Episode 40: Optics - The Mechanical Universe

Summary

This script delves into the physics of light, explaining its wave-like nature and propagation through space. It discusses the electromagnetic field, the role of electric and magnetic fields, and how disturbances in these fields lead to light's propagation. The script explores the historical development of understanding light, from Galileo's telescope and microscope to Newton's work on refraction and dispersion. It also touches on the wave properties of light, such as interference and diffraction, and the technological advancements like the reflecting telescope. The concept of the luminiferous ether and the failed attempts to detect it are also mentioned, setting the stage for future discussions on the nature of light and its interaction with matter.

Takeaways

• 🌐 Maxwell's Theory provides a comprehensive understanding of how light propagates through empty space as a wave-like disturbance in the electromagnetic field.
• 🔍 The electromagnetic field can be detected by electric charges, with forces indicating the presence of electric and magnetic fields.
• 👀 Human eyes are natural instruments that detect disturbances in the electromagnetic field, allowing us to see.
• 🌊 Light exhibits wave properties such as spreading from a point, forming plane waves, and bending around corners, similar to water waves.
• 🌈 The behavior of light waves, including interference and diffraction, was demonstrated by Thomas Young, supporting the wave theory of light.
• 🔭 Galileo's use of the telescope and microscope expanded our ability to observe both macroscopic and microscopic worlds.
• 🌈 The phenomenon of refraction, explained by the bending of light as it passes through different media, is fundamental to the function of lenses in devices like glasses, microscopes, and telescopes.
• 🌈 Dispersion, the spreading of light into its component colors, occurs due to different colors of light refracting by different amounts.
• 🌌 The electromagnetic spectrum includes a wide range of wavelengths, from radio waves to gamma rays, each with distinct properties and applications.
• 🚀 The concept of the luminiferous ether, a medium for light waves, was proposed but never empirically confirmed, leading to significant debates and experiments in the 19th century.

Q & A

What is the electromagnetic field and how can its presence be detected?

The electromagnetic field is a field that is present whenever electrical and magnetic forces are exerted on charged particles. Its presence can be detected using electric charges; an electric field is present if a stationary charge feels a force, and a magnetic field is present if a moving charge feels a force due to its motion.

How does a disturbance in the electromagnetic field propagate?

A disturbance in the electromagnetic field propagates as a wave-like disturbance, with energy sloshing back and forth between the electric and magnetic fields. This disturbance travels at a constant speed, which is one of the fundamental constants of nature.

What is the role of the human eye in detecting disturbances in the electromagnetic field?

The human eye acts as a natural detector of disturbances in the electromagnetic field, specifically in the form of visible light. It allows us to perceive light and thus 'see' the disturbances as part of our visual experience.

How did Galileo contribute to the advancement of our understanding of light and the cosmos?

Galileo made significant contributions by using the telescope to observe astronomical phenomena such as Saturn's rings, sunspots, the phases of Venus, the moons of Jupiter, and the craters of the Moon. He also used the compound microscope to see tiny objects in detail, advancing the field of optics.

What is refraction and how does it relate to the lenses used in glasses, microscopes, and telescopes?

Refraction is the bending of light as it passes from one medium to another, such as from air into glass. It is the principle used in the design of lenses for glasses, microscopes, and telescopes to focus light to a point by grinding curved lenses that take advantage of this bending effect.

How did Isaac Newton's experiments with a prism contribute to our understanding of light?

Isaac Newton's experiments with a prism revealed that white light is composed of all the colors of the rainbow, a phenomenon known as dispersion. This showed that light could be separated into its constituent colors, and it also led Newton to propose that light was made up of particles.

What is the difference between longitudinal and transverse waves, and which type are electromagnetic waves?

Longitudinal waves involve the oscillation of particles in the direction of the wave's travel, while transverse waves involve oscillations perpendicular to the direction of travel. Electromagnetic waves are always transverse, with the electric and magnetic fields oscillating perpendicular to the direction of wave propagation.

How does the wavelength of light affect its behavior, such as casting shadows?

