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

0:08
Speaker 1: Is it possible to be two different things at the
0:11
Speaker 1: same time? Can you like dogs and cats? Can you
0:16
Speaker 1: be a horse and a giraffe at the same time?
0:19
Speaker 1: Can something taste salty and sweet? Can address be black
0:23
Speaker 1: and blue and white and gold? In today's podcast, we
0:27
Speaker 1: talked about the centuries old scientific debate about light. Is
0:32
Speaker 1: light a particle or a wave? Or is it both? Hello?
0:55
Speaker 1: I'm Organ and I'm Daniel. Welcome to Daniel and Jorge
0:58
Speaker 1: Explain the Universe, in which we try to explain the
1:01
Speaker 1: whole universe and everything in it, including light. Now, I'm
1:05
Speaker 1: a cartoonist. I draw something called PhD comics, and I'm
1:09
Speaker 1: a particle physicist. During the day, I smash particles together
1:12
Speaker 1: with the large hadron collider. Yeah. Well, today on the program,
1:15
Speaker 1: we're going to talk about the nature of light. That's right.
1:23
Speaker 1: People have been arguing for centuries what is light? Is
1:26
Speaker 1: it made out of particles? Is it made out of waves?
1:28
Speaker 1: It's something else? Is it tiny little puppies screaming through space?
1:32
Speaker 1: People have gone back and forth on the issue, and
1:34
Speaker 1: today even the topic is not yet totally settled. So
1:38
Speaker 1: we're gonna be taking you through that history and breaking
1:40
Speaker 1: it down it's one of the most mind blowing questions
1:43
Speaker 1: in human scientific history. That's right, what is light made
1:47
Speaker 1: out of? So, as usual, before we dig into it,
1:49
Speaker 1: we went out and we asked people on the street.
1:51
Speaker 1: What do you think light is made out of? What
1:52
Speaker 1: do people know about light? Is light a particle or
1:56
Speaker 1: is it a wave? Here's what people had to say.
1:58
Speaker 1: Do you think light? Is it out of particles or waves?
2:01
Speaker 1: Or both? Are neither? Photos? Yeah? Photons? Yeah, so you
2:05
Speaker 1: think it's a particle. I think it's waves. Yeah, it's both,
2:11
Speaker 1: I think because it moves like a wave, but it
2:15
Speaker 1: also has properties of a particle and there's nothing saying
2:19
Speaker 1: it can't people. Okay, um, light, I think they're made
2:25
Speaker 1: of wavelength Yeah all right. Well, um, it's interesting because
2:30
Speaker 1: I think all of the answers are right or none
2:35
Speaker 1: of them, or or both. Yeah. Well, it seems like
2:40
Speaker 1: a lot of people reflected the fact that there is
2:42
Speaker 1: a controversy like that. You know, it's not really well
2:45
Speaker 1: described by either those. Some people went all in, you know,
2:48
Speaker 1: like it's a photon or it's a wave, or it's
2:50
Speaker 1: a wave length right, Yeah, that was my favorite one.
2:54
Speaker 1: I want to be a wavelength like I've heard of
2:56
Speaker 1: this word. It sounds really cool and scientific. I'm just
2:59
Speaker 1: gonna throw it out there, that's right. Yeah, maybe I
3:02
Speaker 1: get some points. We award no points, people, no points.
3:06
Speaker 1: That's right. There's no prize, your prices. You get to
3:09
Speaker 1: be on our podcast, and maybe we even make fun
3:11
Speaker 1: of you. Yeah, but yeah, I guess what you mean
3:14
Speaker 1: is nobody sort of fell for the trap, right, Like
3:16
Speaker 1: nobody said, oh, of course it's a particle, or nobody said,
3:18
Speaker 1: oh of course it's a wave. Most people sort of
3:21
Speaker 1: needed that there's some sort of duality there, something weird
3:24
Speaker 1: going on. That's right. That science is having some trouble,
3:27
Speaker 1: some difficulty coming up with a way to describe what
3:30
Speaker 1: light is. And that might seem surprising to you because
3:33
Speaker 1: light is everywhere, right, and it runs the universe. It's
3:35
Speaker 1: streaming through the Solar system from the Sun, illuminating our lives,
3:39
Speaker 1: empowering everything on Earth. So you think this would be
3:42
Speaker 1: sort of a high priority topic to figure out, like
3:44
Speaker 1: what is this stuff? What is it made out of? Yeah?
3:47
Speaker 1: I mean, like, what are we paying you for, Daniel,
3:49
Speaker 1: if not to figure these kinds of questions out. I
3:52
Speaker 1: was just about to figure out what light was when
3:55
Speaker 1: you called and said it's time to do this podcast.
3:58
Speaker 1: Totally about your thin train of thought there, that's right,
4:02
Speaker 1: reflect on that for a minute or but no, Yeah,
4:06
Speaker 1: I'm a California taxpayer. Part of my salary goes to
4:10
Speaker 1: being your salary, like you know, one million of a present.
4:13
Speaker 1: That's true. Yeah, so you're you're saying you did pay
4:15
Speaker 1: taxes very against another topics on air Daniel. Anyway, So
4:25
Speaker 1: that's an interesting question, like is light a waiver particle?
4:28
Speaker 1: And it's weird that we don't know, um, but maybe
4:31
Speaker 1: let's bring it down a little bit. What is it? Like,
4:33
Speaker 1: what are we actually talking about when we say that
4:35
Speaker 1: light could be a particle or light could be a wave,
4:38
Speaker 1: like you know, most people probably think of light is
4:41
Speaker 1: just like just like brightness, right. Yeah. The thing to
4:45
Speaker 1: understand here is that we try to describe light in
4:48
Speaker 1: terms of things we know, and that's what science is. Right.
4:52
Speaker 1: You see something weird and new and you wonder, is
4:54
Speaker 1: it like this other thing I know? So we've observed
4:57
Speaker 1: different kinds of phenomenon in the world. Like you see waves, right,
5:00
Speaker 1: you go to the beach, you see waves and water.
5:02
Speaker 1: You drop a rock in a small puddle. You see waves.
5:06
Speaker 1: We know what waves are, and we see different phenomena.
