在成长过程中的每个夏天
Every summer when I was growing up,
我都会从我在加拿大的家
I would fly from my home in Canada
坐飞机去看望我的祖父母
to visit my grandparents,
他们住在印度孟买
who lived in Mumbai, India.
加拿大的夏日可以说 非常温和舒适
Now, Canadian summersare pretty mild at best —
22摄氏度 或72华氏度左右的气温
about 22 degrees Celsiusor 72 degrees Fahrenheit
属于典型的夏日 也不会太热
is a typical summer’s day,and not too hot.
但是孟买 是个炎热潮湿的地方
Mumbai, on the other hand,is a hot and humid place
气温能达摄氏30多度 或华氏90多度
well into the 30s Celsius or 90s Fahrenheit.
我一到那儿 就会问
As soon as I’d reach it, I’d ask
怎么有人能在这样的天气里
“How could anyone live,
生活 工作或者睡觉呢？
work or sleep in such weather?”
更糟糕的是 我祖父母家里没有空调
To make things worse, my grandparentsdidn’t have an air conditioner.
尽管我拼尽全力
And while I tried my very, very best,
却也没能说服他们添置一台
I was never aone to persuade them to get one.
但是情况在迅速发生改变
But this is changing, and fast.
现如今 制冷装置的用电量总共
Cooling systems todaycollectively account for 17 percent
占了全世界用电的17%
of the electricity we use worldwide.
这包括
This includes everythingfrom the air conditioners
我暑假极力想要的空调
I so desperately wantedduring my summer vacations,
超市里保存和冷冻食物的冰箱
to the refrigeration systems that keep our food safe and cold for usin our supermarkets,
还有维持我们数据中心正常运作的工业规模系统
to the industrial scale systems that keep our data centers operational.
这些制冷装置的温室气体排放量总共占
Collectively,these systems account for eight percent
全球温室气体排放量的8%
of global greenhouse gas emissions.
但让我在夜里辗转难眠的
But what keeps me up at night
是我们用于制冷的能耗
is that our energy use for cooling
到2050年 可能会增长六倍
might grow sixfold by the year 2050,
主要是由于亚非国家用量正逐年增长
primarily driven by increasing usagein Asian and African countries.
我已经直接预见到了这一结果
I’ve seen this firsthand.
现在 几乎我祖母家附近的的每个房子
Nearly every apartmentin and around my grandmother’s place
都配备上了空调
now has an air conditioner.
这确实 对于住在气候较热地区人们的
And that is, emphatically, a good thing
身体健康 生活舒适度 和生产力来说
for the health, well-being and productivity
都是一件好事
of people living in warmer climates.
然而 气候变化最令人担忧的事之一
However, one of the mostalarming things about climate change
是随着地球变暖
is that the warmer our planet gets,
我们将会越来越需要这些
the more we’re gonna nee- cooling systems —
本身就会排放大量温室气体的制冷系统
systems that are themselves largeemitters of greenhouse gas emissions.
到那时 就有可能形成一个反馈环路
This then has the potential to cause a feedback loop,
其中单是制冷系统
where cooling systems alone
就可是本世纪最大的温室气体来源之一
could become one of our biggest sources of greenhouse gases later this century.
而最坏的情况是
In the worst case,
到2100年 我们每年用于制冷的电力
we might need more than 10 trillion kilowatt-hours of electricity every year
可能就要耗费十万多亿千瓦时
just for cooling, by the year 2100.
达到了当下我们电力总供量的一半
That’s half our electricity supply today.
仅仅用于制冷哦
Just for cooling.
但这也同时为我们指出了一个努力的方向
But this also points us to an amazing opportunity.
那就是 只要每个制冷装置
A 10 or 20 percent improvement
都提高10%到20%的效率
in the efficiency of every cooling system
就能对温室气体的排放产生巨大影响
could actually have an enormous impacton our greenhouse gas emissions,
无论在今天还是本世纪后期都是这样
both today and later this century.
