经济学人下载:桌面上的天体物理学 怎样构建多元宇宙

Science and technology
科学技术

Table-top astrophysics
桌面上的天体物理学

How to build a multiverse
怎样构建多元宇宙

Small models of cosmic phenomena are shedding light on the real thing
微小模型逐步揭开宇宙中各种现象的奥秘

THE heavens do not lend themselves to poking and prodding.
苍穹由不得人随意翻弄。

Astronomers therefore have no choice but to rely on whatever data the cosmos deigns to throw at them.
天文学家只能使用上天随意赏赐的数据资料，除此之外别无选择。

And they have learnt a lot this way.
不过，他们从中已获悉良多。

Thus you can even study chemistry in space that would be impossible in a laboratory.
现在甚至能在宇宙中完成一些实验室里无法进行的化学研究。

Some astronomers, though, are dissatisfied with being passive observers.
但一些天文学家并不满足于被动观察。

Real scientists, they think, do experiments.
他们认为，真正的科学家应该动手实验。

It is impossible—not to mention inadvisable—to get close enough to a star or a black hole to manipulate it experimentally.
且不论明智与否，要接近星体或黑洞进行实验操作根本毫无可能。

But some think it might be possible to make meaningful analogues of such things, and even of the universe itself, and experiment on those instead.
但有人认为，也许可以模拟这些星体、黑洞甚至整个宇宙并对其进行实验。

Ben Murdin of the University of Surrey, for example, has been making white dwarfs.
比如，萨利大学的本·默丁就一直在模拟白矮星。

A white dwarf is the stellar equivalent of a shrunken but feisty old-age pensioner.
白矮星像是退休的恒星，干瘪瘦小但老当益壮。

It has run out of fuel and is contracting and cooling as it heads towards oblivion—but taking its time about it.
它的燃料已经耗尽，不断收缩冷却，走向死亡的尽头—只是时间极为漫长。

As they shrink white dwarfs pack a mass up to eight times the suns into a volume the size of Earth.
在这一过程中，白矮星能将重达8个太阳的物质压缩至地球大小。

A consequence of stuffing so much matter into so little space is that white dwarfs have powerful magnetic fields.
把这么多东西塞进如此狭小的空间导致白矮星的磁场非常强大。

Many aspects of a white dwarfs mechanics, including how long it will last, are thought to depend on its magnetism. But it is hard to measure.
人们认为白矮星演化过程的诸多方面都决定于它的磁性，包括演化持续的时间。但其磁场一直难以测定。

To make estimates, scientists examine the light a white dwarf emits for telltale patterns left by stellar ingredients like hydrogen.
为进行估测，科学家研究了白矮星发射的光线，在其中寻找氢等星体组成元素留下的踪迹，

They then compare this spectrum with a theory, based on calculations from first principles, of how magnetic fields effect light emitted by hydrogen.
然后将这段光谱与基于第一性原理计算，描述磁场对氢发射光线的影响的理论进行对比。

The predictions agree with experiments up to the strongest fields mankind can muster—about 1,000 tesla, generated in a thermonuclear detonator.
结果与目前最强的人造磁场造成的影响相当。

The problem is that the theory puts white dwarfs magnetic fields at 100,000 tesla or more, well beyond humanitys reach.
但问题是，根据上述理论，白矮星的磁场强度应为100000特斯拉甚至更强，远远超出人类可及的范围。

Dr Murdin built his own little white dwarf to see if the theory looked good.
为检验理论是否适用，默丁博士创造了自己的微型白矮星。

It consists of a silicon crystal sprinkled with phosphorus atoms.
他在硅晶中加入少量磷原子。

A silicon atom has four electrons in its outer shell.
硅原子最外层有4个电子，

In a crystal, all four are used to bind it to neighbouring atoms.
在晶体中，它们都用于与相邻原子结键相连。

Phosphorus has five outer electrons.
璘的最外层则有5个电子。

Insert a phosphorus atom into the silicon lattice and you are left with an unused electron.
将磷原子嵌入硅晶格，就会余下1个电子用不到。

Since phosphorus also has one more proton in its nucleus than silicon does, taken together the extra particles resemble a hydrogen atom:
璘原子核中的质子也比硅多1个，电子与这个多出来的粒子就构成类似氢原子的结构：

a single electron tethered to a single proton.
1个电子围绕1个质子运动。

However, the extra electron is much less tightly held by the extra proton in this pseudo-hydrogen than it would be in real hydrogen.
然而，与真正的氢原子相比，这个仿制品中的质子对电子的约束力要小得多，这意味着要使其光谱发生预设改变所需的磁力也没有真的氢原子那么强。