5:09
Speaker 1: We try to categorize them in terms of things we know. Right,
5:11
Speaker 1: So like when people were studying sound, they discovered, oh,
5:15
Speaker 1: sound is actually a wave. You know, it's a compression
5:17
Speaker 1: wave in the air. And that's cool because he says, oh,
5:20
Speaker 1: I already know how the math for waves works. Right,
5:23
Speaker 1: I've seen waves and water. I've seen waves and other stuff.
5:26
Speaker 1: You can describe it with like equations, right, yeah, wavy equations,
5:31
Speaker 1: that's right, very solid unwavy physics to describe waves. And
5:35
Speaker 1: there's a lot of science that's gone into understanding ways.
5:38
Speaker 1: So if you can cram it into that box and say, oh,
5:40
Speaker 1: this is just another example of something we already know,
5:43
Speaker 1: then you're taking a huge leap forward. Right. So that's
5:47
Speaker 1: something people try to do is say, like, look, can
5:48
Speaker 1: we describe this in terms of other things we know?
5:50
Speaker 1: So we need like we you know, we know about light,
5:54
Speaker 1: but we want to know how it behaves and what
5:55
Speaker 1: makes it work. Yeah, and just on a more general level,
5:58
Speaker 1: you try to see something new you are to describe
6:00
Speaker 1: in terms of things you know, Like, say you taste
6:02
Speaker 1: a new kind of fruit and you'd be like, Oh,
6:04
Speaker 1: it's a little bit like a cherry and a little
6:06
Speaker 1: bit like an apple, and a little bit like you know,
6:08
Speaker 1: it's got a hint of smokiness to it or whatever.
6:10
Speaker 1: You know. You're like, it's a chapel. It's a chapel.
6:13
Speaker 1: How has nobody ever invented that? The cherry apple chapel?
6:16
Speaker 1: Oh my gosh, somebody, if our lawyer is listening, get
6:20
Speaker 1: on that right away. Copyright that idea chapel dot com.
6:24
Speaker 1: That's right. So that's the basic idea is we have
6:26
Speaker 1: these things we've seen. You see something new, you don't
6:29
Speaker 1: want to create a whole new category. You want to
6:30
Speaker 1: fit in into one of the existing categories. So we
6:33
Speaker 1: set a new about light. It came from the sun.
6:35
Speaker 1: You know, if you light a fire, it spreads out
6:38
Speaker 1: into a room. And so we're like, what's going on?
6:41
Speaker 1: Like what? Um? What best describes how this light you know,
6:46
Speaker 1: comes from a source and bounces off the walls and stuff?
6:49
Speaker 1: Exactly exactly, that's the question. And so we've seen things
6:52
Speaker 1: like waves, So what do we mean when we say
6:54
Speaker 1: a wave? Like, how could a light be a wave? Well?
6:56
Speaker 1: How can anything be a wave? Yeah? How can anything
6:58
Speaker 1: be a wave. A wave is a funny thing because
7:01
Speaker 1: it's not a thing itself. It's a property of some medium.
7:04
Speaker 1: Like it's like a ripple on something. Yeah, that's right.
7:08
Speaker 1: Like if you do the wave at a baseball game,
7:10
Speaker 1: you know, there's nothing to the wave itself. It's just
7:13
Speaker 1: a bunch of people moving up and down waving their hands, right,
7:16
Speaker 1: Or like a sound wave is just like air molecules
7:19
Speaker 1: kind of bumping forward. That's right, yeah, exactly. Or a
7:23
Speaker 1: wave in the in the ocean, it's just it's an
7:25
Speaker 1: arrangement of the water, right, It's it's the way the
7:27
Speaker 1: water gets compressed and then stretched out and compressed and
7:30
Speaker 1: then get stretched out. So that's the important thing about
7:32
Speaker 1: a wave is that it moves in this way through
7:35
Speaker 1: a medium. Okay, so that's a wave. It's like a propagation,
7:39
Speaker 1: it's like a ripple through something. But then so then
7:41
Speaker 1: what what would you call a particle? Particle is different
7:44
Speaker 1: than that. A particle is different than that, and it's
7:46
Speaker 1: a totally different kind of thing, you know, and uh,
7:49
Speaker 1: to be a particle physicist, it's kind of odd, but
7:51
Speaker 1: the concept of a particle is not that really well
7:53
Speaker 1: to find you know, um, But when I think of
7:55
Speaker 1: a particle, I think of taking matter and breaking it
7:58
Speaker 1: down to its smallest pieces. Like, if something is made
8:00
Speaker 1: out of particles, it means that at its smallest level,
8:03
Speaker 1: it's made out of this these little bits that can't
8:05
Speaker 1: be chopped into smaller bits, and that they're localized. They're
8:09
Speaker 1: like um, small and contained. Right. If if you discover
8:14
Speaker 1: that something is made of particles, you expect it to
8:16
Speaker 1: be like mostly empty space, but with these little dots
8:20
Speaker 1: of matter, Like it would take something and then you
8:22
Speaker 1: smash it to bits and just keep smashing, and at
8:24
Speaker 1: some point you're going to get to these little like
8:26
Speaker 1: baby balls or like little tiny pellets that you can't
8:30
Speaker 1: break down anymore, that's right. Yeah, It's like seeing a
8:33
Speaker 1: picture on your your computer screen and discovering it's made
8:36
Speaker 1: out of pixels, right, and that those pixels are the
8:39
Speaker 1: basic elements and they come together to make the whole picture. Um.
8:42
Speaker 1: So figuring out this something is made of particles means
8:46
Speaker 1: that there's made of these these little bits that are
8:48
Speaker 1: not um connected to each other, right, they're separated. So
8:52
Speaker 1: a wave and a particle in nature are totally different
8:54
Speaker 1: kinds of things, right Now, water of course is made
8:58
Speaker 1: of particles, but can have waves in it, right, But
9:00
Speaker 1: I think maybe maybe what's important here is that, you know,
9:03
Speaker 1: particles we tend to think of as little tiny bits.