同时这能帮我们避免最坏情况的反馈环路
And it could help us avert that worst-case feedback loop.
我是一个科学家 对于光和热会有很多思考
I’m a scientist who thinks a lot about light and heat.
特别是新材料如何让我们
In particular, how new materialsallow us to alter the flow
以一种我们曾经认为不可能的方式
of these basic elements of nature
改变大自然基本元素的能量流动
in ways we might have once thought impossible.
所以 虽然我一直都很明白
So, while I always understood the value of cooling
制冷在我暑期的重要作用
during my summer vacations,
但我实际上仍然竭力研究这一问题
I actually wound up working on this problem
这源于我六年前碰到的一道智力题
because of an intellectual puzzle that I came across about six years ago.
那就是 生活在沙漠气候的古人如何制冰呢？
How were ancient peoplesable to make ice in desert climates?
这是一张冰室的照片
This is a picture of an ice house,
它又叫Yakhchal 位于伊朗的西南部
also called a Yakhchal,located in the southwest of Iran.
整个伊朗都有很多这种建筑物的废墟
There are ruins of dozensof such structures throughout Iran,
还有贯穿中东其他地区
with evidence of similar such buildings
通往中国的一路上
throughout the rest of the Middle East
都有类似这样建筑的遗迹
and all the way to China.
很多个世纪前控制这座冰室的人
The people who operatedthis ice house many centuries ago,
会在傍晚时分 日落之时
would pour water in the pool you see on the left
将水倒入左边图片的池子里
in the early evening hours, as the sun set.
然后神奇的事发生了
And then something amazing happened.
即使气温可能在凝固点以上
Even though the air temperaturemight be above freezing,
可能5摄氏度 41华氏度的样子
say 5 degreFahrenheit or 41 degrees Fahrenheit,
水仍然会结冰
the water would freeze.
然后生成的冰块会在凌晨时
The ice generated would then be collected
被储集起来
in the early morning hours
并被保存在右图所示的房子里
and stored for use in the building you see on the right,
在长达数月的夏天 以供使用
all the way through the summer months.
如果你曾在一个清朗的夜晚
You’ve actually likely seensomething very similar at play
注意过地面结霜现象
if you’ve ever noticed frost form on the ground
即便当时气温远高于水的凝固点
on a clear night,
那你就很有可能亲眼见过这种情况
even when the air temperatureis well above freezing.
等一下
But wait.
如果气温在凝固点以上 水怎么结冰呢？
How did the water freeze if the air temperature is above freezing?
蒸发也许起了一定作用
Evaporation could have played an effect,
但那远不足以让水变成冰
but that’s not enough to actually cause the water to become ice.
必须要有其他作用让它冷却下来
Something else must have cooled it down.
想想窗台上有一个正在冷却的派
Think about a piecooling on a window sill.
为了能凉下来
For it to be able to cool down,
它的热量需要转移到比它温度低的地方
its heat needs to flow somewhere cooler.
也就是它周围的空气中
Namely, the air that surrounds it.
尽管听起来有些不可思议
As implausible as it may sound,
但那一池水的热量
for that pool of water,
确实流向了外层寒冷空间中
its heat is actually flowing to the cold of space.
这怎么可能呢？
How is this possible?
其实 这池水 就和大多数自然物质一样
Well, that pool of water, like most natural materials,
以光的形式散发热能
sends out its heat as light.
这就是著名的热辐射概念
This is a concept known as thermal radiation.
事实上 我们都正以红外线的形式
In fact, we’re all sending out our heat as infrared light right now
相互并向周围散发着热量
to each other and our surroundings.
通过热感摄像机和热成像
We can actually visualizcamera with thermal cameras
我们将这一过程可视化
and the images they produce,
正如大家现在所看到的
like the ones I’m showing you right now.
所以那池水能把它的热量
So that pool of water is sending out its heat
向上发散到高空大气中去
upward towards the atmosphere.
高空大气和大气分子
The atmosphere and the molecules in it
吸收部分热量 再发送回去
absorb some of that heat and send it back.
