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In 2016, the world's most powerful billionaire set out to build a spacecraft that could reach another star within our lifetime.

They handed over 100 million dollars to Silicon Valley's best engineers to make it real, and today it's stuck by a physics problem no code can solve.

The secret to interstellar travel isn't building a better computer.

It's a microscopic piece of glass sitting in Texas with no engine,

no moving parts, no AI that can steer itself more precisely than any drone ever built.

And it might be the only thing that actually gets us to another star.

Chapter 1.

The 100 Million Dollar Ghost Ship Alpha Centauri, the target of breakthrough starshot, is 4.37 light years from the Earth.

That's 25 trillion miles away.

But how far is that really?

One of the fastest objects humanity has ever launched is the New Horizons probe.

It was moving at roughly 36,000 miles per hour when it launched from Earth.

Still, if you put New Horizons on a track and aimed it at Alpha Centauri, it would arrive in approximately 78,000 years.

Which is to say not in your lifetime, or your children's lifetimes, or during the lifetimes of any civilization that would even recognize the people who built it.

78,000 years ago, the great wave of modern humans hadn't swept across the globe yet.

We hadn't even invented agriculture, writing, the wheel, government, money, or organized religion.

All of that entire timeline fits inside the travel time of our fastest spacecraft to the nearest star.

And if you're wondering, the Apollo moon ships, the fastest piloted spacecraft humanity has ever flown, would do far worse.

They would take a staggering 114,000 years to reach the Alpha Centauri system.

That makes New Horizons' 78,000 years feel almost optimistic.

When Yuri Milner, a Russian billionaire physicist, stood on a stage in New York in 2016, this was the time and distance problem he set out to solve.

Forget chemical rockets, stop trying to carry fuel across trillions of miles, because fuel has mass, and mass requires more fuel to move it,

which adds more mass, which requires more fuel, it's a spiral.

And that's exactly why rockets are mostly just fuel tanks to begin with.

Instead, leave the fuel on the ground and a massive array of lasers,

then build a spacecraft so small and light it weighs just 0.03 ounces or one gram.

At its center is a chip the size of a postage stamp carrying a camera, a processor, a battery, and a transmitter,

and attach it all to a sail 13 feet wide but only a few hundred atoms thick.

All of that means that the pressure of light itself can push the craft through space.

Breakthrough Starshot called it the Star Chip, and it seemed simple in theory fire lasers at its sail

and then watch it accelerate to over 37,200 miles per second in a matter of minutes.

At 20% of the speed of light, it would only take 20 years to arrive at Alpha Centauri, and that's quite an improvement on the whole 78,000.

The timeline has been condensed into a single generation, not all of the generations.

And just to improve the odds that at least some survived the journey, they would send not one star chip but a fleet of a thousand of them.

Even Milner's team knew that redundancy is cheaper than regret.

A twenty-year journey is a number humans can hold in their head.

Never mind the fact that when Star Chip finally arrives at Alpha Centauri, the distances will be

so staggering it would take four years alone to beam the images back to Earth via its own onboard lasers.

Four years is a drop in the bucket.

We could at least conceivably be alive to see that data come back.

And so the crowd at the 2016 event applauded, because this idea was genuinely worth applauding.

What the Enterprise did not spend a lot of time talking about was the all-important laser array.

That alone would need to generate 100 gigawatts of power to function.

That's roughly the combined electrical output of approximately 100 nuclear power plants, all firing simultaneously.

The entire United Kingdom, every light, every factory, every phone charger, and every coffee machine in every office in London,

generally runs on less than 40 gigawatts on a normal day.

So Starshot's lasers would need two and a half times the entire power grid of Britain aimed at a stamp in space.

It's not like this was any secret.

The engineers knew the project's logistical parameters, and they set it anyway.

There was a plan, apparently, to solve this energy problem later.

They didn't.

They also didn't solve the other problem, the one that would have killed the tiny spacecraft before it left the solar system, regardless of how much power was available.

The problem that the 100 million dollar budget could not touch.

Chapter 2.

