August 22, 2024 • 47 mins
What is light made of? A particle, a wave, both, neither? Little puppies?
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Speaker 1 (00:00):
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Is it possible to be two different things at the
same time?
Speaker 4 (02:06):
Can you like dogs and cats?
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Can something taste salty and sweet? Can a dress be
black and blue and white and gold?
Speaker 1 (02:19):
In today's podcast, we talk about the centuries old scientific
debate about light.
Speaker 4 (02:26):
Is light a particle or a wave?
Speaker 1 (02:29):
Or is it both? Hello, I'm Jorge and I'm Daniel.
Speaker 4 (02:51):
Welcome to Daniel and Jorge Explain the Universe.
Speaker 1 (02:54):
In which we try to explain the whole universe and
everything in it, including light.
Speaker 4 (02:59):
Now, I'm a tunis I draw something called PhD comics.
Speaker 1 (03:02):
And I'm a particle physicist. During the day, I smash
particles together at the Large Hadron Collider.
Speaker 4 (03:07):
Yeah. Well, today on the program, we're going to talk
about the nature of light.
Speaker 1 (03:16):
That's right. People have been arguing for centuries. What is light?
Is it made out of particles? Is it made out
of waves? 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.
Speaker 4 (03:34):
It's one of the most mind blowing questions in human
scientific history.
Speaker 1 (03:39):
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?
Speaker 4 (03:48):
Is light a particle or is it a wave.
Speaker 1 (03:50):
Here's what people had to say. Do you think light
is made out of particles or waves or both or neither? Photos? Yeah, photons? Yeah,
so you think light's a particle. I think it's waves,
youth waves. Yeah, cool, it's.
Speaker 5 (04:04):
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 people, okay, light, I think they're
made of wavelength Yeah all right.
Speaker 4 (04:22):
Well it's interesting because I think all of the answers
are right.
Speaker 1 (04:28):
Or none of them are rest or both.
Speaker 4 (04:32):
Yeah.
Speaker 1 (04:33):
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, but either those some people
went all in, you know, like it's a photon or
it's a wave, or it's a wave.
Speaker 4 (04:45):
Length right, Yeah, that was my favorite one.
Speaker 1 (04:48):
I want to be a wavelength, Like I've heard of
this word.
Speaker 4 (04:51):
It sounds really cool and scientific. I'm just going to
throw it out there.
Speaker 1 (04:54):
That's right. Yeah, maybe I get some points. We award
no points people, no points, that's right. There's no price.
Your price is you get to be on our podcast,
and maybe we even make fun of you.
Speaker 4 (05:05):
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's some sort of duality there, something weird going on.
Speaker 1 (05:18):
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 you because light is everywhere, right,
and it runs the universe. It's streaming through the Solar
system from the Sun, illuminating our lives, empowering everything on Earth.
So you think this would be sort of a high
priority topic to figure out, like what is this stuff?
(05:39):
What is it made out of?
Speaker 5 (05:40):
Yeah?
Speaker 4 (05:41):
I mean, like, what are we paying you for, Daniel,
if not to figure these types of questions out.
Speaker 1 (05:46):
I was just about to figure out what light was
when you called and said it's time to do this podcast.
Speaker 4 (05:50):
Sorry, science was totally destroy your train of thought.
Speaker 1 (05:55):
There, that's right. Reflect on that for a minute or again.
Speaker 4 (06:00):
But no, Yeah, I'm a California taxpayer. Part of my
salary goes to paying your salary, Like you know, one
million of a percent.
Speaker 1 (06:07):
That's true. Yes, so you're saying you did pay taxes
last year. Again, that's another topic.
Speaker 4 (06:13):
On air Daniel anyway, So that's an interesting question, like
is light a waver or 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 just
(06:36):
like brightness, right.
Speaker 1 (06:37):
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 and water. You drop a
rock in a small puddle, you see waves. We know
(07:00):
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 he 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.
Speaker 4 (07:20):
You can describe it with like equations, right, yeah, wavy equations.
Speaker 1 (07:24):
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?
Speaker 4 (07:44):
So we need like, you know, we know about light,
but we want to know how it behaves and what
makes it work.
Speaker 1 (07:50):
Yeah, and just on a more general level, you try
to see something new, you try to describe in terms
of things you know, Like, say you taste a new
kind of fruit and you 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.
Speaker 4 (08:04):
You know, You're like, it's a chapel.
Speaker 1 (08:06):
It's a chapel. How has nobody ever invented that the
cherry apple chapel. Oh my gosh, somebody, if our lawyer
is listening, get on that right away. Copyright that idea.
Speaker 4 (08:16):
I'll reserve ww dot chapel dot com. Up.
Speaker 1 (08:18):
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.
Speaker 4 (08:26):
So we sort of knew about light. It came from
the sun. It you know, if you light a fire,
it spreads down into a room. And so we're like,
what's going on? Like what what best describes how this
light you know, comes from a source and bounces off
the walls and stuff.
Speaker 1 (08:42):
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?
Speaker 4 (08:50):
How can anything be a wave?
Speaker 1 (08:51):
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, Like it's.
Speaker 4 (08:59):
The take a rip on something.
Speaker 1 (09:01):
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.