气候变化其实就是温室效应所导致
That’s actually the greenhouse effectthat’s responsible for climate change.
但有一点很关键的是
But here’s the critical thing to understand.
大气层并不吸收传输来的全部热量
Our atmosphere doesn’t absorb all of that heat.
若它吸收全部热量 我们星球就会更暖
If it did, we’d be on a much warmer planet.
在特定的波长 尤其是8到13微米间
At certain wavelengths, in particular between8 and 13 microns,
大气层有一个传送窗口
our atmosphere has what’s knownas a transmission window.
这个窗口可以让
This window allows
一部分作为红外线上升的热量
some of the heat that goes up as infrared light
有效地释放 从而带走水池的热量
to effectively escape, carrying away that pool’s heat.
这部分热量跑到一个温度比池子低得多的地方
And it can escape to a place that is much, much colder.
跑到上层寒冷大气中
The cold of this upper atmosphere
并一路上升到
and all the way out to outer space, which can be as cold
温度能达到零下270摄氏度
as minus 270 degrees Celsius,
454华氏度的外层空间
or minus 454 degrees Fahrenheit.
所以这池水
So that pool of water
才能散发掉比空气返还给它的更多的热量
is able to send out more heat to the sky than the sky sends back to it.
正因如此
And because of that,
池里的水就能冷却到比它周围环境更低的温度
the pool will cool down below its surroundings’ temperature.
这种效应被称作夜空冷却
This is an coolin known as night-sky cooling
或辐射冷却
or radiative cooling.
气候学者和气象学家们都把这一效应
And it’s always been understoodby climate scientists and meteorologists
视作一个极为重要的自然现象
as a very important natural phenomenon.
我遇到这个问题时
When I came across all of this,
正是在斯坦福攻读博士学位的最后一段日子
it was towards the end of my PhD at Stanford.
我当时对于这个冷却方式的简单浅显
And I was amazed by its apparent simplicity
感到很惊讶
as a cooling method,
却又真的很迷惑
yet really puzzled.
我们为何不把这利用起来呢？
Why aren’t we making use of this?
过去几十年里 科学家和工程师们已经着手
Now, scientists and engineershad investigated this idea
研究这一现象
in previous decades.
结果表明至少有一个大问题存在
But there turned out to be at least one big problem.
它被称作“夜空冷却”是有原因的
It was called night-sky cooling for a reason.
什么原因呢？
Why?
我们都知道有个东西叫太阳
Well, it’s a little thing called the sun.
所以 正冷却的物体表面
So, for the surface that’s doing the cooling,
需要能面对着天空
it needs to be able to face the sky.
在中午时分
And during the middle of the day,
也许我们想要某样最凉的东西时
when we might want something cold the most,
意味着你需要将那个东西面对着太阳
unfortunately, that meansyou’re going to look up to the sun.
太阳光会把大多数材料加热直到完全抵消这一冷却效应
And the sun heats most materials up enoughto completely counteract this cooling effect.
我和同事花了很多时间
My colleagues and I spend a lot of our time
考虑怎样才能制造出
thinking amaterial we can structure materials
长度很短很短
at very small length scales
短于光的波长的材料
such that they can do new and useful things with light —
从而让它们通过利用光来达到新的功能和用途
length scales smaller than the wavelength of light itself.
在深入了解了纳米光子学和超材料研究领域的一些知识后
Using insights from this field, known as nanophotonics or metamaterials research,
我们第一次认识到
we realized that
想制作出这种材料
there might be a way to make this possible during the day
并不是不可能的
for the first time.
为达目的 我设计了一种多层的光学材料
To do this, I designed a multilayer optical material
这是它的显微成像
shown here in a microscope image.
它比一般人的头发丝还要细上40多倍
It’s more than 40 times thinnerthan a typical human hair.
而且它能同时完成两件事
And it’s able to dotwo things simultaneously.
