Newton vs Huygens: corpuscular vs wave models of light explained and refuted

Summary

This video script delves into the historical debate on the nature of light between 17th-century scientists Christiaan Huygens and Isaac Newton. Huygens proposed a wave theory, while Newton championed the corpuscular theory. The script explores how each model explained light phenomena like reflection, refraction, and polarization, and how experiments by Young and others eventually favored the wave theory. It concludes with the modern understanding of light's wave-particle duality, highlighting the scientific evolution from Newton's influence to quantum mechanics.

Takeaways

• 🔍 In the 17th century, the nature of light was debated, with Christiaan Huygens and Isaac Newton proposing opposing theories.
• 🌊 Huygens argued that light was a form of a wave, while Newton believed it was made up of particles, called corpuscles.
• 🧪 Both scientists used their models to explain behaviors of light such as reflection, refraction, and polarization.
• 🪞 Newton's corpuscular theory explained reflection by considering light particles as tiny elastic masses that obey the laws of physics.
• 🔍 Newton also used his theory to explain refraction, suggesting that light particles interact with matter, increasing their velocity in denser substances.
• 🌈 Newton's prism experiment demonstrated that white light is made up of different colors, each with particles of different sizes.
• 🌊 Huygens' wave theory explained reflection and refraction using the concept of wave fronts and wavelets, as well as diffraction, which Newton's theory could not.
• 📉 Huygens' model could also explain diffraction and polarization better than Newton's corpuscular theory.
• 📜 Despite the advantages of Huygens' wave theory, Newton's corpuscular theory initially gained more acceptance due to Newton's scientific stature.
• 🔬 The wave theory of light eventually prevailed in the 19th century with key experiments by Thomas Young and Léon Foucault, disproving Newton's model.
• 💡 Light is now understood as having a wave-particle duality, combining aspects of both Huygens' and Newton's theories, as demonstrated by Einstein's work on the photoelectric effect.

Q & A

What were the two main theories about the nature of light in the 17th century?

The two main theories were the wave theory proposed by Christiaan Huygens and the corpuscular theory proposed by Isaac Newton.

What experiment in 1679 helped establish that light travels at a finite speed?

The experiment by La Roma, who studied the eclipses of one of Jupiter's moons, helped establish that light travels at a finite speed.

How did Newton explain the reflection of light using his corpuscular theory?

Newton explained reflection by stating that light particles, or corpuscles, would bounce off surfaces with the same angle of incidence as the angle of reflection, due to elastic collisions.

What was Newton's explanation for the refraction of light?

Newton believed that light particles would slow down when entering a denser medium, causing them to bend towards the normal due to attractive forces, and then speed up again when exiting the medium.

Why did Newton's corpuscular theory fail to explain certain phenomena like diffraction?

Newton's corpuscular theory could not adequately explain diffraction because it did not account for the wave-like behavior of light spreading out after passing through a small opening.

How did Huygens' wave theory explain the reflection and refraction of light?

Huygens' wave theory explained reflection and refraction by considering the wavefronts produced by secondary wavelets at the boundary of the medium, which then interfere constructively to form new wavefronts at different angles.

What experiment by Thomas Young in 1801 challenged Newton's corpuscular theory?

Thomas Young's double-slit experiment demonstrated interference patterns, which supported the wave theory of light and challenged the corpuscular theory.

What experiment in 1854 provided evidence against Newton's theory of light speed in different media?

In 1854, an experiment by Augustin-Jean Fresnel showed that light travels slower in water than in air, which contradicted Newton's expectation that light would speed up in denser media.

What is the modern understanding of light, as per Maxwell's electromagnetic theory?

Maxwell's electromagnetic theory describes light as a transverse wave composed of oscillating electric and magnetic fields, which travels through space at the speed of light.

How does the wave-particle duality concept relate to the historical debate between Newton and Huygens?

The wave-particle duality concept, introduced by Einstein's photoelectric effect, suggests that light behaves both as a wave and as a particle (photons), thus indicating that both Newton's and Huygens' theories had elements of truth.

Outlines

00:00

🔬 The Great Debate of Light: Waves vs. Corpuscles

This paragraph introduces the historical debate on the nature of light during the 17th century, focusing on the contrasting theories of Christiaan Huygens and Isaac Newton. Huygens proposed that light behaves like a wave, while Newton believed light was composed of particles, or 'corpuscles'. The paragraph sets the stage for a deeper exploration of these theories and their implications for understanding light's behavior, such as reflection, refraction, and polarization. It also mentions the experiment by La Roma in 1679, which established that light travels at a finite speed, a key discovery in the scientific understanding of light.

