binney, who is an emeritus professor of physics at the University of Oxford. Really, he is a theoretical astrophysicist, but he has lectured on quantum mechanics for a number of years. And I came across him originally through a youtube video of his lecture on the basics of quantum mechanics. So I thought, perfect, that’s my guy! And when I got there, I asked him to explain to me in the absolute most simple terms what quantum mechanics or quantum physics is.
Professor Binney: Well, in its foundations, it's trying to be real. It's trying to get real about how we know about the world and recognise that we know about the world because we make measurements. Some people would say we just make observations. But physicists are obsessed with numbers, they want to reduce everything to numbers. And indeed, scientists of every sort, social scientists wants to do the same thing, too, I guess. So we want to make measurements, and we do make measurements. And that's how we build a fabric of understanding of the world. In classical physics, you operate under the fiction, the abstraction, that you can measure something without disturbing it. But when you're dealing with small things, atoms, more or not electrons, and so on. You cannot make it you cannot make a measurement, you cannot interact with these things in order to discover something about them without disturbing their state. And quantum mechanics in its core, is being grown up about this is recognising this is the case, measurement implies disturbance. So that the state of the system, the state of the object you're trying to measure before you measure it is not the same as the state you leave it in after you measured it.
EK: And why is that? Why does it have to be disturbed?
PB: Because our tools, we you, in order to measure something, you have to probe it, you have to observe it, you have to, you have to interact with it at some level. And if it's a very small object, the most delicate probing the most sensitive interaction is going to make a material difference to it. So this is this is just a basic piece of common sense.
EK: Ok so to Dr. Binney this might just be common sense, but to me, and maybe to you too, it’s not all that easy to wrap my head around. But what he is saying here is, or let me phrase this differently, what I think he is saying here is that there is a difference between measuring something very small and measuring something large. So, apparently, when you’re dealing with an electron and you want to figure out information about it, like its location, you need to bounce light off of it, for example. And that light carries momentum, so it gives a push to things you could say. When I’m looking at John or if we’re looking at me that push isn’t very important. The light comes through the window and bounces off of us and pushes us back. But that’s a very insignificant effect because we weigh … well, a bunch. But the push from the light is a big deal when it comes to something as small as an electron.
PB: So on small scales, it's obvious you have to engage with this. When you're dealing when you want to deal with very small scale systems. It's clear you have to engage with this. And quantum mechanics at its core is an attempt to do that. Now there's so all of that is very much just common sense. Since we are now discovering about the winner recognising that in order to measure something, we disturbed that thing. And we are recognising that our observing instruments are likely to be a little bit on the clumsy side relative to the very delicate systems we're trying to quantify.
PB: But actually, in the typical, the typical sort of instruments that we use, we don't have this entirely satisfactory degree of knowledge, we have limited knowledge. And the consequence of this limited knowledge is inevitably going to be that there's going to be uncertainty in the nature of the reaction interaction between our measuring kit and the and the measured objects so that the outcome of the measurement is going to be uncertain. Even if we did know the state of the system precisely before we made a measurement. The way that the measurement runs, what actually happens when we interact with um use our probe is going to be uncertain. And the result of this is going to be that we're going to have to calculate probabilities.
PB: But when we're when we're fumbling around with these delicate things like atoms and electrons, with our instruments our clumsy instruments, knocking them all over the place, the probability of the outcome is going to be quite broad, and we're going to have to calculate it and that's going to be very hard work. Nothing is nothing certain but even in classical physics, there's masses of, of, of probability required. There are many random things happening the weather, for example, which is classical phenomenon, but people want to assign probabilities to it's raining or.
EK: This was kind of an AHA moment for me. Somehow this vague comparison Prof. Binney makes to the weather made so much sense to me. So like, basically how I interpret this is like: When you think of meteorologists and how they predict the weather, and they look at the movements of the elements and find patterns and it’s a whole science but at the end of the day, they’re still like: Well, there’s a 60 percent chance it will rain tomorrow morning. And also, this isn’t really relevant but, it ’s all pretty shortsighted to be honest. It’s kind of a bummer that we can’t predict the weather months in advance by now, I’m just realizing. Where is the funding in meteorology?!
