Daniel and Kelly’s Extraordinary Universe - Is Light a Particle or a Wave?

Episode Date: November 13, 2018

What is light made of? A particle, a wave, both, neither? Little puppies? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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can a dress be black and blue and white and gold in today's podcast we talk about the centuries old scientific debate about light is light a particle or a wave or is it both Hello. Hello, I'm Jorge. Welcome to Daniel and Jorge, Explain the universe.

In which we try to explain the whole universe and everything in it, including light. Now, I'm a cartoonist. I draw something called PhD comics. And I'm a particle physicist during the day I smash particles together at the large Hadron Collider. Yeah. Well, today on the program, we're going to talk about the nature of light. That's right. People have been arguing for centuries. What is light? Is it made out of particles? Is it made out of waves? It's something else? Is it tiny little puppies screaming through space? People have gone back and forth on the issue. And today, even, the topic is not yet totally settled. So we're going to be taking you through that history and breaking it down. It's one of the most mind-blowing questions in human scientific history.

That's right. What is light made out of? So as usual, before we dig into it, we went out and we asked people on the street. What do you think light is made out of? What do people know about light? Is light a particle or is it a wave? Here's what people had to say. Do you think light is made out of particles or waves or both or neither? Photons. Yeah, photons.

So you think light's a particle? Yeah. I think it's waves. Yeah. Cool. It's both, I think, because it, like, moves like a wave, but it also has properties of a particle, and there's nothing saying it can't be both. Okay.

Light. I think they're made of wave waves. Yeah. All right. Well, it's interesting because I think all of the answers are right. or none of them are right or both yeah well it seems like a lot of people

reflected the fact that there is a controversy like that you know it's not really well described either though some people went all in you know like it's a photon or it's a wave or it's a wave length right yeah that was my favorite one I want to be a wavelength like I've heard of this word

it sounds really cool and scientific I'm just going to throw it out there that's right yeah maybe I get some points we award no points people no points that's right there's no prize your prize is you get to be on our podcast and maybe we even make fun of you yeah yeah but yeah i guess what you mean is nobody sort of fell for the trap right like nobody said oh of course it's a particle or nobody said oh of course it's a wave most people sort of knew that there is some sort of duality there something weird going on

that's right that science is having some trouble some difficulty coming up with a way to describe what light is and that might seem surprising to you because light is everywhere, right? And it runs the universe. It's streaming through the solar system from the sun, illuminating our lives, and powering everything on Earth. So you think this would be sort of a high priority topic to figure out, like, what is this stuff? What is it made out of? Yeah, I mean, like, what are we paying you for, Daniel? If not to figure these kinds of questions out. I was just about to figure out what light was when you called and said it's time to do this podcast. So sorry, science will have to wait. I totally destroy your train of thought there.

That's right. Reflect on that for a minute. but no yeah I'm a California taxpayer and part of my salary goes to paying your salary like you know one millionth of a percent that's true yes you're you're saying you did pay taxes last year there you go again revealing secrets on air Daniel anyway so that's that's an interesting question like is light a waiver particle and it's weird that we don't know but maybe let's break it down a little bit what is it Like, what are we actually talking about when we say that light could be a particle or light could be a wave? Like, you know, most people probably think of light as just like brightness, right?

Yeah. The thing to understand here is that we try to describe light in terms of things we know. And that's what science is, right? You see something weird and new and you wonder, oh, is it like this other thing I know? So we've observed different kinds of phenomena in the world. Like you see waves, right? You go to the beach. You see waves in water.

a rock in a small puddle you see waves we know what waves are and we see different phenomena we try to categorize them in terms of things we know right so like when people were studying sound they discovered oh sound is actually a wave you know it's a compression wave in the air and that's cool because you says oh i already know how the math for waves works right i've seen waves in water i've seen waves and other stuff you can describe it with like equations right yeah wavy equations that's right very solid, unwavy physics to describe waves. And there's a lot of science that's gone into understanding waves. So if you can cram it into that box and say,

oh, this is just another example of something we already know, then you're taking a huge leap forward, right? So that's something people try to do is say, like, look, can we describe this in terms of other things we know? Meaning, like, you know, we know about light, but we want to know how it behaves and what makes it work. Yeah, and just on a more general level, you try to see something new,

you try to describe in terms of things you know. know, like, say you taste a new kind of fruit. You'd be like, oh, it's a little bit like a cherry and a little bit like an apple and a little bit like, you know, it's got a hint of smokiness to it or whatever. So you're like, it's a chapel. It's a chapel. How has nobody ever invented that, the cherry apple chapel? Oh, my gosh. If our lawyer is listening, get on that right away.