The Slippery Beam The massive laser beam, the one propelling the tiny spacecraft that takes an insane amount of energy to operate, is also the beam that absolutely destroys it.

This will happen immediately by design, as a direct consequence of the laws of physics the moment the sail drifts even slightly off-center.

Which it inevitably will.

The universe is not a laboratory with controlled conditions.

The laser has to travel through hundreds of miles of churning, turbulent atmosphere before it even reaches the spacecraft.

Imagine balancing a marble on top of another marble.

It is theoretically possible.

The geometry allows it, but the instant that the top marble moves even a fraction of a millimeter to the side, gravity won't be there to gently nudge it back.

It accelerates away.

The more it moves, the faster it goes.

The instability feeds itself.

Now imagine the top marble is a spacecraft, made of material thinner than a soap bubble.

The bottom marble is a laser beam carrying the energy output of a hundred nuclear power plants, and falling off means instant vaporization.

That is beam-riding instability.

Researchers who study this problem found something almost poetically discouraging.

A flat sail is never stable on a laser beam.

Even if you spin it or modify the shape any way you want, a flat sail is never stable.

Full stop.

At gentle speeds, this is an annoying engineering problem.

You might even be able to correct for it by installing sensors that detect wobble, onboard computers to process the error,

or maybe some thrusters to just nudge the spacecraft back to center.

That whole loop might take a few hundred milliseconds, which is workable.

But this is all theoretically taking place at 20% the speed of light.

At those speeds, a few hundred milliseconds is an eternity.

By the time the sensors detected the wobble, processed it, and sent the signal to the thruster, and then waited for it to fire,

the spacecraft will have traveled almost 11,200 miles.

That correction window, or just the gap between the wobble beginning and the spacecraft ceasing to exist, is measured in microseconds.

One millionth of a second.

The fastest thrusters on the earth can't act upon a correction loop that fast.

The spacecraft would vaporize before the mechanical valves even had time to open.

And that is before we get to the space dust.

The path from Earth to Alpha Centauri contains an estimated 100 sextillion particles including dust, hydrogen, and helium atoms.

At 20% the speed of light, each one hits the spacecraft like a bullet.

Researchers at the Korea Astronomy and Space Science Institute ran the numbers

and they They found that a steel spacecraft would accumulate craters 0.15 inches wide

and 0.04 inches deep across its surface long before it reached its destination.

A sufficiently large dust particle would destroy the craft entirely.

Breakthrough Starshot was conceived as a Silicon Valley project, and Silicon Valley's answer to this is simply write better code, faster code, smarter code.

If the correction loop is too slow, why not just optimize the correction loop?

Well, if the processor can't keep up, design a faster processor.

This approach works on essentially every problem that software has ever been asked to solve, and that's why it is the default response of an entire

generation of engineers who have watched software eat the world and concluded that software can eat anything.

But it can't eat the scale of this journey.

Because traveling to another star system isn't a software problem dressed up as a hardware problem.

at light speed is not a bug you could easily troubleshoot.

100

The signal that tells the thruster to fire still has to pass through physical hardware.

101

But the spacecraft is moving at incredible speeds, so even a tiny delay means it's already covered in an enormous amount of distance by the time anything responds.

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And that is not a software problem you can optimize, because physics moves faster than code.

103

You have to respect the original Breakthrough Starshot team.

104

Before the project got off the ground, they publicly posted an engineering challenges list for the project, and made it admirably transparent.

105

The list acknowledged this problem directly.

106

Beam instabilities are everything, as are those differential forces on the sail and the differential heating.

107

It reads like a coroner's report before the patient was even born.

108

They sat with this problem for nine years.

109

Nine years of small grants, academic conferences, hopeful papers, and the dawning awareness

110

that the correction problem could not be solved with with the tools and budget the project had brought to solve it.

111

You cannot out-compute a wobble that kills the spacecraft faster than computation is physically possible.

112

What you would need is a spacecraft that corrects the wobble before it knows the wobble happened.

113

A spacecraft that doesn't detect instability and respond to it.

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A spacecraft that simply can't become unstable, by virtue of what it's made of regardless of what the beam does to it.

