## 字幕列表 影片播放

• You may know that it takes light a zippy eight minutes

你可能知道，它需要輕快的八分鐘。

• 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&#39;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&#39;我們先假設所有太陽&#39;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&#39;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&#39;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&#39;最終從太陽&#39;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&#39;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。

You may know that it takes light a zippy eight minutes

# 【TED-Ed】你看到的陽光遠比你想像的還久 (Sunlight is way older than you think - Sten Odenwald)

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稲葉白兎 發佈於 2015 年 05 月 22 日