Speaker 4 (09:10):
Or like a sound wave is just like air molecules
kind of bumping forward.
Speaker 1 (09:15):
That's right, yeah, exactly. Or a wave in the ocean
is just it's an arrangement of the water, right, It's
a way the water gets compressed and then stretched out
and compressed and then gets stretched out. So that's an
important thing about a wave is that it moves in
this way through a medium.
Speaker 4 (09:29):
M Okay, so that's a wave. It's like a propagation,
it's like a ripple through something. But then so then
what would you call a particle? A particle is different
than that.
Speaker 1 (09:38):
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
(09:58):
bits that can't be opt into smaller bits, and that
they're localized. They're like small and contained. Right. 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.
Speaker 4 (10:15):
Like you would take something and then you smash it
to bit and just keep smashing, and at some point
you're going to get to these little like baby balls
or like little tiny pellets that you can't break down anymore.
Speaker 1 (10:25):
That's right. Yeah, It's like seeing a picture on your
computer screen and discovering it's made out of pixels, right,
and that 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 there's made
of these these little bits that are not connected to
each other, right, they're separated. So a wave and a
(10:46):
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.
Speaker 4 (10:54):
But I think maybe what's important here is that, you know,
particles we tend to think of as little tiny it's
they can bounce around, right and like go in a
street 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.
Speaker 1 (11:12):
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
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.
Speaker 4 (11:31):
So that's kind of what we mean by a wave
and a particle, that's right. Yeah, And so the question
is 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?
Speaker 6 (11:43):
Right?
Speaker 1 (11:44):
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.
Speaker 4 (11:51):
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 anywhere different, right.
Speaker 1 (12:03):
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you know, Yeah, if you vote it you can be
or you could be neither. I suppose you shouldn't be
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election law not recommended to violate elections, right, that's right. Yeah, So,
(12:24):
speaking of political shouting matches, this one, this historical scientific
shouting match, began all the way back with the Greeks, right, Democratus,
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
(12:45):
us that seems macroscopic is made out of tiny little things,
smaller than we can see. And you know, as usual,
when somebody comes up with a good idea, they overextended.
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, at
the time, seemed like a totally a crazy reach.
Speaker 4 (13:05):
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.
Speaker 1 (13:18):
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
or if you started a fire, that the light would
immediately illuminate the room. Now, we of course know that
(13:38):
it just happens super duper crazy fast, too fast for
those folks to ever measure, so it's almost like it's instantaneous.
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Speaker 4 (18:19):
So initially we thought light was or the Greeks thought
that light was a.
Speaker 1 (18:23):
Particle, right, And I think we have to qualify that
because it makes the Greeks sound really smart. Just come
up with this idea of atoms and all that stuff, and.
Speaker 4 (18:32):
You say this before you're really down on the Greeks.
Speaker 1 (18:34):
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. You know,
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 nine hundred and ninety
nine ones that were totally off base, you know, and
give them credit for those.
Speaker 4 (18:55):
Yeah, find that Greek we thought life was just little
puppies and be like seeing you guys also thought there
were puppies. You can't be that smart, that's right.
Speaker 1 (19:03):
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 a Descartes, the guy who's famous for you know,
I think therefore I am he thought about He was
one of the earliest scientists, not just philosopher, but a scientist,
back in the day when you know, science really was
(19:25):
part of philosophy, and he thought that light was waves.
Speaker 4 (19:29):
What made him think it was waves?
Speaker 1 (19:30):
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.
Speaker 4 (19:45):
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.
Speaker 1 (19:57):
Yeah. And there's some things that light does that don't
really that don't really seem consistent with particles, you know,
like the way light bends through a lens, right, it's
called we call in science, we call that refraction. You know,
when light changes from going through air to glass, it
bends in this weird way. That's something that's very common
for waves, right.
Speaker 4 (20:17):
And a particle wouldn't bend inside of a lens.
Speaker 1 (20:22):
No, No, a particle that's definitely a wave like behavior, yeah, oh,
not particle 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?
Speaker 5 (20:37):
Right?
Speaker 1 (20:38):
I mean with sound, you know it's the air and
the water waves. Obviously it's the water. But if light
is a wave, then what is waving?
Speaker 4 (20:45):
Meaning? Like, if light is a ripple, what is it.
Speaker 1 (20:48):
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.
Speaker 4 (20:59):
It couldn't just be like stuff that we can't see.
Speaker 1 (21:03):
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, you know,
(21:24):
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.
Speaker 4 (21:38):
Isn't it is that different than the ether?
Speaker 1 (21:40):
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 to 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.
Speaker 4 (21:56):
Okay, So it was a particle. Light was a particle,
then was a wave, and then what happened.
Speaker 1 (22:00):
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,
(22:21):
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. You know, 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 you know, that's not really an explanation. That's just
sort of like a I don't really understand it. But
(22:41):
maybe it's something like this.
Speaker 4 (22:43):
Like, if light is a particle, why does it split
into the rainbow kind of thing?
Speaker 1 (22:47):
Yeah, exactly. And you know this is again back in
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.
Speaker 2 (23:00):
Right.
