評論
打印
Science and technology
科學技術
Table-top astrophysics
桌面上的天體物理學
How to build a multiverse
怎樣構建多元宇宙
Small models of cosmic phenomena are shedding light on the real thing
微小模型逐步揭開宇宙中各種現象的奧秘
THE heavens do not lend themselves to poking and prodding.
蒼穹由不得人隨意翻弄。
Astronomers therefore have no choice but to rely on whatever data the cosmos deigns to throw at them.
天文學家只能使用上天隨意賞賜的數據資料，除此之外別無選擇。
And they have learnt a lot this way.
不過，他們從中已獲悉良多。
Thus you can even study chemistry in space that would be impossible in a laboratory.
現在甚至能在宇宙中完成一些實驗室里無法進行的化學研究。
Some astronomers, though, are dissatisfied with being passive observers.
但一些天文學家并不滿足于被動觀察。
Real scientists, they think, do experiments.
他們認為，真正的科學家應該動手實驗。
It is impossible—not to mention inadvisable—to get close enough to a star or a black hole to manipulate it experimentally.
且不論明智與否，要接近星體或黑洞進行實驗操作根本毫無可能。
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.
但有人認為，也許可以模擬這些星體、黑洞甚至整個宇宙并對其進行實驗。
Ben Murdin of the University of Surrey, for example, has been making white dwarfs.
比如，薩利大學的本·默丁就一直在模擬白矮星。
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，干癟瘦小但老當益壯。
It has run out of fuel and is contracting and cooling as it heads towards oblivion—but taking its time about it.
它的燃料已經耗盡，不斷收縮冷卻，走向死亡的盡頭—只是時間極為漫長。
As they shrink white dwarfs pack a mass up to eight times the suns into a volume the size of Earth.
在這一過程中，白矮星能將重達8個太陽的物質壓縮至地球大小。
A consequence of stuffing so much matter into so little space is that white dwarfs have powerful magnetic fields.
把這么多東西塞進如此狹小的空間導致白矮星的磁場非常強大。
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.
人們認為白矮星演化過程的諸多方面都決定于它的磁性，包括演化持續的時間。但其磁場一直難以測定。
To make estimates, scientists examine the light a white dwarf emits for telltale patterns left by stellar ingredients like hydrogen.
為進行估測，科學家研究了白矮星發射的光線，在其中尋找氫等星體組成元素留下的蹤跡，
They then compare this spectrum with a theory, based on calculations from first principles, of how magnetic fields effect light emitted by hydrogen.
然后將這段光譜與基于第一性原理計算，描述磁場對氫發射光線的影響的理論進行對比。
The predictions agree with experiments up to the strongest fields mankind can muster—about 1,000 tesla, generated in a thermonuclear detonator.
結果與目前最強的人造磁場造成的影響相當。
The problem is that the theory puts white dwarfs magnetic fields at 100,000 tesla or more, well beyond humanitys reach.
但問題是，根據上述理論，白矮星的磁場強度應為100000特斯拉甚至更強，遠遠超出人類可及的范圍。
Dr Murdin built his own little white dwarf to see if the theory looked good.
為檢驗理論是否適用，默丁博士創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.
硅原子最外層有4個電子，
In a crystal, all four are used to bind it to neighbouring atoms.
在晶體中，它們都用于與相鄰原子結鍵相連。
Phosphorus has five outer electrons.
璘的最外層則有5個電子。
Insert a phosphorus atom into the silicon lattice and you are left with an unused electron.
將磷原子嵌入硅晶格，就會余下1個電子用不到。
Since phosphorus also has one more proton in its nucleus than silicon does, taken together the extra particles resemble a hydrogen atom:
璘原子核中的質子也比硅多1個，電子與這個多出來的粒子就構成類似氫原子的結構：
a single electron tethered to a single proton.
1個電子圍繞1個質子運動。
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，與真正的氫原子相比，這個仿制品中的質子對電子的約束力要小得多，這意味著要使其光譜發生預設改變所需的磁力也沒有真的氫原子那么強。
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.
由于吉爾福德的實驗室缺少相關設備，默丁博士在荷蘭內梅亨大學完成了實驗。
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.
他將晶體磁場環境設為30特斯拉，該環境相當于白矮星100000特斯拉的磁場。結果表明，
And the spectrum came out looking just the way the theory predicted.
光譜符合理論計算。
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.
與生成黑洞相比，在實驗室里造星星不過是小菜一碟。
This is an object that is so massive and dense that not even light can flee its gravitational field.
黑洞的質量、密度極大，連光線都無法從它的重力場中逃逸。
Looking inside one is therefore, by definition, impossible.
因此要觀察其內部結構顯然是不可能的。
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國際高等研究學院的西爾克·魏因富特納說，這使其更值得一試。
Dr Weinfurtner plans to make her black hole in the bath.
魏因富特納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.
這里所說的水盆應被稱為水槽，是一個長3米、寬1.5米、高50厘米的盛水容器，能允許精心生成的波動序列通過。
In the middle of the tank is a plug hole.
水槽中央有一個孔塞，
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.
如果水從這里流失時旋轉的速度比波動傳播的還快，那進入水視界的波動就無法再逃出視界，
They are sucked down the drain.
它們被吸進了排水管。
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.
