to reach us from the surface of the Sun,

從太陽表面到達我們這裡。

so how long do you think it takes light

所以，你認為多久，它需要光

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

從太陽的核心傳到太陽的表面？

A few seconds or a minute at most?

最多幾秒鐘還是一分鐘？

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

嗯，奇怪的是，答案是很多萬年。

Here's why.

這裡'的原因。

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

光子是由太陽核心深處的核反應產生的。

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

當光子從核心中流出時，它們與物質相互作用，失去能量。

becoming longer wavelength forms of light.

成為較長波長形式的光。

They start out as gamma rays in the core,

它們在核心中以伽馬射線的形式開始。

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

但在接近地表時卻以X射線、紫外線或可見光的形式結束。

However, that journey is neither simple nor direct.

然而，這一歷程既不簡單也不直接。

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

出生後，每個光子以每秒30萬千米的速度飛行。

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

直到它與質子相撞，並被轉移到另一個方向。

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

就像子彈從每一個帶電粒子上跳彈一樣。

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

這個光子離太陽中心有多遠的問題。

after each collision

每次碰撞後

is known as the random walk problem.

被稱為隨機行走問題。

The answer is given by this formula:

答案由這個公式給出。

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

距離等於步長乘以步數的平方根。

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

所以，如果你從你的前門隨便走走。

with a one meter stride each second,

以每秒一米的步幅。

it would take you a million steps and eleven days

萬步穿楊，十天九空

just to travel one kilometer.

僅僅是行駛一公里。

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

那麼在太陽中心產生的光子需要多長時間呢？

to reach you?

去找你？

We know the mass of the Sun

我們知道太陽的品質

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

並可以用它來計算其中的質子數。

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

讓'我們先假設所有太陽'的質子都是均勻分佈的。

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

使它們之間的平均距離約為1.0×10^-10米。

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

從地心到太陽表面隨機行走69萬公里

would then require 3.9 x 10^37 steps,

那麼就需要3.9×10^37步。

giving a total travel time of 400 billion years.

使得總旅行時間達到4000億年。

Hmm, that can't be right.

嗯，這不可能是對的。

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

太陽只有46億年的歷史，到底出了什麼問題？

Two things:

有兩件事

The Sun isn't actually of uniform density

太陽其實並不是均勻密度的。

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

和光子在每次碰撞之間都會錯過不少質子。

In actuality, a photon's energy,

實際上，一個光子'的能量。

which changes over the course of its journey,

在其旅程中發生變化。

determines how likely it is to interact with a proton.

決定了它與質子相互作用的可能性。

On the density question,

關於密度問題。

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.

發生聚變反應的地方。

Surrounding that is the radiative zone,

圍繞著它的是輻射區。

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

其次是對流區，一直延伸到地表。

The material in the core is much denser than lead,

核心的材料比鉛的密度大得多。

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

而地表附近的熱等離子體的密度要低一百萬倍。

with a continuum of densities in between.

其間有連續的密度。

And here's the photon-energy relationship.

而這裡'是光子-能量關係。

For a photon that carries a small amount of energy,

對於一個攜帶少量能量的光子。

a proton is effectively huge,

一個質子實際上是巨大的。

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

而它更有可能導致光子跳彈。

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

而對於高能光子來說，情況正好相反。

Protons are effectively tiny.

質子有效微小。

Photons start off at very high energies

光子以很高的能量開始

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

相比於他們'最終從太陽'表面輻射出來的時候。

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

現在當我們使用計算機和複雜的太陽內部模型時

to calculate the random walk equation with these changing quantities,

來計算這些變化量的隨機行走方程。

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

它吐出的數字是：17萬年。

Future discoveries about the Sun may refine this number further,

未來關於太陽的發現可能會進一步完善這個數字。

but for now, to the best of our understanding,

但就目前而言，據我們瞭解。

the light that's hitting your eyes today

今天打在你眼睛上的光亮。

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

花了17萬年的時間，以彈球的方式向太陽'的表面前進。

plus eight miniscule minutes in space.

加上太空中的八分鐘。

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

換句話說，那個光子在兩個冰河世紀前就開始了它的旅程。

around the same time when humans first started wearing clothes.

大約在人類第一次開始穿衣服的時候。