《那些古怪又让人忧心的问题》第76期:致命中微子(1)

LETHAL NEUTRINOS

致命中微子

Q. How close would you have to be to asupernova to get a lethal dose of neutrino radiation?

Q．一个人要离超新星多近才能受到致命剂量的中微子辐射？

A. THE PHRASE “LETHAL DOSE of neutrino radiation”is a weird one. I had to turn it over in my head a few times afterI heard it.

A．“致命剂量的中微子辐射”这一说法很奇怪，我脑子转了好几圈才反应过来。

If you're not a physics person, it mightnot sound odd to you, so here's a little context for why it's such a surprisingidea:

如果你不是物理专业人士，你可能不觉得有什么奇怪，所以我要给你科普一下为什么这个说法让人很摸不着头脑：

Neutrinos are ghostly particles that barelyinteract with the world at all. Look at your hand-there are about a trillionneutrinos from the Sun passing through it every second.

中微子就像幽灵一般，它几乎不与任何物质发生反应。看看你的手——每秒钟有约1万亿个来自太阳的中微子穿过你的手掌。

Okay, you can stop looking at your handnow.

好了，别一直看着你的手了。

The reason you don't notice the neutrinoflood is that neutrinos mostly ignore ordinary matter. On average, out of thatmassive flood, only one neutrino will “hit”an atom in your bodyevery few years.1

那么你为什么没有感受到汹涌的中微子洪流呢？这是因为，这些中微子几乎不与常见物质发生作用。平均来说，在这股中微子洪流中，每几年才会有1个中微子直直“撞上”你身体中的某个原子。

In fact, neutrinos are so shadowy that theentire Earth is transparent to them; nearly all of the Sun's neutrino steamgoes straight through it unaffected. To detect neutrinos, people build gianttanks filled with hundreds of tons of target material in the hopes that they'llregister the impact of a single solar neutrino.

实际上，在中微子面前地球也几乎是透明的，来自太阳的几乎所有中微子都能丝毫不受影响地穿过地球。为了探测到中微子，科学家们建造了装有数百吨物质的大箱子，希望能记录到哪怕是一个来自太阳的中微子与这些物质发生碰撞的记录。

This means that when a particle accelerator(which produces neutrinos) wants to send a neutrino beam to a detectorsomewhere else in the world, all it has to do is point the beam at thedetector-even if it's on the other side of the Earth!

所以说，如果一个粒子加速器（会产生中微子）想给世界其他地方的探测器发送中微子的话，它只需要直直地瞄准探测器就行了，即使探测器在地球的另一端也无所谓！

That's why the phrase “lethal dose ofneutrino radiation” sounds weird-it mixes scales in an incongruous way. It'slike the idiom “knock me over with a feather” or the phrase “football stadiumfilled to the brim with ants.” If you have a math background, it's sort of likeseeing the expression “ln(x)e”-it's not that, taken literally, it doesn't make sense-it's that youcan't imagine a situation where it would apply.

这就是为什么“致命剂量的中微子辐射”听起来很怪异——它把风马牛不相及的数量级混在了一起。这就像说“用羽毛把你打倒在地”或者“装满了蚂蚁的体育馆”一样，如果你有数学背景，这有点类似于看到ln(x)e这样的表达式——我不是说它字面上没有意义，只是你很难想象哪里会真的出现这种情况。