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Every summer when I was growing up, I would fly from my home in Canada to visit my grandparents, who lived in Mumbai, India.
在我的成长过程中，每年夏天，我会从我在加拿大的家，搭飞机去看我的祖父母，他们住在印度孟买。
Now, Canadian summers are pretty mild at best
现在加拿大的夏天很暖和，
about 22 degrees Celsius or 72 degrees Fahrenheit is a typical summer's day, and not too hot.
最高大约22度摄氏或72华氏度，这是典型的夏日，不算太热。
Mumbai, on the other hand, is a hot and humid place well into the 30s Celsius or 90s Fahrenheit.
而孟买是个又热又湿的地方，会超过30摄氏度或90华氏度。
As soon as I'd reach it, I'd ask, "How could anyone live, work or sleep in such weather?"
一抵达孟买，我就会问：“怎么可能有人在这种天气下生活、工作或睡觉？”
To make things worse, my grandparents didn't have an air conditioner.
更糟的是，我的祖父母没有空调。
And while I tried my very, very best, I was never able to persuade them to get one. But this is changing, and fast.
我已经尽了我最大的努力，但我始终无法说服他们装一台空调。但这状况在改变，且改变得很快。
Cooling systems today collectively account for 17 percent of the electricity we use worldwide.
现今的冷却系统所用的电量加总起来占全世界用电量的17%。
This includes everything from the air conditioners I so desperately wanted during my summer vacations,
包括从我暑假当中超想要的空调，
to the refrigeration systems that keep our food safe and cold for us in our supermarkets,
到超级市场中确保我们的食物安全且存放于低温的冷藏系统，
to the industrial scale systems that keep our data centers operational.
到确保我们资料储存中心能顺利运作的工业规模冷却系统。
Collectively, these systems account for eight percent of global greenhouse gas emissions.
这些系统所排放的温室气体加起来占全球总排放的8%。
But what keeps me up at night is that our energy use for cooling might grow sixfold by the year 2050,
但让我睡不着觉的是我们用在冷却上的能量，到2050年时可能会增为六倍，
primarily driven by increasing usage in Asian and African countries. I've seen this firsthand.
主要的原因是亚洲和非洲国家的用量增加。我亲眼见过。
Nearly every apartment in and around my grandmother's place now has an air conditioner.
几乎我祖母家附近的每一间公寓，现在都有空调了。
And that is, emphatically, a good thing for the health, well-being and productivity of people living in warmer climates.
就温暖气候地区居民的健康、幸福以及生产力而言，那很明显是件好事。
However, one of the most alarming things about climate change is that the warmer our planet gets,
然而关于气候变迁最大的警讯之一，就是当地球变得更暖和，
the more we're going to need cooling systems -- systems that are themselves large emitters of greenhouse gas emissions.
我们就会更需要冷却系统，这些系统本身就是温室气体排放的来源。
This then has the potential to cause a feedback loop,
这就有可能会形成一个恶性循环，
where cooling systems alone could become one of our biggest sources of greenhouse gases later this century.
光是冷却系统就能在这个世纪后期变成最大的温室气体来源。
In the worst case, we might need more than 10 trillion kilowatt-hours of electricity every year, just for cooling, by the year 2100.
在最糟的情况下，到2100年时，仅仅为了冷却，我们可能每年就会需要超过十兆千瓦小时的电力。
That's half our electricity supply today. Just for cooling.
那是现今我们电力总供应量的一半。仅仅为了冷却。
But this also point us to an amazing opportunity.
但这也为我们点出了一个很棒的机会。
A 10 or 20 percent improvement in the efficiency of every cooling system could actually have an enormous impact on our greenhouse gas emissions,
如果每一种冷却系统在效能上都能有10%到20%的改善，就会对温室气体的排放有非常大的影响，
both today and later this century. And it could help us avert that worst-case feedback loop.