The wavelength of light affects how it bends around corners and how sharply it can cast shadows. Shorter wavelengths do not spread out as much, allowing for more defined shadows. Visible light, with wavelengths in the hundreds of nanometers, is small enough to cast very sharp shadows compared to the sizes of normal objects.

What is the principle of shortest time, and how does it relate to the reflection and refraction of light?

The principle of shortest time states that light takes the path that allows it to reach a destination in the least amount of time. This principle explains why light changes direction upon reflection or refraction, as it chooses the path that ensures the fastest reconstruction of the wavefront through constructive interference.

How does the phenomenon of dispersion affect the performance of telescopes?

Dispersion causes different colors of light to refract by different amounts, which can lead to chromatic aberration and a spreading of light into a spectrum of colors. This limits the performance of refracting telescopes, which is why reflecting telescopes, which do not suffer from dispersion, were developed.

What was the luminiferous ether, and why was it significant in the 19th century?

The luminiferous ether was a hypothetical medium through which light was thought to propagate in the 19th century. It was considered the medium that transmitted light, similar to how air transmits sound. Experiments to detect the motion of the Earth through the ether, such as the Michelson-Morley experiment, were significant in the development of our understanding of the nature of light and led to the theory of relativity.

Outlines

00:00

🌌 Understanding Light Propagation

This paragraph introduces the fundamental understanding of light propagation through empty space, as explained by Maxwell's Theory. It discusses how light is a wave-like disturbance in the electromagnetic field and how disturbances in the electric field can affect the magnetic field, and vice versa, creating a wave that propagates at a constant speed. The human eye is highlighted as a natural instrument for detecting these disturbances, and the paragraph sets the stage for exploring the properties of light, such as its wave nature and the ability to form plane waves, which are foundational to understanding light's behavior.

05:02

🔭 Galileo's Contributions to Optics

The second paragraph delves into Galileo's significant role in advancing the field of optics. Despite not inventing the telescope, Galileo made extensive use of it to observe astronomical phenomena like Saturn's rings and the moons of Jupiter. The paragraph also touches on the invention of the compound microscope, which allowed Galileo to see minute details of insects. The discussion then shifts to the historical use of eyeglasses and the scientific principle of refraction, which is crucial for the function of lenses in both microscopes and telescopes. The concept of dispersion is introduced through the example of a prism, which separates white light into its constituent colors, a phenomenon investigated by Isaac Newton.

10:06

🌈 The Electromagnetic Spectrum

This paragraph explores the electromagnetic spectrum, explaining that electromagnetic waves are transverse and travel at the speed of light in a vacuum. It details the vast range of frequencies and wavelengths that make up the spectrum, from gamma rays with the shortest wavelengths to radio waves with the longest. The paragraph also discusses the role of the atmosphere in protecting living things from harmful ultraviolet light and how different wavelengths interact with matter, leading to the creation of the entire spectrum. The historical contributions of Michael Faraday and James Clerk Maxwell are acknowledged for their work in understanding the nature of light and the electromagnetic field.

15:06

🌈 Light as a Wave: Interference and Shadow Casting

The fourth paragraph focuses on the wave nature of light and Thomas Young's demonstration of light's interference, which confirmed its wave-like properties. It explains how constructive and destructive interference create patterns of bright and dark fringes, respectively. The discussion then moves to the question of how light, being a wave, can cast sharp shadows, which is attributed to the relative sizes of the light's wavelength and the objects it encounters. The paragraph also describes how light waves interact with electric charges, leading to the creation of new waves and the phenomenon of reflection, which is fundamental to both mirrors and lenses.

20:09

🔄 Reflection and Refraction of Light

This paragraph discusses the principles of light reflection and refraction. It explains mirror reflection, where the angle of incidence equals the angle of reflection, and how this principle applies to both mirrors and lenses. The concept of refraction is introduced, detailing how light slows down when it enters a medium like glass, causing it to change direction. The paragraph also addresses the issue of dispersion, which causes different colors of light to refract at different angles, leading to the spread of white light into a spectrum of colors. The historical shift from refracting to reflecting telescopes is mentioned, highlighting Isaac Newton's invention of the reflecting telescope to overcome chromatic aberration.