Speaker 1 (23:01):
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. But you know,
if that's the way nature works, that's the way nature works,
(23:22):
you have to accept it. But that's the sort of
primacy of experimental results came later on. So back in
the day, people just sort of used to argue for
an explanation that made sense to them.
Speaker 4 (23:32):
Right, Well, it was kind of hard for them to
build a particle collider, right.
Speaker 1 (23:36):
That's right, Yeah, exactly, they didn't have the massive government
funding to do that. These were men of leisure studying
science and the spare time.
Speaker 4 (23:45):
In fact, it was called like natural philosophy, right, It
wasn't called science at the time, was it.
Speaker 1 (23:50):
Yeah, that's right exactly. All science grew out of philosophy.
It was called these folks were natural philosophers. But you know,
later on then people started doing experiments. And there are
a bunch of French guys who did a bunch of
experiments and some of some English folks, and they were
studying how light behaved and refraction and reflection. And they
(24:11):
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. Right. 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
(24:33):
hands at once, right, each one is going to send
waves out. And then when those end, 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
(24:54):
rippling up and the other's rippling down, then then they
cancel each other.
Speaker 4 (24:58):
Out right, And so you would see no light.
Speaker 1 (25:01):
Yeah, exactly, And so you can do this kind of stuff.
You know, 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, in some areas
where the waves are low, in some areas where there
are no waves. And so as you say, if you
do it with light then you see these patterns of
(25:21):
dark and light, these stripes.
Speaker 4 (25:23):
And you couldn't do that with particles, right, Like a
particle wouldn't cancel another particle.
Speaker 1 (25:27):
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
(25:47):
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're like, oh, that is true.
You know, this is a 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.
Speaker 4 (26:06):
Yeah, Like you're like, a doughnut can't possibly be a
croissant at the same time, but it turns out that
you can bake something called a cronat.
Speaker 1 (26:15):
Yeah, exactly. I think that's a big debate in pastry
science still though, Yeah, is it from a donut, like
that's like a croissant, or is it a croissant that's
like a donut.
Speaker 4 (26:23):
Yeah, I'm getting my degree in particle baking.
Speaker 1 (26:28):
Yeah, the large pastry Collider. I'm looking forward to the
construction of that project.
Speaker 4 (26:35):
But that's kind of what you mean. It's like you
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, or they're like, they can't possibly
be doing this, or they can't it can't possibly be
doing that, but it just keeps doing all these weird things.
Speaker 1 (26:50):
Yeah, exactly. And that was the experiment it's called the
double slit experiment, the one that really convinced people that
light is a wave because they've shown a strong light
and they had just two little narrow slits which act
like as sources like slapping your hands in the bath
to water, and then on a screen behind it, they
saw these interference patterns, right, is that you could definitely
(27:11):
only get if light was a wave. And so that
was the early eighteen hundreds 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.
Speaker 4 (27:26):
But how did they explain all those particle experiments?
Speaker 1 (27:28):
Well, this was before we even really knew about particles, right,
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 are starting
to think about atoms and molecules and stuff, but they
hadn't really seen any actual particles yet. And it was
(27:48):
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 ascended, 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.
Speaker 4 (28:04):
Now did people extend that to other things, Like, you know,
they thought, oh, light is this weird wavy thing. But
surely us, we're made out of little tiny atoms.
Speaker 1 (28:12):
Yeah, that's a good question. I wonder if people thought, hm,
light's a wave, maybe we're a wave too, right, yeah?
Speaker 4 (28:19):
Or like everything's just like a wave.
Speaker 1 (28:21):
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
(28:42):
and magnetism, and he put together all these equations to
describe electricity 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
(29:04):
it describes how waves move through a.
Speaker 4 (29:07):
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. So you can
describe it as a sine wave or as cosine wave, right.
Speaker 1 (29:22):
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, okay. 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 like the wave equation. Right,
(29:45):
So he said, oh, electricity magnetism has the same equation
as waves moving through water or waves moving through air.
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 this from these equations was the speed
of light. So he had this moment of epiphany. He
(30:07):
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.
Speaker 4 (30:17):
So like a light bulb turned on on top of
his head, emitting waves.
Speaker 1 (30:21):
Exactly the first appropriate light bulb ever.
Speaker 4 (30:24):
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 ways.
And cosine waves right.
Speaker 1 (30:42):
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.
(31:03):
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, 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
(31:26):
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
(31:48):
electron can only absorb one photon. And 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 it
was a wave. Maxwell's equations told us it was wave.
But then we had the photoelectric effect, which didn't quite
make sense to anybody. Okay, and then Einstein said, well,
(32:10):
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 continuous stream of energy. What if it comes in
these little bits? And that explained everything if you thought
that light was came in these little packets, It explained
the photo electric effect, explained these all these other mysteries
(32:30):
in physics, and that was the birth of quantum mechanics.
Speaker 4 (32:33):
Did he think that maybe it was little packets of waves?
Do you know what I mean? Like little short bursts
of ripples.
Speaker 7 (32:40):
You know?
Speaker 4 (32:41):
Do you know what I mean?
Speaker 1 (32:41):
Like?
Speaker 4 (32:41):
Could that explain how it's both things that run through
his brain?