9:06
Speaker 1: They can bounce around, right, and like go in a
9:08
Speaker 1: straight line and then hit something else and then bounce back,
9:13
Speaker 1: or you know, kind of fly through space right in
9:17
Speaker 1: a discrete little package. Exactly. That's exactly the right way
9:20
Speaker 1: to say. It is a discrete little package. Right. So
9:22
Speaker 1: things that have made of particles we think of as
9:24
Speaker 1: being discrete little bits um and they they've broken up
9:27
Speaker 1: into these little little pieces, and you're right, they move
9:30
Speaker 1: in straight lines. Right, Like you throw a rock, your
9:33
Speaker 1: your roll a smooth ball across the surface, you expected
9:36
Speaker 1: to move in a straight line. So that's kind of
9:38
Speaker 1: what we mean by a wave and a particle, that's right. Yeah.
9:41
Speaker 1: And so the question is is like is light a
9:44
Speaker 1: ripple on a medium? Is that what light is? Or
9:47
Speaker 1: is it like actually little things and move around in space? Right?
9:50
Speaker 1: Does it have its own stuff to it? Right? Or
9:53
Speaker 1: is it just a way something else moves right? That's
9:56
Speaker 1: sort of another way to phrase the question, right, And
9:58
Speaker 1: those are two pretty different picture is a reality? Right? Yeah?
10:01
Speaker 1: The light could be little pellets flying around, or it
10:03
Speaker 1: could be some sort of ripple on a medium. To us,
10:06
Speaker 1: in our intuitive sense, it couldn't be any more different, right,
10:10
Speaker 1: that's right. Yeah, it's like you can't be a Democrat
10:12
Speaker 1: and a Republican, you know, just you have to pick one,
10:14
Speaker 1: you know. Yeah, if you can be or you could
10:19
Speaker 1: be neither as opposed, Um, you shouldn't be both though, Yeah,
10:23
Speaker 1: that would be a violation of some some election law
10:27
Speaker 1: not recommended to violate election that's right. Yeah. So, speaking
10:31
Speaker 1: of political shouting matches, this one, this historical scientific shouting match,
10:35
Speaker 1: began all the way back with the Greeks, right Democratus
10:38
Speaker 1: he's the guy sort of the first atomist. He's the
10:40
Speaker 1: first person to look at the world and to say,
10:43
Speaker 1: you know, maybe everything's made out of tiny little bits,
10:46
Speaker 1: not just light, but also matter. And that was sort
10:48
Speaker 1: of the birth of that idea that maybe everything around
10:52
Speaker 1: us that seems macroscopic is made out of tiny little things,
10:55
Speaker 1: smaller than we can see. And you know, as usual,
10:58
Speaker 1: when somebody comes up with a good idea, they overextended.
11:01
Speaker 1: They're like, well, maybe if rocks are made out of stuff,
11:03
Speaker 1: then water is also made out of particles, and maybe
11:06
Speaker 1: even light is made out of particles. You know. It's
11:08
Speaker 1: at the time seemed like a totally a crazy reach.
11:12
Speaker 1: And that makes sense, right, because light seems to go
11:13
Speaker 1: in a straight line. It seems to bounce off of things.
11:17
Speaker 1: So why couldn't light just be like a little tiny
11:19
Speaker 1: little pellets that bounce around the room and then eventually
11:22
Speaker 1: hit your eye and then that's how you see something. Yeah,
11:25
Speaker 1: it certainly seems to have some of those particles like properties, right,
11:27
Speaker 1: it moves in straight lines. Uh, it certainly would be
11:30
Speaker 1: going really really fast. At the time, people thought that
11:33
Speaker 1: light traveled instantly, right. They thought that light um instantaneously
11:37
Speaker 1: went from like the sun to the earth, or or
11:40
Speaker 1: um if you started a fire, that the light would
11:42
Speaker 1: immediately illuminate the room. Now, we of course know that
11:44
Speaker 1: it just happens super duper crazy fast, too fast for
11:47
Speaker 1: those folks to ever measure, so it's almost like it's instantaneous.
11:51
Speaker 1: But they thought that these things just moved instantly through
11:54
Speaker 1: space and filled up the room. Okay, and I want
11:56
Speaker 1: to talk a little bit more about that, but first
11:58
Speaker 1: a quick break. So, initially we thought light was or
12:14
Speaker 1: the Greeks thought that light was a particle, right, And
12:18
Speaker 1: I think we have to qualify that because it makes
12:20
Speaker 1: the Greek sound really smart. Just come up with this
12:22
Speaker 1: idea of atoms and all that stuff, and you say
12:25
Speaker 1: this before you're really really down in the Greeks. Well,
12:28
Speaker 1: I think people give the Greeks too much credit for that, because,
12:30
Speaker 1: as I've probably said to you before, Um, the Greeks
12:33
Speaker 1: had lots and lots of ideas. You know, they had
12:34
Speaker 1: like thousands of these ideas about how the way the
12:36
Speaker 1: world works, and yeah, one of them was close to true.
12:39
Speaker 1: But like, if we're going to do some accounting, let's
12:41
Speaker 1: also remember the n that were totally off base, you know,
12:46
Speaker 1: and and give them credit for those. Yeah, find that
12:48
Speaker 1: Greek we thought life was just little puppies, and be like, see,
12:52
Speaker 1: you guys also thought they were puppies. You can't be
12:54
Speaker 1: that smart, that's right. But it's a cool idea. So
12:58
Speaker 1: give them credit for having that idea and know what
13:00
Speaker 1: they were smoking when they came up with it. But
13:02
Speaker 1: I'd like to figure out where to find something. Um.