25:09

🌐 The Lumiferous Ether and the Nature of Light

The final paragraph ponders the question of what medium light travels through in empty space, a concept historically referred to as the luminiferous ether. It discusses the 19th-century experiments, including Michelson's, aimed at detecting the Earth's motion through this hypothetical medium. The paragraph sets the stage for further exploration of the nature of light and the experiments that would challenge the ether theory, hinting at the upcoming discussion on the consequences of these experiments for our understanding of light and the universe.

Keywords

💡Electromagnetic field

The electromagnetic field is a fundamental concept in physics that describes the electric and magnetic influences on a charged particle. In the video, it is used to explain the propagation of light through space. The script mentions that a disturbance in the electric field disturbs the magnetic field, and vice versa, leading to a wave-like disturbance that propagates at a constant speed, which is the speed of light. This concept is central to understanding how light behaves as a wave in the electromagnetic spectrum.

💡Wave-like disturbance

A wave-like disturbance refers to the way in which energy propagates through a medium or space. In the context of the video, light is described as a wave-like disturbance in the electromagnetic field. This means that light travels as a wave, with peaks and troughs, and this wave motion is what allows light to carry energy from one place to another. The video explains that this wave-like behavior is what allows light to exhibit properties such as interference and diffraction, which are key to understanding its behavior.

💡Maxwell's Theory

Maxwell's Theory, also known as Maxwell's equations, is a set of four equations that describe how electric and magnetic fields are generated and altered by each other and by charges and currents. The video script mentions that Maxwell's Theory explains almost everything we need to know about the propagation of light through empty space. It unifies electricity and magnetism into a single framework, showing that light is an electromagnetic wave, which is a fundamental concept in understanding the nature of light.

💡Refraction

Refraction is the bending of light as it passes from one medium to another with a different refractive index. In the video, refraction is discussed in the context of how lenses work in eyeglasses, microscopes, and telescopes. The script explains that lenses are ground to curve in a way that focuses light to a point by bending or refracting it. This principle is essential for the operation of optical instruments and for understanding how we see the world, as our eyes naturally refract light to form images on the retina.

💡Dispersion

Dispersion is the phenomenon where the different colors of light spread out when passing through a medium, such as a prism. The video script uses the example of a prism to illustrate how white light is dispersed into its constituent colors, creating a spectrum. This occurs because different colors of light have different wavelengths and are refracted by different amounts, leading to the separation of colors. Dispersion is a key concept in understanding the nature of light and its interaction with matter.

💡Interference

Interference is a phenomenon where two or more waves superpose to form a resultant wave of greater, lower, or the same amplitude. The video discusses constructive and destructive interference, where waves either reinforce or cancel each other out. This is a fundamental property of waves and is used to explain how Thomas Young demonstrated that light is a wave. The script describes how light passing through two slits creates a pattern of bright and dark fringes, indicative of interference, thus proving the wave nature of light.

💡Electromagnetic spectrum

The electromagnetic spectrum encompasses all possible frequencies of electromagnetic radiation, ranging from radio waves to gamma rays. The video script explains that the spectrum includes visible light but also extends to wavelengths outside the visible range, such as infrared, ultraviolet, X-rays, and gamma rays. Each type of electromagnetic wave has different properties and applications, and understanding the spectrum is crucial for grasping the diversity of light's behavior and uses.

💡Luminiferous Ether

The luminiferous ether was a hypothetical medium once believed to be the carrier of light waves through space. The video script mentions the ether in the context of 19th-century physics, where it was thought to be a medium that transmitted light in the same way that air transmits sound. The failure to detect the ether through experiments, such as the Michelson-Morley experiment, led to the development of new theories about the nature of light and space, culminating in the theory of relativity.