首先 它能精准地
First, it sends its heat out precisely
将热量散发到大气中散热最佳的地方
where our atmosphere lets that heat out the best.
我们把那个传送窗口对应到了现实空间里去
We targeted the window to space.
其次它能避免被太阳光加热升温
The second thing it does is it avoids getting heated up by the sun.
就像是阳光的一面镜子一样
It’s a very good mirror to sunlight.
我第一次测试这种材料
The first time I tested this
是在斯坦福的一栋楼顶
was on a rooftop in Stanford
如这张图所示
that I’m showing you right here.
我把设备在那放了一会儿
I left the device out for a little while,
几分钟之后再走过去看
and I walked up to it after a few minutes,
不出几秒我就知道它起作用了
and within seconds, I knew it was working.
为什么呢？
How?
我摸过了 它是冷的
I touched it, and it felt cold.
(掌声)
(Applause)
令人感到奇怪和违反常理的是
Just to emphasize how weirdand counterintuitive this is:
这种材料以及和它相似的材料
this material and others like it will get colder
会在阴影之外 有太阳照射的地方
when we take them out of the shade,
变得更冰更冷
even though the sun is shining on it.
现在大家看到的是我们第一次实验得到的数据
I’m showing you data herefrom our very first experiment,
即使当时有太阳光的直射
where that material stayedmore than 5 degrees Celsius,
这个材料也一直保持在5摄氏度 9华氏度多一点
or 9 degrees Fahrenheit, colderthan the air temperature,
低于气温
even though the sun was shining directly on it.
我们用来制造这种材料的生产方式
The manufacturing method we usedto actually make this material
实际上已经大规模投入使用了
already exists at large volume scales.
为此我感到很激动
So I was really excited
因为我们不仅是做了一件很酷的事
because not only did we make something cool,
而且是有机会
but we might actually have the opportunity
做一件有现实意义且有用的事
to do something real and make it useful.
这给我带来了下一个主要问题
That brings me to the next big question.
我如何用这个创意来节能呢？
How do you actuallysave energy with this idea?
我们认为
Well, we believe
最直接的方式
th most direct way to save energy with this technology
是提升我们现在使用的空调和冷藏系统的效率
is as an efficiency boost for today’s air-conditioningand refrigeration systems.
为达到这一目的 我们做出了流体冷却板
To do this, we’ve built fluid cooling panels
就是屏幕上的这种
like the ones shown right here.
这些面板和太阳能热水器形状很相似
These panels have a similar shapeto solar water heaters,
但他们功能完全相反––他们使水冷却
except they do the opposite –they cool the water, passively,
以我们特制的材料
using our specialized material.
这些面板能组合成一个几乎所有冷却系统都有的元件
These panels can thenbe integrated with a component
叫做冷凝器
almost every cooling system has,called a condenser,
来提升系统的基础效能
to improve the system’s underlying efficiency.
SkyCool系统是我们最初的设计
Our start-up, SkyCool Systems,
它最近在加利福尼亚州的戴维斯完成了现场实验
has recently completed a field trial in Davis, California, shown right here.
在这次试验中
In that demonstration,
我们证明了在临床实验中我们确实能够
we showed that we could actually improve the efficiencyof that cooling system
将冷却系统的效率提高12%左右
as much as 12 percent in the field.
在之后的一两年内
Over the next year or two,
我非常高兴地看到
I’m super excited to see
这项研究在空调和冷藏领域
this go to its first commercial-scale pilots
都投入了商业化试用
in both the air conditioningand refrigeration space.
未来
In the future,
我们还可以用这种有更高效能的面板材料
we might be able to integrate these kinds of panels
组装制造成冷却装置
with higher efficiencybuilding cooling systems
可以让系统降低三分之二的能耗
to reduce their energy usage by 2/3.
最终
And eventually, we might actually
我们还有可能制造出一种
be able to build a cooling system
完全不需要电力输入的冷却系统
that requires no electricity input at all.