This weaker grasp means that it takes much less magnetism to make a given change in the pseudo-hydrogens spectrum than it would for real hydrogen.
由于吉尔福德的实验室缺少相关设备，默丁博士在荷兰内梅亨大学完成了实验。

So when Dr Murdin placed the crystal in a 30-tesla magnet at Radboud University in the Netherlands, he was mimicking the conditions in a 100,000-tesla white dwarf.
他将晶体磁场环境设为30特斯拉，该环境相当于白矮星100000特斯拉的磁场。结果表明，

And the spectrum came out looking just the way the theory predicted.
光谱符合理论计算。

A black hole in a bath…
水盆里的黑洞

Creating a star in a laboratory is small beer compared with creating a black hole.
与生成黑洞相比，在实验室里造星星不过是小菜一碟。

This is an object that is so massive and dense that not even light can flee its gravitational field.
黑洞的质量、密度极大，连光线都无法从它的重力场中逃逸。

Looking inside one is therefore, by definition, impossible.
因此要观察其内部结构显然是不可能的。

All the more reason to try, says Silke Weinfurtner of the International School for Advanced Studies, in Trieste, Italy.
意大利的里雅斯特市国际高等研究学院的西尔克·魏因富特纳说，这使其更值得一试。

Dr Weinfurtner plans to make her black hole in the bath.
魏因富特纳博士打算在水盆里做黑洞。

The bath in question, properly called a flume, is a water-filled receptacle 3 metres by 1.5 metres and 50cm deep, across which carefully crafted trains of ripples can pass.
这里所说的水盆应被称为水槽，是一个长3米、宽1.5米、高50厘米的盛水容器，能允许精心生成的波动序列通过。

In the middle of the tank is a plug hole.
水槽中央有一个孔塞，

If the water going down the hole rotates faster than the ripples can propagate, the ripples which stray beyond the aqueous event horizon will not make it out.
如果水从这里流失时旋转的速度比波动传播的还快，那进入水视界的波动就无法再逃出视界，

They are sucked down the drain.
它们被吸进了排水管。

Then the researchers will check whether the simulacrum affects water waves in a way analogous to that which general relativity predicts for light—itself a wave—approaching an astrophysical black hole.
随后研究人员将查看，这种现象对水波的影响，是否与广义相对论预言的黑洞对接近它的光线影响相似。

According to Albert Einsteins theory, a region immediately outside the event horizon of a rotating black hole will be dragged round by the rotation.
阿尔伯特·爱因斯坦的理论指出，视界外的空间会因黑洞旋转产生拖曳现象。

Any wave that enters this region but does not stray past the event horizon should be deflected and come out with more energy than it carried on the way in.
进入该区域的波动，如果未穿过视界，就会发生偏折，且携带的能量增大。

To detect this super-radiant scattering, as the effect is called, Dr Weinfurtner will add fluorescent dye to the water and illuminate the surface waves with lasers.
这种现象被称为超辐射散射，为进行观察，魏因富特纳博士在水中添加了荧光染料并用激光照射表面波，

The waves, often no bigger than one millimetre, can then be detected using high-definition cameras.
如此一来，就可使用高清相机观测波长不足毫米的波动。

Stefano Liberati, Dr Weinfurtners colleague in Trieste, reserves the greatest enthusiasm for another aspect of the experiment.
魏因富特纳博士在的里雅斯特的同事斯蒂凡诺·利博拉蒂对实验中另一个问题很感兴趣。

It might, if the researchers are lucky enough, offer clues to the nature of space-time.
如果研究人员足够幸运的话，实验可能会给出关于时空本质的线索。

Could the cosmic fabric be made up of discrete chunks, atoms of space if you like, rather than being continuous, as is assumed by relativity?
宇宙会不会是由离散的粒子组成—若你愿意，也可称为原子的宇宙—而非像相对论假定的那样是连续的？

This problem has perplexed physicists for decades.
这个问题已经困扰了物理学家几十年。

Many suspect black holes hold the answer, because they are sites where continuous relativity meets chunky quantum physics.
很多人认为答案就在黑洞之中，因为在这里，连续相对论与离散的量子力学相遇了。

Waterborne holes serve as a proxy.
水中的孔洞代表黑洞。

Water is, after all, made up of just such discrete chunks: molecules of H2O.
水由离散的粒子即H2O分子构成。

As wavelengths fall—equivalent to rising energy—waves reach a point where the size of molecules may begin to influence how they behave.
随着波长减小，达到某一特定值后，波可能就会开始受到分子大小的影响。