Speaker 1 (32:45):
Yes? Absolutely, I think that's probably the first way he
thought about it, is 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, Yeah, through a swimming pool,
or something.
Speaker 4 (33:01):
Like a chirp, or like a little sound burst.
Speaker 1 (33:04):
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 these in these little distinct chirps
of a specific size, and the size of those churps
was controlled by their color or their frequency. And so
that was the birth of quantum mechanics, which we could
(33:26):
spend a whole other podcast talking about. But it was
the first clue that maybe light did come in these
distinct little packages.
Speaker 4 (33:33):
Yeah, let's talk about that, But first, let's take a
quick break.
Speaker 2 (33:40):
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Speaker 1 (37:04):
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 slit 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. Right,
(37:25):
if light comes in these little packets, How does that
explain the interference effect? How can light interfere if it's
a particle?
Speaker 4 (37:31):
So like, instead of like 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.
Speaker 1 (37:41):
In 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.
Speaker 5 (37:49):
Right.
Speaker 1 (37:50):
You have interference when you have two waves that are
either adding up or canceling out.
Speaker 4 (37:54):
Meaning like a huge stream of light is going through
these two little slits. Then the two little slits act
like little sources, like little sorts of ripples, which can
cancel ze 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 slid, right, that's right.
Speaker 1 (38:10):
Yeah, and so the should be nothing to interfere, right,
So that's what they expected. But what they what they
saw blew their minds.
Speaker 5 (38:17):
Right.
Speaker 1 (38:18):
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, Throw 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.
Speaker 4 (38:39):
That's crazy.
Speaker 1 (38:40):
What. Yeah, light is a particle, but it's acting like
a wave. Right, how is that? How can that even be? Right?
Speaker 4 (38:46):
It's not just that it's like it's a particle that's
acting like a wave, as if it was in a
huge stream of other particles.
Speaker 1 (38:54):
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's some quantum mechanical wave that determines where
(39:16):
it goes. But what was happening in that experiment was
that a particle photon was approaching the experiment and then
it could either go through the left hand side or
the right hand side slit right, 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
(39:36):
the left slit or the right slit.
Speaker 4 (39:38):
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.
Speaker 1 (39:49):
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 de Brogueli. He came up
with this equation and maybe heard the expression to broguely wavelength.
Speaker 4 (40:02):
I've heard the expression wavelength. That seems to be a.
Speaker 1 (40:04):
Yeah, everything is wavelengths. We were making fun of that guy.
Turns out he was right, oh twist ending, No, everything
has a wavelength, right, 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
(40:25):
like me or you or cantelope, 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
son 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.
Speaker 4 (40:46):
Yeah, that's a crazy thought that you know. We I
think people think quantum is something that doesn't affect their lives,
but quantum ideas and concepts are everywhere, right, Like you
have a sort of like a quantum superposition, or you
you're not really there. You sort of there's a cloud
of you that is.
Speaker 1 (41:06):
I'm not really here, I'm just an AI on the internet.
But that's that's differently cloud. Yeah, there is this quantum
mechanical certainty and everything.
Speaker 4 (41:16):
Guess yeah, yeah, it's just that you can't notice.
Speaker 1 (41:18):
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. Then when the when the photon approaches
(41:40):
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
(42:02):
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 slide of left slit,
there's no more uncertainty. There's nothing to interfere. It just
goes through the left or it goes through the right.
Speaker 4 (42:19):
It's like you're throwing a 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.
Speaker 1 (42:32):
Exactly exactly, and no cats were harmed in the making
of this podcast. I now feel energs 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 become photons, right, Yeah, But
we also know that, like everything else, light is determined
(42:54):
by how its way you function moves. Every particle and
every object has this way you function, and how it
moves is controlled by wave equations.
Speaker 4 (43:03):
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 them. 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.
Speaker 1 (43:17):
Yeah, but it's still confusing. I mean, I think you could.
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 war we
can or a pave you are on fire.
Speaker 4 (43:43):
I am simple spelling, but that's that's a joke.
Speaker 1 (43:49):
But it's also serious because sometimes we discover things which
are unlike anything else we've seen, and how do you
describe them?
Speaker 4 (43:56):
I meaning we should stop using these words. We should
maybe more than new word to describe what it is,
because it's not not described by either word.
Speaker 1 (44:04):
Particle, that's right, it's a chapel, it's a cherry apple combination.
Speaker 4 (44:08):
Yeah, let's not call it a particle or a wave.
Let's just make up any word that embodies these two
ways to behave that's right.
Speaker 1 (44:15):
But here we've discovered something which is different from anything
in our microscopic 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 it's not like anything else,
and that these are approximations. But you know, like we
(44:38):
were talking about earlier, you can be different contradictory things
like how would you describe yourself? You know, sometimes your husband,
sometimes your father, sometimes you're a cartoonist. Sometimes you're just
a sleep you know. Like all these things describe you,
they're contradictory. There are different facets of who you are
at your core, and none of them define you right.
Speaker 4 (44:56):
Right, But if you don't happen to have the right label,
you make up an you know.
Speaker 1 (44:59):
Yeah, that's right, Yes, we need a new thing.
Speaker 5 (45:02):
Right.
