跟读练习: Can You Keep Zooming In Infinitely? - 通过视频学习英语口语

This is a tiny piece of metal just three millimeters across, and here's what happens if you just keep zooming in.

A thousand times...

A hundred thousand times...

50 million times.

Each of these blobs is an actual atom.

- I saw this the other day at the University of Sydney, and it kind of blew my mind, because up until just 30 years ago, directly seeing atoms like this was thought to be impossible.

The rooms that you're going to see here are perhaps the most shielded rooms on campus, or even in the whole of Sydney, I would say.

And perhaps also the most expensive.

That's wild.

So why is it so hard to see atoms?

Well, you can't actually see atoms with visible light.

That's because while light has wavelengths between 380 and 750 nanometers, an atom is still over 3 ,000 times smaller, just 0 .1 nanometers.

much bigger than the thing you're trying to see, the light will just diffract or bend around it, so you won't be able to see it.

So if you want to see atoms, you need something with a much, much smaller wavelength.

The best candidate isn't even light.

It's electrons.

In 1924, a French physicist named Louis de Broly worked out that everything was sort of wave -like.

Not just light, but matter too.

Atoms, molecules, even you yourself have a wavelength.

And the formula for this wavelength is Planck's constant divided by the object's momentum, that is, mass times velocity.

So here what you actually see, that's the column of the microscope where we accelerate the 300 kV electrons down.

300 kilovolts, these electrons.

Yes.

So they are relativistic particles.

How fast are they moving?

99 % the speed of light or...?

Well, around 80.

80 % the speed of light.

Yes.

So what would be their wavelength?

The wavelength is the Planck constant over the momentum, right?

So if we calculate that we come to around...

between 2 to 3 picometers.

Whoa.

That's over 100 ,000 times smaller than visible light, so theoretically, you get 100 ,000 times more resolution.

Shortly after de Broglie's discovery, a group of scientists in Germany started working on a microscope that would use these high -speed electrons.

The only problem is you can't bend electrons using glass lenses.

So how do you focus them?

Hans Busch, a German physicist, suggested that an electromagnetic lens might do the trick.

He published his results in 1926, but never actually built one.

Fortunately, a copy of his paper fell into the hands of an eager young PhD student, Ernst Ruska.

Ruska built his first prototype by coiling up some wire and surrounding it with iron, taking care to leave a gap in the middle.

Then when he passed a current through the coil, it induced a donut -shaped magnetic field through the metal and across this gap.

This was his lens.

To test it, Ruska first boiled electrons off a tungsten filament, the same kind of filament you'd find in an incandescent light bulb.

He accelerated these free electrons through a positively charged anode down to his electromagnetic lens.

As an electron approaches the lens, the magnetic field exerts a force on it.

So if an electron is traveling in the y direction, the magnetic fields are in the x direction, this force, called the Lorentz force,

pushes other magnetic field lines along the donut shape,

which constantly point its motion in a circle.

But then this circular motion means the Lorentz force starts pushing the electron inwards as well, spiraling it into the center of the lens.

Now if you trace the path of the whole beam of electrons, you'll see they all get steered into the center, focusing the beam.

By 1931, Ruska and his colleague Max Noll used this kind of design to build the first working electron microscope.

It was pretty basic, made of brass roughly bolted together.

But it worked.

The image itself was created once the focused electron beam hit a sample sitting at the focal point.

The sample needed to be incredibly thin, only around 100 nanometers thick.

More electrons would make it through the thinner parts of the sample than the thicker parts, creating an electron imprint of the sample.

Then, a second electromagnetic lens magnified this imprint down onto a fluorescent detector, producing the final image.

This was known as a transmission electron microscope, or TEM.

Now, early versions of the microscope barely magnified at all.

In fact, it wasn't even better than an optical microscope.

But Ruska was determined.

Over the next few years, he experimented with adding more lenses onto the microscope to create bigger and bigger images.

By the mid -1930s, Ruska had gotten the TEM way past 10 ,000 times magnification.

It could produce close -ups of insects, bacteria, and even viruses, at a level far surpassing the optical microscope.

But right as Reska's TEM was taking off, a German physicist named Otto Scherzer published a paper, claiming that the microscope was about to hit a brick wall.

"There was a flaw in the electromagnetic lens," he wrote,

"that was completely unavoidable." For an electron to make it to the focus of the lens, it needs to be deflected by a specific amount.

If you simplify its trajectory, you can define that ideal deflection with this angle theta.

