Daniel and Kelly’s Extraordinary Universe - How do we know the photon is real?

Episode Date: October 17, 2019

What is a photon and how do we know it exists? Particle Physicist Professor Daniel Whiteson explains the photon. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very wonderfully experiential sporting event. To hear this and more, listen to Good Game with Sarah Spain, an IHeart women's sports production in partnership with Deep Blue Sports and Entertainment on the IHeart Radio

app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network. Do you know who won a Nobel Prize for Relativity? That might feel like a trick question because you want to say Einstein because you think relativity. And Einstein, well, I'll tell you, it's not Einstein. Now, maybe you're scrambling through your mind to think about the names of other physicists you might know. How many physicists can you name anyway? You got Einstein.

You got me. Well, I give you a clue. It's neither Einstein nor me. So, who was it, right? Well, some folks won it for proving that relativity was correct. There were Nobel Prizes for gravitational waves and for binary pulsars. but the answer is that nobody wanted for relativity. Nobody who came up with this incredible, earth-shattering idea

that now frames all of modern physics won the Nobel Prize for it. But you might be thinking, hold on, didn't Einstein win a Nobel Prize? And he did. But he won it essentially for quantum mechanics. Hello, everyone. I'm Daniel. I'm a particle physicist, and I'm the co-host of this podcast, together with Jorge Cham, who can't be here this week. So you're just listening to me talking about the joys of physics and trying to simulate Jorge in my mind. Every time I'm talking, I'm thinking, here's what Jorge would say at this moment. I'm trying to interject a little Jorgeism for you, since we've all miss him. And you were listening to our podcast, Daniel and Jorge Explain the Universe, a production of IHeart Radio, in which we zoom all around the universe and try to find interesting, fascinating, cool little nuggets of physics that would blow your mind, but take them apart so they don't

actually explode your head and cause your brains to splatter anywhere. Instead, we want to smoothly and calmly insert them into your mind so you understand them, so you can talk to your friends about them so you can actually comprehend these amazing, wonderful facts that we have learned about the universe. And also, understand all the things we don't know about the universe, which is my favorite part of physics. And that's why Jorge and I wrote the book, We Have No Idea, a guide to the unknown universe, which takes you on an amazing tour of all the big and basic questions about the universe that we still have no idea what the answers are. And on the podcast, we've been doing something fun, which is taking a little tour of how,

we know what we know, and specifically how we know anything about particle physics. It's still incredible to me when I look around at the world that everything is made out of these tiny microscopic objects that we can't see that we've taken thousands of years to even discover that they exist. Yet we have this really complex, really elaborate, really amazingly effective model of what's happening down there at the microscopic scale. these tiny quantum particles interacting and zooming around. Physicists can do calculations to tell you exactly what's going to happen when this particle hits that particle. It's really incredibly

complex and mature, though, of course, we have lots of questions. But I think a lot of times people think of this as sort of like an idea, something people came up with, a description of the universe. But it's critical that everybody understand that this isn't just an idea that came out of our heads. This is something born out of desperation. This is our attempt to grapple with the weird and bizarre and counterintuitive and frankly mind-blowing experiments that have shattered our perceptions of reality. We thought the universe worked a certain way. We thought everything was smooth, that you could cut objects as many times as you wanted to infinitely small pieces, but you can't. We thought the universe was deterministic, that if you did the same experiment twice, you would get the same outcome, right?

That would make sense. but it's not. It's fundamentally random. And the core of that is particle physics because it attempts to describe the entire universe in terms of these tiny, weird, non-deterministic little particles in terms of these tiny little weird, non-deterministic particles that seem to follow rules that just do not describe the world that we are familiar with. So my goal is to take you on a tour of those experiments, the ones that change the way we think about the universe that showed us that the universe is different from what we imagined, because it's not just the final idea that I want you to understand. I want you to know what the evidence is. How do we know what we know? Now, recently

we talked about the discovery of the first particle, the first experiment that revealed this incredible revelation that the universe is made out of tiny little dots. And so today we are continuing that tour. We are talking about... How do we know the photon is a thing? You're familiar with photons to you. Photon is a very normal word. You hear it bandied about. You hear it talked about.