对于现今以及本世纪后期都是如此。并且它能协助我们避免发生最糟状况的恶性循环。
I'm a scientist who thinks a lot about light and heat.
我是一位常常在思考光和热的科学家。
In particular, how new materials allow us to alter the flow of these basic elements of nature in ways we might have once thought impossible.
我特别着重研究新材料如何能协助我们改变大自然这些基本元素的流动方式，用我们以前认为不可能的方式来做到。
So, while I always understood the value of cooling during my summer vacations,
所以，我一直都清楚暑假降温的重要性，
I actually wound up working on this problem because of an intellectual puzzle that I came across about six years ago.
由于六年前我遇到的智力难题，我实际上已经完成了解决这个问题的工作。
How were ancient peoples able to make ice in desert climates?
古人怎么能在沙漠气候下制冰？
This is a picture of an ice house, also called a Yakhchal, located in the southwest of Iran.
这张照片中的是一间冰室，也叫做“Yakhchal”，位于伊朗西南部。
There are ruins of dozens of such structures throughout Iran,
在伊朗各地，有数十个这类建筑物的遗迹，
with evidence of similar such buildings throughout the rest of the Middle East and all the way to China.
有证据显示，这类建筑物还遍及了中东其它地区，一路延伸到中国。
The people who operated this ice house many centuries ago,
几百年前使用这些冰室的人
would pour water in the pool you see on the left in the early evening hours, as the sun set. And then something amazing happened.
会把水倒入照片左侧的池子中，时机是太阳下山，刚刚进入傍晚的时候。接着，神奇的事就会发生。
Even though the air temperature might be above freezing, say five degrees Celsius or 41 degrees Fahrenheit, the water would freeze.
虽然空气中的温度还在冰点以上，比如5摄氏度，或41华氏度，水却会结冰。
The ice generated would then be collected in the early morning hours and stored for use in the building you see on the right,
一大清早，产出的冰就会被收集起来，储存放在右边的建筑物里备用，
all the way through the summer months.
夏季的所有月份就是这样度过。
You've actually likely seen something very similar at play
你们其实有可能见过类似的现象发生，
if you've ever noticed frost form on the ground on a clear night, even when the air temperature is well above freezing.
如果你有注意过，在晴天晚上，即使空气温度在冰点以上，地面也会形成霜，就是类似的现象。
But wait. How did the water freeze if the air temperature is above freezing?
但稍等一下。如果空气温度没有低于冰点，为什么水会结冰？
Evaporation could have played an effect, but that's not enough to actually cause the water to become ice.
蒸发的效应就很重要了，但光是这点还不够让水变成冰。
Something else must have cooled it down.
还要有其他东西来将水冷却。
Think about a pie cooling on a window sill.
想像一个派，在窗台上冷却。
For it to be able to cool down, its heat needs to flow somewhere cooler. Namely, the air that surrounds it.
若要让它冷下来，就要让热流到比较冷的地方。也就是，流到它周围的空气中。
As implausible as it may sound, for that pool of water, its heat is actually flowing to the cold of space.
虽然这听起来很不合情理，一池水的热怎么可能流到低温的外太空中。
How is this possible? Well, that pool of water, like most natural materials, sends out its heat as light.
这怎么有可能发生？嗯，那池水和大部分的自然材料一样，以光的方式将热发送出去。
This is a concept known as thermal radiation.
这概念就是大家所知的“热辐射”。
In fact, we're all sending out our heat as infrared light right now, to each other and our surroundings.
事实上，我们现在都在用红外线光的方式把我们的热发送给彼此和周遭的环境。
We can actually visualize this with thermal cameras and the images they produce, like the ones I'm showing you right now.
使用热感摄影机就能将这现象视觉化，它们所产出的影像，就会类似各位现在看到的这一张。
So that pool of water is sending out its heat upward towards the atmosphere.
所以，这一池水把它的热向上发送到大气中。
The atmosphere and the molecules in it absorb some of that heat and send it back.