This angle depends on the horizontal distance of the electron from the optical axis, and how far down the axis the focus is, also known as the focal length.

The shorter the focal length, the stronger the magnification.

If you graph this angle as a function of distance to the optical axis, you'll see that it can be approximated as linear.

The problem is that the magnetic field doesn't scale linearly.

It's much stronger near the edges of the magnet.

So if you plot the curve for the actual deflection of the electrons, you'll see that the magnetic field over deflects the electrons further out.

Their angles are bigger than they should be, so they end up focusing before the rays in the middle.

And as a result, the focus is spread across the optical axis instead of being contained in a single point.

The blur starts out around the edges of the image, but it gets worse the higher the magnification.

This is called spherical aberration and it distorts every radially symmetric magnetic lens.

In fact, it doesn't just affect magnetic lenses.

Every spherical lens from a camera to a telescope to a magnifying glass also suffers from it.

But there is a surprisingly simple way to minimize spherical aberration.

Just add a second lens, one that diverges light instead of converging it.

Now a diverging lens also suffers from spherical aberration, but if it has the same amount of aberration as your converging lens,

just in reverse, the two to essentially cancel out their effects, and that removes the aberrations almost entirely.

Almost all modern lens systems in cameras and microscopes use some sort of correcting divergent lens.

So you might imagine that the TEM simply needs its own version of a diverging spherical lens to magnify further,

but with magnets, this is physically impossible.

Every magnet has two poles, a north and a south.

It's impossible to just have one.

Even if you split a magnet down the middle, it creates two smaller magnets, both with a north and a south.

And all magnetic field lines have to start at one pole and end at the other, forming a closed loop.

is a direct result of the second Maxwell equation, because the field that you create has field lines that start and end at the same magnet.

So the electrons will always cross through.

Two lights.

The first time it passes through by the Lawrence Falls, it's brought into the spiraling motion and then the second time,

from that spiraling motion, which has then a slightly different direction, it's pushed towards the axis.

That's why all electromagnetic lenses.

100

By default, will converge the beam and never diverge it.

101

Even if you shot electrons in from the other side of the lens, they would still get focused.

102

This is what Otto Scherzer's paper proved in 1936,

103

stopping progress on the TEM: it is impossible to produce a radially symmetric magnetic lens that diverges.

104

And this was of course a big roadblock for the development of electron microscopy, because people saw: "Okay, we can accelerate electrons as much as we want.

105

The presence of the spherical aberration will always be in the way." Because of this roadblock, advancements in the microscope's resolution slowed significantly.

106

By 1955, another microscope beat the TEM to the punch, and took the first generally accepted image of atoms.

107

This was called the field ion microscope, and it worked by shooting helium or neon atoms at an atomically sharp needle tip.

108

The tip was positively charged, so when the gas atoms hit the needle, they got ionized and were ejected off perpendicular to the surface.

109

And that could form an impression of the atomic structure of the tip.

110

But this method was limited.

111

You could only get a sense of the atomic structure of the very tip of the needle, and the images weren't all that impressive.

112

Luckily, Ruska's electron microscope wouldn't stay stuck in the realm of insects and bacteria forever.

113

Now, you might not be an insect getting bombarded with relativistic electrons, but it can sometimes feel like it when you're getting bombarded with spam calls and targeted ads.

114

It's a real problem when we're researching for our videos.

115

I was reading up on lenses and optics, and a few days later I started getting targeted ads for glasses and eye surgery.

116

So, someone out there is probably selling my browsing data.

117

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118

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119

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120

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121

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124

That's incogni .com /veritasium.

125

And now back to the electron microscope.

126

Despite Scherzer's aberration limit, work on the transmission electron microscope continued.

127

During the next four decades, people tried boosting the resolution with clever workarounds, and perhaps none more so than British American physicist Albert Crewe.

128

His idea was to replace the tungsten filament, which fired off electrons at random, with a more directed source.

129

So instead of boiling electrons off the surface, he tried pulling them off with a stronger electric field.

130

And by sharpening the tungsten into a fine tip, he was able to create a narrow beam which was over a thousand times brighter than before.

131

He paired his new narrow beam with an unlikely technology.

132

The cathode ray tube TV.

133

These TVs worked by scanning an electron beam across a screen.

134

The screen was coated in a phosphor that produced light when hit by electrons.

135

And by varying the intensity of the electron beam, you could vary the brightness of the screen, giving you a black and white image.

