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Science and technology
科学技术
Einstein and car batteries
爱因斯坦和汽车电池
A spark of genius
天才的灵光
Without the magic of relativity, a car's starter motor would not turn
要不是相对论的魔力，汽车的发动马达就转不起来
ALBERT EINSTEIN never learned to drive.
阿尔伯特.爱因斯坦从没去学开车。
He thought it too complicated and in any case he preferred walking. What he did not know—indeed, what no one knew until now—is that most cars would not work without the intervention of one of his most famous discoveries, the special theory of relativity.
他觉得开车太复杂，再者，他更喜欢走路。而他不知道的—也是直到现在人们才知道的是—没有他的伟大发现之一，即狭义相对论，大多数汽车不可能发动起来。
Special relativity deals with physical extremes.
狭义相对论同物理极限相关。
It governs the behaviour of subatomic particles zipping around powerful accelerators at close to the speed of light and its equations foresaw the conversion of mass into energy in nuclear bombs.
该理论掌握了亚原子粒子在强大的加速器的作用下可以达到接近光速的速度这一表现行为。相对论的公式也预见了核弹中质能转换的现象。
A paper in Physical Review Letters, however, reports a more prosaic application.
然而，一篇发表在物理评论快报上的文章，讲述了狭义相对论更为一般的应用。
According to the calculations of Pekka Pyykko of the University of Helsinki and his colleagues, the familiar lead-acid battery that sits under a car's bonnet and provides the oomph to get the engine turning owes its ability to do so to special relativity.
根据赫尔辛基大学的Pekka Pyykko和他同事们的计算，我们所熟悉的在汽车发动机罩下，给汽车引擎发动提供能量的铅酸电池，它之所以有这样的能力都归功于狭义相对论。
Relative values
相对的价值
The lead-acid battery is one of the triumphs of 19th-century technology.
铅酸电池是19世纪技术发展的产物之一。
It was invented in 1860 and is still going strong.
它于1860年发明，迄今为止仍然具有很强的实用性。
Superficially, its mechanism is well understood. Indeed, it is the stuff of high-school chemistry books.
表面上，其机制为人熟知这些都是高中化学课本上的东西
But Dr Pyykko realised that there was a problem.
但Pyykko博士发觉了哪里不对劲。
In his view, when you dug deeply enough into the battery's physical chemistry, that chemistry did not explain how it worked.
在他看来，越是深入研究电池的物理化学特性，这些化学特性反而越不能解释电池到底是怎么工作的。
A lead-acid battery is a collection of cells, each of which contains two electrodes immersed in a strong solution of sulphuric acid.
铅酸电池是电池单元构成的集合，其中每个电池都有两个电极，浸泡在硫酸溶液的电解液里。
One of the electrodes is composed of metallic lead, the other of porous lead dioxide.
金属铅充当一处电极，另一处电极是多孔二氧化铅。
In the parlance of chemists, metallic lead is electropositive.
化学家认为，金属铅是电正性物质。
This means that when it reacts with the acid, it tends to lose some of its electrons.
这表明，当铅和酸发生反应时，它很可能失去一些电子。
Lead dioxide, on the other hand, is highly electronegative, preferring to absorb electrons in chemical reactions.
而另一方面，二氧化铅是电负性物质，在化学反应中更喜欢吸收电子。
If a conductive wire is run between the two, electrons released by the lead will run through it towards the lead dioxide, generating an electrical current as they do so.
如果把一根导电金属丝放在金属铅和二氧化铅之间，铅释放的电子会经金属丝传递到二氧化铅，这个过程会产生电流。
The bigger the difference in the electropositivity and electronegativity of the materials that make up a battery's electrodes, the bigger the voltage it can deliver.
组成电池两级的物质的正负电荷差越大，他们发生化学反应时产生的电伏数越大。
In the case of lead and lead dioxide, this potential difference is just over two volts per cell.
以铅和二氧化铅为例的电池，每节电池的电位差可产生2伏电压。
That much has been known since the lead-acid battery was invented.
自铅酸电池发明以来，上述的理论就已为人熟知。
However, although the properties of these basic chemical reactions have been measured and understood to the nth degree, no one has been able to show from first principles exactly why lead and lead dioxide tend to be so electropositive and electronegative.
然而，尽管很大程度上我们都掌握和了解这些基础化学反应，却没有人能够真正说明最根本的原理—为什么铅和二氧化铅带有这般的电正性和电负性呢？
This is a particular mystery because tin, which shares many of the features of lead, makes lousy batteries.
这一点显得颇为神秘，因为和铅特性差不大多的锡，无法用来做电池。
Metallic tin is not electropositive enough compared with the electronegativity of its oxide to deliver a useful potential difference.
