B2 High-Intermediate US 143 Folder Collection
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Over 100 years
ago, physicists were

trying to figure
out how things glow,

like molten glass or hot lava.
It seems like a simple
question and was

being pondered by
such physicists

as Lord Rayleigh at the
turn of the 20th century.

I give you a wooden skewer
that, when touched to a flame,

glows orange-red.
Rayleigh knew that
the color of this glow

depends on temperature,
like the sun that

has a surface temperature of
5,500 degrees Celsius radiates

a bunch of different colors
that together look white to us.

Or me-- at 37 degrees Celsius,
I have this invisible halo

of infrared light.
Fun fact.
Infrared light is
invisible to humans,

but snakes can actually sense
it from up to a meter away

to detect prey.
Rayleigh wanted to understand
where the light came from

and come up with
a rule that would

predict how much of each
color it would emit.

This is its spectrum.
Another fun fact.
Lord Rayleigh was the guy who
figured out, mathematically,

why the sky is blue.
So Rayleigh thought of the
simplest possible object,

something that
absorbs all light.

Objects absorb, emit,
and reflect light.

Rayleigh's object would only
absorb and emit, but not

So all you would see
when you look at it

is its glow or its radiation.
Physicists call
this a blackbody.

Technically, a blackbody
isn't black, it's glowing.

But whatever, physicists.
A true blackbody doesn't
exist in real life

because nothing
absorbs all light

and radiates perfectly,
although stars like the sun

come pretty close.
Kind of funny, right,
that the brightest thing

we know in our solar
system is the closest thing

we know to a blackbody.
Anyway, at that time,
physicists didn't really

understand atoms and molecules.
They thought everything
was made of particles

that vibrate like springs.
Rayleigh and his
colleague, James Jeans,

imagined a blackbody made
of these vibrating particles

where the vibration
was continuously

converted to light.
From that model, they
came up with a rule

to predict what colors a
blackbody would radiate

at certain temperatures.
But the unfortunate happened.
Their reasoning implied
that a blackbody

should emit infinite amounts
of ultraviolet light.

They tried to apply their usual
rules of Newtonian physics

and came up with nonsense.
We now call this the
ultraviolet catastrophe.

Oh, eye of a Newton.
Something was very
wrong with their work.

A blackbody can't emit
infinite amounts of radiation

because that would violate
laws of conservation of energy.

And just from, like,
experience, when you put toast

in your toaster,
it doesn't promptly

burn your toast to smithereens.
When observation contradicts
theory like this,

it often means there's
something missing in the theory.

Rayleigh and Jeans had
found a glaring error

in physics theory.
Bum, bum, bum!
The same year that Rayleigh
and Jeans published their work,

a German physicist,
named Max Planck,

was studying radiation
for a different .

Reason he wanted to
understand why heat always

flows from a hot object
to a cold object.

And in his quest to
solve that problem,

he unintentionally
fixed their error.

He assumed that a blackbody
could only emit light

in discrete quantities.
Its energy comes in chunks,
equal to the frequency

of the light multiplied
by this-- a number we now

know as Planck's Constant.
This is weird.
It would be like if
your faucet could only

pour full glasses
of water at a time.

But when Planck assumed
light was quantized,

theory matched with observation.
He solved the
ultraviolet catastrophe.

But here's the crazy part.
Max Planck didn't immediately
realize how big of a deal

this was.
Nobody did.
He was just doing
the thing that we all

do with our math homework,
when your answer doesn't match

the answer in the
back of the book

so you just switch
a plus for a minus

but you're not really sure why.
Planck didn't
understand what his work

meant in the real world.
It wasn't until a couple years
later that Einstein realized

that these packets of energy
meant that light wasn't just

a wave.
It's made of particles
that we now call photons.

So then physicists
started thinking

about what this meant for
atoms that emit those photons,

and The Theory of Quantum
Mechanics began to unfold.

Atoms emit photons when
their electrons lose energy,

and so their electrons must lose
energy in chunks-- in quanta.

Quantum mechanics.
The consequences of
Max Planck's discovery

that light comes in
quanta, in packets,

snowballed into what we now
know as quantum mechanics.

Quantum mechanics is bizarre.
The microscopic world
just misbehaves.

Like, we're talking many
billions of times smaller

than the width of a human hair.
For example, an electron
can be in multiple places

at the same time.
In fact, an electron
has no precise location.

But the weird thing is, when
you measure the electron,

you find it in a specific place.
It's like it has no location
until you measure it.

This popular image
of an atom is wrong.

Instead, most of
the time it looks

like a cloud of probability
around the proton.

This cloud of probability
is the electron.

Think about it.
The particles that
make up your body

aren't a stack of solid objects.
They're a collection
of probability clouds.

Quantum mechanics is
unsatisfyingly unintuitive.

But time and again, it
has proven to be real,

applied in computer
chips, lasers, even LEDs.

An electron probability
cloud is only

a nibble of the cookie
that is quantum weirdness.

And after more than 100
years of study on the topic,

there's still more
to learn, which

is why we're doing things
like colliding particles

at the Large Hadron Collider.
Just as a small example.
I love this story because
it shows how important it

is to be wrong.
Science isn't fixed
facts and figures.

It's constantly being
modified and improved.

Without Rayleigh uncovering
this huge theoretical error that

was the ultraviolet
catastrophe, physicists

may have never come
up with the rules

to describe a brand new
tiny, tiny universe.

Thank you so much for
watching, and happy physicsing.

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The Ultraviolet Catastrophe

143 Folder Collection
曾柏勳 published on February 9, 2019
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