136

Crew was inspired to design a similar electron beam for the TEM that would scan across the nanoscopic sample.

137

So instead of creating an imprint of the whole sample at once, Crew's electron beam made smaller imprints, mapping the sample out bit by bit.

138

This wasn't the first time someone had tried to make a scanning version of the TEM.

139

German researcher Manfred von Arden built an early prototype in the 1930s.

140

But it was destroyed during World War II.

141

When Crewe revived Arden's design, he made several drastic improvements,

142

and by 1970, he had this: the first image of single atoms taken with the electron microscope.

143

Researchers quickly jumped to employ his tech, producing countless images of atoms.

144

After nearly a century of improvements from Ruska,

145

Crew, and many others, the magnification upgrades on the TEM had reached their peak. But Scherzer's problem persisted.

146

Spherical aberrations set a hard limit on how small you could see.

147

Even Crew himself gave up on trying to get around it after over ten years of work.

148

Unfortunately, we could never make it work.

149

After many heartbreaking attempts, we were forced to admit defeat.

150

Around this time, other microscopes emerged that could also image atoms.

151

These probe microscopes work by gliding an incredibly small stylus across the sample.

152

The stylus detects variations in quantum effects or nanoscale forces to then map the surface structure of the sample.

153

These were easier to build, and because they didn't use any lenses, they weren't limited by spherical aberration.

154

Their images were even 3D.

155

But the looming issue was that these probes weren't really seeing atoms.

156

It was more like feeling atoms.

157

Throughout the 80s and 90s, this was all we had.

158

But what if there was another way?

159

Schurzer's theorem proved that a diverging radially symmetric lens isn't possible.

160

But if you're willing to give up on that symmetry, the theorem no longer applies.

161

The problem is that radial symmetry is arguably the most important property of any lens, because if you break the symmetry, you also break the image.

162

But three maverick scientists thought there might be a way.

163

Newt Urban, Max Hader, and Harold Rose were known in the electron microscope community as troublemakers.

164

And for years, barely anyone had been interested in their research.

165

or more importantly, in funding it.

166

And for a good reason too.

167

Their idea was kind of crazy.

168

I mean, they purposefully wanted to break the image using a lens that wasn't symmetric.

169

Their hope was that there would be a small part of this distorted image that would be slightly diverging,

170

and maybe Just maybe this small part could correct the spherical aberration of the original lens.

171

So they got to work.

172

To distort the image, they used a massive nest of electromagnets with six, eight, or even ten separate coils and magnets with bumpy magnetic fields.

173

These were known as the hexapole, octapole, and decapole magnets.

174

So as the electron beam passed through a hexapole, it would twist and squeeze the flat 2D image into a triangular saddle.

175

and the circumference of the original beam would be pushed into the three corners, with the rest of the interior stretched out.

176

But now, the middle of the image would have a slight concave bow, giving the effect of a small divergence.

177

Then Rose, Hayter, and Urban forced the beam through a second hexapole, one that worked the opposite way, so it would unbend the distorted image back into a circular shape.

178

But now, they calculated, this new image might have the remnants of that tiny divergence still in its center, with spherical aberration pointing in the opposite way.

179

So if they got their maths and engineering exactly right, they could feed an image with spherical aberration through these two lenses to almost completely counteract the effect.

180

And I imagine a lot of people in the field thought it was a crazy idea when it was proposed, right?

181

Not only the concept, but that this is like technical feasible, I believe.

182

It was thought that this is not possible.

183

By May 1997, the group had just two months of development time left before their last sponsor withdrew their backing.

184

And to make matters worse, their latest lens iteration was still just on the drawing board.

185

But somehow by the 23rd of July, just a week before their funding ran out, the new lens was ready to test.

186

They gingerly placed it into the microscope, but like every time before it, the lens was unstable and failed.

187

So they decided to switch off the equipment for 24 hours the magnets to settle.

188

And then, at 2 AM on the 24th, They turned it on again.

189

And almost magically, the picture started to stabilize.

190

- I'm sorry.

191

Suddenly, there was no aberration.

192

only beautiful, clear images of atoms.

193

After more than 60 years of failed attempts, Urban, Rose, and Hayter pulled off the seemingly impossible.

194

With this method, they cut the resolution of the TEM down to only 0 .13 nanometers.

195

an average TEM image went from looking like this to this.

196

A few months after the group's breakthrough, Newt Urban attended a microscopy conference to share these results.