But how do we know that photons are there? How do we know that light is made out of photons that is chopped up into these little pieces that can't be cut down even further? What is the actual experiment that proves to us that photons are a thing? That light is not just electromagnetic waves, but it does these other weird things that you have to give it particle status. to explain. So as usual, I was wondering how many people out there know why we think the photon is a thing, why we don't just think about light as electromagnetic waves. So I walked around the campus of UC Irvine and accosted a bunch of friendly and unsuspecting students, and I asked them, do you know how the photon was discovered? Do you have an idea of why we think the photon is a thing?

So before you listen to these answers, think to yourself, or pause the podcast, or just take a moment. How do you know photons are a thing? Are you just believing physicists when they tell you, or do you know what the data says? I'm not entirely sure. I just don't know. I feel I should know, but I don't. Sorry.

I probably should know, but... It was the slit experiments, wasn't it? And they projected a laser beam onto a single slit or double slits, and it diffracted the beam, and that's how they discovered it. Particle wave duality. Photoelectric? Yeah, the photoelectric. You shone a light on a metal, and then the metal you cross, and you start conducting it.

That's a no doubt prize for Einstein. I don't remember the year. Yeah, I don't remember who did it, but I remember that you shine a light on a metal. Okay. You give the electron enough energy to start conducting. It's... How does that prove that photons or particles? Well, we know it's a wave because it travels through vacuum,

and we know that it's a particle because you can transfer energy from it, right? Yeah, it hasn't defined. Hasn't defined momentum, even though it has no mass. Well, the slit experiment, double-slit one, showed that it was a wave. Like a single slit shows it's a particle? Well, it's not necessarily a particle. It's both a particle and a wave. And for a really long time, we thought it was just a wave.

But I believe the first time we figured out that it was a particle had to do exciting metals to release photons and realize that the distributions were discreet. So I was really impressed with these answers. A lot of understanding here that photons are particles and that they're part of this larger idea of light being a wave and a particle. Even some discussion of the double slit experiment, which I'm dying to get into in a future podcast and talk all about the amazing facts of quantum mechanics. But the double slit experiment actually shows you that the photon is a wave. But there was somebody out there who talked about the photoelectric effect,

and that's the key. That was the experiment that showed us that photons were a thing. But before we talk about the crazy experiment to prove that quantum mechanics is our reality that showed us that the universe is probably sliced up into little bits and not infinitely smooth, let's set the stage. Okay, let's remember how people. thought about light. And to get the context of the story, you have to rewind all the way back to Isaac Newton. Isaac Newton, of course, very famous, not just for the cookies, but also for his

discovery of his theory of gravity, which unified motion of objects here on Earth with motion of objects in the heavens. It really gave us access to the whole universe to imagine, wow, maybe physics can actually describe things not just here in front of us, but out there in the universe. Those are things out there that follow laws of physics. Incredible accomplishment. But Newton also made amazing discoveries in the field of optics. He spent a lot of time with lenses and with prisms, and he was convinced that light was a particle. And he thought a lot about how light traveled, saw it moving in straight lines, except when it was bent by these lenses. And he was convinced that light was a particle.

And because he was a genius and he's a staggering influence on the field of physics, people listen to him, and rightly so. And for hundreds of years, people were convinced that it was a particle. even though other folks had really nice theories of light as a wave. And it wasn't until the 1800s when people started observing, light doing things that particles couldn't do, that they had to adapt their mindset. And that's the key. There you see experiment rearing its uncomfortable head again saying,

oh, no, no, you thought you understood the universe. You have an idea in your mind. You have a mental model of how this is working, but it can't describe what's actually happening. And that's why I'm an experimentalist. That's why I think experiment is the place to be, because experimentalists are the ones who make the discoveries. They are on the forefront of knowledge.

They're out there, exploring the universe, discovering things that don't make sense. The theorists, of course, do an incredible job. They tie it all together. They understand. They predict future phenomena. But for me, the bit about physics that's wonderful is the experimental side, is making those discoveries, is asking nature a question and demanding an answer, pinning nature in a corner so that nature has to tell you, oh, is the universe this way or that way? And so the thing

that told people that photons couldn't just be a particle were wave-like effects, things like interference. And you're familiar with interference. Maybe you have noise-canceling headphones. Noise-canceling headphones work via interference. Sound is a wave. It's a shaking of air, and the air comes towards your head. And if you can create waves that shake in the other direction And at the same time, they basically cancel out those waves that are coming in your head. So sound canceling headphones are proof that sound is a wave because they can do this wave-like thing that particles just cannot do. In the same way, people saw light behaving in a way that could only be described by a wave. And so you had interference effects and you had all sorts of theories, sort of built momentum until you get to James Clerk Maxwell.