💡Reflection

Reflection is the bouncing back of a wave, such as light, from a surface. The video script explains reflection in the context of mirrors and how it works in telescopes. It mentions that the angle of incidence is equal to the angle of reflection, which is a principle used in mirror reflection. Reflection is essential for understanding how mirrors work and how telescopes, such as the reflecting telescope invented by Isaac Newton, are designed.

💡Transverse waves

Transverse waves are waves in which the oscillations are perpendicular to the direction of the wave's travel. The video script describes electromagnetic waves as transverse, meaning the electric and magnetic fields oscillate up and down while the wave moves forward. This is in contrast to longitudinal waves, where the oscillations occur in the direction of travel. Understanding that light is a transverse wave is key to comprehending its behavior and how it interacts with matter.

Highlights

Maxwell's Theory provides a comprehensive understanding of the propagation of light through empty space.

Light is a wave-like disturbance in the electromagnetic field that propagates at a definite speed.

The presence of electric and magnetic fields can be detected using electric charges.

Disturbances in electric and magnetic fields propagate energy back and forth between the two fields.

The human eye is a natural instrument for detecting disturbances in the electromagnetic field.

Galileo's extensive use of the telescope revolutionized astronomy by observing celestial bodies in detail.

Galileo's compound microscope allowed for the detailed observation of small objects.

Refraction is the bending of light as it enters a medium like glass, which is used in lenses of glasses, microscopes, and telescopes.

A glass prism demonstrates that white light is composed of all colors of the rainbow through a process called dispersion.

Isaac Newton's investigations into refraction and dispersion led to the understanding that light is made up of particles.

Christian Huygens proposed that light is made up of waves, a theory that would later be proven correct.

All waves, including electromagnetic waves, share common properties such as frequency and wavelength.

The electromagnetic spectrum includes a range of wavelengths from gamma rays to radio waves.

Visible light is a narrow range of the electromagnetic spectrum with wavelengths from 400 to 700 nanometers.

Thomas Young demonstrated that light exhibits wave properties, specifically interference, through the double-slit experiment.

The nature of light's interaction with matter is determined by the electrical properties of the matter.

Mirror reflection and refraction are explained by the principle that light takes the path of least time.

The reflecting telescope, invented by Isaac Newton, overcomes the limitations of dispersion in refracting telescopes.

The principle behind radar and telescopes is the reflection of electromagnetic waves, including light and radio waves.

The luminiferous ether was a hypothesized medium for the transmission of light, which was later disproven.

Albert Michelson's experiment aimed to detect the Earth's motion through the luminiferous ether using light wave interference.

Transcripts

foreign media

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[Applause]

thank you

thank you

I'm the traditional Central problems of

physics there's one that we now seem to

understand pretty well

that's the propagation of light through

empty space

Maxwell's Theory seems to tell us just

about everything we need to know about

that problem

light is a wave-like disturbance in the

electromagnetic field that propagates at

a definite speed

now those are all nice words but what do

they mean

first of all what do we mean by the

electromagnetic field

well it's possible to detect the

presence of electric and magnetic field

using electric charges if there's an

electric charge in space and it feels a

force then there's an electric field

present

if the charge is in motion and it feels

a force due to its motion then there's a

magnetic field present

we also know what happens when the

electric and magnetic fields are

Disturbed a disturbance in an electric

an electric field disturbs the magnetic

field which in turn disturbs the

electric field again energy sloshes back

and forth between the two fields and the

whole disturbance propagates along at a

speed which is one of the fundamental

constants of nature

in principle that disturbance can be

detected in the same way that we

detected the field Itself by means of an

electric charge

fortunately we don't always have to

detect disturbances in that way because

we come equipped with built-in

detectives of disturbances in the

electromagnetic field they're called

eyes

the eye is one of Nature's most

versatile instruments

and from the first Visionary onward

the human race has tried to broaden

visual experience well beyond its

Collective nose

to extend eyesight into the wonders of

the world large and small near and

distant

clear

be clear

what they say less of course for a

thorough examination that takes not only

a perception of light it takes a clear

perspective on its properties

and the properties of light are best

seen in the simple fact that light is a

wave

that means light must have properties

that are common to all waves

for example

waves can spread uniformly outward from

a single point disturbance

but waves from a carefully coordinated

array of Point sources can add up to

form flat wave fronts called plane waves

plane waves in turn can be made to

spread out again because weaves bend

around corners

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and when wave fronts encounter one

another they can interfere to produce

stronger waves or weaker ones

certainly water waves do all these

things

can it be that light waves do them too

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seeing the connection between Water and