Copyright that idea. I'll reserve www.chapel.com. That's right. So that's the basic idea is we have these things we've seen. You see something new. You don't want to create a whole new category. You want to fit into one of the existing categories. So we sort of knew about light.

It came from the sun. You know, if you light a fire, it spreads out into a room. And so we were like, what's going on? Like what best describes how this light, you know, comes from a source and bounces off the walls and stuff? Exactly. Exactly. That's the question. And so we'd seen things like waves.

So what do we mean when we say a wave? Like, how could a light be a wave? Well, how can anything be a wave? Yeah. How can anything be a wave? A wave is a funny thing because it's not a thing itself. It's a property of some medium. It's like a ripple on something.

Yeah, that's right. Like if you do the wave at a baseball game, you know, there's nothing to the wave itself. It's just a bunch of people moving up and down and waving their hands, right? Or like a sound wave is just like air molecules kind of bumping forward. That's right. Yeah, exactly. Or a wave in the ocean is just an arrangement of the water, right?

It's a way the water gets compressed and then stretch. out and compressed and then get stretched out. So that's the important thing about a wave is that it moves in this way through a medium. Okay, so that's a wave. It's like a propagation. It's like a ripple through something. So then what would you call a particle? A particle is different than that.

A particle is different than that. And it's a totally different kind of thing, you know. And to be a particle physicist, it's kind of odd, but the concept of a particle is not that really well-defined, you know? But when I think of a particle, I think of taking matter and breaking it down to its smallest pieces like if something's made out of particles it means that at its smallest level it's made out of these little bits that can't be chopped into smaller bits and that they're localized they're like small and contained right if if you discover that something is made of particles you expect it to be

like mostly empty space but with these little dots of matter like you would take something and then you'd smash it to bits and just keep smashing and at some point you're going to get to these little like BB balls or like little tiny pellets that you can't break down anymore. That's right, yeah. It's like seeing a picture on your computer screen and discovering it's made out of pixels, right?

And those pixels are the basic elements and they come together to make the whole picture. So figuring out that something is made of particles means that it's made of these little bits that are not connected to each other, right? They're separated. So a wave and a particle

in nature are totally different kinds of things, right? Now, water, of course, is made of particles but can have waves in it. Right. But I think maybe what's important here is that particles, we tend to think of as little tiny bits that can bounce around, right? And, like, go in a straight line and then hit something else and then bounce back or, you know, kind of fly through space, right, in a discrete little package. Exactly. That's exactly the right way to say. It's a discrete little package.

Right. So things that are made of particles we think of as being discrete little bits. And they're broken up into these little pieces. And you're right, they move in straight lines, right? Like you throw a rock, you roll a smooth ball across the surface. You expect it to move in a straight line. So that's kind of what we mean by a wave and a particle. That's right, yeah.

And so the question is, is it like, is light a ripple on a medium? Is that what light is? Or is it like actual little things and move around in space? Right. Does it have its own stuff to it, right? Or is it just a way something else moves? Right. That's sort of another way to phrase the question. Right. And those are two pretty different pictures of reality, right?

Yeah. Light could be little pellets flying around or it could be some sort of ripple on a medium. To us, in our intuitive sense, it couldn't be any more different, right? That's right. Yeah. It's like you can't be a Democrat and a Republican, you know, just you have to pick one, you know? Yeah. If you vote. You can be. Or you could be neither, I suppose. You shouldn't be both, though. Yeah. That would be a violation of some. some election law, not recommended to violate election.