His incredible genius pulled together lots of ideas about electricity and magnetism into his unified theory. of electromagnetism that described light as oscillations of electromagnetic fields. And when he pulled all these equations together, he saw the equations fit together in a way to describe the oscillations of electromagnetic fields moving at a certain speed, a speed he could calculate. And that speed came out to be, boom, exactly the speed of light. What a moment of epiphany that must have been for him. He pulls together all this knowledge.

He gets new insight. He looks at the world in a new way. And then it pops out this obvious, amazing prediction. that light moves at this speed of light, this number that we had already known. So what amazing confirmation for him. So that was dominant and people thought, okay, well, light's definitely a wave, right? Does all these wave-like things. We have this beautiful theory.

It's got to be a wave. Okay. So if light is a wave, right, we think about it in terms of electromagnetic radiation. It's just the waving of the field. Just the same way sound is waving of the air. Different kinds of waves, but that doesn't really matter. And the key thing to understand, if light is just electromagnetic radiation, it's just oscillations of electromagnetic fields, that means they could have any value.

You can just turn up the intensity of the light. To make the light brighter, what happens when you make light brighter in the wave theory is you just increase how much the waves are shaking? They're just shaking more, so they have more energy. So that's sort of the classical theory of electromagnetic radiation of light as just these wiggling of the waves that can have any value. value at all. You can turn it up. You can turn it down. Just the same way you can make music louder or softer. And you can have essentially any value to that volume. So that was the sort of prevailing thinking at the time before the photon was discovered. But then, of course, an experiment came along that couldn't be explained. An experiment came along that just had answers that did not make sense in the wave theory of the universe. So we'll dig into what that experiment was and how it worked. But first, let's take a quick break. I'm Dr. Joy Harden Bradford, and in session 421 of therapy for black girls, I sit down with Dr. Afea and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal.

Because I think hair is a complex language system, right, in terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyper fixation. and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. You talk about the important role hairstylists play in our community,

the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

Get fired up, y'all. Season 2 of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show, and we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino.

Take a listen. What do you miss the most about being a pro athletes? athlete. The final. The final. And the locker room. I really, really, like, you just, you can't replicate, you can't get back, showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar AZ Fudd. I mean, seriously, y'all, the guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Presented by Capital One, founding partner of IHeart Women's Sports. The OGs of Uncensored Motherhood are back and bader than ever. I'm Erica. And I'm Mila. And we're the host of the Good Mom's Bad Choices podcast, brought to you by the Black Effect Podcast Network every Wednesday. Historically, men talk too much. And women have quietly listened. And all that stops here. If you like witty women, then this is your job. tribes with guests like Corinne Steffens. I'd never seen so many women protect predatory men. And then me too happened. And then everybody else wanted to get pissed off

because the white said it was okay. Problem. My oldest daughter, her first day in ninth grade, and I called to ask how I was going. She was like, oh dad, all they were doing was talking about your thing in class. I ruined my baby's first day of high school. And slumflower. What turns me on is when a man sends me money.

Like, I feel the moisture between my legs when the man sends me money. I'm like, oh my God, it's go time. Hi, you actually sent it? Listen to the Good Mom's Bad Choices podcast. Every Wednesday on the Black Effect Podcast Network. The IHeart Radio app, Apple Podcasts, or wherever you go to find your podcast. So we're back and we're talking about why we think the photon is a thing. What experiment back there in history convinced people that photons had to be a particle?

And remember that in the context of this experiment, light was thought to be a wave. It was thought to be electromagnetic radiation. Just this oscillation of the fields. Somebody essentially shouting in the electromagnetic spectrum. And then came along this crazy experiment. The name of the experiment is not critical, but what it's studied was something called the photoelectric effect. Essentially, what you're doing here is you're shining a really powerful beam of light

at some surface. And the surface, of course, we know now is made out of atoms. And what they observed is that if you shone light at a surface, electrons would boil off of it. You could pull them off by putting them in an electric field and then you can measure their energy. So people thought, ooh, that's cool. We can boil particles off of the surface by shooting light beams at it. What would a physicist do in this scenario? She would probably think, oh, let me see what I can do.