13:04
Speaker 1: And then it was thousands of years later before people
13:07
Speaker 1: had another idea. It was a Descartes, the guy who's
13:09
Speaker 1: famous for you know, I think therefore I am he
13:12
Speaker 1: thought about He was one of the early scientists, not
13:14
Speaker 1: just philosopher, but a scientist, back in the day when
13:17
Speaker 1: you know, science really was part of philosophy, and he
13:20
Speaker 1: thought that light was waves. What made him think it
13:23
Speaker 1: was waves? You know, I don't think he had much
13:25
Speaker 1: justification for it. This is back in the early days
13:27
Speaker 1: when science wasn't really an empirical study where you didn't
13:30
Speaker 1: like go out and do experiments to test your hypothesis. Um,
13:34
Speaker 1: it just made more sense to him for light to
13:36
Speaker 1: be like these wave like disturbances, which kind of makes sense, right,
13:40
Speaker 1: Like if you have a speaker in a room emitting
13:43
Speaker 1: sound waves, Um, it's not that different from like a
13:46
Speaker 1: light bulb in the middle of the room emitting light
13:49
Speaker 1: all around it. Right. Yeah. And there's some things that
13:52
Speaker 1: light does that don't really that don't really seem consistent
13:55
Speaker 1: with particles, you know, like the way light bends through
13:59
Speaker 1: a lens, right, it's called we call in science, we
14:02
Speaker 1: call that refraction. You know, with light changes from going
14:04
Speaker 1: through air to glass, it bends in this weird way.
14:07
Speaker 1: That's something that's very common for waves, right, And a
14:12
Speaker 1: particle wouldn't bend inside of a lens. No particle, that's
14:16
Speaker 1: definitely a wave like behavior, yeah, not particle like behavior.
14:21
Speaker 1: And so Descartes saw that and he's like, oh, you know,
14:23
Speaker 1: we have optics, we have these lenses, so maybe light
14:26
Speaker 1: is a wave. But if light is a wave, then
14:27
Speaker 1: it opens this other question. What's doing the waving? Right?
14:31
Speaker 1: I mean with sound, you know it's the air, and
14:33
Speaker 1: in water waves obviously it's the water. But if light
14:36
Speaker 1: is a wave, then what is waving? Meaning? Like, if
14:39
Speaker 1: light is a ripple, what is it a ripple of
14:42
Speaker 1: that's right? Yeah, what's doing the rippling? Right? If it's
14:44
Speaker 1: a wave, it has to be a wave in something,
14:46
Speaker 1: because a wave is just a description of some other
14:49
Speaker 1: form of matter rippling, right, It couldn't just be like
14:53
Speaker 1: a stuff that we can't see. Yeah, and so you
14:56
Speaker 1: have to invent some stuff that we can't see, right,
14:59
Speaker 1: So explain light being a wave. You have to invent
15:01
Speaker 1: this universe filled with stuff or there has to be
15:04
Speaker 1: that stuff between us and the sun for example, right,
15:06
Speaker 1: which is a huge amount of this new stuff you're inventing.
15:09
Speaker 1: And if you're looking at the stars, there has to
15:10
Speaker 1: be that stuff between you and the stars. Right, So
15:13
Speaker 1: now we're talking about billions of miles of this new stuff,
15:16
Speaker 1: and Decart, you know, didn't know. So he just gave
15:19
Speaker 1: it a name. He's called I don't even know how
15:20
Speaker 1: to pronounce it, but he called it plenum. And he thought, well,
15:23
Speaker 1: there must be if light is a wave, there must
15:25
Speaker 1: be some stuff that's doing the waving, and we'll just
15:27
Speaker 1: give it a name and maybe we'll be right, and
15:29
Speaker 1: then we'll be famous forever. Isn't it is that different
15:32
Speaker 1: under either it's similar in concept, right, it's a different idea,
15:36
Speaker 1: but it's similar in concept that like, if light is
15:38
Speaker 1: a wave, it must be waving through something, and we
15:40
Speaker 1: don't know what it is, which is invents something to
15:43
Speaker 1: give it a name as a placeholder so when later
15:45
Speaker 1: people do the hard work of actually discovering it will
15:48
Speaker 1: still get credit. So it was a particle. Light was
15:51
Speaker 1: a particle, then it was a wave, and then what happened, Well,
15:53
Speaker 1: then Newton came along, right, And Newton is a really
15:55
Speaker 1: smart guy, and everybody knows that he's famous for thinking
15:58
Speaker 1: about gravity, but he also like to think about optics
16:01
Speaker 1: and lenses. And he thought for sure that light was
16:04
Speaker 1: a particle because he saw it moving in straight lines,
16:07
Speaker 1: and he saw distinct shadows. But you know, Newton also
16:11
Speaker 1: did a lot of experiments with optics. He did he
16:13
Speaker 1: studied prisms, and he saw light bending, and he saw
16:15
Speaker 1: light splitting into colors. And you can't explain that if
16:18
Speaker 1: light is a particle, but he tried. You know, He's like, well,
16:21
Speaker 1: maybe when a particle hits the glass, it gets some
16:25
Speaker 1: sort of weird sideways force, um, and that makes it bend.
16:29
Speaker 1: But you know, that's not really an explanation. That's just
16:32
Speaker 1: sort of like a I don't really understand it. But
16:34
Speaker 1: maybe it's something like this, like, if light is a particle,
16:38
Speaker 1: why does it split into the rainbow kind of thing? Yeah, exactly.
16:42
Speaker 1: And you know this is again back in the day
16:44
Speaker 1: when empirical studies of science weren't the main way to
16:47
Speaker 1: answer questions. It was mostly thinking in your head about
16:50
Speaker 1: things that made sense to you, and then they would
16:52
Speaker 1: argue about them. Right. A lot of a way scientific
16:55
Speaker 1: disputes he used to be resolved was people would argue
16:57
Speaker 1: about it and then say, well, that makes no sense,
16:59
Speaker 1: so it can't be true. Um. And we know now,
17:02
Speaker 1: of course, that the universe doesn't always make sense to us.