115

Now that sounds like science fiction.

116

It also sounds like exactly what a team of doctoral students in Texas spent the last several years building.

117

Chapter 3.

118

The Dart and the Texans The doctoral students in Dr. Shofeng Lun's lab at Texas A&M University were not,

119

by any conventional measure, the people you would expect to solve this.

120

A $100 million Silicon Valley initiative had already failed, and they were backed by some of the most famous scientists alive.

121

They didn't have the benefit of any celebrity spokespeople or press events in New York.

122

Instead, they were working with a fabrication facility on a campus in College Station, Texas, a city best known for football and being roughly two hours from anywhere else.

123

What they built is called a MetaJet.

124

The current prototypes are tens of microns across.

125

For reference, a single strand of human hair is roughly 50 to 120 microns wide.

126

Which means you could line up a small fleet of MetaJets across something you previously considered too small to see.

127

The whole device weighs less than a paperclip.

128

It has no thrusters, no moving parts, no onboard computer, and no steering system of any kind.

129

And the best part?

130

A laser still propels it, but the structure of the material itself keeps it on course, the same way a groove keeps a needle in a record.

131

Or in other words, the beam does one job and the material does another.

132

Here's why that second part matters so much.

133

Even if breakthrough Starshot solved the beam riding problem, managed to build a sail that stays perfectly centered on the laser

134

and the craft survived the thermal load while accelerating to 20% the speed of light, there is still a massive problem waiting on the other side of that journey.

135

You don't know where you're going.

136

Space is not empty.

137

There are rogue particles, gravitational tugs from objects hundreds of billions of kilometers away, and absolutely no landmarks.

138

A spacecraft crossing 4.37 light years is subject to every one of those influences for every second of a twenty-year journey.

139

Each nudge is tiny, but they add up.

140

The Starshot engineers defined a successful arrival as getting within one astronomical unit of Alpha Centauri.

141

That doesn't sound like much until you realize what one astronomical unit actually means.

142

It allows for a missed distance of up to 93.2 million miles.

143

That's roughly the distance from the Earth to the Sun.

144

And that was them being generous.

145

The bullseye was already the size of Earth's entire orbit, and an unsteered light sail couldn't reliably hit it.

146

Their own researchers admitted

147

that the tiny vibrations in the laser array alone were many orders of magnitude away from the accuracy the mission required.

148

Even with help, the probe would probably still miss the target the size of a planet's entire orbital path.

149

Imagine throwing a dart from New York City and trying to hit a bullseye in London, but you can't see the target, and the target is moving,

150

and once the dart leaves your hand And you won't be able to adjust it for 20 years.

151

That's the navigation problem.

152

As we know, any conventional fix to the steering problem adds mass.

153

Add mass on a spacecraft whose entire propulsion system is light pressure, and that can lead to an inevitable collapse.

154

The steering system that saves the mission is also the steering system that makes the mission impossible.

155

That is, the specific, elegant, maddening trap that breakthrough Starshot never escaped.

156

The MetaJet escapes it by refusing to play.

157

There's no steering system to add mass because the steering isn't a system, it's a property, built into the material before the ship even leaves the ground.

158

Which means understanding how it works requires getting very small very fast.

159

Chapter 4.

160

The Groove in the Record The MetaJet is built from a class of material called MetaSurface, an ultra-thin sheet of silicon covered in arrays of nanoscale pillars.

161

The pillars are far smaller than the width of a human hair.

162

They're also so small

163

that the patterning across a mere surface the size of your fingernail contains enough structural variation to encode an entire multi-volume encyclopedia.

164

The height, the diameter, and the spacing of those metasurface pillars are precisely designed to control exactly what happens to light when it strikes the surface.

165

Change one pillar by a few nanometers and you change the trajectory of your ship.

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The entire navigation of an interstellar spacecraft is encoded in measurements you could not resolve with a standard lab microscope.

167

Here's what those pillars do.

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When you hold a garden hose and water shoots straight forward, the hose kicks straight back in your hands.

169

That's basic physics.