If Dr Weinfurtner and Dr Liberati observe some strange behaviour around their event horizons, theorists will be thrilled.
如果魏因富特纳和利博拉蒂博士在视界外围观察到波的反常表现，理论学家将会为此兴奋不已。

And home-brewed universes
还有自造的宇宙

Even benchtop black holes, though, are nothing compared with the ambitions of Igor Smolyaninov of the University of Maryland.
若是跟马里兰大学伊戈尔·斯诺利亚尼诺夫的抱负比起来，实验台上的黑洞也不值一提了。

For Dr Smolyaninov wants to create entire universes.
斯诺利亚尼诺夫博士打算再造一个宇宙。

The way light travels through the four dimensions of space-time is mathematically akin to how it moves through metamaterial.
从数学描述来看，光在四维时空中的运动与在超材料中的相似。

These are substances with features measured in nanometres, or billionths of a metre, which let them bend light in unusual ways.
超材料的很多特性都需在纳米层面上刻画，因此光线穿过时会产生异常弯曲。

For example they can force light to skirt along the outside of an object, hiding it from view as if behind an invisibility cloak.
比如说，这种材料能使光沿物体表面运动，如此一来物体就好像藏在了隐形斗篷后面无法观测。

Space-time, too, bends light, in ways that depend on how mass is distributed within it.
同样，时空也可以使光线弯曲，具体方式取决于其中的质量分布。

In principle, then, metamaterials ought to be able to mimic how light moves not just through the space-time scientists on Earth are familiar with, but also other possible space-times to which they do not, and never will, have access.
原则上，超材料应该能模拟光在不同时空中的运动，这既包括地球上的科学家们熟悉的时空，也包括他们现在以及将来都接触不到的时空。

Two years ago Dr Smolyaninov suggested an experiment with various metamaterials, corresponding to universes with different properties lashed together into a home-brewed multiverse.
两年前，斯诺利亚尼诺夫设计了一个实验，他以不同的超材料代表特性各异的宇宙，将其聚合在一起形成自造的多元宇宙。

In a paper to be published in Optics Express, he and his colleagues report that they have succeeded.
在《光学快报》即将发表的论文中，斯诺利亚尼诺夫等宣布实验已取得成功。

Rather than fine-tune metamaterial to exact specifications, which is finicky and expensive, the researchers used nanoparticles of cobalt, which are relatively easy to get hold of, and suspended them in kerosene.
研究人员并未对超材料进行微调使其达到精确的参数，因为这样工序繁琐、耗资巨大，而是把相对容易控制的纳米级钴颗粒悬浮在煤油中。

They then applied a magnetic field which, thanks to cobalt's ferromagnetic nature, arranged the particles into thin columns.
钴具有铁磁性，因此他们可以施加磁场，使粒子构成一个个细长的圆柱。

In space-time terms the length of the columns is time and the two axes perpendicular to the length represent the three spatial dimensions in a real universe.
与时空进行类比，圆柱的长度代表时间，与柱长垂直的两轴则代表真实宇宙中的三维空间。

To build his multiverse, Dr Smolyaninov added slightly less cobalt to the kerosene, about 8% by volume, than was needed to maintain stable nanocolumns.
为构建多元宇宙，斯诺利亚尼诺夫向煤油中加入适量钴颗粒，约为维持稳定纳米柱所需体积的92%。

Natural fluctuations in the density of the fluid then lead to the spontaneous erection of transient nanocolumns—equivalent to space-times popping up only to fizzle and re-emerge elsewhere in the multiverse.
自然状态下液体密度的变化会使纳米柱不断自发形成、坍塌，就像时空在多元宇宙中突然生成、走向消亡，又在其他地方再次出现。

They could be detected by their effect on polarised light shone through the material.
偏振光穿过该液体时会受到纳米柱的作用，通过这一效应即可检测纳米柱。

Whether all this ingenuity unravels any cosmic truth is uncertain.
这一创新之举能否揭示宇宙的真相还有待检验。

Cliff Burgess, a theorist at Perimeter Institute for Theoretical Physics in Ontario, has his doubts.
安大略省普里美特理论物理研究所的理论学家克里夫·伯吉斯对此也心存怀疑。

But he thinks that such experiments are nevertheless worth pursuing.
但他认为这样的实验还是仍然值得尝试。

Like tap-dancing snakes, he says, the point is not that they do it well, it is that they do it at all.
就像跳踢踏舞的蛇一样，他说，重点不在于他们做得好不好，而在于他们是否去做了。