Best Of: Questioning Quantum Mechanics

0:07Unless you're a physicist, you've probably only encountered quantum mechanics on television. Oh, man, another quantum fissure? This is like the third one this month. Boo, interdimensional portal. They have been appearing with statistically abnormal regularity. Someone has to close the space-time potholes, or who knows what kind of parallel universe stuff could drift into our dimension. And even when it was explained by one of the characters, you might have still been a little confused. Guys, I think we found ourselves in a quantum leap. What the hell's a quantum leap? Oh, a great show from the coke-fueled era of 80s television where Scott Bakula would leap into other people's bodies, but he didn't know it unless he saw his reflection.

0:44I feel like whoever's at us here is probably listening. And who is that? Who's at us? I don't know, Ziggy? They never really clarified on quantum leap. They just accepted it. What? The field of quantum mechanics was created 100 years ago this year. Today, scientists are using it to create methods of communication that can't be hacked, higher quality images on our phone and TV screens, and to develop medications more quickly. But many of us don't even understand what quantum mechanics is or how it's deepening our understanding of the universe. For this installment of our series, The Scientific Method, we answer all your quantum-related questions.

1:21We meet our panel after the break. I'm Jen White. You're listening to the 1A Podcast, where we get to the heart of the story. Stay with us. We've got a lot to get to.

1:34Joining us for the conversation is Erica Carlson. She's a professor of physics and astronomy at Purdue University. She also hosts a YouTube show called The Quantum Age. Professor Carlson, it's great to have you. Thanks for having me. Also with us is Shohini Ghosh. She's a professor of physics and computer science at Wilfrid Laurier University in Ontario, Canada. She's also the director of research and programs at the Center for Women in Space. Professor Ghosh, welcome to the program. Thanks for having me. So let's just start with the very, very basics. Professor Ghosh, when we say quantum, what does that mean?

2:11Well, quantum has come to be referring to what we call the very microscopic world. So the world of atoms and photons, which are particles of light and electrons and such. But actually, quantum is actually a bigger idea than that. because, of course, if you think about it, we all are made up of atoms and electrons and photons. So the fundamental laws that govern the behavior of these particles are actually the fundamental laws of the universe because they essentially describe how all of the particles in the universe interact with each other, how they behave, how they interact with energy, and those foundational principles are really what are governing literally the laws of the universe.

3:00So it's a big idea in that small world, I guess. So we got this message from one of you. I don't know enough about quantum mechanics to come up with any wild theories, but I really need a simplified explanation of what it is and how it works. Now, Professor Carlson, if you were going to explain quantum mechanics in the most simplified way possible, how would you do it? Sure. I love a challenge. So the word quantum itself comes from the word quantized. It's about how you count something. So an example of something in your everyday life that's quantized is the number of unopened Coca-Cola cans in your refrigerator.

3:40You can have three, you can have six, 24, but you can't have one and a half unopened soda pop cans in your refrigerator. So the quantum or quantized part comes from the fact that these tiny particles, their properties, like their energy or their position, become quantized. A little bit like when we ride an elevator, you can't get off at the one and a half floor. You have to get off at a quantized floor. So that's what puts the quantum in quantum mechanics. Okay. So I'm going to try to, I'm going to tell you what I heard and you tell me if I'm, if I'm right. Oh boy. Okay. So the quantum and quantum mechanics is the whole, it's the whole of something.

4:29It's the, not the half of a Coca-Cola can. It's the whole unopened can. them? Well, that's correct. I'm drawing an analogy between the fact that, you know, how many unopened cans you have, that's a number that comes back in discrete packets, right? You have discrete packets of soda pop cans in your fridge that are unopened, or the discreteness of when you go into an elevator and you push a floor to get off that, there's only a certain number of buttons. So what we're used to in our everyday life is that the properties we encounter, something can have, you know, any value to it. So when I put my coffee mug down on my desk, I can put it here or there or there.

5:10I can put it anywhere I want. If my desk were quantum and if my coffee mug were quantum, I could only put it on the left side or on the right side and nowhere in between. That's one of the weirdnesses of quantum. Okay. So then extrapolate that out to quantum mechanics. So that's quantum. If you're going to explain quantum mechanics, is that also the explanation or is it something beyond that? It's exactly quantum mechanics. So we just, we physicists, we throw the word mechanics into something to just mean how it works. So when we say quantum mechanics, we just mean how it works or the mechanics of these tiny particles.

5:46Now, Professor Ghosh, we may hear quantum mechanics or quantum science or quantum physics used interchangeably. Are they all essentially the same thing? um yeah so i agree that we're not very good in physics with sticking to one thing to uh you know describe a particular idea we kind of keep switching around but i'd say broadly it's fine to think about quantum physics quantum mechanics quantum science essentially is referring generally to the same thing which is this very very weird description of this fundamental behavior of particles and light and matter. And where does quantum technology fit into this, Professor Ghosh?