大气以及大气中的分子会吸收其中一些热，再发送回来。
That's actually the greenhouse effect that's responsible for climate change.
那其实就是造成气候变迁的温室效应。
But here's the critical thing to understand.
但在这里要了解一个关键点。
Our atmosphere doesn't absorb all of that heat. If it did, we'd be on a much warmer planet.
我们的大气并不会吸收所有的热。如果会的话，地球就会更暖和许多。
At certain wavelengths, in particular between eight and 13 microns, our atmosphere has what's known as a transmission window.
在某些波长，特别是在8到13微米之间，我们的大气有个所谓的传送窗口。
This window allows some of the heat that goes up as infrared light to effectively escape, carrying away that pool's heat.
这扇窗会让其中一些以红外线方式向上发送的热有效地发散传送，将池水的热给带走。
And it can escape to a place that is much, much colder.
这些热会发散到一个更冷的地方。
The cold of this upper atmosphere and all the way out to outer space,
大气上层的低温当中，以及一路到外太空中，
which can be as cold as minus 270 degrees Celsius, or minus 454 degrees Fahrenheit.
外太空的温度可以低到零下270摄氏度，或零下454华氏度。
So that pool of water is able to send out more heat to the sky than the sky sends back to it.
所以那池水发送到天空中的热就多于天空发送回来的热。
And because of that, the pool will cool down below its surroundings' temperature.
基于这个理由，那池水会冷却到比环境更低的温度。
This is an effect known as night-sky cooling or radiative cooling.
这就是我们常说的夜空冷却，或称辐射冷却。
And it's always been understood by climate scientists and meteorologists as a very important natural phenomenon.
气候科学家和气象学家一直都知道这是个非常重要的自然现象。
When I came across all of this, it was towards the end of my PhD at Stanford.
当我接触到这些信息时，我已经快要拿到斯坦福的博士学位了。
And I was amazed by its apparent simplicity as a cooling method, yet really puzzled.
这种冷却方法表面是如此简单，背后却又是个复杂的谜，这让我感到困惑。
Why aren't we making use of this? Now, scientists and engineers had investigated this idea in previous decades.
我们为什么不好好利用它？在过去数十年，科学家和工程师都在研究这个机制。
But there turned out to be at least one big problem. It was called night-sky cooling for a reason. Why?
但结果发现，至少有一个大问题。它被称为夜空冷却是有原因的。为什么？
Well, it's a little thing called the sun. So, for the surface that's doing the cooling, it needs to be able to face the sky.
因为有个小东西，叫做太阳。要进行冷却的表面，必需要能够面向天空。
And during the middle of the day, when we might want something cold the most, unfortunately, that means you're going to look up to the sun.
在日正当中时，我们最希望的就是能冷到最低点，很不幸的，在那时候你得要向上看向太阳。
And the sun heats most materials up enough to completely counteract this cooling effect.
而太阳会把大部分的物质加热，热到足以完全抵消掉这种冷却效应。
My colleagues and I spend a lot of our time thinking about how we can structure materials at very small length scales such
我的同事和我花了很多时间思考要如何建构出波长极短的材料，
that they can do new and useful things with light -- length scales smaller than the wavelength of light itself.
让它们能与光反应产生新的、有用的东西--波长要小于光本身的波长。
Using insights from this field, known as nanophotonics or metamaterials research,
使用这个领域的见解，也就是一般所知的奈米光子或超材料研究，
we realized that there might be a way to make this possible during the day for the first time.
我们第一次发现了可能有种办法能够在白天实现这一点，
To do this, I designed a multilayer optical material shown here in a microscope image.
我为此设计了一种多层的光学材料，在这张显微镜影像中可以看见。
It's more than 40 times thinner than a typical human hair. And it's able to do two things simultaneously.