EK: Anyway, that’s a different story. And we have all accepted the uncertainty of weather predictions. At the same time, we know they are real, the weather is real, meteorology is real, don't let anybody tell you otherwise, and we know there’s a good chance that the predictions will be correct. But there’s also a high degree of randomness that we are all ok with. And so, and this is where I’m like, Eureka, quantum physics is like predicting the weather, just on a really really small scale. Does that make sense to anyone other than me? Let me know. Ok, so jumping back into my talk with Binney:
EK: And is that the same in quantum?
PB: That is the same as what we have the same issues in quantum mechanics, we wish to express the extent of our knowledge and our knowledge is is is is is uncertainty that but we are very conscious that this the best that our knowledge is going to be probabilistic is going to be uncertain, we're going to say it's, there's a 60% chance that if I measure the spin of this electron on along this direction, I will get a positive rather than negative result. That's the I want to calculate that probability. That's what quantum mechanics exists to do.
EK: The probabilities of the potential outcomes.
PB: Yes, of experiments so that if you make a measurement, what is the chance with this system that I get this result.
EK: And so we're currently kind of like a bull in a china shop.
PB: Yes.
EK: In the quantum world.
PB: In the quantum world, we are fumbling around. And that's generating this uncertainty that the lack of precision, and it's very serious uncertainty. So the thing which is absolutely mysterious about quantum mechanics, which nobody understands and a bit about which people physicists speak remarkably little, because they are aware they haven't anything intelligent to say on this topic, is the way that these probabilities turn out to be coming.
PB: It turns out you have to calculate these probability distributions. I guess the real answer, though, why is quantum mechanics kind of important is that our civilization simply rests on it, right? Because all of our electronic devices depend entirely, and I mean, have been, have been constructed and devised and exploit the quantum nature of, of matter on small scales. And so it's, there's there's essentially nothing we do now, which isn't dependent on, on on our mastery, our understanding of the quantum mechanics provides.
EK: Alright, so that was me and Dr. Binney at Oxford. I had actually never been to Oxford before, so it was really cool to see. There’s some nice shops there.
JH: Oh yeah? Did you buy anything?
EK: Yeah I did. There was this cute little, what do you call those stores where they have paper?
JH: Stationary shop!
EK: Yeah I think there’s a nicer name for it though, a French name.
JH: Papitery?
EK: [lauhs] Something like that.
JH: Anyway, I’ve never been to Oxford so lucky you to get up there.
EK: Yeah it was nice [laughs]
JH: [laughs] Except for all the quantum bullshit.
EK: No that was nice!
JH: Okay okay sorry, yes of course.
EK: Don’t hate on the quantum John.
EK: For our next act, I’m going to attempt to explain a few of the quantum buzzwords you have heard floating around. We’re going to grab quantum by the throat
JH: That’s so violent!
EK: And at the end of this, I promise you, we’re gonna get it. Some of it. Uncertainty, Non-locality, entanglement, double-slit experiment, which is essentially what Dr. Binney just talked about there at the end, the magic, but I am going to boil it down for you, and we’re going to forget about Schrodinger's Cat, I know someone out there was waiting for it, apparently most scientists agree it’s silly, so you let em know at that dinner party the next time someone mentions Schrodinger's Cat. It’s silly
EK: Ok, so there are a few basic principles of Quantum mechanics. Just realizing how hilarious this is, that I of all people am teaching a class on quantum mechanics. Ok, so one that I think is probably heard of the most is the Uncertainty principle.
JH: Yeah wow, which is not very promising as a title.
EK: No, it isn’t. Now, this is how Lee Smolin, whose name you have also heard a few times already in this episode – he is a theoretical physicist and renowned for his contributions to the problem of something called quantum gravity, he is the big leagues – anyway, so this is how Smolin explains the Uncertainty Principle:
EK: “Make a list of everything you need to know about a system to completely describe it. This will be the information needed to correctly predict each future precisely. In quantum mechanics, you can only know half this information, at any one time, although which half you know is up to you. If you know the half precisely, the other half is completely random. In a quantum state you have complete knowledge of half.”