6:29Well, actually, quantum technology, in some sense, is actually more familiar than you might think to all of us, because quantum technology is essentially any application that we have today that we use that has come out of understanding and controlling the laws of quantum mechanics. So this theory, as you mentioned, is now about 100 years old. So over that time, as we understand more and more of the behavior of fundamental particles, we can actually control that and build new types of technologies. For example, we might think of quantum mechanics as being very, very far from our lives, but it's actually been a fundamental part of all of what we use today in terms of our devices.

7:17So everything that is based on electronics and integrated circuits and chips, the entire semiconductor industry was built because we understood what, for example, the properties of silicon are and how electrons in silicon behave. And from that, we were able to build out this entire interesting material to use for building all of our electronics. So every time you're using your TV or your computer or any kind of device today, you're actually using quantum technologies. Or if you're, for example, if you're at the hospital and you need some kind of imaging test done, MRIs, those are also based on quantum technologies.

8:03Anything based, all of our telecom laser-based technologies are actually possible because the laser came about because we understood the behavior of light and photons. better. So all of this is quantum technologies. And now we are just on the brink of what we call the second quantum revolution, which is about building out even better quantum technologies in terms of new kinds of computers, new ways of communication, and doing encryption and cryptography. So that's what's coming up with our second wave of quantum technologies. Professor Carlson, you focus on astronomy and quantum materials. What are quantum materials?

8:44Well, actually, I don't do astronomy myself. My department does physics and astronomy, but I do study quantum materials. And in fact, I study what electrons do inside of quantum materials. And as Professor Gosher already said, everything has quantum in it, right? Everything is made of these little quantum properties. But what do we mean specifically by a quantum material? That's where we're trying to bring the quantum properties that are typically locked away at the scale of an atom or smaller. And we want to bring those properties to the forefront where we can control them and use them. Examples include superconductors.

9:20As Professor Gauch already said, she mentioned MRI machines. Superconductors make those MRI machines go. They make our cell phone calls clear, that sort of thing. What's particularly interesting about quantum materials is that inside of these materials, it's like a whole new universe in the sense of we can get fundamentally new particles that you can't get outside of these materials, things like spin-ons and holons and magnetic monopoles and anions, and we could go on and on. It's a really fun field. We're going to head to a quick break here. We'll be back with more of our conversation on quantum mechanics in just a moment.

9:53Stay with us.

10:00Let's get back to the discussion with this question we got from Danny, who says, I'm having trouble wrapping my brain around how one programs a quantum computer to do a task. How do you send instructions to a qubit without knocking that qubit out of superposition? Professor Carlson, let's pick this question apart. First, superposition is a common quantum mechanics term. What does it mean? Superposition is a fancy word for add. So we mean we've added two states together. You probably hear superposition most often in terms of something being able to be in two places at once. very tiny objects, have a wave associated with them.

10:41We talk about particle wave duality, so particles are wavy and waves also have a particle nature to them. And that waving corresponds to where you're likely to find the particle. If it's waving a lot, you're likely to find the particle there. But a wave can do anything. You can make a wave wiggle here and wiggle over there, in which case the particle is technically in two places at once. And that's fundamentally what we're trying to do differently with a quantum computer. The computers you use right now have little bits that encode the information, and those little bits are ones and zeros. With a quantum bit, you can put the quantum bit in a superposition.

11:18We just add the two states together, a superposition of zero and one at the same time. And it's an excellent question how you can program such a strange device. And the answer is going to lie in exactly how you made your quantum bit. So right now, we don't have a standard, like, you know, if you're using a computer, your laptop, your phone, that's built on silicon. We don't have a standard material yet that all the quantum computers are built out of. People are using different types. People are still doing research on the best ones. And so exactly how you reach in and program that thing depends on exactly which system you decided it's used.

11:56Well, Professor Ghosh, you're a computer scientist. I want to turn Danny's question to you as well. Yeah, well, actually, I am a physicist by training, but I work a lot now with computer scientists and think about, you know, the physics of quantum mechanics as applied to computer science. So maybe one way to think about it is to go back and think of what happens in a regular classical computer when you're trying to program that on our sort of laptops. we don't really see what's going on inside the computer, of course. We just write our code and tell the computer what to do. But really, when we're writing code, we're basically sending instructions to tell the computer, which is calculating things all in terms of zeros and ones.