它比一般人的头发的40分之一还要细。它能够同时做两件事。
First, it sends its heat out precisely where our atmosphere lets that heat out the best. We targeted the window to space.
首先，它能精准地把热发送到大气层，达到最佳的降温效果。我们对准了通往太空的窗户。
The second thing it does is it avoids getting heated up by the sun. It's a very good mirror to sunlight.
第二是它能避免被太阳加温。它是面很好的太阳光反射镜。
The first time I tested this was on a rooftop in Stanford that I'm showing you right here.
我第一次测试它时，是在斯坦福的屋顶上，各位在照片上可以看见。
I left the device out for a little while, and I walked up to it after a few minutes, and within seconds, I knew it was working.
我把这个装置留在那里一阵子，几分钟之后，我走向它，在几秒钟之内，我就知道它有用。
How? I touched it, and it felt cold.
如何知道的？我摸了它，摸起来是冷的。
Just to emphasize how weird and counterintuitive this is:
再强调一下这个现象有多怪异且和直觉不符：
this material and others like it will get colder when we take them out of the shade, even though the sun is shining on it.
这种材料及其它相似的材料，如果离开阴影反而会变得更冷，即使是被阳光直射着。
I'm showing you data here from our very first experiment,
各位现在看到的是我们第一次实验的资料，
where that material stayed more than five degrees Celsius, or nine degrees Fahrenheit, colder than the air temperature,
当时那材料的温度比空气的温度，要低5摄氏度或9华氏度，
even though the sun was shining directly on it.
即使太阳光直射在它上面。
The manufacturing method we used to actually make this material already exists at large volume scales.
实际量产这种材料的方法已然存在。
So I was really excited, because not only do we make something cool,
我非常兴奋，因为我们不只是发明出了很清凉的东西，
but we might actually have the opportunity to do something real and make it useful.
我们可能真的有机会做出很有用的东西来。
That brings me to the next big question.
那就带出了下一个大问题。
How do you actually save energy with this idea?
要如何用这个点子来节省能源？
Well, we believe the most direct way to save energy with this technology
我们相信，若要用这项技术来节省能源，最直接的方式就是，
is as an efficiency boost for today's air-conditioning and refrigeration systems.
对现在的空调和冰箱系统进行效能的提升。
To do this, we've built fluid cooling panels, like the ones shown right here.
为此，我们打造了液态的冷却板，就像画面上的这种。
These panels have a similar shape to solar water heaters, except they do the opposite
它们的外型和太阳能热水器很相似，差别在于功能相反，
they cool the water, passively, using our specialized material.
它们能用我们的特殊材料被动地让水冷却。
These panels can then be integrated with a component almost every cooling system has,
这些冷却板可以和一个元件整合，几乎所有冷却系统都有这个元件：
called a condenser, to improve the system's underlying efficiency.
冷凝器，目的是要改善系统的根本效率。
Our start-up, SkyCool Systems, has recently completed a field trial in Davis, California, shown right here.
我们的初创公司叫SkyCool Systems，目前已经在加州戴维斯完成了实地测试，如照片所示。
In that demonstration, we showed that we could actually improve the efficiency of that cooling system as much as 12 percent in the field.
在那次展示中，我们展现了我们在实际当中，真的能够改善冷却系统的效率达12%。
Over the next year or two, I'm super excited to see this go to its first commercial-scale pilots in both the air conditioning and refrigeration space.
在接下来的一、两年，我很兴奋地期待能看到商业规模的测试开始进行，用于包括空调以及冰箱上。
In the future, we might be able to integrate these kinds of panels with higher efficiency building cooling systems to reduce their energy usage by two-thirds.
在未来，我们也许可以把这些冷却板整合到更高效能的建筑冷却系统中，将这些系统所需要使用的能源减少三分之二。
And eventually, we might actually be able to build a cooling system that requires no electricity input at all.