EK: So, in classical physics, things come in pairs. If you want to figure out when something will be somewhere, you need to know its position and its momentum. In a quantum state, you would only get to know half of the stuff you need. And why is that? Nobody knows. Here is Smolin himself on the topic. This is from a lecture held at the perimeter institute for theoretical physics. You can find it on Youtube.
Lee Smolin: The uncertainty principle says, that’s what you need to know? Tough. You can only have half of it. And thats really what it says. And why it’s exactly half we don’t know. That’s why its a principle. I always teach this and a student raises her hand and it’s a good question, explain to me why the principle is true. That’s the point, it’s a principle. It’s the part, everything else can be explained given it. So we don’t know why it’s half. We don’t know why you can choose the half. You can know as much as you want about any half you’d like. And I’m going to make use of that in a little bit.
EK: And there is a formula that expresses this uncertainty principle, and that expression was invented by Werner Heisenberg or Werner Heisenberg, who, you’re going to tell us more about later, right John?
JH: Yes, let’s see, maybe in the next episode he will come up again.
EK: Ok, next up: Entanglement. Here is Smolin on the topic:
LS: Let's consider that we have two particles A and B and we put them in some quantum state. Now I told you the first principle is that if we consider them as one system we can have a state that describes half the information that we might imagine we need about them. But here’s an interesting thing we can do in quantum mechanics, we can put them in a state where we know everything precisely about some relationship between them and nothing at all about them individually. And this is called an entangled state. An example is the contrary state I call it. It’s actually known as the bell state and some other technical things but we’re going to call it the contrary state. In which you pick some property, say the position or the momentum of particle A and particle B and we measure them both.
LS: And whatever is the result of particle A the opposite will be the result for particle B. So if the property is momentum if particle A is going that way with some momentum particle B is going that way with some momentum. If the property is whether you like dogs or cats, if particle A likes dogs particle B will like dogs. And so on. It’s true for all the properties that you might be sensibly thinking about. So that’s the property called entanglement.
EK: He goes on to talk about how for a long time, the property of entangled states wasn’t understood right away, in the 1920s when it was discovered. The first time it was somewhat understood was by Einstein who wrote a paper about it in 1935. But it wasn’t until many years later that it became useful. And now, there is a whole world of quantum technology based on using these entangled states. Like quantum computing. There is another example that I think visualizes entanglement quite well.
EK: Think about two balls, one is white and the other is black. If you are given the white ball, you know for certain that the other ball is the black one. But the weird thing is that the properties of the balls, in this case thier colors, aren't fixed until the moment they are observed or examined. So in this scenario, both balls would be gray until they are looked at, and in that moment one turns white and the other black. And so this suggests that the two balls are somehow connected with each other.
JH: This helps me a lot, some of this is actually sinking in. But didn’t Einstein famously referred to Entanglement as spooky actions at a distance?
EK: Yeah. He didn’t get it.
JH: So that’s entanglement: spooky actions at a distance.
EK: Alright, next on the list: Non-locality. And Non-locality and Entanglement sort of go hand in hand. So, the word non-locality sort of makes you assume that naturally there should also be such a thing as locality right? Which is easier to wrap your head around I think. Locality in physics means that if I have a particle A and I somehow want to measure that system, I need to disturb it somehow. Dr. Binney was talking about that earlier. I have to interact with it in a way. Which in turn, means I need to be in proximity to it. Whether that be by going over to it or firing light at it or whatever, I need to be close, or in other words I need to be local.
EK: In quantum mechanics, there is something called non-locality and there is a very technical definition in physics to do with relativity, but the central idea is, which, now we are back at entanglement, imagine you have a pair of particles, particle A and particle B. Somehow, they interacted with each other and then they spun off in different directions. And now they are in a contrary state with each other, they are entangled. And if you measure, for example, the direction of the spin of particle A all the way over there, then you know for certain that particle B will spin in the opposite direction. Just like the balls.