17:04
Speaker 1: What's real doesn't isn't necessarily the things that we would
17:07
Speaker 1: have accepted as true or or accepted as a reasonable
17:11
Speaker 1: way to describe the universe. But you know, if that's
17:13
Speaker 1: the way nature works, that's the way nature works, you
17:15
Speaker 1: have to accept it. But that's the sort of primacy
17:18
Speaker 1: of experimental results came later on. So back in the day,
17:21
Speaker 1: people just sort of used to argue for an explanation
17:24
Speaker 1: that made sense to them. Right, Well, it was kind
17:26
Speaker 1: of hard for them to build a particle collider, right,
17:29
Speaker 1: that's right, yeah, exactly. They they didn't have the massive
17:34
Speaker 1: government funding to do that. These were men of leisure
17:36
Speaker 1: studying science in the spare time. In fact, it was
17:39
Speaker 1: called like natural philosophy, right, It wasn't called science at
17:43
Speaker 1: the time, wasn't. Yeah, that's right exactly. Science All science
17:45
Speaker 1: grew out of philosophy. Um, it was called these folks
17:49
Speaker 1: were natural philosophers. But you know, later on then people
17:52
Speaker 1: started doing experiments. And there were a bunch of French
17:55
Speaker 1: guys um who did a bunch of experiments, and some
17:58
Speaker 1: of some English folks, and they were studying how life
18:01
Speaker 1: behaved and refraction and reflection, and they saw it doing
18:04
Speaker 1: these things, and they thought, there's no way Newton's right,
18:06
Speaker 1: this has to be a wave. Um. You know, they
18:09
Speaker 1: saw things like interference patterns. Right. Interference patterns is when
18:14
Speaker 1: you have two waves and sometimes one is rippling up
18:17
Speaker 1: at the same time another one is rippling down. Right.
18:20
Speaker 1: So imagine, for example, you have a bathtub of water
18:24
Speaker 1: in front of you, and you slap it with two
18:26
Speaker 1: hands at once, right, each one is going to send
18:28
Speaker 1: waves out, and then when those end, those waves are
18:32
Speaker 1: either rippling up or rippling down. And when they reach
18:35
Speaker 1: each other, if they're both rippling up at the same time,
18:38
Speaker 1: then they constructively interfere to get a double wave. If
18:41
Speaker 1: they're both rippling down at the same time, they constructively
18:44
Speaker 1: interfered to get a double down wave. If one is
18:47
Speaker 1: rippling up and the others rippling down, then they then
18:50
Speaker 1: they cancel each other out right, And so you would
18:53
Speaker 1: see no light, yeah, exactly, And so you can do
18:57
Speaker 1: this kind of stuff in you know, in your bathtub,
18:59
Speaker 1: you can see interfe Auran's patterns, um. And what happens
19:02
Speaker 1: if you have two sources like that, like one from
19:04
Speaker 1: each of your hands, is you get some areas where
19:06
Speaker 1: the waves are high in some areas where the waves
19:08
Speaker 1: are are low, in some areas where there are no waves.
19:11
Speaker 1: And so as you say, if you do with light,
19:13
Speaker 1: then you see these patterns of dark and light, these stripes,
19:16
Speaker 1: And you couldn't do that with particles, right, like a
19:18
Speaker 1: particle wouldn't cancel another particle. Yeah, there's no way to
19:21
Speaker 1: explain that with particles. People thought, well, look, um, this
19:24
Speaker 1: is something that waves do and light is doing it,
19:26
Speaker 1: and there's no way to explain it with particles, so
19:28
Speaker 1: light must be a wave. In fact, there's even famous
19:32
Speaker 1: cases where they said, well, you know, um, if light
19:35
Speaker 1: is a wave, then you know, if you set up
19:37
Speaker 1: this various experiment, you would get this crazy effect and
19:40
Speaker 1: so that's absurd and so it definitely can't be true.
19:43
Speaker 1: And then they went and did the experiment and saw
19:45
Speaker 1: the crazy wave effect and they're like, oh, that is true.
19:48
Speaker 1: You know, this is a I love that because it's
19:51
Speaker 1: the primacy of experimental experimentalism, right, like, go and check
19:55
Speaker 1: the data, Go and actually get some data and see
19:57
Speaker 1: what the universe tells you. Yeah, Like you're like a
20:00
Speaker 1: doughnut can't possibly be a croissant at the same time,
20:04
Speaker 1: But it turns out that you can bake something called
20:07
Speaker 1: the cronut. Yeah exactly. I think that's a big debate
20:10
Speaker 1: in pastry science still though. And is it from a
20:13
Speaker 1: donut like that's like a croissant or is it a
20:15
Speaker 1: croissant that's like a donut. Yeah. I'm getting my degree
20:17
Speaker 1: and I'm particle baking. Yeah, the large Pastry Collider. I'm
20:23
Speaker 1: looking forward to the construction of that project. But that's
20:29
Speaker 1: kind of what you mean. It's like you, people don't
20:30
Speaker 1: think it's possible until they actually see it. And waves
20:33
Speaker 1: and light has been doing this to people for hundreds
20:36
Speaker 1: of years, or they're like, they can't possibly be doing this,
20:39
Speaker 1: or they can't it can't possibly be doing that, but
20:41
Speaker 1: it just keeps doing all these weird things. Yeah, exactly.
20:44
Speaker 1: And and that was the experiment, it was called the
20:46
Speaker 1: double slit experiment, the one that really convinced people that
20:50
Speaker 1: light is a wave because they shone a strong light
20:53
Speaker 1: and they had just two little narrow slits which act
20:56
Speaker 1: like sources like slapping your hands in the bathtub water
20:59
Speaker 1: and and on the screen behind it, they saw these
21:01
Speaker 1: interference patterns, right, is that you could definitely only get
21:04
Speaker 1: if light was a wave. And so that was the
21:07
Speaker 1: early eighteen hundreds, and everybody was absolutely certain light was
21:10
Speaker 1: totally a wave. The question was settled. We knew forever
21:14
Speaker 1: light was a wave, and we still didn't know what
21:17
Speaker 1: was it waving through. But how did they explain all
21:20
Speaker 1: those particle experiments? Well, this was before we even really
21:23
Speaker 1: knew about particles, right, No real particles had been discovered
21:27
Speaker 1: at this point. With this idea from the Greeks of
21:30
Speaker 1: thousands of years ago that maybe things were made out
21:32
Speaker 1: of particles and the chemistry was getting warmed up, and
21:35
Speaker 1: you know, people are starting to think about atoms and
21:37
Speaker 1: molecules and stuff, um, but they hadn't really seen any
21:40
Speaker 1: actual particles yet. It was decades later when the electron
21:44
Speaker 1: was discovered, um, that people started to think about the
21:47
Speaker 1: particle model again. But you know, the wave theory was
21:49
Speaker 1: definitely ascended, right. Everybody definitely looked at these double slit
21:52
Speaker 1: experiments and saw light doing all this wavy stuff, and
21:55
Speaker 1: they were sure that light was a wave. Now that
21:57
Speaker 1: people extend that to other things, like, you know, they thought, oh,
22:01
Speaker 1: light is this weird wavy thing, but surely us, we're
22:03
Speaker 1: made out of little tiny atoms. Yeah, that's a good question.