170

Newton's third law, the water goes one way, your hand gets pushed the other.

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Now put a bent nozzle at the end of it.

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Suddenly, the water exits at an angle and the hose kicks sideways instead of backwards.

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It's the same water pressure, enacting a completely different direction of force.

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The nozzle doesn't add any energy, it simply changes where the water went, and the reaction follows automatically.

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The Meta-Surface pillars are the nozzle, and the laser is the water pressure.

176

When light strikes a conventional reflective surface like a mirror, it bounces straight back and pushes the sail straight forward.

177

The Meta-Jet's pillars are designed to bend the outgoing light at a precise angle, so If the light exits sideways, the sail is pushed sideways.

178

Nobody or nothing is required on board to program the nozzle.

179

The shape is the program.

180

That's the beauty of this system.

181

The further it drifts, the harder it gets pushed back into position.

182

It literally can't stay off course.

183

As for the heat, which we were told would vaporize any conventional reflective materials under full laser load,

184

the metasurface survives as a consequence of its ability to reflect light, not absorb it.

185

The photons do all the work, changing the direction and transferring momentum, rather than dumping all their energy into the material as heat.

186

For context, the previous best answer to this problem was graphene, one of the strongest materials humans have ever produced.

187

Then, to survive the dust particles during the journey,

188

researchers proposed folding the sail into a needle-like profile to minimize the cross-sectional area hitting the particles.

189

The MetaJet silicon metasurface is a different answer entirely.

190

just stronger, smarter.

191

In laboratory testing, Lens' team demonstrated full three-dimensional movement using a single fixed laser beam.

192

They got the MetaJet prototype to go forward, sideways, and lift from all one light source with no fuel, no steering input, or any contact of any kind.

193

It was the first time any optical propulsion system had ever achieved this, and to the team's knowledge, nobody else has done it.

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The beam does one job, the material does the other.

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And the material never gets tired, runs out of propellant, or never has to wait for a computer to tell it what to do.

196

Chapter 5.

197

4.37 Light Years, Give or Take Lant's team is not alone.

198

Researchers at Caltech have been working on a similar stability problem for laser drive light sales, and other groups have been working on the same problem from other angles.

199

The fact multiple serious research teams have independently converged on material-based

200

solutions to the steering problem posed by Breakthrough Starshot is no coincidence.

201

The field has realized

202

that the Silicon Valley instinct to throw software at it was always the wrong tool for this particular job.

203

The MetaJet prototypes are currently tens of microns across.

204

A real interstellar sail needs to be feet wide, and nobody at Texas A&M or anywhere else is pretending that that gap is small.

205

But here's what makes it bridgeable in a way no previous approach was.

206

The physics scale with laser power, not device size.

207

The same principles that move a micron-scale prototype in a laboratory tank will move a meter-scale sail under gigawatt-class beams.

208

The mechanism doesn't change, only the engineering does, and engineering unlike physics, negotiates.

209

The next milestone is microgravity testing, demonstrating that the metajet behaves in space conditions the way it behaves in the lab.

210

Landsteam is currently applying for funding to make that happen.

211

Certainly a quieter, smaller, less photogenic task than a press conference at One World Trade Center with Stephen Hawking in attendance.

212

It will also, if it works, mean considerably more.

213

In the end, Breakthrough Starshot threw millions of dollars and nine years at the stars and quietly ran out of road.

214

A group of doctoral students in College Station spent roughly the same period asking a different question entirely.

215

Instead of building a better computer for the ship, what if the ship didn't need one at all?

216

The device that may eventually carry humanity's first message to another star has no engine, No steering computer or moving parts, it weighs less than an eyelash,

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and it steers using light the same way a bowling ball uses a hill.

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Alpha Centauri is still 4.37 light years away.

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That number hasn't changed.

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What did change in a fabrication lab two hours away from

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anywhere is whether we as a species have any business believing we might actually get there.

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And we just might.

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Because every attempt to go further into space keeps running into the same truth, you have to solve the problems closest to home first, find out why NASA wants to go back to the moon,

224

or watch this instead.

