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  • The universe

    譯者: Yakun Li 審譯者: Lily Yichen Shi

  • is really big.

    宇宙

  • We live in a galaxy, the Milky Way Galaxy.

    是浩瀚的

  • There are about a hundred billion stars in the Milky Way Galaxy.

    我們生活在宇宙中的一個星系裡 也就是銀河系

  • And if you take a camera

    銀河系裡大約有上千億的恆星

  • and you point it at a random part of the sky,

    如果你拿一個照相機

  • and you just keep the shutter open,

    隨便對著天空的某一個角落

  • as long as your camera is attached to the Hubble Space Telescope,

    打開快門

  • it will see something like this.

    如果你的照相機連接著一個哈勃天文望遠鏡的話

  • Every one of these little blobs

    你就會看到這樣一幅景象

  • is a galaxy roughly the size of our Milky Way --

    這一團一團的

  • a hundred billion stars in each of those blobs.

    都是是跟銀河系差不多大小的星系

  • There are approximately a hundred billion galaxies

    就是說這枚一團裡都有上千億的恆星

  • in the observable universe.

    並且在我們可以觀測到的宇宙範圍內

  • 100 billion is the only number you need to know.

    存在着上千億這樣的團

  • The age of the universe, between now and the Big Bang,

    上千億——你記住這個數字就可以了

  • is a hundred billion in dog years.

    宇宙的年齡 也就是從宇宙大爆炸至今

  • (Laughter)

    大概是一千億“狗年”(一狗年約等於八年)

  • Which tells you something about our place in the universe.

    (笑聲)

  • One thing you can do with a picture like this is simply admire it.

    我這麼說也是為了告訴你我們在宇宙中的位置

  • It's extremely beautiful.

    對於這樣一幅圖像 我們能做什麼呢?也就是純粹的欣賞景仰吧

  • I've often wondered, what is the evolutionary pressure

    多麼美麗的圖像

  • that made our ancestors in the Veldt adapt and evolve

    我時常會想 在星系的圖像還不存在的時候

  • to really enjoy pictures of galaxies

    是什麼進化壓力 促使我們非洲大草原的的祖先

  • when they didn't have any.

    不斷地適應 進化

  • But we would also like to understand it.

    並開始欣賞星系?

  • As a cosmologist, I want to ask, why is the universe like this?

    但是我們還想試圖理解它們

  • One big clue we have is that the universe is changing with time.

    作為一個宇宙學家 我的疑惑是 為什麼宇宙是這樣的?

  • If you looked at one of these galaxies and measured its velocity,

    一個線索就是宇宙是隨著時間而不斷變化的

  • it would be moving away from you.

    如果你關注一個星系 並度量這個星系變化的速率

  • And if you look at a galaxy even farther away,

    你會發現這個星系是不斷離你遠去的

  • it would be moving away faster.

    如果你再去關註一個更遠距離以外的星系

  • So we say the universe is expanding.

    這個星系會以更快的速度離你遠去

  • What that means, of course, is that, in the past,

    所以我們說宇宙是在不斷膨脹的

  • things were closer together.

    這是什麼意思呢?就是說 在過去

  • In the past, the universe was more dense,

    物質是很緊密的聚合在一起的

  • and it was also hotter.

    在過去 宇宙是相對更加緊實的

  • If you squeeze things together, the temperature goes up.

    並且其溫度也更高

  • That kind of makes sense to us.

    你把東西擠壓到一起 溫度自然會升高

  • The thing that doesn't make sense to us as much

    這個很好理解

  • is that the universe, at early times, near the Big Bang,

    難以令人理解的是

  • was also very, very smooth.

    宇宙在非常早期的時候 也就是大爆炸之後不久

  • You might think that that's not a surprise.

    也是非常非常平滑的

  • The air in this room is very smooth.

    你可能想 這沒什麼可驚訝的

  • You might say, "Well, maybe things just smoothed themselves out."

    這個房間裡的空氣就很平滑

  • But the conditions near the Big Bang are very, very different

    你也許會說 “可能物質自然就平滑了”

  • than the conditions of the air in this room.