EK: They can be incredibly far away from each other but instantaneously know the state of the other particle and behave accordingly, or in contrast. The key point is that these particles, which were correlated, now carry information about each other. Even though there's no possibility of communication, there's no way that physically, anything that A does could affect B’s environment. But the person measuring A knows that if they get the white ball then the person measuring B will get the black ball. Even if they’re on different continents. That’s entanglement right? And Non-locality refers to the fact that observers can produce instantaneous effects over distant systems. They can be very far away from each other and influence each other’s outcome.
EK: It’s super romantic actually. I know this is not a very good mathematical explanation but to me it is sufficient to understanding what non-locality means. And it kind of made me think of how, sometimes when you think of a person and you're like: Oh, I should text them. And then 1 minute later, they text you. And you’re like: I was just thinking about you, that’s so weird! Or sometimes, a person you haven't seen in forever, or even thought about in forever pops into your mind, you suddenly think of a childhood friend, an ex lover, maybe a school teacher you had or someone random you usually never think about. And you wonder: Why did this person pop into my head? I like to wonder if they were thinking about me in that moment and that somehow I guess you could say, you remain entangled with each other. Do you know what I mean?
JH: Yeah.
EK: Ok, the double-slit experiment, which I’m actually really excited about this, because after listening to many many explanations of it, including Dr Binney earlier, I think, I get it now. And it’s actually really cool. I feel like it sort of sums up the weirdness of quantum physics. And this also kind of represents the culmination of my knowledge of quantum physics, like, I feel, this is as far as it’s gonna go for me, you know? Like, this is where the journey ends for me. I’ll wave you guys off into the future, but I’m honestly just really pleased with myself that I understand something about it, so I’m just going to hang back here. Ok, ready?
EK: So, imagine a screen with a slit in it and then behind that screen, there’s a wall. And what we’re going to do, is we’re going to fire a small type of matter, like a marble, at the screen and see what happens. And just for the sake of argument, imagine that these marbles would leave a mark when they hit a surface. Maybe we just call them paint balls. And what would happen if we did that? Some of the paintballs would hit the screen, but some of them would fly through the slit. And then a pattern would emerge on the wall behind it, like a line that would correlate with the position of the slit, right? Now, imagine we place a screen with two slits in front of the wall. What would happen if we fired the paintballs at the screen?
JH: There would be two lines on the back wall?
EK: Yeah, exactly. Makes sense. Ok, and now we’re going to do the same thing, but with waves.
JH: Just you’re average waves?
EK: Just water waves.
JH: Okay.
EK: So picture, we’re submerging the room that holds the screen and the wall in water, like half full. And we’re gonna start with the single slit screen again. And we’re going to give the water a push, and a wave travels through the slit toward the wall and the place where the wave hits the wall with like the most force, lights up. Just imagine that that’s what it would do, it would light up. So we go through the slit and the wave sort of radiates outward in a half moon shape and hits the wall with the most intensity directly in line with the slit. So like the same as with the paint balls. But if we do this with two slits and waves, then something different happens. So now, the wave travels through the double-slitted screen and two mini waves come out the other side of the screen, out of either slit, right?
EK: And maybe this is hard to imagine, so you could like recreate it I guess next time you're by the beach or in the tub or something, but if the top of one wave meets the bottom of another wave, they cancel each other out, and they kind of like multiply and radiate outward. And all these waves hitting each other, and bouncing off each create new waves, and that creates an interference pattern. On the wall, the places where the two tops of waves meet are at the highest intensity and they light up and where they cancel each other out, there is nothing. So what you get on the back wall is like a pattern of stripes basically, an interference pattern.
JH: Okay. I think I’m following this yeah.
EK: And so, what does this tell us? When we throw matter at the double slit screen, we get two lines of hits on the wall that are in line with where the slits are. And with waves we get an interference pattern of many lines. So this is what we know and again, makes sense right? You just have to remember, matter two lines, waves many lines.