That's right, that's right. Yeah, so speaking of political shouting matches, this one, this historical scientific shouting match began all the way back with the Greeks, right? Democritus, he's the guy, sort of the first atomist. He's the first person to look at the world and to say, you know, maybe everything's made out of tiny little bits, not just light, but also matter. And that was sort of the birth of that idea, that maybe everything around us that seems macroscopic is made out of tiny little

things smaller than we can see and as usual when somebody comes up with a good idea they overextend it they're like well maybe if rocks are made out of stuff then water is also made out of particles and maybe even light is made out of particles you know it at the time seemed like a totally

crazy reach and that makes sense right because light seems to go in a straight line it seems to bounce off of things so why couldn't light just be like little tiny little pellets that bounce around the room and then eventually hit your eye and then that's how you see something. Yeah, it certainly seems to have

some of those particle-like properties, right? It moves in straight lines. It certainly would be going really, really fast. At the time, people thought that light traveled instantly, right? They thought that light instantaneously went from like the sun to the earth or if you started a fire that the light would

immediately illuminate the room. Now, we of course know that it just happens super-duber crazy fast, too fast for those folks to ever measure, so it's almost like it's instantaneous. But they thought that these things just moved instantly through space and filled up the room. Okay. And I want to talk a little bit more about that, but first, a quick break.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. now he's insisting we get to know each other, but I just want her gone.

Now hold up, isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. It's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him?

Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

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Listen to America's Crime Lab on the IHeart Radio app Apple Podcasts or wherever you get your podcasts. Right. And I think we have to qualify that because it makes the Greeks sound really smart to come up with this idea of atoms and all that stuff. I've seen you say this before. You're really down on the Greeks. Well, I think people give the Greeks too much credit for that because, as I've probably said to you before, the Greeks had lots and lots of ideas.

They had like thousands of these ideas about how the way the world works. And, yeah, one of them was close to true. But, like, if we're going to do some accounting, let's also remember the 999 ones that were totally off base, you know, and give them credit for those. Yeah. Find that Greek who thought life was just little puppies and be like, see, you guys also thought they were puppies. You can't be that smart. That's right. But he's a cool idea. So give him credit for having that idea. I don't know what they were smoking when they came up with it, but I'd like to figure out where to find some. And then it was thousands of years later before people had another idea. It was Descartes, the guy who's famous for, you know, I think therefore I am, he thought about, he was one of the early scientists, not just a philosopher, but a scientist back in the day when, you know, science really was part of philosophy. And he thought that light was waves. What made him think it was waves?

You know, I don't think he had much justification for it. This is back in the early days when science wasn't really an empirical study where you didn't like go out and do experiments to test your hypothesis. It just made more sense to him for light to be like these wave-like disturbances. Right. Which kind of makes sense, right? Like if you have a speaker in a room emitting sound waves, it's not that different from like a light bulb in the middle of the room

emitting light all around it, right? Yeah. And there's some things that light does that don't really seem consistent with particles. You know, like the way light bends through a lens, right? It's called, in science, we call that refraction. You know, with light changes from going through air to glass, it bends in this weird way. And that's something that's very common for waves, right? But a particle wouldn't bend inside of a lens.

No, a particle that's definitely a wave-like behavior. Yeah. Oh, interesting. like behavior. And so Descartes saw that and he's like, oh, you know, we have optics, we have these lenses, so maybe light is a wave. But if light is a wave, then it opens this other question, what's doing the waving, right? I mean, with sound, you know, it's the air and in water waves. Obviously, it's the water. But if light is a wave, then what is waving? Meaning like if light is a ripple, what is it a ripple of?

That's right. Yeah, what's doing the rippling? Right. If it's a wave, it has to be a wave in something because a wave is just a description of some other form of matter rippling, right? It couldn't just be like stuff that we can't see. Yeah, and so you have to invent some stuff that we can't see, right?

So to explain light being a wave, you have to invent this universe filled with stuff, or there has to be that stuff between us and the sun, for example, right, which is a huge amount of this new stuff you're inventing. And if you're looking at the stars, there has to be that stuff between you and the stars, right? So now we're talking about billions of miles of this new stuff,

And Descartes didn't know, so he just gave it a name. He's called, I don't even know how to pronounce it, but he called it Plenum. And he thought, well, there must be, if light is a wave, there must be some stuff that's doing the waving, and we'll just give it a name. And maybe we'll be right, and then we'll be famous forever. Isn't it, is that different than the ether? It's similar in concept, right? It's a different idea, but it's similar in concept that, like, if light is a wave, it must be waving through something. And we don't know what it is.