    但是要知道宇宙大爆炸之後初期的情況

  • In particular, things were a lot denser.

    與現在這個屋子裡的情況是非常不一樣的

  • The gravitational pull of things

    具體來說 就是物質都很緊密

  • was a lot stronger near the Big Bang.

    這些物質之間的引力

  • What you have to think about

    在大爆炸之後初期比現在要強烈得多

  • is we have a universe with a hundred billion galaxies,

    你可以這樣想

  • a hundred billion stars each.

    我們這個宇宙裡 有上千億的星系

  • At early times, those hundred billion galaxies

    每個星系裡 有上千億的恆星

  • were squeezed into a region about this big --

    在很早期的時候 這樣的上千億的星系

  • literally -- at early times.

    被擠壓到了僅僅這樣大小的一個空間裡

  • And you have to imagine doing that squeezing

    真的是這樣的 在早期的時候

  • without any imperfections,

    並且 你要知道 這樣的擠壓必須

  • without any little spots

    以一種完美的方式發生

  • where there were a few more atoms than somewhere else.

    沒有任何一處疏鬆

  • Because if there had been, they would have collapsed under the gravitational pull

    即使僅僅是某一處比另一處多了幾個原子

  • into a huge black hole.

    因為假如有任何疏鬆或不平均的話 整個宇宙就會在引力的作用下垮塌

  • Keeping the universe very, very smooth at early times

    從而變成一個巨大的黑洞

  • is not easy; it's a delicate arrangement.

    在宇宙早期保證宇宙處於一個非常平滑的狀態

  • It's a clue

    是很不容易的 需要精心的安排

  • that the early universe is not chosen randomly.

    這就從一個側面說明了

  • There is something that made it that way.

    早期的宇宙不是一個隨機的組合

  • We would like to know what.

    有某種原因的存在導致了這樣的組合的發生

  • So part of our understanding of this was given to us by Ludwig Boltzmann,

    我們研究就是為了明白這種原因

  • an Austrian physicist in the 19th century.

    路德維希 波茲曼 一個生活在19世紀的奧地利物理學家

  • And Boltzmann's contribution was that he helped us understand entropy.

    向我們提供了部分的解釋

  • You've heard of entropy.

    波茲曼的貢獻就在於他幫我們理解了“熵”這個概念

  • It's the randomness, the disorder, the chaoticness of some systems.

    你應該聽說過熵

  • Boltzmann gave us a formula --

    熵是指一種存在於某些系統中的隨意性 無序性和混亂性

  • engraved on his tombstone now --

    波茲曼給出了一個方程式 ——

  • that really quantifies what entropy is.

    這個方程式現在是刻在他的墓碑上的——

  • And it's basically just saying

    來給熵定量

  • that entropy is the number of ways

    這個方程式大概就是說

  • we can rearrange the constituents of a system so that you don't notice,

    熵是一個值 用來描述在你未發現一個系統

  • so that macroscopically it looks the same.

    產生了變化的前提下 可以對系統進行重組的方式的數目

  • If you have the air in this room,

    這裡的變化是指外部大體上的變化

  • you don't notice each individual atom.

    比如說這個屋子裡的空氣

  • A low entropy configuration

    你不會看到每個原子

  • is one in which there's only a few arrangements that look that way.

    一個低熵值的形態 是指一個

  • A high entropy arrangement

    只能有少數的組合方式的變化來保證外在沒有變化的形態

  • is one that there are many arrangements that look that way.

    一個高熵值的組合 是指在這種形態裡

  • This is a crucially important insight

    可以有很多種排列組合的方式並不影響其外在沒有變化

  • because it helps us explain

    這是一個非常重要的見解

  • the second law of thermodynamics --

    因為這個見解可以幫助我們來解釋

  • the law that says that entropy increases in the universe,

    熱力學第二定律

  • or in some isolated bit of the universe.

    這個定律告訴我們 宇宙的熵值在不斷提高

  • The reason why entropy increases

    或是說宇宙各部分的熵值在各自提高

  • is simply because there are many more ways

    熵值升高的原因很簡單

  • to be high entropy than to be low entropy.