比起铅来，金属锡的电正性没有二氧化锡的电负性强，所以无法产生可用的电位差。
This is partly explained because the bigger an atom is, the more weakly its outer electrons are bound to it and hence the further those electrons are from the nucleus.
原子越大，其外层电子受原子束缚力越弱，这是解释铅和锡两者差别的一部分原因。
In all groups of chemically similar elements the heaviest are the most electropositive.
在化学性质相似的同族元素中，质量越重带的正电越强。
However, this is not enough to account for the difference between lead and tin.
然而这依然不能充分说明铅和锡的差别。
To put it bluntly, classical chemical theory predicts that cars should not start in the morning.
直截了当地说， 古典化学理论预言了早上要离家上班汽车是发不动的。
Which is where Einstein comes in.
那爱因斯坦怎么被扯进来了，
For, according to Dr Pyykko's calculations, relativity explains why tin batteries do not work, but lead ones do.
根据Pyykko博士的计算，相对论解释了为什么铅可以用来做电池，而锡不可以。
His chain of reasoning goes like this.
他一连串的理由是这样解释的。
Lead, being heavier than tin.
铅比锡重，核子里的质子数更多。
That means its nucleus has a stronger positive charge and that, in turn, means the electrons orbiting the nucleus are more attracted to it and travel faster, at roughly 60% of the speed of light, compared with 35% for the electrons orbiting a tin atom.
这表明原子核的正电更强，同理表明更容易吸引绕着原子核的电子，电子传播的速度也更快，其速度是光速的60%，相比之下，绕着锡原子的电子速度只能达到光速的35%。
As the one Einsteinian equation everybody can quote, E=mc2, predicts, the kinetic energy of this extra velocity makes lead's electrons more massive than tin's—and heavy electrons tend to fall in and circle the nucleus in more tightly bound orbitals.
人人都会引用的爱因斯坦相对论公式：E=mc2，公式表明这一额外速度即更高的能量产生的动能使得铅的电子比锡的更重不断增加的质量—而重的电子往往会下落，围着结合更紧密的原子核轨道绕行。
That has the effect of making metallic lead less electropositive than classical theory indicates it should be—which would tend to make the battery worse.
产生的结果是，金属铅的电正性没有古典化学理论认为的那么强看起来似乎铅不适合用来做电池。
But this tendency is more than counterbalanced by an increase in the electronegativity of lead dioxide.
但是， 二氧化铅电负性的增加不但全部抵消了这个趋势还有剩余。
In this compound, the tightly bound orbitals act like wells into which free electrons can fall, allowing the material to capture them more easily. That makes lead dioxide much more electronegative than classical theory would predict.
在这个混合物里，结合紧密的轨道就像一口井，自由电子落入其中，使得物质更容易捕获电子。二氧化铅的电负性其实比古典化学理论认为的要更强。
And so it turned out.
然后他们得出了结论。
Dr Pyykko and his colleagues made two versions of a computer model of how lead-acid batteries work.
Pyykko博士和他的同事们作了两个版本的电脑模型，来观察铅酸电池是怎么工作的。
One incorporated their newly hypothesised relativistic effects while the other did not.
其中一个模型结合使用了相对论效应的新假设，另一个没有用。
The relativistic simulations predicted the voltages measured in real lead-acid batteries with great precision.
相对论模拟模型预测的铅酸电池产生的电压相当精确。
When relativity was excluded, roughly 80% of that voltage disappeared.
而那个不用相对论的模型大约80%的电伏都没有计算到。
That is an extraordinary finding, and it prompts the question of whether previously unsuspected battery materials might be lurking at the heavier end of the periodic table.
这是个非同凡响的发现，这个发现也提出了一个问题。是否还有以前没想到的，潜伏在元素周期表末端的电池材料？
Ironically, today's most fashionable battery material, lithium, is the third-lightest element in that table—and therefore one for which no such relativistic effects can be expected.
讽刺的是，现在最时髦的电池材料，锂，是周期表中第三轻的元素—如果用相对论效应是料不到它可以用来做电池。
And lead is about as heavy as it gets before elements become routinely radioactive and thus inappropriate for all but specialised applications.
铅是周期表中放射性元素之前最重的元素，因此除了用于专门应用外不适用于他处。
Still, the search for better batteries is an endless one, and Dr Pyykko's discovery might prompt some new thinking about what is possible in this and other areas of heavy-element chemistry.
而有关更好的电池材料的研究是没有止境的，Pyykko博士的发现也许给我们提供了一些新的思考方向—化学重金属在电池和其他地方还有什么作为？