22:07
Speaker 1: I wonder if people thought lights a wave. Maybe we're
22:09
Speaker 1: a wave too, right yeah, or like everything is just
22:13
Speaker 1: like a wave. Yeah, probably not because um, nobody thought
22:17
Speaker 1: that light had any mass to it, right, whereas we
22:20
Speaker 1: definitely know that we have mass. Right, we feel pretty
22:23
Speaker 1: heavy sometimes after a big meal. Um. Even before the
22:26
Speaker 1: discovery particles, though, there was a huge advance in the
22:29
Speaker 1: theory of light, which was a Scottish guy named Maxwell.
22:33
Speaker 1: He was working on electricity and magnetism and he put
22:36
Speaker 1: together all these equations to describe electricity magnetism, and he
22:41
Speaker 1: just sort of wrote them down in a new way.
22:43
Speaker 1: This is like the way you could do theoretical physics
22:45
Speaker 1: back in the days. You just take existing ideas and
22:47
Speaker 1: you find a new way to write them down. Um.
22:50
Speaker 1: But he wrote them down in this way that looked
22:53
Speaker 1: like the mathematics of a wave. We have this equation,
22:56
Speaker 1: it's called a wave equation, and it describes how waves
22:59
Speaker 1: moved medium I meaning like it could be described by
23:02
Speaker 1: the equations that looked like sign waves and co sine waves, right,
23:05
Speaker 1: I mean, just in case anyone remembers high school math,
23:09
Speaker 1: that's kind of that's kind of what we mean by
23:11
Speaker 1: mathematical equations that you can describe it as a sign
23:14
Speaker 1: wave ver cosine waves. Right, that's right. Yeah, the solution
23:17
Speaker 1: of these equations are sign waves and cosine waves. These
23:19
Speaker 1: are differential equations to describe how things move through the medium.
23:23
Speaker 1: And if things follow these equations, then their waves. Right.
23:27
Speaker 1: And so he looked at the equations for electricity and
23:31
Speaker 1: for magnetism and he rewrote them and he realized, you
23:34
Speaker 1: can rewrite them in a way that looks just like
23:36
Speaker 1: the wave equation. Right, So he said, oh, electricity magnetism
23:40
Speaker 1: has the same equation as waves moving through water or
23:45
Speaker 1: waves moving through air. And in fact, if you write
23:48
Speaker 1: it in terms of this wave equation, you can pull
23:51
Speaker 1: out what the speed of those waves must be. And
23:54
Speaker 1: the speed that he pulled out from this from these
23:56
Speaker 1: equations was the speed of light. So he had this
23:59
Speaker 1: moment of a pi any. He must have been like
24:01
Speaker 1: in his office late one night, rearrange these equations and realized, oh,
24:05
Speaker 1: my gosh, light is a wave and it's a wave
24:09
Speaker 1: of electromagnetism. So like a light bulb turn on on
24:12
Speaker 1: top of his head, emitting waves exactly the first appropriate
24:16
Speaker 1: light bulb ever. Yeah, So then that seems pretty definitive um.
24:23
Speaker 1: The double slid experiment shows it light interferes with itself.
24:28
Speaker 1: And also this guy figured out that it's mathematically describable
24:33
Speaker 1: by sign ways and cosign waves right right right, That
24:36
Speaker 1: light is waves of electromagnetism. Yeah, exactly. So then it
24:40
Speaker 1: all seems really nice and tidy. But then the particle
24:43
Speaker 1: revolution comes, right. People discover the electron, people discover the neutron,
24:47
Speaker 1: people discovering all these particles. But then they were doing
24:50
Speaker 1: experiments where they were shining light onto materials and trying
24:55
Speaker 1: to get it to kick off electrons. So you shine
24:57
Speaker 1: a really bright light at something and you hope that
24:59
Speaker 1: some of the electrons in the material absorb that light
25:02
Speaker 1: and get enough energy to be free right to run away.
25:06
Speaker 1: And so this is called the photo electric effect. You
25:08
Speaker 1: shine light is something and you measure the electrons that
25:10
Speaker 1: come off. So what they saw in this experiment only
25:14
Speaker 1: made sense if the energy of the light comes in
25:17
Speaker 1: little packets rather than a continuous stream like waves. So
25:21
Speaker 1: they turned up the intensity of the light and they
25:23
Speaker 1: made it brighter, but that didn't increase the energy the
25:26
Speaker 1: electrons that were coming off, which doesn't make sense if
25:29
Speaker 1: it's a wave. It only makes sense if photons come
25:32
Speaker 1: in little packets, So then increasing the intensity of the
25:35
Speaker 1: light means more photons, but it doesn't give more energy
25:39
Speaker 1: to any one electron because each electron can only absorb
25:43
Speaker 1: one photon. And nobody understood this at all. There's made
25:46
Speaker 1: no sense to anybody. Was a huge puzzle. We totally
25:49
Speaker 1: believe that it acted like a wave. We had the
25:51
Speaker 1: double slit experiment told us it was a wave. Maxwell's
25:54
Speaker 1: equations told us it was a wave. But then we
25:57
Speaker 1: had the photo electric effect, which didn't quite make sense
25:59
Speaker 1: to anybody, Okay, and then Einstein said, well, what if
26:03
Speaker 1: light comes in these little packets like you were saying before.
26:07
Speaker 1: But if light is not this continuous stream of energy
26:10
Speaker 1: like a wave, is right, a wave is continuous stream
26:12
Speaker 1: of energy. What if it comes in these little bits
26:15
Speaker 1: and um? And that explained everything if you if you
26:18
Speaker 1: thought that light was came into little packets, it explained
26:20
Speaker 1: the photo electric effect, explained these all these other mysteries
26:23
Speaker 1: in physics, and that was the birth of quantum mechanics.
26:26
Speaker 1: Did they think that maybe it was little packets of waves?