Light may be much harder than seeing the

handwriting on the wall

for example no one tried harder to

extend the conventional view than

Galileo

but as he saw for himself

not everyone sees things in the same

light nor accepts that which is new at

first glance

but by 1610 at least to a certain extent

he had a very powerful tool with which

to make his argument

although contrary to popular opinion

Galileo didn't invent the first

practical telescope

he made the most extensive use of it

and at the turn of the 16th century his

simple refracting telescope zoomed

astronomy toward the future

as his sketches reveal

Galileo saw Saturn's rings

and sunspots

the phases of Venus the moons of Jupiter

and the craters of the Moon

if a man can finally see the large and

distant Galileo must have wondered why

not the very tiny and close at hand

and with the question of that nature he

peered through another invention for

which he's given credit

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it was the compound microscope

and as his sketch illustrates with its

crude but magnificent power

Galileo was able to see an ordinary

Italian bee in extraordinary detail

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has he done in the science of astronomy

here he had also made an enormous

advance in the field of Optics

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contrary to another popular opinion

eyeglasses aren't as new as they often

look

in fact in an array of models since the

13th century they have continued to

create quite a spectacle

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however while the frames have been

subject to this or that designers win

the lenses have usually been based on an

unchanging scientific principle

this principle applies to the lenses of

microscopes and telescopes as well and

it's called refraction

refraction occurs when light enters a

medium such as glass and bends

to make use of this phenomenon makers of

glasses microscopes and telescopes can

grind curved lenses that focus light to

a point

but before that it it's possible to see

refraction in its natural state and

here's a clear-cut example

a glass prism not only bends or refracts

a beam of light it also reveals that

plain white light is composed of all

colors of the rainbow

this process is called

aspersion

and it was seen very clearly by Isaac

Newton who investigated both refraction

and dispersion

according to Newton light was made up of

particles that obeying the law of

inertia traveled through empty space in

straight lines

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fraction or the bending of light by

matter could be explained by the

gravitational attraction between light

and matter

however at about the same time and on

the same subject

an opposing Viewpoint arose in Holland

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Christian Huygens a Dutch physicist and

astronomer theorized that rather than

being composed of particles or

corpuscles as Newton called them light

was made up of waves

and in the long run his idea would be

seen as the correct one

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a wave is a disturbance that propagates

from one place to another

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and no matter whether they're

electromagnetic waves

or water waves or any other kind of

waves all waves have certain properties

in common

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for example

a waves frequency times its wavelength

equals its speed

but mechanical waves can be longitudinal

or transverse

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while electromagnetic waves are always

transverse and in empty space they

always travel at the speed of light

but although they always have the same

speed they can have vastly different

frequencies and wavelengths

and in doing so these waves go so far as

to create the entire electromagnetic

spectrum

as a matter of fact only when

electromagnetic waves have a wavelength

in the narrow range from 4 to 700

nanometers are the waves visible light

that is the Spectrum from red to Violet

even shorter wavelengths called

ultraviolet light are radiated by the

Sun

though these invisible rays are

dangerous to living things they're

absorbed and rendered harmless by the

ozone in the Earth's atmosphere

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shorter still are X-rays with

wavelengths the size of atoms

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and finally gamma rays with the shortest

wavelengths of all

gamma rays with wavelengths as Tiny as

the atomic nucleus itself are created by

nuclear reactions

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longer wavelengths extending to visible