We just invent something and give it a name as a placeholder. So when later people do the hard work of actually discovering it, we'll still get credit. Okay. So it was a particle, light was a particle, then it was a wave, and then what happened? Well, then Newton came along, right? And Newton's a really smart guy, and everybody knows that he's famous for thinking about gravity. But he also liked to think about optics and lenses. And he thought for sure that light was a particle, because he saw it moving in straight lines,

and he saw distinct shadows. But, you know, Newton also did a lot of experiments with optics. He studied prisms and he saw light bending and he saw light splitting into colors. And you can't explain that if light is a particle. But he tried. He's like, well, maybe when a particle hits the glass, it gets some sort of weird sideways force and that makes it bend. But that's not really an explanation. That's just sort of like a, I don't really understand it, but maybe it's something like this.

Like if light is a particle, why does it split into the rainbow kind of thing? Yeah, exactly. And, you know, this is, again, back on the day when empirical studies of science weren't the main way to answer questions. It was mostly thinking in your head about things that made sense to you. And then they would argue about them, right? A lot of the way scientific disputes used to be resolved was people would argue about it and then say, well, that makes no sense so it can't be true. And we know now, of course, that the universe doesn't always make sense to us.

What's real isn't necessarily the things that we would have accepted as true or accepted as a reasonable way to describe the universe. universe. But, you know, if that's the way nature works, that's the way nature works. You have to accept it. But this sort of primacy of experimental results came later on. So back on the day, people just sort of used to argue for an explanation that made sense to them. Right. Well, it was kind of hard for them to build a particle collider, right? That's right. Yeah, exactly. They didn't have the massive government funding to do that. These were men of leisure studying science in their spare time. In fact, it was called like natural philosophy, right? It wasn't called science.

At the time, was it? Yeah, that's right. Exactly. All of science grew out of philosophy. It was called these folks were natural philosophers. Okay. But, you know, later on, then people started doing experiments, and there were a bunch of French guys who did a bunch of experiments and some English folks.

And they were studying how light behaved and refraction and reflection. And they saw it doing these things, and they thought there's no way Newton's right. This has to be a wave. You know, they saw things like interference patterns. interference patterns is when you have two waves and sometimes one is rippling up at the same time another one is rippling down right so imagine for example you have a bathtub of water in front of you

and you slap it with two hands at once right each one is going to send waves out and then when those waves are either rippling up or rippling down and when they reach each other if they're both rippling up at the same time then they constructively interfere to get a double wave if they're both rippling down at the same time, they constructively interfere to get a double down wave. If one is rippling up and the other's rippling down, then they cancel each other out, right? And so you would see no light? Yeah, exactly.

And so you can do this kind of stuff in your bathtub. You can see interference patterns. And what happens if you have two sources like that, like one from each of your hands, is you get some areas where the waves are high and some areas where the waves are low and some areas where there are no waves. And so, as you say, if you do it with light, then you see these patterns of darken light, these stripes. And you couldn't do that with particles, right? Like a particle wouldn't cancel another particle. Yeah, there's no way to explain that with particles.

People thought, well, look, this is something that waves do, and light is doing it, and there's no way to explain it with particles. So light must be a wave. Right. In fact, there's even famous cases where they said, well, you know, if light is a wave, then, you know, if you set up this various experiment, you would get this crazy effect. And so that's absurd, and so it definitely can't be true. And then they went and did the experiment and saw the crazy wave effect. And they were like, oh, it turns out it is true, you know? Wow.

I love that because it's the primacy of experimentalism, right? Like, go and check the data. Go and actually get some data and see what the universe tells you. Yeah, like you're like, a donut can't possibly be a croissant at the same time. But it turns out that you can bake something called a cronut. Yeah, exactly. I think that's a big debate. in pastry science still though.

Is it a donut that's like a croissant or is it a croissant that's like a donut? Yeah, I'm getting my degree and I'm particle baking. Yeah, the large pastry collider. I'm looking forward to the construction of that project. But that's kind of what you mean. It's like people don't think it's possible until they actually see it. And waves and light has been doing this to people for hundreds of years. They're like, they can't possibly be doing this or it can't possibly be

doing that but it just keeps doing all these weird things yeah exactly and and that was the experiment it was called the double slit experiment the one that really convinced people that light is a wave because they shown a strong light and they had just two little narrow slits which act like as sources like slapping your hands in the bathtub water and then on a screen behind it they saw these interference patterns right is that you could definitely only get if light was a wave and so that was the early 1800s and everybody was absolutely certain light was totally a wave the question was settled we knew forever light was a wave and we still didn't know what was it waving through but how did they explain all those particle experiments well this is before we even really knew about particles right oh no real