12:42These are just regular bits. They're not quantum bits or qubits. So any bit inside our quantum computer is basically described and represented using circuits where there are currents being switched on and off. So every time we write code, we're just instructing those switches to either be on or off. And that's like a zero or a one. So it's all kind of very simple. Everything is just a sequence of switches. Whereas in a quantum computer with a qubit, we can do more than just switch because as Professor Carlson described, the qubit can be in a superposition of zero and one. So in a way, it's kind of like thinking of a dial rather than a switch.

13:23Where instead of trying to just flip between zero and one, we can maybe build a dial for our qubit depending on what we use as our hardware to control this qubit and what the qubit actually is. It may be a superconducting device. It could be based on photons and particles of light that have properties like a polarization. These are all different properties. And we have to basically be clever to pick out a property where we can build a dial to control it in such a way that instead of switching it, we can actually dial it up into a whatever superposition or combination, if you like. So, but when you say build a dial, are you talking about, I mean, I know it comes to mind for me, it's a physical dial, like maybe what you'd see on your oven where you can put the temperature in one direction or another.

14:13Or are you talking about a type of code? Because Danny wants to better understand, as do I, how you send the instructions to the qubit without knocking it out of superposition. So what's the actual mechanism? So there are many levels to how a computer works. For example, when you write the code itself, again, to use our more familiar kind of computer, when you write code, you basically program using your favorite language. And that program, as I said, It is translated on the back end into a sequence of operations or gates, if you like. And those gates are just these flips that I was talking about.

14:55So in a quantum computer, similarly, up front, there's going to be some kind of coding language. And there are different companies that are now building out different kinds of front-end coding languages. So if you go on IBM's website, for example, you will see this interesting language they call QuizKit that they're building. that is about sending instructions to the quantum computer. And in that language, the code you can write will not just be based on telling those qubits to flip between zero and one, but in that QuizKit code, you will be able to pick out other types of gates that are these dials that I was talking about.

15:35And then when you write the code saying, okay, apply this gate and do this kind of superposition and then switch this other qubit and so on, all of that is translated on the back end into these physical dials that I was referring to. So I don't know if that helps to clarify how that all works. I hope it helps, Dani. We also got this question from Jeff who says, will quantum computers be able to mine or steal Bitcoin? Professor Ghosh, your thoughts? Well, in principle, there are algorithms that exist that can actually search through large amounts of data very fast. And because of the way that Bitcoin and the process of mining currencies happens, it's really about being able to find very specific, almost like needles in an information haystack.

16:25So if you can do that search faster, then you can mine faster. Now, in order to make that difficult or prevent hacking and so on, you want to hide that needle even better. So you can make larger haystacks. So at this point, it's not quite clear whether in future, if we build even larger data sets, can we find quantum algorithms that can still find the needle? That's kind of an open question. But there seems to be some indication that that could be possible. So there's no way to prove for sure right now that Bitcoin is safe. And that's kind of what people are doing a lot of research on to try to figure out what are the limits on quantum algorithms, What are the possibilities?

17:11And how do we keep data safe for future? So it's a big question. We got this message from Robin who writes, this conversation is making me think of Firesign Theater's second album, How Can You Be in Two Places at Once When You're Not Anywhere at All? And I'll note that as we were preparing for this show, several colleagues made jokes about being in two places at once. Professor Carlson, we touched on this, but what do particles being in two places at once have to do with quantum mechanics? Oh, a lot. But let me circle back real quick and mention another way to look at Danny's question of how do you send information to a qubit.

17:45Like I said, it depends which one. But if you have a qubit that's based on, say, the electron's spin, which you can think of it as spinning up or down, what we send in is we send in light of a particular frequency, and we take that particular frequency tuned to the energy that that electron's at, and we put it in for a particular amount of time, and by doing that, we can program it. That's one example. The rest will depend on other architectures, we call them. But this question about, yeah, two places at once, boy, we physicists would love to extend that to human beings, wouldn't we? I mean, I'm absolutely terrible at calendaring.

18:21I got fired from the family calendar with cause within like a few weeks of being married because I would make us need to be in three places at once and not realize it until an hour in advance. So we would love this. And the way it works, as I said before, is because each quantum particle has a wave associated with it. And where that wave wiggles corresponds to where the particle is. And you can make your wave wiggle over here and wiggle over there. So if, you know, if we were tiny, so if we could like shrink down like Ant-Man and get into like a quantum living room or something like that, we could also sit in two or three or four places at once.

18:56Or there's this other way to think about doing it. There's a parameter called, well, physicists call it h-bar, but it's Planck's constant. It's a constant of nature. And if you could crank that number up, which we cannot do. It's set by God. It's just determined. It's there. But if we could crank that number way up, then we humans could start to display these kind of properties. I mean, we have them. It's just that your personal wave function is so tiny. The extent to which you could make yourself in two places at once is much smaller than the distance between two atoms. So it just doesn't matter for your everyday life.