05:01

🌈 Newton's Corpuscular Theory: Reflection, Refraction, and Prism Experiment

This paragraph delves into Isaac Newton's corpuscular theory of light, explaining his views on reflection and refraction. Newton posited that light particles, or corpuscles, behave like tiny, perfectly elastic particles traveling at high speeds, obeying the laws of physics. The paragraph describes Newton's explanation of the law of reflection and his concept of how light bends when it enters a different medium, attributing this to attractive forces within the material. It also discusses Newton's famous prism experiment, which dispersed white light into a spectrum of colors, supporting his idea that light is made up of different-sized corpuscles, each corresponding to a color in the visible spectrum.

10:02

🌊 Huygens' Wave Theory: Reflection, Refraction, and Diffraction

The paragraph shifts focus to Christiaan Huygens' wave theory of light, which describes light as emanating in wave fronts that generate successive wave fronts. It explains how Huygens used this model to explain reflection and refraction, using animations to visualize the wavelets forming at boundaries and demonstrating how both reflection and refraction can occur simultaneously. The paragraph also touches on diffraction, a phenomenon that Huygens' wave model could explain but Newton's corpuscular theory could not, and mentions the lack of a satisfactory explanation for double refraction from either model at the time.

📉 The Rise and Fall of Theories: From Corpuscles to Waves

This final paragraph summarizes the historical reception of the two theories, noting that Newton's corpuscular theory was more widely accepted due to his scientific stature and the lack of a mathematical explanation for Huygens' wave theory. It discusses the key experiments in the 19th century that eventually led to the downfall of the corpuscular theory: Thomas Young's double-slit experiment demonstrating interference, a phenomenon consistent with the wave model, and an experiment by Augustin-Jean Fresnel that showed light travels slower in water than in air, contradicting Newton's predictions. The paragraph concludes with a modern understanding of light as having wave-particle duality, acknowledging the contributions of both Huygens and Newton to our comprehension of light.

Keywords

💡Reflection

Reflection is the phenomenon where light bounces off a surface. In the video, Newton's corpuscular theory is used to explain reflection by considering light as particles that bounce off surfaces in a predictable manner, adhering to the law of reflection (incident angle equals reflected angle). This concept is essential to understand how light behaves when it encounters different surfaces.

💡Refraction

Refraction is the bending of light as it passes from one medium to another, changing speed. Newton's particle theory explains refraction by suggesting that light particles speed up when entering a denser medium, while Huygens' wave theory explains it through the bending of wave fronts. This concept helps explain phenomena like lenses focusing light.

💡Diffraction

Diffraction is the spreading out of light waves when they pass through a small opening or around an obstacle. The video discusses how Newton's particle theory couldn't explain diffraction, whereas Huygens' wave theory could, demonstrating the wave nature of light.

💡Interference

Interference is the phenomenon where two or more waves overlap, resulting in a new wave pattern. In the video, interference is highlighted as a key behavior that Newton's particle theory couldn't explain, but Huygens' wave theory could. This is important for understanding wave properties and phenomena like the double-slit experiment.

💡Polarization

Polarization refers to the orientation of light waves in a particular direction. The video touches on how neither Newton's nor Huygens' theories could fully explain polarization, which later became understood through the wave theory of light. This concept is crucial for understanding how light behaves in crystals and other media.

💡Wave-particle duality

Wave-particle duality is the concept that light exhibits both wave-like and particle-like properties. The video concludes that both Newton and Huygens were partially correct, as modern physics recognizes light as having this duality. This duality is a fundamental concept in quantum mechanics and explains various light behaviors.

💡Corpuscular theory

Corpuscular theory, proposed by Isaac Newton, suggests that light is made up of particles called corpuscles. The video explains how Newton used this theory to describe reflection, refraction, and dispersion, but it couldn't account for diffraction and interference. This theory was dominant until wave theory gained acceptance.

💡Wave theory

Wave theory, proposed by Christiaan Huygens, describes light as a series of wave fronts. The video uses this theory to explain reflection, refraction, and diffraction, showing that light behaves as a wave. This theory laid the groundwork for understanding many optical phenomena and eventually led to the acceptance of wave-particle duality.

💡Ether

Ether was a hypothesized medium through which light waves were thought to travel. Huygens believed in the existence of ether to explain how light waves could propagate through space. The concept of ether was eventually discarded with the advent of electromagnetic theory and the understanding that light does not require a medium to travel.

