Why don't perpetual motion machines ever work? - Netta Schramm

翻译人员: Xi Zhang 校对人员: Haocun Yu

Around 1159 A.D.,

大约公元1159年的时候，

有一位叫做婆什迦罗智者的数学家，

a mathematician called Bhaskara the Learned

sketched a design for a wheel containing curved reservoirs of mercury.

构想出了一种带有很多弯形水银蓄池的轮子。

He reasoned that as the wheels spun,

他觉得随着轮子的转动，

the mercury would flow to the bottom of each reservoir,

每个池子里的水银会流到池底，

leaving one side of the wheel perpetually heavier than the other.

导致轮子的一端总是比另一端更重一点，

这种力矩的不平衡会让轮子永远地转下去。

The imbalance would keep the wheel turning forever.

Bhaskara's drawing was one of the earliest designs

婆什迦罗的设想是最早期的

for a perpetual motion machine,

永动机构想之一，

一种不依赖外界能量来源 而能永远工作下去的机器。

a device that can do work indefinitely without any external energy source.

Imagine a windmill that produced the breeze it needed to keep rotating.

想象一个可以不断鼓出吹动自己的风的风车。

或者一个可以为自己供电的灯泡。

Or a lightbulb whose glow provided its own electricity.

这些机器绞尽了许许多多发明家的脑汁

These devices have captured many inventors' imaginations

因为它们可以改变我们和能量间的关系。

because they could transform our relationship with energy.

For example, if you could build a perpetual motion machine

比如说，如果我们能造出一个永动机

that included humans as part of its perfectly efficient system,

它的永动系统包含了人类，

it could sustain life indefinitely.

那永生就不再是梦了。

There's just one problem.

但只有一个问题，

They don't work.

永动机是不可能的。

Ideas for perpetual motion machines

所有有关永动机的想法

all violate one or more fundamental laws of thermodynamics,

都违背了至少一个热力学基本定律，

热力学是描述不同形式能量之间关系

the branch of physics that describes the relationship

between different forms of energy.

的物理学分支。

The first law of thermodynamics says that energy can't be created or destroyed.

热力学第一定律是， 能量不会凭空产生或消失

You can't get out more energy than you put in.

你不可能从机器里得到比你放进去更多的能量。

That rules out a useful perpetual motion machine right away

这就排除了任何可行的的永动机的可能

because a machine could only ever produce as much energy as it consumed.

因为一台机器最多只能产生和它消耗的同样多的能量。

不可能还有多余的能量 用来驱动车或者给手机充电。

There wouldn't be any left over to power a car or charge a phone.

But what if you just wanted the machine to keep itself moving?

但是如果你只是想让机器自己不停地运行下去呢？

Inventors have proposed plenty of ideas.

发明家们想出了很多点子。

Several of these have been variations on Bhaskara's over-balanced wheel

有一些就是婆什迦罗非平衡轮的变型

with rolling balls or weights on swinging arms.

比如有着滚动的小球或者是悬挂着重物的杆子。

None of them work.

但是没一种有用。

The moving parts that make one side of the wheel heavier

移动的部分确实让轮子的一端更重一些

also shift its center of mass downward below the axle.

但同时降低了轮子整体的重心到轮轴以下。

在低重心下，

With a low center of mass,

the wheel just swings back and forth like a pendulum,

轮子只会像钟摆一样前后摆动，

最终停下来。

then stops.

换一种思路呢？

What about a different approach?

在17世纪，罗伯特·波义尔想出了个点子，

In the 17th century, Robert Boyle came up with an idea

for a self-watering pot.

一种自己给自己浇水的壶。

He theorized that capillary action,

他理论上证明了毛细作用，

the attraction between liquids and surfaces

一种液体和容器表面间的吸引力

that pulls water through thin tubes,

足以使水吸进毛细管，

might keep the water cycling around the bowl.

这样也许能使水不断的围绕壶循环。

But if the capillary action is strong enough to overcome gravity

但是如果毛细作用大到足以克服重力

并可以把水从管中提上来，

and draw the water up,

it would also prevent it from falling back into the bowl.

那毛细作用也应该会阻止水再掉回到壶中。

Then there are versions with magnets, like this set of ramps.

再后来，又有了一些和磁铁有关的永动机设想， 比如这套斜坡装置。

The ball is supposed to be pulled upwards by the magnet at the top,

小球应该会被顶端的磁铁吸引上斜坡，

fall back down through the hole,

然后从洞中掉回底部，

循环往复。

and repeat the cycle.

这个装置也没能成功， 就像之前所说的能给自己浇水的水壶，

This one fails because like the self-watering pot,

the magnet would simply hold the ball at the top.

磁铁只可能把小球吸在顶部不动。

Even if it somehow did keep moving,

即使小球能不断运动，

the magnet's strength would degrade over time

磁铁的磁力也会随着时间流逝而消退，

最终停止运行。

and eventually stop working.

For each of these machines to keep moving,

对于所有的这些机器， 如果想要保持运动

they'd have to create some extra energy

它们必然需要产生一些额外的能量

to nudge the system past its stopping point,

将整个系统推过停止点，

这就违反了热力学第一定律。

breaking the first law of thermodynamics.

There are ones that seem to keep going,

有一些永动机看上去会一直运行下去，

but in reality, they invariably turn out to be drawing energy

但事实上，它们总归会

从外界获取额外的能量。

from some external source.

即使工程师们能够以某种方式造出了

Even if engineers could somehow design a machine

that didn't violate the first law of thermodynamics,

不违反第一定律的永动机，

it still wouldn't work in the real world because of the second law.

由于第二定律 它仍旧不可能实现。

The second law of thermodynamics

热力学第二定律

tells us that energy tends to spread out through processes like friction.

告诉我们能量总是通过某些方式趋于散失，比如摩擦。

Any real machine would have moving parts

任何现实生活中的机器都有着移动的部件

or interactions with air or liquid molecules

或者是与气体及液体分子的互相作用

that would generate tiny amounts of friction and heat,

这就会产生微量的摩擦与热量，

even in a vacuum.

在真空中也不例外。

That heat is energy escaping,

那些热量就是能量损失，

and it would keep leeching out,

并且它一直在流失，

reducing the energy available to move the system itself

不断地减少可供系统自身运动的能量

until the machine inevitably stopped.

直到机器不可避免地停下来。

So far, these two laws of thermodynamics

到目前为止， 这两条热力学定律

have stymied every idea for perpetual motion

已经排除了任何关于永动机的设想

and the dreams of perfectly efficient energy generation they imply.

以及100%效率产能的可能。

Yet it's hard to conclusively say we'll never discover a perpetual motion machine

但是，这并不能绝对地说 我们将永远无法找到永动机，

because there's still so much we don't understand about the universe.

因为我们对整个宇宙的了解还是太少了。

Perhaps we'll find new exotic forms of matter

也许我们将找到一种新的奇异的物质存在形式

that'll force us to revisit the laws of thermodynamics.

让我们不得不重新审视热力学的定律。

Or maybe there's perpetual motion on tiny quantum scales.

又或许在极小的量子尺度会有永动机的存在。

What we can be reasonably sure about is that we'll never stop looking.

我们能确定的是 我们永远不会停止寻找。

For now, the one thing that seems truly perpetual is our search.

现在，唯一看上去“永动”的，是我们的搜寻。