最终，我们可能可以打造一个完全不需要电力输入的冷却系统。
As a first step towards that, my colleagues at Stanford and I have shown that
要做到这点，第一步，我和斯坦福的同事已经让大家看到，
you could actually maintain something more than 42 degrees Celsius below the air temperature with better engineering. Thank you.
确实可以将物体维持在比空气温度低42摄氏度的状态，用更好的工程方式就能做到。谢谢。
So just imagine that -- something that is below freezing on a hot summer's day.
想像一下，在炎热的夏日，有低于冰点的东西。
So, while I'm very excited about all we can do for cooling, and I think there's a lot yet to be done,
所以，虽然我对于我们能为冷却做出的贡献感到很兴奋，但我认为还有很多还没完成的，
as a scientist, I'm also drawn to a more profound opportunity that I believe this work highlights.
身为科学家，我也被这项发明所突出的无限机会给深深吸引着。
We can use the cold darkness of space to improve the efficiency of every energy-related process here on earth.
我们可以利用太空的寒冷黑暗来改善地球上每一项与能源有关过程的效能。
One such process I'd like to highlight are solar cells.
我想要特别提出来的其中一种过程，就是太阳能板。
They heat up under the sun and become less efficient the hotter they are.
在太阳下，它们会被加温，当它们本身越热，就越没没效率。
In 2015, we showed that with deliberate kinds of microstructures on top of a solar cell,
2015年，我们展示出在太阳能板上方刻意加上微结构，
we could take better advantage of this cooling effect to maintain a solar cell passively at a lower temperature.
就能够更善加利用这种冷却效应，来被动地将太阳能板保持在较低的温度。
This allows the cell to operate more efficiently. We're probing these kinds of opportunities further.
这样太阳能板就能更有效地运作。我们还在进一步研究这些机会。
We're asking whether we can use the cold of space to help us with water conservation.
我们在问的问题是，我们是否能用太空的低温来协助我们做水资源保存。
Or perhaps with off-grid scenarios. Perhaps we could even directly generate power with this cold.
或许协助我们不再使用电网。我们甚至可以直接用这低温来发电。
There's a large temperature difference between us here on earth and the cold of space.
我们地球这里的温度和太空的低温有很大的落差。
That difference, at least conceptually, could be used to drive something called a heat engine to generate electricity.
那种落差，至少在概念上，可以被用来驱动所谓的热引擎来产生电力。
Could we then make a nighttime power-generation device that generates useful amounts of electricity when solar cells don't work?
那么我们是否能够做出一种夜晚的发电装置，能够产生够用的电力，在太阳能板不能运作时代劳呢？
Could we generate light from darkness?
我们能否用黑暗来产生光？
Central to this ability is being able to manage the thermal radiation that's all around us.
这项能力的关键，在于要能够管理我们周遭的热辐射。
We're constantly bathed in infrared light;
我们经常处在红外线光之中；
if we could bend it to our will, we could profoundly change the flows of heat and energy that permeate around us every single day.
如果我们愿意改变这一切，我们就能深深地改变每天在我们周围比比皆是的热与能量之流动。
This ability, coupled with the cold darkness of space, points us to a future where we, as a civilization,
这种能力，再加上太空的寒冷黑暗，就能为我们的文明指点未来的方向，
might be able to more intelligently manage our thermal energy footprint at the very largest scales.
让我们能在非常大的规模下，更智慧地管理我们的热能足迹。
As we confront climate change, I believe having this ability in our toolkit will prove to be essential.
我们正在面临气候变迁，我相信把这种能力放入我们的工具箱是非常重要的。
So, the next time you're walking around outside, yes, do marvel at how the sun is essential to life on earth itself,
所以，下次当你在外面四处走动时，是的，当我们对太阳在地球生命的重要性感到惊艳时，
but don't forget that the rest of the sky has something to offer us as well. Thank you.
也别忘了天空中的其它部分，也能为我们提供某些资源。谢谢。