💡Scientific Revolution

The Scientific Revolution was a period of major scientific advancements in the 16th and 17th centuries. The video places Newton and Huygens within this context, showing how their work on light was part of a broader movement towards modern scientific understanding. This era laid the foundations for many principles and discoveries in physics and other sciences.

Highlights

In the 17th century, the nature of light was a mystery, with two opposing theories by scientists Christiaan Huygens and Isaac Newton.

Huygens proposed light as a wave, while Newton believed in light being composed of particles called corpuscles.

Newton's corpuscular theory explained reflection and refraction by treating light particles as tiny, perfectly elastic objects.

Huygens' wave theory suggested that each wavefront generates new wavelets, creating a pattern of spherical waves.

Newton's model could not explain phenomena like diffraction, where light bends around obstacles.

Huygens' wavefront model provided a better explanation for diffraction, showing how waves bend around barriers.

Newton's theory was favored due to his scientific stature and the lack of a mathematical framework for Huygens' theory.

The wave theory gained support with Thomas Young's double-slit experiment demonstrating light interference in 1801.

The speed of light experiment by Foucault in 1854 contradicted Newton's theory, supporting the wave nature of light.

Maxwell's electromagnetic theory later described light as a transverse wave of oscillating electric and magnetic fields.

Einstein's photoelectric effect in 1905 showed light also has particle-like properties, introducing the wave-particle duality.

Huygens and Newton's theories were both partly correct, illustrating the complexity of understanding light's nature.

The historical debate between wave and particle theories of light has led to a deeper understanding of quantum mechanics.

The scientific community's initial preference for Newton's theory highlights the influence of a scientist's reputation.

The evolution of light theories from the 17th to the 20th century reflects the dynamic nature of scientific knowledge.

Huygens' wave model was able to explain reflection and refraction more consistently than Newton's corpuscular theory.

The wave-particle duality of light is a fundamental concept in modern physics, bridging classical and quantum theories.

The historical journey of light theories exemplifies the scientific method's iterative process of hypothesis, experiment, and revision.

Transcripts

like we all see it and its effects

reflection refraction just to name a

couple but what actually is it now today

we've got some good answers but back in

the 17th century

nobody scientists had any idea but to

scientists at the time had some IDs

however they were in complete opposition

so today we're gonna look at their two

models and how they explain various

light behaviors and see who won out in

the end

just a tune

[Music]