light and Beyond can be created or

absorbed when atoms change from one

energy state to another

Beyond visible light there's infrared

with wavelength longer than red light

infrared radiation can be detected only

by the heat it deposits

the universe is suffused with long

wavelength radiation

seen as the cool remnants of the big

bang that started it all

that includes not only infrared

radiation but also microwaves

microwaves are the first part of the

spectrum whose frequency is low enough

to be generated by human-made

alternating current electronic circuits

the universe is likewise full of radio

waves

centimeters meters or even kilometers in

length radio waves complete the

electromagnetic spectrum

of course the great Michael Faraday

didn't live to see the electromagnetic

spectrum

nevertheless it began to take shape when

envisioning electric charges surrounded

by lines of force Michael Faraday asked

himself a question

what happens when these lines are set

into vibration

Faraday didn't quite see the whole

answer

but he wouldn't have been surprised by

the picture that emerged

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an oscillating electric charge creates

waves

that propagate along the lines of force

at the speed of light

these ripples are transverse waves in

the electric field

propagating in wave fronts that become

flatter and flatter farther from the

source

coming more and more to resemble

the plain parallel wavefronts that are

called plane waves

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as the wave fronts pass through each

point in Space the electric field Vector

oscillates up and down

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marking the passage of Peaks and valleys

of the propagating wave

thus an oscillating electric charge is

indeed the source of outward spreading

ripples in the electromagnetic field

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it took James Clark Maxwell's Theory to

explain the nature of light

and to project the image of the

electromagnetic spectrum as a whole

but for all his amazing insights Maxwell

wasn't the first to see light as a wave

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in the early 1670s Christian Huygens

formulated a principle of light waves

stating that every point on a wavefront

is a source of New Waves

and in 1801 despite the prominence of

Newton's rival corpuscular Theory

another Englishman Thomas Young proved

beyond a shadow of a doubt that light is

a wave

he accomplished that by proving that

light has the wave property called

interference

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wave interference can be seen to be

constructive

or destructive

if the waves as they travel encounter

each other in Step they can reinforce

each other create a stronger wave and

produce what's known as constructive

interference

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but when they're out of Step waves can

cancel each other completely

in other words destructive interference

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as Thomas Young suspected all waves in

all media behave in this fashion

and to prove that light is a wave he

merely had to illustrate that light

exhibits interference

the behavior common to all waves

here's the principle

light from a single Source enters two

slits which are side by side and not

much farther apart than the wavelength

of the light itself

after passing through the slits the

light shows up as a distinctive pattern

on the screen

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when a single plane wave encounters two

slits

each slit becomes the source of

spreading wave fronts

and because both New Waves originate

from the same plane wave their

oscillations are synchronized

the result is a stable pattern of up and

down ripples alternating with directions

along which the waves cancel one another

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this produces a pattern of bright

fringes of constructive interference on

the screen

separated by dark fringes of destructive

interference

and that was it a series of alternating

fringes to prove that light is a wave

it was a conclusive demonstration and

ever since physicists have had to

explain the behavior of light in terms

of the properties of waves

for example if light waves like all

other waves bend around corners how can

it be that light can cast a well-defined

shadow

the answer can be found in the relative

magnitudes of the wavelength of the

light and the size of the opening

through which it passes

the shorter the wavelength the less

completely the wave spreads in all

directions

foreign

even with the wavelength equal to the

width of the opening the beginnings of a

shadow can be seen

foreign

is really due to destructive

interference of light from different

parts of the gap

and the result of it all is

the shorter the wavelength the more

nearly the light emerges in a

well-defined beam

wavelength of visible light

hundreds of nanometers is so small

compared to the sizes of normal objects

that they can cast very sharp Shadows

indeed

but that explanation doesn't shed much

light on an even more important question

since everything ever seen is the result

of light encountering matter the

question is

what is the nature of that encounter

and the answer is

since all matter is electrical in nature

it all comes down to light waves and

electric charges

for example when a light wave encounters

an electric charge

the oscillating electric field makes the

charge oscillate

which creates a new outgoing wave

notice the shadow that forms behind the

oscillating charge

a line of electric charges

they might be electrons bound to atoms

in a crystal

can produce outgoing plane wave fronts

in new directions

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and if the charges are free to move