What happens if I turn it up? What happens if I turn it down? What happens if I make the light purple? What happens if I make the light green, right? a physicist would want to know if the results make sense under all conditions. Sure, maybe we can understand how this works in this scenario, but can we push our limits of knowledge? Can we find some wrinkle, some corner of the space in which it doesn't make sense? That's right. Experimentalists are always just trying to spoil everything for theorists.

That's not true at all, actually, as Jorge would say, because every time experimentalists do something and find a result that doesn't make sense, that's an amazing clue. That's the clue the theorists need, to come up with a new theory of the universe. Anyway, back to the photoelectric effect. What happens when you shine light at the surface? Electrons come off. Now, if you're thinking of light as electromagnetic waves, then what should happen if you turn up the intensity?

If you turn up the intensity, then electrons should shoot off with more energy. Because under the classical idea, the original idea of light as a wave, then if you turn up the intensity of the light, the strength of the light beam, then you're putting more energy, It's just electromagnetic waves oscillating with more energy.

And so there should be more energy there to dump into the electrons. And so the electrons should boil off with more energy. And there should be no dependence on the frequency. You can just get the energy out of the electromagnetic waves. It doesn't matter how fast they're shaking, as long as the energy is there. The energy there depending just on the intensity. So that's the idea. They thought if we turn up the intensity of the light, we make the light brighter,

then you should get electrons coming off. with more energy. And there should be no dependence on the color. All right, so that's what they thought. Makes perfect sense. And then because they're experimentalists, because they actually want to go out and explore the universe, not just do thought experiments in their head

the way the old Greeks did, they went out and they actually tried this. And what they found, of course, blew their mind. What they found is two things that didn't make any sense at all. First of all, the energy of the electrons that came off the surface didn't depend on intensity at all. You could turn up the intensity and the energy the electrons wouldn't change.

You could turn down the intensity and the energy electrons wouldn't change. Weirdly, if you turned up the intensity, you got more electrons. You didn't get any electrons with more energy, but you got more electrons boiling off. And if you made the light dimmer, if you turned down the intensity, again, the energy didn't change, but the number of electrons dropped. And this didn't make any sense at all in the classical idea. If light is just a wave, if it's just oscillation of the electromagnetic field, then it should depend on the intensity. But there was no dependence on the intensity at all. Instead, changing the intensity didn't change the energy the electrons coming off. It only changed the number of electrons we saw. So then they said, all right, that's weird. So let's try changing

the frequency of the light. So it go from blue light down to red light and back to purple light and just to see. And they found that the energy electrons weirdly did depend on the frequency of the light. At higher frequencies, the electrons had more energy. And at low enough frequencies, you wouldn't get any electrons at all. So this made no sense to anybody. People who were thinking, who are confident that light was just electromagnetic radiation could not explain either these effects. One, the fact that the energy electrons didn't depend on the intensity of the radiation, which made no sense because they thought these are just classical waves and the intensity means more energy. So why aren't we getting more energy out of the electrons?

And number two, that the energy electrons coming off did depend on the color of the light. But it made no sense to people because people were thinking about light as waves. Now, there was somebody thinking about light in other terms. And that was Plunk. Plunk was studying a totally different problem. Another unsolved question in physics, which had to do with black body radiation, which we'll talk about it in another episode. And he was trying to solve that problem and he just couldn't.

He was trying to explain why we didn't see in the lab what we expected to see based on the theory. And to solve his problem, he had to come up with a crazy idea. He said, well, I don't know why, and I can't justify this at all. But if I assume that light comes in little packets of energy, that you can have like zero or one or two little bits of energy, but you can't have integer numbers in between, then it solves my problem. And for him, it was sort of a mathematical thing.

He was like, I'm trying to do this calculation. It's not working. Nobody can figure it out. Oh, look, if I make this totally unjustified assumption, then my calculation works, and it explains the data. And that's cool. That's a totally valid way to do theory and to do physics. And then you've got to go back and say, well, what does that mean, right?