    那就是高熵值的情況下比在低熵值的情況下

  • That's a wonderful insight,

    存在有更多的可能性

  • but it leaves something out.

    這是一個很好的觀點

  • This insight that entropy increases, by the way,

    但是卻不盡全面

  • is what's behind what we call the arrow of time,

    順便說一下 這個熵值不斷提高的說法

  • the difference between the past and the future.

    就是我們說的單向時間軸 時間之箭

  • Every difference that there is

    也就是過去與未來的區別

  • between the past and the future

    之所以有這個過去

  • is because entropy is increasing --

    與現在之間的區別

  • the fact that you can remember the past, but not the future.

    原因就是不斷上升的熵值

  • The fact that you are born, and then you live, and then you die,

    你能記住過去的事情 卻不能對未來的事情有印象

  • always in that order,

    你出生 生活 然後死亡

  • that's because entropy is increasing.

    這些事情都是依次發生的

  • Boltzmann explained that if you start with low entropy,

    原因都是熵值在不斷提高

  • it's very natural for it to increase

    博茨曼解釋說 如果一個初始狀態是低熵值

  • because there's more ways to be high entropy.

    很自然的這個狀態會升高到高熵值

  • What he didn't explain

    因為這樣就提供了更多種的存在可能性

  • was why the entropy was ever low in the first place.

    但是博茨曼沒有解釋

  • The fact that the entropy of the universe was low

    為什麼低熵值是一個初始狀態

  • was a reflection of the fact

    宇宙早期的熵值很低

  • that the early universe was very, very smooth.

    這就反映了

  • We'd like to understand that.

    早期的宇宙是非常平滑的

  • That's our job as cosmologists.

    我們需要理解的就是這一現象

  • Unfortunately, it's actually not a problem

    我們宇宙學家就是做這個的

  • that we've been giving enough attention to.

    可惜的是 我們並沒有給予

  • It's not one of the first things people would say,

    這個問題足夠的重視

  • if you asked a modern cosmologist,

    如果你問一個宇宙學家

  • "What are the problems we're trying to address?"

    ”宇宙學界現在在試圖解決的哪些問題?“

  • One of the people who did understand that this was a problem

    這個問題不會是他最先給你的答案之一

  • was Richard Feynman.

    認識到這個問題的人之一

  • 50 years ago, he gave a series of a bunch of different lectures.

    便是理查德·費曼

  • He gave the popular lectures

    五十年前 他給了一系列講座

  • that became "The Character of Physical Law."

    他面向大眾的講座

  • He gave lectures to Caltech undergrads

    被編成了一本書 叫做『物理理論的特性』

  • that became "The Feynman Lectures on Physics."

    他給加州理工本科生做的講座

  • He gave lectures to Caltech graduate students

    變成了『費曼物理講座』一書

  • that became "The Feynman Lectures on Gravitation."

    他給加州理工研究生做的講座

  • In every one of these books, every one of these sets of lectures,

    被編成了『費曼引力講座』一書

  • he emphasized this puzzle:

    在每本書 每組講座裡

  • Why did the early universe have such a small entropy?

    費曼都強調了這個難題

  • So he says -- I'm not going to do the accent --

    為什麼宇宙早期有如此低的一個熵值?

  • he says, "For some reason, the universe, at one time,

    他說——我就不學他的口音了——

  • had a very low entropy for its energy content,

    他說”出於某種原因 宇宙曾經

  • and since then the entropy has increased.

    有一個很低的熵值

  • The arrow of time cannot be completely understood

    而從那時起 熵值在不斷的升高

  • until the mystery of the beginnings of the history of the universe

    如果宇宙初期歷史這個謎團

  • are reduced still further

    沒有被我們從簡單的揣測

  • from speculation to understanding."

    帶入到理解這個層次

  • So that's our job.

    我們便無法去完全理解時間之箭”

  • We want to know -- this is 50 years ago, "Surely," you're thinking,

    我們就是要解決這個問題

  • "we've figured it out by now."

    我們想解決——從五十年前開始 你可能會想 ”那肯定

  • It's not true that we've figured it out by now.