now there were two great scientists in

that time christiaan huygens for Holland

and Isaac Newton from England who lived

roughly around the same time in the 17th

century right at the midst of what we

now call the Scientific Revolution and

in the latter half of that century a key

experiment took place that established

that life wasn't some instantaneous

substance but that like travel at a

finite speed so to speak and that was

the experiment by la Roma in 1679 as he

studied the eclipses of one of the moons

of Jupiter now I did a video on that

that discusses that not pop a

description just above but the question

was what was light actually made up of

now Christian Huygens argue that light

was a form of a wave Isaac Newton

however believed that light was actually

made up of particles which he called

corpuscles now both used their models to

explain various behaviors of Lights such

as reflection and refraction and

polarization and what I plan to do is

use their models to explain these

behaviors now I want to stress though

that what I'm presenting is not the real

explanation of the behavior of light but

how these men believed it to be so let's

start with Newton now Newton believed

that these corpuscles of light were tiny

perfectly elastic particles traveling at

very high speeds they behaved with the

laws of physics like any masses such as

balls and planets but since there was so

tiny when two light beams intersected

they did not scatter with each other so

let's have a look how he explained

various phenomena so let's talk about

Newton's understanding of reflection

using this corpuscular method I'm going

to assume you understand the law of

reflection that is the incident angle

equals of the reflected angle now here's

our particle it's coming in and it's

bouncing off the surface and of course

it's coming off of the other side now

let's have a look at the path - here's

our path and Newton said well hold on

it's moving in two directions it's

moving horizontally but it's also moving

vertically so horizontally he's saying

well that's going to be exactly the same

velocity it's not gonna change

velocities in terms of the horizontal

motion but because it's an elastic

collision as far as Newton understood it

he said to all the

vertically is the same verb as the

velocity vertically on the other side

obviously in the opposite direction and

so when you resolve those two vectors

you're going to see that the actual

angle coming in is the same as the angle

alpha and so there is Newton's

understanding of reflection let's now

look at refraction so he is our particle

and it is also moving and in this case

our particle is not bouncing off the

surface it is now entering into the

surface and again in this case Newton's

nose that it bends towards the normal I

assume you understand the nature of

refraction at least in that terminology

and so he said again horizontally we

have motion in that direction and we

still have that velocity also in that

direction once we go into the surface

why doesn't Bend well it's a particle

and so this particle interacts with the

matter and so as a result there's these

attractive forces now while sits inside

the matter those forces cancel out so

therefore the path remains straight same

outside as well but the issue is what

happens at the interface and so Newton

argued said well hold on what's going to

happen here is that there's a source of

attraction and so what that means is

that it's going to be pulled in and so

as a result if the velocity of the

situation here is that value here he's

saying look the matter interacts with it

and pulls it in stronger and as a result

it's going to have a velocity that is

bigger and so when you resolve those two

vectors you're going to get an angle

here like so and an angle here like so

and here's the critical point if the way

that Newton saw it is that the velocity

increases as it passes through the

substance and you can see that by just

looking at the mathematics of these

vectors is that the vector is now larger

and so that's a critical point here with

Newton's corpuscular theory is that he

assumed that the velocity of the core

bustles is actually greater in the

denser substance and because of the fact

that denser substances have more

particles there

go traveling faster and therefore you

have different refractive indexes which

is about the relationship of the

velocities with the outside and the

inside but I want you to note though we

often see reflection and refraction

happening for example if you look at a

glass you see reflection but you also

see through it to your self refraction

and unfortunately Newton's corpuscular

theory doesn't allow for an explanation

for that so now let's have a look at his

famous experiment to do with prisms and

many of you may have be recognized

something similar into this image of

what Newton did and so we had the light

passing through a prism and of course it

dispersed and we produced a rainbow now

how did he explain this so let's have a

closer look and so here is our white

light and here we look at just the path

of the red corpuscle well if it's a red

corpuscle we need a corpuscle

in place and so what Newton argued is

like this corpuscle is reasonably large

and so therefore the material interacts

with it bends it as we discussed it

before in refraction and only bends it a

certain amount because of the size of

the Capasso

but what about the other colors well

they also made up of corpuscles but they

progressively get smaller as we move up

the spectrum and so therefore the

smaller the particle the smaller the

corpuscle the more effect the

interaction of the material of the glass

and so it bends more so he was able to

show that white light isn't a single

entity it's actually made up of

different colors why because different

colors have different size of corpuscles

and so by using a prism he was able to

spread them out and therefore show the

colors of the rainbow now here I've got

five representative examples of our

colors of the rainbow and you say all

aren't there supposed to be seven well

really the number seven was actually put

in placement by Newton why seven well

actually he thought seven was a nice

number to spread the colors of the

rainbow out into it because in the Greek

mythology seven was a mystical number

and so that's why we have seven colors

of the rainbow it has nothing to do with

the fact that there is only seven colors

in the Roma there's actually an almost

infinite number of colors of in the

rainbow now unfortunately he failed to

come up with an adequate explanation for

a

a phenomena and that was diffraction you

see when light passes through a small

hole it spreads out and if light was

made of particles why would it do that

and then there was the observation by

Erasmus battlin who observed a double

refraction of light through it calcite

crystals now two images appeared and

they moved as you turn the crystal maybe

the light was split into two types and

Ethan's best response was on this idea

was that that the cop fossils had some

sort of sides but really that wasn't

satisfactory so now let's have a look at

Huygens heigen believed that light