Speaker 1 (45:02):
Light is definitely its own weird kind of thing.
Speaker 4 (45:07):
All right, Well, until next time.
Speaker 1 (45:17):
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 Danielandorge dot com. When you
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black and blue and white and gold?
Speaker 1 (02:19):
In today's podcast, we talk about the centuries old scientific
debate about light.
Speaker 4 (02:26):
Is light a particle or a wave?
Speaker 1 (02:29):
Or is it both? Hello, I'm Jorge and I'm Daniel.
Speaker 4 (02:51):
Welcome to Daniel and Jorge Explain the Universe.
Speaker 1 (02:54):
In which we try to explain the whole universe and
everything in it, including light.
Speaker 4 (02:59):
Now, I'm a tunis I draw something called PhD comics.
Speaker 1 (03:02):
And I'm a particle physicist. During the day, I smash
particles together at the Large Hadron Collider.
Speaker 4 (03:07):
Yeah. Well, today on the program, we're going to talk
about the nature of light.
Speaker 1 (03:16):
That's right. People have been arguing for centuries. What is light?
Is it made out of particles? Is it made out
of waves? 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.
Speaker 4 (03:34):
It's one of the most mind blowing questions in human
scientific history.
Speaker 1 (03:39):
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?
Speaker 4 (03:48):
Is light a particle or is it a wave.
Speaker 1 (03:50):
Here's what people had to say. Do you think light
is made out of particles or waves or both or neither? Photos? Yeah, photons? Yeah,
so you think light's a particle. I think it's waves,
youth waves. Yeah, cool, it's.
Speaker 5 (04:04):
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 people, okay, light, I think they're
made of wavelength Yeah all right.
Speaker 4 (04:22):
Well it's interesting because I think all of the answers
are right.
Speaker 1 (04:28):
Or none of them are rest or both.
Speaker 4 (04:32):
Yeah.
Speaker 1 (04:33):
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, but either those some people
went all in, you know, like it's a photon or
it's a wave, or it's a wave.
Speaker 4 (04:45):
Length right, Yeah, that was my favorite one.
Speaker 1 (04:48):
I want to be a wavelength, Like I've heard of
this word.
Speaker 4 (04:51):
It sounds really cool and scientific. I'm just going to
throw it out there.
Speaker 1 (04:54):
That's right. Yeah, maybe I get some points. We award
no points people, no points, that's right. There's no price.
Your price is you get to be on our podcast,
and maybe we even make fun of you.
Speaker 4 (05:05):
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's some sort of duality there, something weird going on.
Speaker 1 (05:18):
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 you because light is everywhere, right,
and it runs the universe. It's streaming through the Solar
system from the Sun, illuminating our lives, empowering everything on Earth.
So you think this would be sort of a high
priority topic to figure out, like what is this stuff?
(05:39):
What is it made out of?
Speaker 5 (05:40):
Yeah?
Speaker 4 (05:41):
I mean, like, what are we paying you for, Daniel,
if not to figure these types of questions out.
Speaker 1 (05:46):
I was just about to figure out what light was
when you called and said it's time to do this podcast.
Speaker 4 (05:50):
Sorry, science was totally destroy your train of thought.
Speaker 1 (05:55):
There, that's right. Reflect on that for a minute or again.
Speaker 4 (06:00):
But no, Yeah, I'm a California taxpayer. Part of my
salary goes to paying your salary, Like you know, one
million of a percent.
Speaker 1 (06:07):
That's true. Yes, so you're saying you did pay taxes
last year. Again, that's another topic.
Speaker 4 (06:13):
On air Daniel anyway, So that's an interesting question, like
is light a waver or 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 just
(06:36):
like brightness, right.
Speaker 1 (06:37):
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 and water. You drop a
rock in a small puddle, you see waves. We know
(07:00):
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 he 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.
Speaker 4 (07:20):
You can describe it with like equations, right, yeah, wavy equations.
Speaker 1 (07:24):
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?
Speaker 4 (07:44):
So we need like, you know, we know about light,
but we want to know how it behaves and what
makes it work.
Speaker 1 (07:50):
Yeah, and just on a more general level, you try
to see something new, you try to describe in terms
of things you know, Like, say you taste a new
kind of fruit and you 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.
Speaker 4 (08:04):
You know, You're like, it's a chapel.
Speaker 1 (08:06):
It's a chapel. How has nobody ever invented that the
cherry apple chapel. Oh my gosh, somebody, if our lawyer
is listening, get on that right away. Copyright that idea.
Speaker 4 (08:16):
I'll reserve ww dot chapel dot com. Up.
Speaker 1 (08:18):
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.
Speaker 4 (08:26):
So we sort of knew about light. It came from
the sun. It you know, if you light a fire,
it spreads down into a room. And so we're like,
what's going on? Like what what best describes how this
light you know, comes from a source and bounces off
the walls and stuff.
Speaker 1 (08:42):
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?
Speaker 4 (08:50):
How can anything be a wave?
Speaker 1 (08:51):
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, Like it's.
Speaker 4 (08:59):
The take a rip on something.
Speaker 1 (09:01):
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.
Speaker 4 (09:10):
Or like a sound wave is just like air molecules
kind of bumping forward.