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このレッスンの語彙とスピーキングのポイント

このB2レベルのスピーキングレッスンは、動画「20% Speed of Light!! NEW Light Engine is INSANE!」を教材にしています。繰り返し出てくる語は次のとおりです：spacecraft, laser, beam, sail。この動画には、シャドーイング用の文が224文、単語が3234語あります。音声の長さは18:33です。話す速さは1分あたり約174語で、日常会話に近い自然なペースです。英語の頻出3,000語に含まれる単語は76%だけなので、語彙は難しめです。

この動画の重要語彙

動画の中で特に難しい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
spacecraft 名詞	/ˈspeɪsˌkɹæft/	宇宙機
laser 名詞	/ˈleɪzɚ/	レーザー
sail 名詞	/seɪl/	帆
beam 名詞	/ˈbiːm/	梁, 桁
steer 動詞	/stɪɹ/	操縦する, 舵を取る
breakthrough 名詞	/ˈbɹeɪk.θɹuː/	突破
silicon 名詞	/ˈsɪləˌkɑn/	ケイ素, 珪素
wobble 動詞	/ˈwɑbl̩/	ブラブラする, 震える
pillar 名詞	/ˈpɪlɚ/	柱
researcher 名詞	/ˈɹiˌsɝ.t͡ʃɚ/	研究員, 研究者
correction 名詞	/kəˈɹɛkʃən/	訂正, 修正
marble 名詞	/ˈmɑɹ.bəl/	大理石, マーブル
nozzle 名詞	/ˈnɒzəl/	ノズル
prototype 名詞	/ˈpɹəʊtətaɪp/	プロトタイプ, 原型
particle 名詞	/ˈpɑɹtək(ə)l/	粒子

動画に出てくる句動詞

単語	意味
come back 動詞	戻る, 帰る
dress up 動詞	着飾る
find out 動詞	見出す, 調べる
get off 動詞	降りる
hand over 動詞	引き渡す, 手渡す

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	has been condensed · is measured · was conceived
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	has ever launched · has ever flown · has been condensed
関係詞節 who / which + 節 — 人や物について情報を加える	people who built · milliseconds, which is

注意したい発音

話し手はcan't, didn't, doesn'tなど、短縮形や弱形を27回使っています。聞こえたとおりの短い形で発音しましょう。

「th」の音: breakthrough /ˈbɹeɪk.θɹuː/, thruster /ˈθɹʌ.stɚ/, thermal /ˈθɜːməl/
「sh」と「zh」の音: correction /kəˈɹɛkʃən/, fabrication /fæbɹɪˈkeɪʃən/, propulsion /pɹəˈpʌlʃən/, differential [dɪfəˈɹənʃəɫ], navigation /nævɪˈɡeɪʃən/
長い単語（アクセントの位置に注意）: instability /ɪnstəˈbɪlɪti/, astronomical /ˌæs.tɹəˈnɑm.ɪ.kəl/, fabrication /fæbɹɪˈkeɪʃən/, millisecond /ˈmɪlɪˌsɛkənd/, differential [dɪfəˈɹənʃəɫ]

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: marble /ˈmɑɹ.bəl/, particle /ˈpɑɹtək(ə)l/, doctoral /ˈdɒktəɹəl/, astronomical /ˌæs.tɹəˈnɑm.ɪ.kəl/, propulsion /pɹəˈpʌlʃən/
/v/ — /b/ にならないように、上の歯を下唇に当てる: reflective /ɹɪˈflɛktɪv/, groove /ɡɹuv/, behave /bɪˈheɪv/, navigation /nævɪˈɡeɪʃən/, invent /ɪnˈvɛnt/
/f/ — 「フ」ではなく、上の歯と下唇で出す: spacecraft /ˈspeɪsˌkɹæft/, fabrication /fæbɹɪˈkeɪʃən/, reflective /ɹɪˈflɛktɪv/, drift /dɹɪft/, differential [dɪfəˈɹənʃəɫ]

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。spacecraft, laser, sailなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: 20% Speed of Light!! NEW Light Engine is INSANE! - 動画で英語スピーキングを学ぶ

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