source emanated in the form of wave

fronts and that there were spherical and

that each wave front would generate the

next wave front and so forth well let me

explain this so here I have a wave I'm

going to imagine here is a wavefront or

a set of a ring of waves after you've

dropped a stone in the pond and this is

the way that heigen tried to imagine why

there were successive wave fronts so

this wave front he will produce a

particular wavelet in a particular

direction now it's actually spherical

but we've got a two-dimensional aspect

here now we know of course that sphere

goes backwards and side words and at

least as far as heigen he really didn't

explain why are we only having this one

he in this direction but we're going to

use that as our example now obviously

that's not the only point there are lots

of points all around that that also

produce these wavelets now I've only got

a certain number here but there are

actually many many more but what happens

is that all of those add up to produce

our next wavefront and then of course

you get your successive wave fronts

after that each being produced by the

one that was previous if we then look at

the direction of the wave fronts you'll

see that the path the Ray so to speak is

perpendicular to the wave fronts at all

junctions and now what we're going to do

is we're going to use Christian Huygens

understanding of wave fronts to see how

he explained reflection and refraction

but in this case we're going to use an

animation to help us understand that and

I'll use this animation from water faint

and I'm going to put a link in the

description below if you want to have

more at some of his great animations so

here you can see the wave front coming

in and of course it's moving from the

left side of the screen now watch what

happens when it hits the surface you can

see little wavelets being formed and as

a result it produces a wave front that

is moving off at exactly the same angle

then the wave front that arrived so

here's a wave front coming in and in

this case you'll see that our wave front

in this case produces these little

wavelets that are now passing through

the material but because the wavelets

are now moving slower you'll see that

the wave front that's produced when they

add up is actually moving at a different

angle towards the normal and you can see

that now and now what you're going to

see is both reflection and refraction

occurring at the same time and you'll

see that Huygens model adequately

explains why that occurs we have the

wavelets forming at the boundary that

are reflecting and also wavelets bound

happening at the boundary that are

refracting and you see both take place

the key thing here is is that Huygens

model also was able to explain

diffraction let me explain so as you can

see from this great animation from Phet

you see the wave fronts hitting the

barrier but there's a small opening but

because the wave fronts are made up of

successive little wavelets the one

wavelet that meets the opening continues

and so therefore you get these

concentric circles on the other side of

the wall

you see diffraction and the waves are

bending around the wall and what about

the double refraction now Huygens didn't

really have an answer but it was later

as polarization was further studied in

the 19th century and a wave model best

describes the behavior of polarization

so in essence Huygens saw light is a

form of a longitudinal wave traveling

through space now what would the medium

be well he believed there existed this

unseen medium called the ether which

allowed light to travel through space so

let's summarize so in terms of

reflection in terms of their models we

can argue that Newton did a pretty good

job but so did Hogan in terms of

refraction yes Newton did a reasonably

good job of understanding wide bends

as did Huygens what about diffraction

well diffraction is problematic in terms

of mutants oh no that doesn't work there

but Huygens understanding definitely

works polarization which is the double

refraction that was observed neither

could really provide a good explanation

as to why they occurred and then we go

interference now in terms of

interference that wasn't really studied

properly until the 19th century

Newton's understanding doesn't help us

understand it at all

whereas Huygens understanding of waves

does so how did the scientific community

respond well Newton's corpuscular theory

was the one that held sway in a

scientific community

and there are really two reasons for

this now first Newton was a huge man of

scientific stature his Principia are we

discussed the laws of motion and the

calculus that supported it was hugely

popular and accepted now who was one to

argue with him on his use of light now

Newton did have his critics of the

Cabasa Coulomb model and one of his most

vocal critics was Francis Bacon who

supported the wave model and it's

possibly the reason why I'm Newton

delayed publishing his book optics until

Bacon died now secondly Hogan was lesser

known and he also only provided a

geometric explanation for light and not

a mathematical one and that was what's

needed if it was to be accepted by the

scientific community and that really

didn't come until the work of Fresnel in

the early 1800s and so the capacitor

theory stood for some time until that is

two key experiments in the 1800s

now the first was in 1801 by Thomas

Young with his double slit experiment

again I have a video already on that and

I encourage you to look at the link

above but the key finding here is that

he was able to demonstrate interference

using the wave model of light however

there are still some resistance in the

scientific community to reject the

corpuscular theory and then in 1854 coal

in a modified setup of his apparatus to

measure the speed of light determined

that light traveled slower in water than

air now this was in direct opposition to

Newton's model where he expected the

light to speed up but only ways would

slow down in water and thus that spelled

the end of the cost

theory it's funny how a single

experiment can destroy a whole world

constructive model but science works

that way light was a wave after all

now both models actually are flawed and

they've been replaced with Maxwell's

electromagnetic theory yes light is a

wave or it's a transverse wave composed

of oscillating electric and magnetic

fields and I encourage you to check out

my video on Maxwell so is that how the

story ends well no in 1905 Einstein

published his work on the photoelectric

effect which demonstrated that light

travelled in discrete packets which he

called quanta or photons as we now call

them so light troubles as a wave and a

particle now we refer to this as the

wave particle duality of light so in a

roundabout way Newton and Huygens were

both right after all I hope that's

giving you a better understanding of the

history behind understanding of the

nature of light check out my other

videos on Maxwell's theory as well as

the history behind determining the speed

of light please like share and subscribe

drop a comment down below if this video

has been particularly helpful my name is

Paul from high school physics explained

take care bye for now