Speaker 1 (09:15):
That's right, yeah, exactly. Or a wave in the ocean
is just it's an arrangement of the water, right, It's
a way the water gets compressed and then stretched out
and compressed and then gets stretched out. So that's an
important thing about a wave is that it moves in
this way through a medium.
Speaker 4 (09:29):
M Okay, so that's a wave. It's like a propagation,
it's like a ripple through something. But then so then
what would you call a particle? A particle is different
than that.
Speaker 1 (09:38):
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
(09:58):
bits that can't be opt into smaller bits, and that
they're localized. They're like small and contained. Right. 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.
Speaker 4 (10:15):
Like you would take something and then you smash it
to bit and just keep smashing, and at some point
you're going to get to these little like baby balls
or like little tiny pellets that you can't break down anymore.
Speaker 1 (10:25):
That's right. Yeah, It's like seeing a picture on your
computer screen and discovering it's made out of pixels, right,
and that 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 there's made
of these these little bits that are not connected to
each other, right, they're separated. So a wave and a
(10:46):
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.
Speaker 4 (10:54):
But I think maybe what's important here is that, you know,
particles we tend to think of as little tiny it's
they can bounce around, right and like go in a
street 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.
Speaker 1 (11:12):
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
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.
Speaker 4 (11:31):
So that's kind of what we mean by a wave
and a particle, that's right. Yeah, And so the question
is 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?
Speaker 6 (11:43):
Right?
Speaker 1 (11:44):
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.
Speaker 4 (11:51):
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 anywhere different, right.
Speaker 1 (12:03):
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 it you can be
or you could be neither. I suppose you shouldn't be
both though, Yeah, that would be a violation of some
election law not recommended to violate elections, right, that's right. Yeah, So,
(12:24):
speaking of political shouting matches, this one, this historical scientific
shouting match, began all the way back with the Greeks, right, Democratus,
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
(12:45):
us that seems macroscopic is made out of tiny little things,
smaller than we can see. And you know, as usual,
when somebody comes up with a good idea, they overextended.
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, at
the time, seemed like a totally a crazy reach.
Speaker 4 (13:05):
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.
Speaker 1 (13:18):
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
or if you started a fire, that the light would
immediately illuminate the room. Now, we of course know that
(13:38):
it just happens super duper 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
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Speaker 4 (18:19):
So initially we thought light was or the Greeks thought
that light was a.
Speaker 1 (18:23):
Particle, right, And I think we have to qualify that
because it makes the Greeks sound really smart. Just come
up with this idea of atoms and all that stuff, and.
Speaker 4 (18:32):
You say this before you're really down on the Greeks.
Speaker 1 (18:34):
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. You know,
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 nine hundred and ninety
nine ones that were totally off base, you know, and
give them credit for those.
Speaker 4 (18:55):
Yeah, find that Greek we thought life was just little
puppies and be like seeing you guys also thought there
were puppies. You can't be that smart, that's right.
Speaker 1 (19:03):
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 a Descartes, the guy who's famous for you know,
I think therefore I am he thought about He was
one of the earliest scientists, not just philosopher, but a scientist,
back in the day when you know, science really was
(19:25):
part of philosophy, and he thought that light was waves.
Speaker 4 (19:29):
What made him think it was waves?
Speaker 1 (19:30):
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.
Speaker 4 (19:45):
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.
Speaker 1 (19:57):
Yeah. And there's some things that light does that don't
really that don't really seem consistent with particles, you know,
like the way light bends through a lens, right, it's
called we call in science, we call that refraction. You know,
when light changes from going through air to glass, it
bends in this weird way. That's something that's very common
for waves, right.
Speaker 4 (20:17):
And a particle wouldn't bend inside of a lens.
Speaker 1 (20:22):
No, No, a particle that's definitely a wave like behavior, yeah, oh,
not particle 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?
Speaker 5 (20:37):
Right?
Speaker 1 (20:38):
I mean with sound, you know it's the air and
the water waves. Obviously it's the water. But if light
is a wave, then what is waving?
Speaker 4 (20:45):
Meaning? Like, if light is a ripple, what is it.
Speaker 1 (20:48):
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.
Speaker 4 (20:59):
It couldn't just be like stuff that we can't see.
Speaker 1 (21:03):
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, you know,
(21:24):
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.
Speaker 4 (21:38):
Isn't it is that different than the ether?
Speaker 1 (21:40):
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 to 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.
Speaker 4 (21:56):
Okay, So it was a particle. Light was a particle,
then was a wave, and then what happened.
Speaker 1 (22:00):
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,
(22:21):
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. You know, 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 you know, that's not really an explanation. That's just
sort of like a I don't really understand it. But
(22:41):
maybe it's something like this.
Speaker 4 (22:43):
Like, if light is a particle, why does it split
into the rainbow kind of thing?
Speaker 1 (22:47):
Yeah, exactly. And you know this is again back in
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.
Speaker 2 (23:00):
Right.
Speaker 1 (23:01):
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. But you know,
if that's the way nature works, that's the way nature works,
(23:22):
you have to accept it. But that's the sort of
primacy of experimental results came later on. So back in
the day, people just sort of used to argue for
an explanation that made sense to them.