particles had been discovered at this point with this idea from the greeks of thousands of years ago that maybe things were made out of particles and chemistry was getting warmed up and you know people We were starting to think about atoms and molecules and stuff, but they hadn't really seen any actual particles yet. It was decades later when the electron was discovered that people started to think about the particle model again. But, you know, the wave theory was definitely ascendant, right? Everybody definitely looked at these double-slit experiments

and saw light doing all this wavy stuff, and they were sure that light was a wave. Now, did people extend that to other things? Like, you know, they thought, oh, light is this weird, wavy thing, but surely us were made out of little tiny atoms. Yeah, that's a good question. I wonder if people thought, hmm, light's a wave. Maybe we're a wave, too, right?

Yeah, or like everything's just like a wave. Yeah, probably not because nobody thought that light had any mass to it, right? Whereas we definitely know that we have mass, right? We feel pretty heavy sometimes after a big meal. Even before the discovery particles, though, there was a huge advance in the theory of light, which was a Scottish guy named Maxwell. He was working on electricity and magnesium. And he put together all these equations to describe electricity and magnetism.

And he just sort of wrote them down in a new way. This is like the way you could do theoretical physics back in the days. You just take existing ideas and you find a new way to write them down. But he wrote them down in this way that looked like the mathematics of a wave. We have this equation. It's called a wave equation. And it describes how waves move through a medium. Meaning like it could be described by equations that look like sine waves and cosine waves, right?

I mean, just in case anyone remembers high school math, that's kind of what we mean by mathematical equations. It's like you can describe it as a sine wave or a cosine wave, right? That's right, yeah. The solution to these equations are sine waves and cosine waves. These are differential equations to describe how things move through the medium. And if things follow these equations, then they're waves, right? And so he looked at the equations for electricity and for magnetism, and he rewrote them, and he realized you can rewrite them in a way that looks just.

just like the wave equation, right? So he said, oh, electricity and magnetism has the same equation as waves moving through water or waves moving through air. Wow. And in fact, if you write it in terms of this wave equation, you can pull out what the speed of those waves must be. And the speed that he pulled out from these equations

was the speed of light. So he had this moment of epiphany. He must have been like in his office late one night, rearranged these equations and realized, oh my gosh, light is a wave and it's a wave of electromagnetism. So like a light bulb turned on on top of his head, emitting waves.

Exactly, the first appropriate light bulb ever, yeah. So then that seems pretty definitive. The double slit experiment shows that light interferes with itself. And also, this guy figured out that it's mathematically describable by sine waves and cosine ways, right? Right, right, that light is waves of electromagnetism. Yeah, exactly.

So then it all seems really nice and tidy, but then the particle revolution comes, right? People discover the electron, people discover the neutron, people discovering all these particles. But then they were doing experiments where they were shining light onto materials and trying to get it to kick off electrons. So you shine a really bright light at something and you hope that some of the electrons in the material absorb that light and get enough energy to be free, right? to run away. Right. And so this is called the photoelectric effect. You shine light at something

and you measure the electrons that come off. So what they saw in this experiment only made sense if the energy of the light comes in little packets rather than a continuous stream like waves. So they turned up the intensity of the light and they made it brighter, but that didn't increase the energy

of the electrons that were coming off, which doesn't make sense if it's a wave. It only makes sense if photons come in little packets so that increasing the intensity of the light means more photons, but it doesn't give more energy to any one electron. Because each electron can only absorb

one photon. Nobody understood this at all. This made no sense to anybody. It was a huge puzzle. We totally believe that it acted like a wave. We had the double-slit experiment told us it was a wave. Maxwell's equations told us it was a wave. But then we had the photoelectric effect, which didn't

quite make sense to anybody. And then Einstein said, well, what if light comes in these little packets like you were saying before what if light is not this continuous stream of energy like a wave is right a wave is a continuous stream of energy what if it comes in these little bits and and that explained everything if you if you thought that light was came in these little packets it explained the photoelectric effect explained these all these other mysteries in physics and that was the birth of quantum mechanics did he think that maybe it was little packets

of waves do you know what I mean like little short bursts of ripples you know do you know what I mean Could that explain how it's both things that run through his brain? Yes, absolutely. I think that's probably the first way he thought about it. It's like a little localized ripple, right? Like a little, yeah, that's the best way to put it, a little localized ripple. Like the way you can send a little ripple of water through a swimming pool or something.