    這個問題現在肯定已經解決了”

  • The reason the problem has gotten worse,

    但事實並非如此

  • rather than better,

    這個問題現在更難解決了

  • is because in 1998

    而不是更加容易

  • we learned something crucial about the universe that we didn't know before.

    原因就是在1998年

  • We learned that it's accelerating.

    我們對於宇宙有了一個突破性的發現

  • The universe is not only expanding.

    我們了解到了 宇宙是在加速擴張的

  • If you look at the galaxy, it's moving away.

    宇宙不僅是在擴張而已

  • If you come back a billion years later and look at it again,

    如果你看著那個星系 他在離你遠去

  • it will be moving away faster.

    如果你隔了10億年後再回來看

  • Individual galaxies are speeding away from us faster and faster

    這個星系會離你更遠

  • so we say the universe is accelerating.

    每個星係都是以加速度不斷離我們遠去的

  • Unlike the low entropy of the early universe,

    所以我們說宇宙是在加速擴張的

  • even though we don't know the answer for this,

    與早期宇宙低熵值的狀態不同的是

  • we at least have a good theory that can explain it,

    儘管我們不知道為什麼宇宙是在加速擴張的

  • if that theory is right,

    我們有一個還沒有確認的理論

  • and that's the theory of dark energy.

    如果這個理論是正確的話

  • It's just the idea that empty space itself has energy.

    這就是暗能量理論

  • In every little cubic centimeter of space,

    根據這個理論 一個空的空間裡也是有能量的

  • whether or not there's stuff,

    在空間的每一個立方厘米裡

  • whether or not there's particles, matter, radiation or whatever,

    不管有沒有東西存在 都是有能量的

  • there's still energy, even in the space itself.

    不管有沒有粒子 物質 放射 還是別的什麼

  • And this energy, according to Einstein,

    空間 就因為空間本身 也是有能量的

  • exerts a push on the universe.

    這個能量 愛因斯坦認為

  • It is a perpetual impulse

    會對於宇宙施加一個推力

  • that pushes galaxies apart from each other.

    這個推理是一個永存的推力

  • Because dark energy, unlike matter or radiation,

    推動著星系互相遠去

  • does not dilute away as the universe expands.

    這個暗能量 與物質或者放射性不同的是

  • The amount of energy in each cubic centimeter

    不會因為宇宙的擴張而被稀釋

  • remains the same,

    每立方厘米裡能量

  • even as the universe gets bigger and bigger.

    是不變的

  • This has crucial implications

    即使宇宙變得越來越大

  • for what the universe is going to do in the future.

    這個對於解釋宇宙走向何方

  • For one thing, the universe will expand forever.

    有很關鍵的意義

  • Back when I was your age,

    首先 宇宙將會永遠擴張

  • we didn't know what the universe was going to do.

    當我想你們這個年級的時候

  • Some people thought that the universe would recollapse in the future.

    我們不知道宇宙將會怎樣

  • Einstein was fond of this idea.

    有人說宇宙將會又一次垮塌

  • But if there's dark energy, and the dark energy does not go away,

    愛因斯坦很喜歡這個理論

  • the universe is just going to keep expanding forever and ever and ever.

    但是 如果有暗能量的話 並且它不會消失的話

  • 14 billion years in the past,

    這個宇宙將不斷 永遠的擴張下去

  • 100 billion dog years,

    在過去與的140億年裡

  • but an infinite number of years into the future.

    也就是一千億狗年

  • Meanwhile, for all intents and purposes,

    但是我們不能估計未來還有多少年

  • space looks finite to us.

    同時 不管怎麼看

  • Space may be finite or infinite,

    空間對於我們都看起來是有限的

  • but because the universe is accelerating,

    空間可能是有限的 也可能是無限的

  • there are parts of it we cannot see

    但是因為宇宙是加速度擴張的

  • and never will see.

    有一部分宇宙 我們是看不到的

  • There's a finite region of space that we have access to,

    並且永遠都看不到

  • surrounded by a horizon.

    我們能夠接觸到的宇宙只是很有限的一部分

  • So even though time goes on forever,

    在一個有限的視線範圍之內

  • space is limited to us.