隨后研究人員將查看，這種現象對水波的影響，是否與廣義相對論預言的黑洞對接近它的光線影響相似。
According to Albert Einsteins theory, a region immediately outside the event horizon of a rotating black hole will be dragged round by the rotation.
阿爾伯特·愛因斯坦的理論指出，視界外的空間會因黑洞旋轉產生拖曳現象。
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.
進入該區域的波動，如果未穿過視界，就會發生偏折，且攜帶的能量增大。
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.
這種現象被稱為超輻射散射，為進行觀察，魏因富特納博士在水中添加了熒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.
如此一來，就可使用高清相機觀測波長不足毫米的波動。
Stefano Liberati, Dr Weinfurtners colleague in Trieste, reserves the greatest enthusiasm for another aspect of the experiment.
魏因富特納博士在的里雅斯特的同事斯蒂凡諾·利博拉蒂對實驗中另一個問題很感興趣。
It might, if the researchers are lucky enough, offer clues to the nature of space-time.
如果研究人員足夠幸運的話，實驗可能會給出關于時空本質的線索。
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?
宇宙會不會是由離散的粒子組成—若你愿意，也可稱為原子的宇宙—而非像相對論假定的那樣是連續的？
This problem has perplexed physicists for decades.
這個問題已經困擾了物理學家幾十年。
Many suspect black holes hold the answer, because they are sites where continuous relativity meets chunky quantum physics.
很多人認為答案就在黑洞之中，因為在這里，連續相對論與離散的量子力學相遇了。
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.
水由離散的粒子即H2O分子構成。
As wavelengths fall—equivalent to rising energy—waves reach a point where the size of molecules may begin to influence how they behave.
隨著波長減小，達到某一特定值后，波可能就會開始受到分子大小的影響。
If Dr Weinfurtner and Dr Liberati observe some strange behaviour around their event horizons, theorists will be thrilled.
如果魏因富特納和利博拉蒂博士在視界外圍觀察到波的反常表現，理論學家將會為此興奮不已。
And home-brewed universes
還有自造的宇宙
Even benchtop black holes, though, are nothing compared with the ambitions of Igor Smolyaninov of the University of Maryland.
若是跟馬里蘭大學伊戈爾·斯諾利亞尼諾夫的抱負比起來，實驗臺上的黑洞也不值一提了。
For Dr Smolyaninov wants to create entire universes.
斯諾利亞尼諾夫博士打算再造一個宇宙。
The way light travels through the four dimensions of space-time is mathematically akin to how it moves through metamaterial.
從數學描述來看，光在四維時空中的運動與在超材料中的相似。
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納米層面上刻畫，因此光線穿過時會產生異常彎曲。
For example they can force light to skirt along the outside of an object, hiding it from view as if behind an invisibility cloak.
比如說，這種材料能使光沿物體表面運動，如此一來物體就好像藏在了隱形斗篷后面無法觀測。
Space-time, too, bends light, in ways that depend on how mass is distributed within it.
同樣，時空也可以使光線彎曲，具體方式取決于其中的質量分布。
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.
原則上，超材料應該能模擬光在不同時空中的運動，這既包括地球上的科學家們熟悉的時空，也包括他們現在以及將來都接觸不到的時空。
Two years ago Dr Smolyaninov suggested an experiment with various metamaterials, corresponding to universes with different properties lashed together into a home-brewed multiverse.
兩年前，斯諾利亞尼諾夫設計了一個實驗，他以不同的超材料代表特性各異的宇宙，將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《光學快報》即將發表的論文中，斯諾利亞尼諾夫等宣布實驗已取得成功。
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.
研究人員并未對超材料進行微調使其達到精確的參數，因為這樣工序繁瑣、耗資巨大，而是把相對容易控制的納米級鈷顆粒懸浮在煤油中。
They then applied a magnetic field which, thanks to cobalt's ferromagnetic nature, arranged the particles into thin columns.
鈷具有鐵磁性，因此他們可以施加磁場，使粒子構成一個個細長的圓柱。
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.
與時空進行類比，圓柱的長度代表時間，與柱長垂直的兩軸則代表真實宇宙中的三維空間。
To build his multiverse, Dr Smolyaninov added slightly less cobalt to the kerosene, about 8% by volume, than was needed to maintain stable nanocolumns.
為構建多元宇宙，斯諾利亞尼諾夫向煤油中加入適量鈷顆粒，約為維持穩定納米柱所需體積的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.
自然狀態下液體密度的變化會使納米柱不斷自發形成、坍塌，就像時空在多元宇宙中突然生成、走向消亡，又在其他地方再次出現。
They could be detected by their effect on polarised light shone through the material.
偏振光穿過該液體時會受到納米柱的作用，通過這一效應即可檢測納米柱。
Whether all this ingenuity unravels any cosmic truth is uncertain.
這一創新之舉能否揭示宇宙的真相還有待檢驗。
Cliff Burgess, a theorist at Perimeter Institute for Theoretical Physics in Ontario, has his doubts.
安大略省普里美特理論物理研究所的理論學家克里夫·伯吉斯對此也心存懷疑。
But he thinks that such experiments are nevertheless worth pursuing.
但他認為這樣的實驗還是仍然值得嘗試。
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樣，他說，重點不在于他們做得好不好，而在于他們是否去做了。
