Name: How Does Light Actually Work?
Uploaded: 2023-04-18T11:43:16.000Z
Duration: 54 min 58 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

The newly born universe buzzed and frothed with boundless energy.

Even after the raging furnace of the first few minutes had died away,

Temperatures universe-wide were more than a hundred million degrees.

For thousands of years, this primal heat burned - a cosmos of plasma, a super-hot mix of particles

That day arrived when the universe was almost four hundred thousand years old, and had cooled

In this now comparatively tepid soup lone electrons met lone protons, and finally could

stick together - forming the first atoms.

For as each electron and proton bound together, a small amount of energy was released.

A packet of energy that raced away at the cosmic speed limit, the speed of light.

A particle of energy born in the formation of a hydrogen atom.

A particle we call a photon, a particle of light itself.

But as the universe began transitioning from plasma into neutral gas, light could then,

for the first time, stream freely through its reaches.

And so, our photon's long, long journey began.

It headed out first into the universe’s dark ages

A time before the first stars burned, a time before the first galaxies formed.

In the eerie darkness, gravity pulled on mass to mold the first seeds of cosmic structure.

But the photon sped on, and noticed nothing.

Eventually, the first stars burst into life around it,

Massive and bloated, these ancient suns burned themselves out in a cosmic blink of an eye

as the first supergiant black holes grew rapidly between them as they eagerly devoured mass.

The first galaxies began to assemble The sky lit up with the fires of uncountable

young stars across the cosmos as they began to fuse the initial hydrogen and helium atoms

Millions steadily turned into billions of years,

And as galaxies grew and matured, eventually, the intense light of young stars began to

The photon’s journey could have potentially lasted forever into eternity

But after almost 14 billion light years of travel, a large spiral galaxy steadily came

Near a small blue dot orbiting a small white star.

After crossing the last few thousand years, the photon collided with a piece of metal

Part of a telescope built by humans and orbiting near the planet Earth

The photon’s energy was completely absorbed, energising electrons, and registering on detectors.

But as the photon vanished from existence, its billions-year long journey complete - it

Because to the photon itself, the journey never took place.

13.8 billion years of cosmic time disappeared in an instant.

Light has existed in the universe from its earliest moments,

And will continue to exist long after humanity and the stars are shred to dust.

And perhaps most importantly - what even is it?

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Light had played a pivotal role since the cosmos´ very beginning.

In these earlier times, it had only existed for the very briefest moments,

Slamming into speeding particles before it had a chance to travel anywhere, one piece

of light dying as another was born However our parcel of light was born into

a very different, very transparent, universe.

Forged with the first true atoms from featureless plasma.

With the cosmic maelstrom of the Big Bang finally abated,

Our photon could begin its immense journey unhindered.

As it travelled, many generations of stars lead to our Sun, forming in the collapse of

an immense gas cloud, and billions of years after, humans began to walk on the surface

And so eventually, as our photon was a couple of thousand light years distant from Earth

An indication of this is the delight we take in our senses…(and) above all others the

sense of sight…The reason is that this, most of all the senses, makes us know and

brings to light many differences between things.”

The ancient Greeks wondered if light emanated from the eyes, touching and feeling the world

But clearly, there are times when it is dark when we can’t see anything.

So, they concluded light must be something external, something captured by our eyes.

Islamic scientists began to unravel the properties of light,

Finding rules of reflection and the magnification properties of glass lenses.

Light was clearly a natural part of the universe around us.

But it took the coming of the scientific revolution, and a fight between two giants of science,

for light’s deep secrets to be finally uncovered.

The year was 1652, and Dutch physicist, astronomer, mathematician and all round genius Christiaan

He had noted how light travelled through lenses and bounced off mirrored surfaces, and was

particularly interested in the phenomenon of refraction - where the path of light is

bent when it passes from one medium to another.

Huygens noticed that light was often split into the colours of the rainbow by his instruments,

And sometimes strange patterns of dark and light would be produced.

Clear evidence, to him, that light was some sort of wave.