    所以即使時間不斷前行

  • Finally, empty space has a temperature.

    空間對於我們來說仍然是有限的

  • In the 1970s, Stephen Hawking told us

    最後 空的空間裡是有一個溫度的

  • that a black hole, even though you think it's black,

    在上世紀70年代 史蒂芬·霍金告訴我們

  • it actually emits radiation

    黑洞 即使你認為它是黑壓壓的一片

  • when you take into account quantum mechanics.

    也是有放射性的

  • The curvature of space-time around the black hole

    如果你從量子力學的角度來考慮問題

  • brings to life the quantum mechanical fluctuation,

    黑洞周圍的時間-空間曲率

  • and the black hole radiates.

    帶來了量子力學意義上的波動

  • A precisely similar calculation by Hawking and Gary Gibbons

    並且黑洞開始具有放射性

  • showed that if you have dark energy in empty space,

    霍金跟加利 吉布森有一個很類似的計算

  • then the whole universe radiates.

    這個計算顯示 如果你在一個空的空間裡有暗能量

  • The energy of empty space

    那麼整個宇宙都是會有放射性的

  • brings to life quantum fluctuations.

    空的空間裡的能量

  • And so even though the universe will last forever,

    帶來量子波動

  • and ordinary matter and radiation will dilute away,

    並且即使宇宙永遠存在

  • there will always be some radiation,

    普通物質跟放射性被稀釋

  • some thermal fluctuations,

    宇宙中總是會有一些放射性存在的

  • even in empty space.

    還有熱波動

  • So what this means

    即使是在這樣一個空的空間裡

  • is that the universe is like a box of gas

    這就說明

  • that lasts forever.

    宇宙就像一個永遠存在的

  • Well what is the implication of that?

    装满的气体的盒子

  • That implication was studied by Boltzmann back in the 19th century.

    那麼這說明了什麼呢

  • He said, well, entropy increases

    博茨曼在19世紀就對此進行了研究

  • because there are many, many more ways

    他說 熵值增加

  • for the universe to be high entropy, rather than low entropy.

    因為相比起低熵值的狀態

  • But that's a probabilistic statement.

    宇宙有更多方式達到一個高熵值的狀態

  • It will probably increase,

    但這是一個概率問題

  • and the probability is enormously huge.

    熵值很有可能升高

  • It's not something you have to worry about --

    並且這個可能性是非常巨大的

  • the air in this room all gathering over one part of the room and suffocating us.

    但是你不用擔心說

  • It's very, very unlikely.

    這個房間裡所有的空氣將聚集到房間的一個角落 讓我們窒息

  • Except if they locked the doors

    這是非常非常不可能的

  • and kept us here literally forever,

    除非門被鎖上

  • that would happen.

    我們真的永遠的在這里呆下去

  • Everything that is allowed,

    剛才所說的情況才能有可能發生

  • every configuration that is allowed to be obtained by the molecules in this room,

    所有可能發生的情形

  • would eventually be obtained.

    所有這個屋子裡的原子所可能形成的所有的組合

  • So Boltzmann says, look, you could start with a universe

    最後總會被實現

  • that was in thermal equilibrium.

    所以博茨曼說 你看 宇宙可以從一個

  • He didn't know about the Big Bang. He didn't know about the expansion of the universe.

    熱平衡的狀態開始發展

  • He thought that space and time were explained by Isaac Newton --

    他不知道宇宙大爆炸理論 更不知道宇宙擴張理論

  • they were absolute; they just stuck there forever.

    他以為牛頓對於時間空間的解釋是正確的 那就是

  • So his idea of a natural universe

    時間空間是絕對的 永遠不變的

  • was one in which the air molecules were just spread out evenly everywhere --

    所以博茨曼的自然宇宙的理論

  • the everything molecules.

    認為空氣分子就是平均分散在各處的

  • But if you're Boltzmann, you know that if you wait long enough,

    構成各種東西的分子

  • the random fluctuations of those molecules

    但是如果你是博茨曼 你會想 如果你足夠耐心