Sunlight is way older than you think - Sten Odenwald

譯者: 育霆 熊 審譯者: Regina Chu

You may know that it takes light a zippy eight minutes

你可能知道光只要短短八分鐘

to reach us from the surface of the Sun,

就能從太陽表面抵達我們這裡

so how long do you think it takes light

那你認為光從太陽的核心到表面

to travel from the Sun's core to its surface?

需要多少時間呢？

A few seconds or a minute at most?

幾秒鐘或是最多一分鐘？

Well, oddly enough, the answer is many thousands of years.

嗯，很奇怪地 答案是好幾萬年

Here's why.

以下解釋為什麼

Photons are produced by the nuclear reactions deep in the core of our Sun.

光子在太陽很深的核中 透過核反應產生

As the photons flow out of the core, they interact with matter and lose energy,

光子從核心噴出來後 與物質相互作用而失去能量

becoming longer wavelength forms of light.

變成波長較長的光波

They start out as gamma rays in the core,

它們在核心中 以伽瑪射線的形式出發

but end up as x-rays, ultraviolet or visible light as they near the surface.

但最終在表面變成 X 射線、紫外線或可見光

However, that journey is neither simple nor direct.

但是，光的旅程不簡單也不直接

Upon being born, each photon travels at a speed of 300,000 kilometers per second

每個光子製造出來後 就會以每秒 30 萬公里的速度旅行

until it collides with a proton and is diverted in another direction,

直到它碰撞到質子並轉向

acting like a bullet ricocheting off of every charged particle it strikes.

像子彈一樣被每一個 它撞到的帶電粒子反彈

The question of how far this photon gets from the center of the Sun

而光子從太陽中心 經過每個碰撞之後

after each collision

行經的距離有多長的問題

is known as the random walk problem.

被稱為隨機漫步問題

The answer is given by this formula:

答案可由以下算式解出

distance equals step size times the square root of the number of steps.

距離等於一步長 乘以步數的平方根

So if you were taking a random walk from your front door

所以如果你從你家大門 開始隨機漫步

with a one meter stride each second,

以每秒一步且步幅一公尺

it would take you a million steps and eleven days

則你花費一百萬步和十一天的時間

just to travel one kilometer.

只能走一公里遠

So then how long does it take for a photon generated in the center of the sun

而光子從太陽中心誕生 直到抵達我們這裡

to reach you?

需要多久呢？

We know the mass of the Sun

我們知道太陽的質量

and can use that to calculate the number of protons within it.

可以用這個計算有多少質子在裡面

Let's assume for a second that all the Sun's protons are evenly spread out,

我們暫時假設太陽 所有的質子都均勻攤開

making the average distance between them about 1.0 x 10^-10 meters.

使得它們之間的平均距離約為 10 的負 10 次方公尺

To random walk the 690,000 kilometers from the core to the solar surface

從核心到太陽表面 隨機漫步 69 萬公里

would then require 3.9 x 10^37 steps,

將需要 3.9 乘 10 的 37 次方步

giving a total travel time of 400 billion years.

需要四千億年的總時間

Hmm, that can't be right.

嗯，這樣不對

The Sun is only 4.6 billion years old, so what went wrong?

太陽只有 46 億歲 那什麼出錯了？

Two things:

有兩件事

The Sun isn't actually of uniform density

實際上太陽的密度並不均勻

and photons will miss quite a few protons between every collision.

光子每次碰撞會錯過一些質子

In actuality, a photon's energy,

實際上，一個光子的能量

which changes over the course of its journey,

會隨著它旅行的過程而改變

determines how likely it is to interact with a proton.

因而決定它如何與質子相互作用

On the density question,

至於密度的問題

our models show that the Sun has a hot core,

我們的模型顯示太陽有一個熱核

where the fusion reactions occur.

是核融合反應發生的地方

Surrounding that is the radiative zone,

它的周圍是輻射區

followed by the convective zone, which extends all the way to the surface.

其次是對流區 就這樣一直延伸到表面

The material in the core is much denser than lead,

核心的密度比鉛還要大得多

while the hot plasma near the surface is a million times less dense

而靠近表面的熱電漿密度 則小了一百萬倍

兩者之間則是連續密度

with a continuum of densities in between.

And here's the photon-energy relationship.

這裡是光子與能量的關係

For a photon that carries a small amount of energy,

相對於一個攜帶少量能量的光子

a proton is effectively huge,

質子其實非常大

and it's much more likely to cause the photon to ricochet.

它更容易使光子被彈飛

And for a high-energy photon, the opposite is true.

而對於高能光子，情況正好相反

Protons are effectively tiny.

質子相對來說非常微小

Photons start off at very high energies

與光子在太陽表面 被輻射出去時的能量相較

compared to when they're finally radiated from the Sun's surface.

光子出發時的能量非常高

Now when we use a computer and a sophisticated solar interior model

現在我們使用電腦 和一個複雜的太陽內部模型

to calculate the random walk equation with these changing quantities,

用變數計算隨機漫步方程

it spits out the following number: 170,000 years.

它算出來的是以下數字：17 萬年

Future discoveries about the Sun may refine this number further,

未來有關太陽的發現 可以進一步細化這個數字

but for now, to the best of our understanding,

但是現在，盡我們的理解

the light that's hitting your eyes today

今天進入我們眼睛的光

spent 170,000 years pinballing its way towards the Sun's surface,

花了 17 萬年 以彈珠台遊戲的方式到太陽表面

plus eight miniscule minutes in space.

加上在宇宙穿梭的微小 8 分鐘

In other words, that photon began its journey two ice ages ago,

換句話說，光子在兩個 冰河時期前就開始了它的旅程

around the same time when humans first started wearing clothes.

同一時間人類才剛開始穿衣服