And it was Einstein who put it together. Einstein heard about Planck's idea. He said, hmm, that's fascinating. and he heard about the photoelectric effect. He said, ooh, interesting puzzle, and he put them together. And so Einstein, who never actually won the Nobel Prize for relativity, did win the Nobel Prize later for putting these two ideas together. Even though he didn't do the experiments for the photoelectric effect,

and he also didn't have the original idea to break light down into little pieces, he just put the idea in the right place to solve the problem and explain this experiment. All right, so let's talk about how, the idea that photons might be little particles, little packets of energy, explains this experiment. But first, let's take another break. I'm Dr. Joy Harden Bradford. And in session 421 of therapy for black girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right? In terms of it can tell

how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyper fixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. You talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to Therapy for Black Girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway.

We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete? The final. The final.

And the locker room. I really, really, like, you just, you can't replicate. You can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Park. and college superstar A. Z. Fudd. I mean, seriously, y'all. The guest list is absolutely stacked for season two.

And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. The OGs of Uncensored Motherhood are back and badder than ever. I'm Erica. And I'm Mila.

And we're the host of the Good Mom's Bad Choices Podcast. brought to you by the Black Effect Podcast Network every Wednesday. Historically, men talk too much. And women have quietly listened. And all that stops here. If you like witty women, then this is your tribes. With guests like Corinne Steffens. I've never seen so many women protect predatory men.

And then me too happened. And then everybody else wanted to get pissed off because the white said it was okay. Problem. My oldest daughter, her first day in ninth grade, and I called to ask how I was going. She was like, oh, dad, all they were doing was talking about your thing in class. I ruined my baby's first day of high school.

And slumflower. What turns me on is when a man sends me money. Like, I feel the moisture between my legs when the man sends me money. I'm like, oh my God, it's go time. You actually sent it? Listen to the Good Mom's Bad Choices podcast every Wednesday on the Black Effect Podcast Network. The IHeart Radio app, Apple Podcast, or wherever you go to find your podcast. All right, we're back and we're talking about why photons are a thing.

We reminded ourselves why people originally thought that photons were waves. And then we talked about the photoelectric effect, this experiment with a weird result and a result that could not be explained using classical theory that could not be understood if you thought about light as a wave. So how do we explain the photoelectric effect? How do we understand the weird results of this experiment just by saying that light comes in little packets. All right. Well, Einstein said, I'm going to assume that light comes in these little packets and that the energy inside one packet is proportional to the frequency.

That means that higher frequencies, things like blue, have more energy than photons at lower frequencies, things like red. What that means is if you want more energy in your photon, you need purple or photons. If you want less energy in your photons, you need redder photons. His microscopic understanding of what's happening is you have this surface of metal and it's got electrons in it. And electrons need a certain amount of energy in order to escape. They're bound to their atoms. They're happy there. They're circling the nuclei, right? They don't necessarily want to leave. In order for them to leave, they have to get a certain minimum of energy. So what happens when a photon comes and hits the surface? Well, a photon hits the electron

and either it has enough energy to kick the electron off or it doesn't. If it doesn't, no electron is kicked off. And what that means is that the frequency of the light has to be right, high enough frequency to have a high enough energy to kick off any electrons. And that explains why when they turn the frequency down on the light, no matter how bright it was, if they turned the color down to deep, deep red, they just didn't see any electrons coming off. And they couldn't explain that with their classical theory. With their classical theory, they thought, well, lights a wave, but the color doesn't matter. We can make it red. As long as we make it really, really bright, electrons should still come off, but they didn't. And this theory explains why, because the photons in little

chunks, and each electron can only absorb energy from one photon at a time. That's the critical idea. You can only interact with one photon at a time. So if the photon doesn't have enough energy because it's too low frequency, it's too red, then it just can't get you out of your atom trap. And yeah, there are other photons coming down the pike if you have a really, really intense beam, but those don't help because once that first photon has failed to get you out of the atom, then you're back in the atom again. And the next one's also going to fail. The photons can't work together.

So that's the key idea, the fact that the beam of light is not just one wave that's shaking the electrons so that if you turn it up, you're shaking them more and getting them enough energy to get out of those atoms, but it's broken up into pieces. And each piece needs enough energy on its own to get those electrons out of the atom. So the way you do it, the way you can get the electrons out of the atom is by changing the frequency because that gets more energy into each photon. And so if a purple one comes, remember purple being very high frequency, it has enough energy to get the electrons out of the atom and it's a little bit left over. So as you increase the frequency of the light, you're increasing the energy per photon, essentially the energy that each electron has access to. And then it has enough energy to get out of the atom and to zoom off with a good amount.