26:29
Speaker 1: Do you know what I mean? Like little short bursts
26:32
Speaker 1: of ripples? You know, you know what I mean, Like,
26:34
Speaker 1: could that explain how it's both things that run through
26:37
Speaker 1: his brain? Yes? Absolutely, I think that's probably the first
26:41
Speaker 1: way he thought about it. Is like a little localized ripple, right,
26:44
Speaker 1: like um, a little Yeah, that's the best way to
26:48
Speaker 1: put it, A little localized ripple, like the way you
26:50
Speaker 1: can send a little ripple of water um through swimming pool,
26:54
Speaker 1: or something like a chirp or like a little sound burst. Yeah, exactly,
26:58
Speaker 1: like a little chirp. But it's strange because you know,
27:02
Speaker 1: you can make a chirp of any size. You can
27:04
Speaker 1: make a big one, a little one, along one, a
27:05
Speaker 1: fat one. But light, for some reason, wanted to come
27:08
Speaker 1: only these in these little distinct chirps of a specific size,
27:12
Speaker 1: and the size of those chirps was controlled by their
27:15
Speaker 1: their color or their frequency. And so that was the
27:17
Speaker 1: birth of quantum mechanics, which we could spend a whole
27:20
Speaker 1: other podcast talking about um. But it was the first
27:22
Speaker 1: clue that maybe light did come in these distinct little packages. Yeah,
27:26
Speaker 1: let's talk about that, but first let's take a quick break.
27:41
Speaker 1: And that's what we talked about, Like what is a particle.
27:43
Speaker 1: It's a distinct little package and then here's the part
27:47
Speaker 1: that blew my mind is that then they went back
27:49
Speaker 1: and they did that double slit experiment again, but they
27:52
Speaker 1: slowed it down. Instead of shining a really big beam
27:55
Speaker 1: of light, they just shown one photon at a time, right, Okay,
27:59
Speaker 1: because they wanted to see what's going to happen, right
28:02
Speaker 1: if it light comes in these little packets, How does
28:03
Speaker 1: that explain the interference effect? How can light interfere if
28:07
Speaker 1: it's a particle? So like, instead of like pointing the
28:09
Speaker 1: hose of water at these two little holes and just
28:13
Speaker 1: seeing what happens on the other side, they were throwing
28:16
Speaker 1: one droplet of water at a time, yes, exactly, and
28:20
Speaker 1: they what they expected to see was that there would
28:22
Speaker 1: be no interference pattern, right, because the interference comes from
28:25
Speaker 1: having two sources. Right. You have interference when you have
28:28
Speaker 1: two waves that are either adding up or canceling out,
28:31
Speaker 1: meaning like a huge stream of light is going through
28:34
Speaker 1: these two little slids. Then the two little slits act
28:38
Speaker 1: like little sources, like little sorts of ripples, which can
28:41
Speaker 1: cancel that exactly. But if you throw one drop at time,
28:43
Speaker 1: it's either going to go in one slid or it's
28:46
Speaker 1: going to go on the other slid. Right, that's right, yeah,
28:48
Speaker 1: and so there should be nothing to interfere. Right, so
28:51
Speaker 1: that's what they expected. But what they what they saw
28:53
Speaker 1: blew their minds. Right. What happens if you slow the
28:56
Speaker 1: experiment down, you send one photon at a time, is
28:59
Speaker 1: that you will get an interference pattern. It's just that
29:01
Speaker 1: it builds up piece by piece. So used to throw
29:04
Speaker 1: one photon through and it lands someplace on the screen.
29:08
Speaker 1: Through another photon through lands somewhere else on the screen.
29:11
Speaker 1: After you add up a million photons, you rebuild the
29:14
Speaker 1: original interference pattern you saw. What Light is a particle,
29:19
Speaker 1: but it's acting like a wave? Right, How is that?
29:22
Speaker 1: How can that even be? Right? It's not just that
29:24
Speaker 1: it's like it's a particle that's acting like a wave,
29:27
Speaker 1: as if it was in a huge stream of other particles. Right,
29:31
Speaker 1: that's right, And this blew everybody's mind. And the answer,
29:36
Speaker 1: of course, is that light is a particle. But like
29:40
Speaker 1: every kind of matter, like every particle, how it moves
29:44
Speaker 1: is governed by mathematics of wave equations. So every particle
29:49
Speaker 1: carries with it's some quantum mechanical wave that determines where
29:53
Speaker 1: it goes. But what was happening in that experiment was
29:56
Speaker 1: that a particle photon was approaching the experiment and then
30:00
Speaker 1: you could either go through the left hand side or
30:02
Speaker 1: the right hand side slit right, And because it's quantum mechanical,
30:07
Speaker 1: it did both. It had a chance to do both,
30:10
Speaker 1: and what was interfering was the probability to go through
30:13
Speaker 1: the left slit or the right slit. So that's interesting.
30:16
Speaker 1: I don't think i've heard that explanation before that it's
30:18
Speaker 1: a it's a particle and a wave in the sense
30:21
Speaker 1: that it is a particle, but it moves according to
30:24
Speaker 1: wave equations. Yes, everything moves according to wave equations. It's
30:29
Speaker 1: just the wavelength for things depends on how much energy
30:32
Speaker 1: they have. So that was this guy to Brogueli. He
30:35
Speaker 1: came up with this equation and maybe you've heard the
30:37
Speaker 1: expressions and Brogueli wavelength. I've heard the expression wavelength. That
30:40
Speaker 1: seems to be everything is wavelength. We were making fun
30:46
Speaker 1: of that guy. Turns out he was right, twist ending, No, um,
30:52
Speaker 1: everything has a wavelength, right, Um, you can describe the
30:56
Speaker 1: motion of anything in terms of a wave. Now, the
30:59
Speaker 1: wavelength pends on the mass and the momentum and for
31:01
Speaker 1: most things like me or you or cantelope, the wavelength
31:06
Speaker 1: of its quantum mechanical um wave function is tiny, and
31:10
Speaker 1: so you can't even notice, right, there's the wave effects
31:13
Speaker 1: of you and your son walking down the hallway and
31:15
Speaker 1: interferring with each other are basically negligible. But on the
31:19
Speaker 1: scale of particles, these wave functions interfere with each other. Yeah,
31:23
Speaker 1: that's a crazy thodd that you know. We I think
31:27
Speaker 1: people think quantum is something that doesn't affect their lives,
31:29
Speaker 1: but quantum ideas and concepts are everywhere, right, Like you
31:35
Speaker 1: have a sort of like a quantum superposition, or you
31:39
Speaker 1: you're not really there, you sort of there's a cloud
31:42
Speaker 1: of you that I'm not really here. I'm just an
31:45
Speaker 1: a on on the internet. But that's a that's definitely cloud. Yeah,
31:50
Speaker 1: there is this quantum mechanical certainty and everything. Yes, yeah, yeah,
31:54
Speaker 1: it's just you can't notice. That really blew people's minds.