197

But because of the group's reputation, he was relegated to a small back room that barely anyone noticed.

198

- Thank you.

199

Soon, however, word spread that against all odds his pictures seemed real.

200

Then a crowd of hundreds formed.

201

People were lining up outside, hoping to get a glimpse of their stunningly sharp images.

202

So we're gonna get a sample holder.

203

Yes, now we get a sample holder out.

204

We put that under the optical microscope.

205

So the sample itself is a small lamella that you can't see without the optical microscope.

206

Here, have a look through that.

207

Beautiful.

208

On top of the B there's a prong.

209

Yeah.

210

And on the very top of that, on the left hand side, looks like a little bit of dust.

211

That's our actual sample.

212

Okay, now I simply go up with the magnification.

213

and I do a very few, like, more basic alignments.

214

In this electron microscope, because it's called transmission electron microscope, the electrons always transmit the sample.

215

Here we look through our entire sample at the same time.

216

And that's why it's so important that we align the sample.

217

If you imagine atoms in a high -symmetry direction are lined up like pearls on a string, when we look down it, well, we can see an image.

218

But if we are in some random direction, then everything would be just blurred.

219

So that's why we have to do some tilting in the end.

220

And this is where the actual sample starts, the strontium titanate.

221

And this is the thin region where we hope to get atomic resolution.

222

So this is 5 ,000 times?

223

Yes.

224

Wow and we see strontium, titanium, we see oxygen, We see carbon, that's contamination, so most likely what we're looking at here is carbon contamination.

225

When you do this focus, what are you really looking for?

226

I look for this edge to become sharp.

227

- Bye.

228

Seattle's what?

229

Just like that.

230

That's wild.

231

Shortly after the group successfully corrected the aberrations in the TEM,

232

Andrei Krivanek independently achieved the same for Crew's version of the microscope, the scanning TEM.

233

And in 2020, all four were awarded the prestigious Kavli Prize in nanoscience for accomplishing what so many others thought impossible.

234

Through their persistence and ingenuity, seeing atoms like this is...

235

Well, normal.

236

How big of a difference does aberration correction make?

237

If you want to see atoms, and if you want to, for example, measure interatomic distances, and if you want to learn what type of atoms you have.

238

you need aberration correction.

239

Any research that's materials science, materials engineering, chemical engineering, you will need to see what's happening at the atomic level

240

because you want to relate the properties to the structure.

241

If you can't see the structure at the atomic level, you only have half of the information.

242

So that was a game changer.

243

That's why nowadays every university in principle needs a microscope like that.

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背景与背景信息

在这段视频中，讲者展示了如何通过不断放大微小的物体，如原子，来获取详尽的视觉信息。30年前，人们认为直接观察原子是不可能的，但如今，借助于电子显微镜，我们能够观察到小于可见光波长的物质。通过对金属小块进行放大，讲者揭示了科学研究的奇妙之处以及为此所需的高端设备和技术，这为学习者提供了一种探索科学语言的机会。

日常交流的五个短语

放大（Zooming in）
波长（Wavelength）
观察原子（Seeing atoms）
设备（Equipment）
显微镜（Microscope）

逐步阴影练习指南

要掌握此视频的内容并提升你的英语口语表达，建议采用阴影练习的方法。这种方法能帮助你熟悉科学术语及其使用。遵循以下步骤：

观看视频并集中注意力：第一次观看时，专心关注讲者的讲解和视频中的概念，而不必过度分析。
分段重播：将视频分成几个小段（例如，每段1分钟），逐段重复观看，以便更好地理解内容。
跟读练习：启用视频字幕，跟随讲者的语调和节奏进行模仿，注意发音和语调变化。这是进行shadow speak的环节。
记录难点：在练习过程中，记录下你不理解或难以发音的单词和短语，针对性地进行练习。
重复和巩固：多次回放视频，尝试在日常生活中使用这些新学的短语和表达，提高自己的交际能力。

使用这些技巧，你将不仅能够理解视频内容，还能有效地提高你的英语口语能力。此外，这种阴影练习方法（shadowspeak）非常适合想要在学术或专业环境中交流的学习者。不断实践，你将能够自信地进行shadow speech，提升自己的英语表达水平。

视频中的语法

说话人最常用的结构，并附上视频中的原话：

结构	视频中的用法
被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的	was thought · was created · was known
定语从句 who / which + 从句 — 补充说明人或事物	motion, which has · beam which was

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