为实现这一目标的第一步
As a first step towards that,
我和我在斯坦福的同事发现
my colleagues at Stanford and I have shown that you could actually maintain
凭借更佳的设计 我们实际上可以将温度高于42摄氏度的物体
something more than 42 degrees Celsiusbelow the air temperature
维持在气温以下
with better engineering.
谢谢
Thank you.
（掌声）
(Applause)
所以想象一下 在夏天一个大热天里
So just imagine that —
有物体保始终持在零摄氏度以下
something that is below freezing on a hot summer’s day.
虽然我对我们目前取得的研究成果
So, while I’m very excited
感到很兴奋
about all we can do for cooling,
并且我觉得我还有很多可以做的
and I think there’s a lot yet to be done,
但身为一个科学家 我同时也致力于
as a scientist, I’m also drawnto a more profound opportunity
利用这项研究助我们达成更有意义的目的
that I believe this work highlights.
比如可以利用外层空间的寒冷黑暗
We can use the cold darkness of space
提高世界上任何一种涉及到能量转化过程的效率
to improve the efficiency of every energy-related process here on earth.
其中一个典型案例就是太阳能电池
One such process I’d like to highlightare solar cells.
它们在阳光照射下升温转化效率随温度的升高越来越低
They heat up under the sun and become less efficientthe hotter they are.
2015年 我们研究发现
In 2015, we showed that with deliberate kinds of microstructures
在太阳能电池上专门装配一种显微构造
on top of a solar cell,
咱们就能很好地利用冷却效应
we could take better advantage of this cooling effect
迫使太阳能电池保持在低温状态
to maintain a solar cell passivelyat a lower temperature.
这能让它们保持更高效率工作
This allows the cellto operate more efficiently.
我们在进一步探寻类似的可能
We’re probing these kinds of opportunities further.
探求是否能利用外层寒冷大气
We’re asking whetherwe can use the cold of space
帮我们节约水资源
to help us with water conservation.
或者应用在离网场景
Or perhaps with off-grid scenarios.
我们甚至可以直接利用低温产能
Perhaps we could even directlygenerate power with this cold.
地球上不同地方有温差
There’s a large temperature differencebetween us here on earth
空气中的寒冷低温也是一样
and the cold of space.
至少从理论上来看
That difference, at least conceptually,
这种温差能用来驱动
could be used to drivesomething called a heat engine
一类叫热机的机器发电
to generate electricity.
那我们能做一个夜间发电装置吗
Could we then make a nighttimepower-generation device
在太阳能电池不工作时
that generates usefulamounts of electricity
生产大量有用的电能
when solar cells don’t work?
我们能从黑暗中汲取能量产生光吗
Could we generate light from darkness?
实现这一技术的核心问题
Central to this abilityis being able to manage
是能掌控我们周围的热辐射
the thermal radiationthat’s all around us.
我们持续地沐浴在红外光线的海洋之中
We’re constantly bathed in infrared light.
如果能让它屈从于人的意志
If we could bend it to our will,
我们就能深刻地改变
we could profoundly changethe flows of heat and energy
每天渗透我们生活每一处的热和能的流动
that permeate around us every single day.
这种能力 还有外层大气的黑暗低温
This ability, coupledwith the cold darkness of space,
将我们指向了这样一个未来：
points us to a futurewhere we, as a civilization,
作为现代文明人 我们也许能更智能地
might be able to more intelligently manageour thermal energy footprint
在最大程度上控制我们自身的热能轨迹
at the very largest scales.
当我们遭遇气候变化问题时
As we confront climate change,
我相信拥有这种能力
I believe havingthis ability in our toolkit
会是很有必要的
will prove to be essential.
所以
So, the next timeyou’re walking around outside.
下次你在室外行走
Yes,
在感叹太阳对于地球生命的重要性的同时
do marvel at how the sun is essential to life on earth itself,
也请不要忘记
but don’t forget
天空中还有其他物质也能为我们所用
that the rest of the sky has something to offer us as well.
谢谢大家
Thank you.
（掌声）
(Applause)