Speaker 4 (23:32):
Right, Well, it was kind of hard for them to
build a particle collider, right.
Speaker 1 (23:36):
That's right, Yeah, exactly, they didn't have the massive government
funding to do that. These were men of leisure studying
science and the spare time.
Speaker 4 (23:45):
In fact, it was called like natural philosophy, right, It
wasn't called science at the time, was it.
Speaker 1 (23:50):
Yeah, that's right exactly. All science grew out of philosophy.
It was called these folks were natural philosophers. But you know,
later on then people started doing experiments. And there are
a bunch of French guys who did a bunch of
experiments and some of some English folks, and they were
studying how light behaved and refraction and reflection. And they
(24:11):
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. Right. 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
(24:33):
hands at once, right, each one is going to send
waves out. And then when those end, 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
(24:54):
rippling up and the other's rippling down, then then they
cancel each other.
Speaker 4 (24:58):
Out right, And so you would see no light.
Speaker 1 (25:01):
Yeah, exactly, And so you can do this kind of stuff.
You know, 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, in some areas
where the waves are low, in some areas where there
are no waves. And so as you say, if you
do it with light then you see these patterns of
(25:21):
dark and light, these stripes.
Speaker 4 (25:23):
And you couldn't do that with particles, right, Like a
particle wouldn't cancel another particle.
Speaker 1 (25:27):
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
(25:47):
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're like, oh, that is true.
You know, this is a 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.
Speaker 4 (26:06):
Yeah, Like you're like, a doughnut can't possibly be a
croissant at the same time, but it turns out that
you can bake something called a cronat.
Speaker 1 (26:15):
Yeah, exactly. I think that's a big debate in pastry
science still though, Yeah, is it from a donut, like
that's like a croissant, or is it a croissant that's
like a donut.
Speaker 4 (26:23):
Yeah, I'm getting my degree in particle baking.
Speaker 1 (26:28):
Yeah, the large pastry Collider. I'm looking forward to the
construction of that project.
Speaker 4 (26:35):
But that's kind of what you mean. It's like you
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, or they're like, they can't possibly
be doing this, or they can't it can't possibly be
doing that, but it just keeps doing all these weird things.
Speaker 1 (26:50):
Yeah, exactly. And that was the experiment it's called the
double slit experiment, the one that really convinced people that
light is a wave because they've shown a strong light
and they had just two little narrow slits which act
like as sources like slapping your hands in the bath
to water, and then on a screen behind it, they
saw these interference patterns, right, is that you could definitely
(27:11):
only get if light was a wave. And so that
was the early eighteen hundreds 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.
Speaker 4 (27:26):
But how did they explain all those particle experiments?
Speaker 1 (27:28):
Well, this was before we even really knew about particles, right,
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 are starting
to think about atoms and molecules and stuff, but they
hadn't really seen any actual particles yet. And it was
(27:48):
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 ascended, 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.
Speaker 4 (28:04):
Now did people extend that to other things, Like, you know,
they thought, oh, light is this weird wavy thing. But
surely us, we're made out of little tiny atoms.
Speaker 1 (28:12):
Yeah, that's a good question. I wonder if people thought, hm,
light's a wave, maybe we're a wave too, right, yeah?
Speaker 4 (28:19):
Or like everything's just like a wave.
Speaker 1 (28:21):
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
(28:42):
and magnetism, and he put together all these equations to
describe electricity 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
(29:04):
it describes how waves move through a.
Speaker 4 (29:07):
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. So you can
describe it as a sine wave or as cosine wave, right.
Speaker 1 (29:22):
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, okay. 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 like the wave equation. Right,
(29:45):
So he said, oh, electricity magnetism has the same equation
as waves moving through water or waves moving through air.
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 this from these equations was the speed
of light. So he had this moment of epiphany. He
(30:07):
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.
Speaker 4 (30:17):
So like a light bulb turned on on top of
his head, emitting waves.
Speaker 1 (30:21):
Exactly the first appropriate light bulb ever.
Speaker 4 (30:24):
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 ways.
And cosine waves right.
Speaker 1 (30:42):
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.
(31:03):
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, 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
(31:26):
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
(31:48):
electron can only absorb one photon. And 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 it
was a wave. Maxwell's equations told us it was wave.
But then we had the photoelectric effect, which didn't quite
make sense to anybody. Okay, and then Einstein said, well,
(32:10):
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 continuous stream of energy. What if it comes in
these little bits? And that explained everything if you thought
that light was came in these little packets, It explained
the photo electric effect, explained these all these other mysteries
(32:30):
in physics, and that was the birth of quantum mechanics.
Speaker 4 (32:33):
Did he think that maybe it was little packets of waves?
Do you know what I mean? Like little short bursts
of ripples.
Speaker 7 (32:40):
You know?
Speaker 4 (32:41):
Do you know what I mean?
Speaker 1 (32:41):
Like?
Speaker 4 (32:41):
Could that explain how it's both things that run through
his brain?
Speaker 1 (32:45):
Yes? Absolutely, I think that's probably the first way he
thought about it, is 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, Yeah, through a swimming pool,
or something.
Speaker 4 (33:01):
Like a chirp, or like a little sound burst.