19:30But I wish it could. It would be really cool. We're talking to quantum physicists Erica Carlson and Shohini Ghosh. We got this email from Mike who says, I majored in physics in university. Back in the day when Newton and Kepler and the gang found math that explained the motion of the planets, a fundamental question remained. Why do the planets follow the rules? How do the planets and the sun know where each other are and which way to go? Scientists in the day accepted that the angels must know how the math works, and the angels steer the planets. So here's my question. Why do we accept modern theories requiring dark matter and dark energy?

20:04If you call them angels, it would be the same thing. Professor Carlson, your thoughts? Wow, I think that was like three or four questions at once. So that's an excellent question, Mike. I just, I love this question so much. So as far as dark matter and dark energy goes, I just have to confess right now, you've stumped the professor. I don't work on dark matter and dark energy. But this deep philosophical question you're asking about how do the planets know to follow the rules? How does a quantum particle know to follow the rules? The short answer to that is we don't know. We use the scientific method to figure out how the world works.

20:38And we will sometimes apply the language why to something. You know, why did it do that? But ultimately, the reason we give is because some other thing happens that we understand. So, for example, we might say that an electron and a proton, you know, they attract each other because of the Coulomb attraction. How did they know to do it? we don't know. What we do is we are empiricists, meaning we follow empirical things, right? So we figure out the way the world is, and we write down laws and models that correspond to it. We also got this question from Wendell, who says, articles pop up on my Google search indicating breakthrough unified theory between Einstein's theory of relativity and quantum physics, which previously seemed irreconcilable.

21:23Is there something to this or just more clickbait? Professor Ghosh? Well, if somebody did come up with a way to unify relativity and quantum physics, I think that would be an instant Nobel. And so that is one of the biggest and most interesting questions out there. There are many different approaches. I don't think we have a verified, conclusive answer as yet. But hey, if you have something, please do think about it. This is, as I said, one of the big, big questions. Very much worth spending your life on, I guess. Well, the idea of a multiverse often gets grouped into quantum mechanics. First, Teresa Carlson, what is the multiverse theory?

22:07Well, there are actually a few different levels of it. But the one that tends to come up in quantum mechanics is an idea that, yeah, there's this universe, but then there's, you know, the multiverse comes out of quantum mechanics from what's called the relative state wave function interpretation. That was too many words, and you don't really, you don't need to know what that is. But it's the idea that as these quantum events happen, to the best of our ability to model quantum mechanics, we use probabilities. This is standard quantum theory. We use probabilities. Will we ever get beyond probabilities, we don't know, but we use these probabilities.

22:44And one of the ideas for interpreting that, right, and this isn't just an interpretation, is the multiverse theory, where the idea is that when this dice roll happened, part of the universe went one way and part of the universe went the other way. So that's where the quantum comes into the multiverse. Now, as you might imagine, that is quite an extraordinary claim. Now, when I kind of poll my colleagues and say, do you buy this sort of interpretation of quantum mechanics. I find that a lot of people do and a lot of people don't. So I'm actually one of the skeptics. I'm kind of what we all are, right?

23:18All scientists are show me the money, show me the data people. And if you wanted to get hardcore evidence of that, you'd have to show me the other universe or the other branch of the universe. But by definition, you can't because it's separate. So you would have to, the best evidence you could come up with would be indirect. Now that's not a showstopper. We do this all the time in science. We come up with indirect evidence, but we're just not there yet on this multiverse theory to convince the entire community. Let's head to a quick break. We'll be back with more of our conversation in a moment.

23:48Stay with us.

23:54Let's get back to the conversation with this question we got from one of you. If quantum foam is quanta blinking in and out of existence, then how do objects have any permanence? Okay, so physicists believe the universe began with quantum foam that expanded. Professor Carlson, what's your response? Oh, this is a great question. So things blinking in and out of existence. You know, there are lots of fundamental issues here that we just haven't settled yet. So I'm going to tell you why I don't know the answer to your question. Okay, it's a great question. But the thing is that, you know, we're used to things that, used to, meaning we can currently measure things that right now are, in a sense, kind of blinking in and out of existence.

24:39And we call those virtual particles, okay? You might have like a positron-electron pair, for example, a matter-antimatter pair pop into existence and then pop back out. And what we find empirically, and there are good reasons for this to be the case from quantum theory, what we find empirically is that there's a little mass violation there, which corresponds to an energy violation. But it's a little bit, you can think of it as like borrowing from the quantum energy bank of the universe. You can have these things fluctuate in and out of existence as long as they stuff themselves back into nothing fast enough.