amount of speed. So the higher the frequency of the light, the more energy in each photon, the more energy these electrons come out at. And that is exactly what they saw in the experiment. And that can only be explained if electrons can only interact with one particle of light at a time. And that light is, in fact, a particle. It also explains why the energy of electrons does not depend on the intensity of the beam. You can have a really powerful red beam, but it's too low frequency. All those photons are wasted because none of them have enough energy to get the electrons out. It doesn't matter how high you turn it up. And even if you turn it up to green and you have enough energy to get the electrons out of there,

you don't get more energetic electrons by increasing the intensity. Again, you have to change the energy in each photon that's hitting the electron. You can only do that by changing the frequency. And this assumes, again, that electrons can only interact with one photon at a time, which is pretty solid assumption. So the amazing thing is that this idea, which really came from Plank, explained these experiments, which really were done by other people, but the unification of it, the bringing together the idea,

the moment of insight, the explanation of this weird experiment was done by Einstein. And that's what Einstein won the Nobel Prize for, not for doing the experiment, not for having the idea, but for being sort of in the right place, at the right time, to bring that idea to solve this open problem. now the photon was not named as a particle for decades later all this happened just around the turn of the 19th century and Einstein won the Nobel Prize later for it but it wasn't until 1926 that people started calling these things photons and it comes from the Greek word for light but it also touches on something I think is really interesting which is the sort of concept of a particle I like to imagine what were physicists thinking back then what did they think that the universe looked like at a microscopic scale because to us, the notion of a particle is kind of familiar. I mean, they're weird.

They do things that we don't understand. They follow rules and make no sense to us. But we're comfortable with the idea that the universe is atomic, meaning that's made up of little bits. And all we have to do is sort of figure out what those bits do. But at the time, this whole concept of a particle was kind of new. Remember, where they had discovered the electron, that was only recently. That was the first piece of evidence that there was something as a particle,

sort of the invention of the concept of a particle was the discovery of the electron. And all he really did there was identify something tiny that had both mass and charge. And so he said, oh, look, there's a thing there and has these two attributes. I'm going to call it a particle. Actually, he called it corpuscule, but the concept, the sort of intellectual groundwork was laid then for a particle. So then you get to the photon. Now the photon has energy.

It has direction, but it doesn't have mass. It's not a thing in that sense. There's no stuff to it. So that immediately sort of bends your mind around what is this concept of a particle anyway? We've created this idea to accommodate the discovery of the electron. We hope, oh, maybe there are other particles. And later on the podcast, we'll take a tour of the discoveries of other particles, which have hilarious and amazing and dramatic stories to them.

But very early in the history of particles, we had to already bend the rules to say, oh, well, we were talking about particles as little bits of stuff, but they can also be not stuff, right? They can also just be energy. And so to me, it's amazing that this field of particle physics was founded on such crazy discoveries. So to me, it's wonderful that the field of particle physics is founded on such crazy discoveries. And you've got to give a lot of credit to the theorists, of course, who put these ideas together and helped us understand what we were seeing. But to me, the most exciting moments are those moments of experimental surprise.

When the universe does something that we don't understand, when we predict the universe will do A, and instead it does B, because that's the universe talking to us, or that's the universe answering our questions. That's the universe being the subject of our interrogation, when we say, we want to know how this works, prove it to us, or reveal to us the underlying mechanism. And that's what experimental physics is about, is about cornering the universe and forcing it to reveal something new to you. And a lot of times that revelation happens when you didn't expect that you thought, oh, we're just double-checking this over here. We're pretty sure we understand it.

We're just dot in the eyes and crossing the T's, and all of a sudden, oops, you get something totally surprising. But those are the moments that we learn something new about the universe. And those are the moments I'm striving for my own personal research. When I'm smashing particles together at the LHC, we think we understand what's going to happen, but I'm always secretly hoping that a student will come to me and say, hey, Daniel, what's this?

I found this weird thing in our data that just doesn't make any sense. And that's only happened once or twice in my entire career, and I look forward to it happening again. So maybe one day we'll be hearing about a crazy discovery we made at the Large Hadron Collider. Until then, thanks for listening to this description of how we know the photon is a thing. And please, if you're interested in learning more about the history of physics or understanding how we know how the universe works and what we don't know, please send me a suggestion to feedback at danielanhorpe.com. Thanks for tuning in.

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. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHartRadio, for more podcasts from IHore. Heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

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