Speaker 1 (33:04):
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 these in these little distinct chirps
of a specific size, and the size of those churps
was controlled by their color or their frequency. And so
that was the birth of quantum mechanics, which we could
(33:26):
spend a whole other podcast talking about. But it was
the first clue that maybe light did come in these
distinct little packages.
Speaker 4 (33:33):
Yeah, let's talk about that, But first, let's take a
quick break.
Speaker 2 (33:40):
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Speaker 1 (37:04):
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 slit 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. Right,
(37:25):
if light comes in these little packets, How does that
explain the interference effect? How can light interfere if it's
a particle?
Speaker 4 (37:31):
So like, instead of like 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.
Speaker 1 (37:41):
In 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.
Speaker 5 (37:49):
Right.
Speaker 1 (37:50):
You have interference when you have two waves that are
either adding up or canceling out.
Speaker 4 (37:54):
Meaning like a huge stream of light is going through
these two little slits. Then the two little slits act
like little sources, like little sorts of ripples, which can
cancel ze 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 slid, right, that's right.
Speaker 1 (38:10):
Yeah, and so the should be nothing to interfere, right,
So that's what they expected. But what they what they
saw blew their minds.
Speaker 5 (38:17):
Right.
Speaker 1 (38:18):
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, Throw 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.
Speaker 4 (38:39):
That's crazy.
Speaker 1 (38:40):
What. Yeah, light is a particle, but it's acting like
a wave. Right, how is that? How can that even be? Right?
Speaker 4 (38:46):
It's not just that it's like it's a particle that's
acting like a wave, as if it was in a
huge stream of other particles.
Speaker 1 (38:54):
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's some quantum mechanical wave that determines where
(39:16):
it goes. But what was happening in that experiment was
that a particle photon was approaching the experiment and then
it could either go through the left hand side or
the right hand side slit right, 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
(39:36):
the left slit or the right slit.
Speaker 4 (39:38):
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.
Speaker 1 (39:49):
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 de Brogueli. He came up
with this equation and maybe heard the expression to broguely wavelength.
Speaker 4 (40:02):
I've heard the expression wavelength. That seems to be a.
Speaker 1 (40:04):
Yeah, everything is wavelengths. We were making fun of that guy.
Turns out he was right, oh twist ending, No, everything
has a wavelength, right, 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
(40:25):
like me or you or cantelope, 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
son 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.
Speaker 4 (40:46):
Yeah, that's a crazy thought that you know. We I
think people think quantum is something that doesn't affect their lives,
but quantum ideas and concepts are everywhere, right, Like you
have a sort of like a quantum superposition, or you
you're not really there. You sort of there's a cloud
of you that is.
Speaker 1 (41:06):
I'm not really here, I'm just an AI on the internet.
But that's that's differently cloud. Yeah, there is this quantum
mechanical certainty and everything.
Speaker 4 (41:16):
Guess yeah, yeah, it's just that you can't notice.
Speaker 1 (41:18):
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. Then when the when the photon approaches
(41:40):
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
(42:02):
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 slide of left slit,
there's no more uncertainty. There's nothing to interfere. It just
goes through the left or it goes through the right.
Speaker 4 (42:19):
It's like you're throwing a 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.
Speaker 1 (42:32):
Exactly exactly, and no cats were harmed in the making
of this podcast. I now feel energs 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 become photons, right, Yeah, But
we also know that, like everything else, light is determined
(42:54):
by how its way you function moves. Every particle and
every object has this way you function, and how it
moves is controlled by wave equations.
Speaker 4 (43:03):
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 them. 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.
Speaker 1 (43:17):
Yeah, but it's still confusing. I mean, I think you could.
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 war we
can or a pave you are on fire.
Speaker 4 (43:43):
I am simple spelling, but that's that's a joke.
Speaker 1 (43:49):
But it's also serious because sometimes we discover things which
are unlike anything else we've seen, and how do you
describe them?
Speaker 4 (43:56):
I meaning we should stop using these words. We should
maybe more than new word to describe what it is,
because it's not not described by either word.
Speaker 1 (44:04):
Particle, that's right, it's a chapel, it's a cherry apple combination.
Speaker 4 (44:08):
Yeah, let's not call it a particle or a wave.
Let's just make up any word that embodies these two
ways to behave that's right.
Speaker 1 (44:15):
But here we've discovered something which is different from anything
in our microscopic 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 it's not like anything else,
and that these are approximations. But you know, like we
(44:38):
were talking about earlier, you can be different contradictory things
like how would you describe yourself? You know, sometimes your husband,
sometimes your father, sometimes you're a cartoonist. Sometimes you're just
a sleep you know. Like all these things describe you,
they're contradictory. There are different facets of who you are
at your core, and none of them define you right.
Speaker 4 (44:56):
Right, But if you don't happen to have the right label,
you make up an you know.
Speaker 1 (44:59):
Yeah, that's right, Yes, we need a new thing.
Speaker 5 (45:02):
Right.
Speaker 1 (45:02):
Light is definitely its own weird kind of thing.
Speaker 4 (45:07):
All right, Well, until next time.
Speaker 1 (45:17):
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 Danielandorge dot com. When you
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