31:57
Speaker 1: This concept that like, okay, light is a particle, but
31:59
Speaker 1: it's so acts like a wave. We can use these
32:02
Speaker 1: wave equations to describe it um. And you know, there's
32:06
Speaker 1: another layer to that experiment which is even crazier, right,
32:09
Speaker 1: which is if what's interfering is the probability to go
32:13
Speaker 1: through the left slit or the right slit right. Then
32:15
Speaker 1: when the when the photon approaches the experiment, it can
32:18
Speaker 1: go through one or the other. The interference pattern comes
32:20
Speaker 1: from the uncertainty of which is going to go through.
32:24
Speaker 1: So what you can do is you can add a
32:25
Speaker 1: little detector to one slit that like gives you a
32:28
Speaker 1: ping if it goes through that slit right, so you
32:30
Speaker 1: know for sure if it goes through one slit or
32:32
Speaker 1: the other. If you do that, the interference pattern disappears.
32:38
Speaker 1: Why does it disappear. It disappears because the interference only
32:41
Speaker 1: came from the interference of the possibility of the particle
32:45
Speaker 1: to go through the left slit or the right slit,
32:47
Speaker 1: our lack of knowledge. Once you know it goes through
32:50
Speaker 1: the right slit of left slit, there's no more uncertainty.
32:52
Speaker 1: There's nothing to interfere. It just goes through the left
32:54
Speaker 1: or goes through the right. It's it's like you're throwing
32:58
Speaker 1: boxes full of hats that are either dead or alive,
33:03
Speaker 1: and you see what happens on the other side. It's
33:05
Speaker 1: different if you take a peek inside the box before
33:08
Speaker 1: it gets there exactly exactly, and no cats were harmed
33:12
Speaker 1: in the making of this podcast. I now feeling hers
33:15
Speaker 1: to point out, Um, that's sort of where we are today,
33:22
Speaker 1: is that we know that light is a particle and
33:24
Speaker 1: then it comes in these little discrete packets become photons, right,
33:28
Speaker 1: But we also know that, like everything else, light is
33:31
Speaker 1: determined by how it's wave function moves. Every particle and
33:34
Speaker 1: every object has this wave function and how it moves
33:38
Speaker 1: is controlled by wave equations. It's not like, uh, it's
33:41
Speaker 1: both particle and a wave and people don't really know
33:44
Speaker 1: which one it is, or people are still confused about that.
33:47
Speaker 1: But it sort of sounds like you're not that confused
33:48
Speaker 1: about it, right, It sort of sounds like you know
33:50
Speaker 1: it's a particle, but it moves around like a wave. Yeah,
33:54
Speaker 1: and but it's still confusing. I mean, I think you could.
33:57
Speaker 1: It's totally reasonable to say it's both. It's a particle
34:01
Speaker 1: but it acts like a wave. Right. It's also totally
34:03
Speaker 1: reasonable to say it's neither. It's not a particle, it's
34:07
Speaker 1: not a wave, it's something else. It's something weird, something
34:10
Speaker 1: totally strange we've never seen before, or a pave you
34:18
Speaker 1: are on fire. The simple spelling. But but that's that's
34:25
Speaker 1: a joke. But it's also serious because sometimes we discover
34:29
Speaker 1: things which are unlike anything else we've seen, and how
34:32
Speaker 1: do you describe them? I mean, we should stop using
34:35
Speaker 1: these words. We should maybe come up with a new
34:37
Speaker 1: word to describe what it is, because it's not not
34:40
Speaker 1: described by either word particle. That's right, it's a chapel,
34:43
Speaker 1: it's a cherry apple combination. Yeah, let's not call it
34:47
Speaker 1: a particle or a wave. Let's just make up a
34:49
Speaker 1: new word that embodies these two ways to behave. That's right.
34:52
Speaker 1: But here we've discovered something which is different from anything
34:55
Speaker 1: in our macroscopic world. There's nothing in our world particles, waves,
35:00
Speaker 1: little puppies that is a good analogy for what light is.
35:03
Speaker 1: So we have to try to sort of describe it
35:05
Speaker 1: in terms of sometimes it's like this, sometimes like this.
35:08
Speaker 1: My personal belief is that it's it's not like anything else,
35:11
Speaker 1: and that these are approximations. But you know, like we
35:15
Speaker 1: were talking about earlier, you can be different contradictory things
35:17
Speaker 1: like how would you describe yourself? You know, sometimes your husband,
35:20
Speaker 1: sometimes your father, sometimes your cartoonist. Sometimes you're just asleep.
35:24
Speaker 1: You know, like all these things describe you their contradictory
35:28
Speaker 1: There are different facets of who you are at your core,
35:30
Speaker 1: and none of them define you right right, But if
35:33
Speaker 1: you don't have to have the right label, you make
35:35
Speaker 1: up and you do right. Yes, we need a new thing.
35:39
Speaker 1: Right light is definitely its own weird kind of thing.
35:44
Speaker 1: All right, Well, until next time. If you still have
35:55
Speaker 1: a question after listening to all these explanations, please drop
35:58
Speaker 1: us a line. We'd love to hear from you. You
36:00
Speaker 1: can find us at Facebook, Twitter, and Instagram at Daniel
36:04
Speaker 1: and Jorge That's one word, or email us at Feedback
36:07
Speaker 1: at Daniel and Jorge dot com.