EK: Alright, so now, we’re going to do the same thing with electrons. And electrons are matter, they're just really small particles of matter. Now, when we fire the electrons at the single slit screen, they behave the same way the paint balls did. There is a single line of hits that appears on the back wall. But if we fire electrons through the double slit screen, and this is where it gets strange, they create an interference pattern on the back wall. They behave like waves. It doesn’t make sense! Because it’s matter! Ok so then scientists were like, maybe we’re firing all these electrons out at the same time, and they’re bouncing off each other and that is what is creating the interference pattern, so why don't we just, fire them out one at a time, play it safe, so there is no way the electrons can interfere with each other in the air while they travel?
EK: So they do that, but after a while of firing the single electrons through the screen, the same interference pattern emerges like it would with a wave. Which is really weird! Because there was nothing that could have interfered with them right! But the conclusion of that is that the electron leaves the firing machine as a particle, then before it arrives at the double slit screen, it becomes a wave of potentials, travels through both slits, and interferes with itself, then hits the wall as a particle. Mathematically, this means that it goes through both slits, but also through no slits, and it goes through only one or the other of the slits. All of these possibilities are in superposition with each other. And again, scientists we’re like, mhmmhmm, this is crazy, why don't we just set up a camera, or some type of measuring device, and be really sneaky and watch the electron to see which slit it travels through.
EK: And this is where it gets really mind blowing, because now, the electrons suddenly go back to behaving like marbles, or paintballs, or any type of typical matter and they create two lines on the back wall that are in line with the two slits in the screen, not an interference pattern like they did before. So the act of measuring or observing changed the behavior of the electrons. Which, I mean what do you make of that right? It’s like they knew they were being watched and adjusted their behavior. The electron decided to act differently like it was aware it was being watched! Which is so trippy! And so weird! And cool! And the reason this gets me so excited, which I never thought quantum could, is that this is like actual magic! And that’s the buzzword I wanted to circle back to, Magic. If there’s magic, I’m in. And now, I see the magic.
JH: Yeah it is kind of magical in a way. The power of observation and measuring -
EK: Let’s finish this episode where we started it. Let’s go back to the pub and let Mundi tell us some more about the magic.
MV: I don’t know where god fits into the background. I think it’s something much deeper. I think imagine you have reality on the stage in front of you. You really want to know whats happening behind the stage, behind the curtain. That’s kind of what I feel like quantum physics is all about. We’re trying to get behind the curtain and see what the universe is made up of and then maybe we get close to god or we understand some divine being is behind all of this. I don’t know that I would love to believe that, and I don’t disbelieve it either. It is magical in many ways. There is something so profound about the magic of quantum physics. I think it’s also the hardest problem. I many never live to see any true discoveries in the space but there’s…
EK: And this went on for hours! No, I’m just kidding. It’s really quite beautiful, all of it. Looking at it from the perspective of something profound, something that is emotionally moving even.
JH: Yeah. And also in terms of the science establishment so to speak, the Nobel Prize in Physics in 2022, which of course was a big deal. It was won by Alain Aspect, John F Clauser, and Anton Zeilinger for their work on quantum entanglement.
EK: I’m excited for the next episode, because you’re going to talk about them, right?
JH: Yeah, they will come up again. As well as that we’re going to double back a bit and look at the origins of quantum, and how for example those Nobel winners have been working on this for half a century.
EK: Can’t wait! Never thought I would say it.
JH: Give me more quantum, sign me up!
EK: Thanks for listening. Thanks so much to Professor Binney for his time.
JH: This episode was written and produced by Eva Kelley with additional writing by me, John Holten.
EK: Sound editing and design was by David Magnusson.
JH: Mundi Vondi is our executive producer and also created the artwork for this episode in collaboration with Midjourney.
EK: Additional research, script supervision, and fact checking by Savita Joshi.
JH: Follow us on social media and subscribe for more episodes wherever it is you listen to your podcasts.
EK: And please reach out if you’d like. We’d love to hear from you!