马云对话奥巴马:中微子：你应该知道的一切

切西·怀特 赛勒斯特·比佛尔2011年9月27日

Read more: "Neutrinos: Complete guide to the ghostly particle"

更多资料，可阅读“中微子：幽灵粒子的完整指南”。

"…We don't allow faster-than-light neutrinos in here," says the barman. A neutrino walks into a bar…" As reports spread of subatomic particles moving faster than light and potentially travelling through time, such gags were born. But apparently super-hasty motion is not the only strange thing about neutrinos.

“……我们不允许比光速还快的中微子进到这儿，”酒保说。话刚落，一颗中微子就走进了酒吧”。人类发现速度快于光速的亚原子微粒子，这种微粒子有可能穿越时间，随着这一报道的广泛传播，便有了上面的那种笑话。然而，这种明显的超极限速度运动并不是中微子唯一的奇特之处。

What exactly are they?

中微子到底是什么物质？

With a neutral charge and nearly zero mass, neutrinos are the shadiest of particles, rarely interacting with ordinary matter and slipping through our bodies, buildings and the Earth at a rate of trillions per second.

带中性电荷，质量几乎为零，中微子是最为隐秘的微粒子。它很少与普通物质相互作用，以每秒万亿的速度穿过了我的身体、建筑物以及整个地球。

First predicted in 1930 by Wolfgang Pauli, who won a Nobel prize for this work in 1945, they are produced in various nuclear reactions: fusion, which powers the sun; fission, harnessed by humans to make weapons and energy; and during natural radioactive decay inside the Earth.

中微子是由沃尔夫冈·泡利于1930年首先预测到，为此他获得了1945年的诺贝尔奖。中微子在各种核反应过程中产生：例如为太阳提供动力的聚合反应，人们利用来制造武器，生产能源的裂变反应，以及在地球内部自然放射性衰变。

If they are so stealthy, how do we know they are there at all?

如果中微子那么隐秘，我们到底如何知道它们的存在？

Wily neutrinos usually avoid contact with matter, but every so often, they crash into an atom to produce a signal that allows us to observe them. Fredrick Reines first detected them in 1956, garnering himself a Nobel prize in 1995.

诡异的中微子通常避免与物质接触，但每隔一段时间，总要与一个原子发生碰撞，产生使人们可以观察到的信号。1956年弗雷德里克·莱因斯首次检测到中微子，为此他获得了1995年的诺贝尔物理学奖。

Most commonly, experiments use large pools of water or oil. When neutrinos interact with electrons or nuclei of those water or oil molecules, they give off a flash of light that sensors can detect.

最常见的情况是，实验中使用大量的水或油。当中微子与那些水分子或油分子的电子或原子核相互作用时，会发出传感器可以检测到的闪光。

Where are these experiments found?

在哪里这些实验做？

These days, a lot of expense and extreme engineering go into detectors that are sunk into the ground to shield them from extraneous particles that might interfere with them. For instance, OPERA, which detected the apparently faster-than-light neutrinos beamed from CERN, lies inside the Gran Sasso mountain in Italy. This works because neutrinos shoot straight through such shields.

近年来，大量的费用及尖端工程投入沉入地面以下的监测器，以避免外来微粒子对中微子的干扰。譬如，监测到从欧洲核子研究中心（CERN）发射的中微子明显快于光速的中微子振荡实验项目（OPERA）就设在意大利Gran Sasso的山区。这种安排是可行的，因为中微子束可以直接穿过这些盾牌。

Other detectors pick up naturally-produced neutrinos. One such detector – ANTARES – is miles under the Mediterranean Sea, while another, IceCube , is buried under Antarctic ice.

其它的监测装置则收集自然生产的中微子。一台监测器名叫ANTARES位于地中海数英里的深处，而另一台叫做冰立方（IceCube）则埋在南极洲的冰下。

What's cool about neutrinos?

中微子有什么了不起的？

Their stealth belies their potential importance. Take extra dimensions. Most particles come in two varieties: ones that spin clockwise and ones that spin anticlockwise. Neutrinos are the only particles that seem to just spin anticlockwise. Some theorists say this is evidence for extra dimensions, which could host the "missing", right-handed neutrinos.

中微子隐形性隐藏着潜在的重要性。具有额外的维度。大多数微粒子有两种：顺时针旋转的和逆时针旋转的。而中微子是唯一似乎只会逆时针旋转的微粒子。有些理论家认为，这足以证明额外维度的存在，这种维度能够保存那些“失踪的”右手中微子。

Anything else?

还有别的什么？

Unseen right-handed neutrinos may also account for mysterious dark matter. This is thought to make up 80 per cent of all matter in the universe and to stop galaxies from flying apart. The idea is that right-handed neutrinos might be much heavier than left-handed ones and so could provide the requisite gravity.

看不见的右手中微子也许还可以解释神秘的暗物质的存在。人们认为暗物质占宇宙物质的80%，是暗物质将星系聚在一起，防止彼此飞离。这种观点是，右手中微子可能比左手的中微子重得多，因此可以提供必要的重力。

And what's this about them coming in "flavours"?

中微子有不同“风格”是怎么回事情？

Another strange thing about neutrinos is that they come in at least three types or "flavours" – tau, electron and muon – and can morph from one flavour to another. Recent experiments suggest there may be differences in the ways that antineutrinos and neutrinos morph, which might in turn explain how an imbalance of matter and antimatter arose in the early universe.

中微子奇特的另一点是至少有三个种类或“风格”——电子中微子、μ子中微子和τ中微子，而且可以从一种风格变异为另一种。最近的实验表明，反中微子与中微子变异的方法可能存在差异，这样反过来解释宇宙早期物质与反物质之间出现的不平衡现象。

Do they have any practical applications?

中微子有什么实际用途？

Sort of – and more are in the works. Some physicists hope to detect neutrinos given off by secret nuclear reactors. Others dream of using them as the basis of a novel communication system that would allow messages to be transmitted to the other side of the world without wires, cables or satellites. Meanwhile the underwater ANTARES detector is doubling up as a telescope for marine life. That's because, as well as neutrinos, it can detect the light given off by luminous organisms and bacteria.

有点用途，更多用途还在研究中。一些物理学家希望发现能够监测出秘密核反应堆产生的中微子。另外一些科学家则梦想使用中微子作为一种新形通信系统的基础，使邮件可以传递到世界另一端，无需使用电线、电缆或卫星。同时，水下的ANTARES探测器使远方观察海洋生物的能力倍增。这是因为，在监测中微子的同时，它还能够监测到发光生物体和细菌发出的光亮。