Or like a chirp or like a little soundburst. Yeah, exactly, like a little chirp. But it's strange because you know, you can make a chirp of any size. You can make a big one, a little one, a long one, a fat one. But light, for some reason, wanted to come only in these little distinct chirps of a specific size. And the size of those chirps was controlled by their color or their frequency. And so that was the birth of quantum mechanics, which we could spend a whole other podcast talking about. But it was the first clue that maybe light did come in these distinct little packages.

Yeah, let's talk about that. But first, let's take a quick break. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK Storytime podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. December 29th, 1975, LaGuardia Airport. The Holiday Rush. Parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass.

The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Hey, Suss, what if I could promise you you never had to listen to a condescending finance bro. Tell you how to manage your money again. Welcome to Brown Ambition. This is the hard part when you pay down those credit cards. If you haven't gotten to the bottom of why you were racking up credit or turning to credit cards, you may just recreate the same problem a year from now. When you do feel like you are bleeding from these high interest rates, I would start shopping for a debt consolidation loan, starting with your local credit union, shopping around online, looking for some online lenders because they tend to have fewer fees and be more affordable. Listen, I am not here. to judge. It is so expensive in these streets. I 100% can see how in just a few months you can have this much credit card debt when it weighs on you. It's really easy to just like stick your head in the sand. It's nice and dark in the sand. Even if it's scary, it's not going to go away just because you're avoiding it. And in fact, it may get even worse. For more judgment-free money advice, listen to Brown Ambition on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. And that's what we talked about.

Like, what is a particle? It's a distinct little package. And then here's the part that blew my mind is that then they went back and they did that double-slid experiment again, but they slowed it down. Instead of shining a really big beam of light, they just shown one photon at a time, right? Okay.

Because they wanted to see what's going to happen. If light comes in these little packets, how does that explain the interference effect? How can light interfere if it's a particle? So instead of pointing the hose of water at these two little holes and just seeing what happens on the other side, they were throwing one droplet of water at a time. Yes, exactly. And what they expected to see was that there would be no interference pattern, right? Because the interference comes from having two sources.

You have interference when you have two waves that are either adding up or canceling out. Meaning a huge stream of light is going through these two little slits, then the two little slits. then the two little slits act like little sources, like little sorts of ripples, which can cancel out. Exactly. But if you throw one drop at time, it's either going to go in one slit or it's going to go on the other slit, right? That's right, yeah.

And so there should be nothing to interfere, right? So that's what they expected, but what they saw blew their minds, right? What happens if you slow the experiment down, you send one photon at a time, is that you still get an interference pattern. It's just that it builds up piece by piece. So you throw one photon through,

and it lands someplace on the screen. There are another photon through. It lands somewhere else on the screen. After you add up a million photons, you rebuild the original interference pattern you saw. So they thought, what? Light is a particle, but it's acting like a wave, right? How can that even be, right?

It's not just that. It's a particle that's acting like a wave as if it was in a huge stream of other particles, right? That's right. And this blew everybody's mind. And the answer, of course, is that light is a particle, but like every kind of matter, like every particle, how it moves is governed by mathematics of wave equations.

So every particle carries with it some quantum mechanical wave that determines where it goes. So what was happening in that experiment was that a particle, a photon, was approaching the experiment, and then it could either go through the left-hand side or the right-hand side slit, And because it's quantum mechanical, it did both. It had a chance to do both.

And what was interfering was the probability to go through the left slit or the right slit. So that's interesting. I don't think I've heard that explanation before, that it's a particle and a wave in the sense that it is a particle, but it moves according to wave equations. Yes. Everything moves according to wave equations. It's just that the wavelength for things depends on how much energy they have. So that was this guy, DeBrogly. He came up with this equation,

and maybe you've heard the expression DeBrogly wavelength. I've heard the expression, wavelength. That seems to be a... Everything is wavelength, man. We were making fun of that guy. Turns out he was right.

Oh, twist ending. No, everything has a wavelength. You can describe the motion of anything in terms of a wave. Now, the wavelength depends on the mass, and the momentum, and for most things like me or you, you or a cantalope, the wavelength of its quantum mechanical wave function is tiny,

and so you can't even notice, right? The wave effects of you and your sun walking down the hallway and interfering with each other are basically negligible. But on the scale of particles, these wave functions interfere with each other. Yeah. That's a crazy thought that, you know, I think people think quantum is something that doesn't affect their lives, but quantum ideas and concepts. are everywhere, right?

