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  • 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'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。

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。

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B2 中高級 中文 TED-Ed 光子 太陽 質子 密度 表面

【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
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