easily as our electrons inside a metal

the result can be to stop the wave from

penetrating at all

Instead The Wave is completely reflected

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this is mirror reflection

in which the angle of incidence is equal

to the angle of reflection

that's true no matter from what

direction the beam arrives

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but reflection can also be described in

a different way

of all the possible paths from source to

mirror to destination

true path is the one that arrives in the

shortest time

because a metal surface with its mobile

electric charges is just what it takes

to bounce the light back

mirrors are made of silver which is

plated onto the surface of glass

but if that's why mirrors work

why do lenses work

they work because when light travels

through a transparent medium such as

glass the continual reconstruction of

the Light Beam by each molecule of the

material makes for slow going

in other words the speed of light inside

the glass is slower than it is out in

the air

when a light beam incident at an angle

first encounters a piece of glass

one side is slowed down before the other

forcing the wave front to change

direction

spending of light weathering glass water

or any other transparent material is

called refraction

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foreign

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closer to the direction perpendicular to

the interface

whenever it enters a medium that slows

it down

this occurs no matter what the direction

of incidence

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and as in the case of reflection

of all the paths that light could follow

from source to destination

the one that arrives in the shortest

time is the true path

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whether in reflection are in refraction

principle of shortest time chooses the

unique Direction along which wavefronts

are reconstructed by means of

constructive interference

eyes have a built-in lens and it tends

to refract entering light

and thereby form an accurate image on

the retina

does that look pretty clear if the eyes

lenses aren't refracting properly

artificial lenses can come to the rescue

and bend light to focus images on

Nature's behalf

foreign

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of course refraction often entails

another kind of distortion because the

refraction of light depends on its color

light of different colors initially

mixed together in white light

is spread out into a rainbow of Colors

by this prism

this is the phenomenon of dispersion

the reason why despite all its

noteworthy power at the time

Galileo's telescope a refracting

telescope was actually rather Limited

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but Isaac Newton realized that a prism

and a lens effect light the same way

which meant that the refracting

telescope would remain limited and

that's the reason why he invented the

reflecting telescope

as it encounters a reflecting telescope

a beam of light reflected from a

parabolic surface is reflected to a

single point at the focus of the

parabola without dispersion regardless

of color

and that's why ever since Isaac Newton

invented it the reflector telescope has

been the handiest tool of the optical

astronomer

of course light isn't the only wave in

the heavens nor the only kind of wave

that encounters a mirror and bounces

back

just as light waves reflect so do radio

waves

that's why the principle behind radar

and the telescope are one and the same

the dish of a radar reflector has the

same parabolic shape as the mirror in a

telescope

so whether it's the Coast Guard's

indispensable radar for the latest

design of a 10 meter optical telescope

the object is to detect electromagnetic

radiation

following on the same laws and

reflecting off similar metal surfaces

no matter the object

from an eye chart at a few meters

to an incredibly distant star in the

reflecting lens of a modern telescope

light waves continue to review the most

amazing sites

and to a certain extent the journeys

just begun

once we understand that light is a wave

many of its peculiar properties become

comprehensible because they're just

properties of waves

but in the case of light what is it that

brings light from the sun through empty

space to the Earth

what's waving

there being no obvious answer to that

question 19th century physicists at

least gave it a name

it was called The luminiferous Ether

and it was what waved when light passed

through it was the medium that transmits

light in exactly the same sense that the

air is the medium that transmits sound

throughout the 19th century a number of

ingenious experiments were done in an

attempt to detect the motion of the

Earth with respect to the luminiferous

ether

for one reason or another all of those

experiments failed

and then in the 1880s

Albert Michelson designed an experiment

of Exquisite sensitivity

which used the interference of light

waves themselves as a measuring tool to

detect the motion of the earth Through

The Ether

the story of that experiment

and its repercussions and consequences

is what we'll speak about when we meet

again next time

everything

thank you

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Annenberg media

for information about this and other

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