Like you have sort of like a quantum superposition or you you're not really there. You sort of, there's a cloud of you that is here. I'm not really here. I'm just an AI on the internet, but that's a different Yeah, there is this quantum mechanical uncertainty and everything, yes.

Yeah, yeah. It's just you can't notice. That really blew people's minds, this concept that like, okay, light is a particle but it sort of acts like a wave. We can use these wave equations to describe it. And, you know, there's another layer to that experiment, which is even crazier, right,

which is if what's interfering is the probability to go through the left slit or the right slit, right? When the photon approaches the experiment, it can go through one or the other. The interference pattern comes from the uncertainty of which it's going to go through. So what you can do is you can add a little detector

to one slit that, like, gives you a ping if it goes through that slit, right? So you know for sure if it goes through one slit or the other. If you do that, the interference pattern disappears. Whoa. Why does it disappear? It disappears because the interference only came from the interference of the possibility of the particle to go through the left slit or the right slit. Our lack of knowledge.

Once you know it goes through the right slit or left slit, there's no more uncertainty. There's nothing to interfere. It just goes through the left or it goes through the right. It's like you're throwing boxes full of cats that are either dead or alive. and you see what happens on the other side. It's different if you take a peek inside the box before it gets there. Exactly, exactly. And no cats were harmed in the making of this podcast.

I now feel an urge to point out. That's sort of where we are today, is that we know that light is a particle and then it comes in these little discrete packets, we call photons, right? But we also know that like everything else, light is determined by how its wave function moves. Every particle and every object has this wave function

and how it moves is controlled by wave equations. It's not like it's both a particle and a wave and people don't really know which one it is or people are still confused about that. But it sort of sounds like you're not that confused about it, right? It sort of sounds like you know it's a particle, but it moves around like a wave. Yeah, but it's still confusing.

I mean, I think it's totally reasonable to say it's both. It's a particle, but it acts like a wave, right? It's also totally reasonable to say it's neither. It's not a particle. It's not a wave. It's something else. It's something weird. Something totally strange we've never seen before.

It's a wordical. Or a pave. You are on fire. I am on fire with these simple spelling mashups here. That's a joke, but it's also serious because sometimes we discover things which are unlike anything else we've seen. And how do you describe them? Meaning we should stop using these words.

We should maybe come up with a new word to describe what it is, because it's not described by either word, particle. That's right. It's a chapel. It's a cherry apple combination. Yeah. Let's not call it a particle or wave. Let's just make up a new word that embodies these two ways to behave.

That's right. But here we've discovered something which is different from anything in our macroscopic world. There's nothing in our world. particles, waves, little puppies, that is a good analogy for what light is. So we have to try to sort of describe it in terms of sometimes it's like this, sometimes like this. My personal belief is that it's not like anything else and that these are approximations. But you know, like we were talking about earlier, you can be different contradictory things.

Like, how would you describe yourself? You know, sometimes you're a husband, sometimes you're a father, sometimes you're a cartoonist, sometimes you're just asleep, you know, like all these things describe you. They're contradictory. there are different facets of who you are. At your core, none of them define you, right? Right. But if you don't happen to have the right label, you make up a new label.

That's right. Yes, we need a new thing. Light is definitely its own weird kind of thing. Cool. All right. Well, until next time. If you still have a question after listening to all these explanations, Please drop us a line we'd love to hear from you.

You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge. That's one word. Or email us at Feedback at Danielandhorpe.com. Ah, come on. Why is this taking so long? This thing is ancient. Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon, ultra-light, ultra-powerful, and built for serious productivity with Intel core ultra-processors,

blazing speed, and AI-powered performance. It keeps up with your business, not the other way around. Whoa, this thing moves. Stop hitting snooze on new tech. Win the tech search at Lenovo.com. Lenovo, Lenovo. Unlock AI experiences with the ThinkPad X1 Carbon, powered by Intel Core Ultra processors so you can work, create, and boost productivity all on one device.

December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System. on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious.

Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Oh, hold up. Isn't that against school? policy that seems inappropriate maybe find out how it ends by listening to the okay storytime podcast and the iHeart radio app apple podcast or wherever you get your podcasts this is an iHeart

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