This thought eventually changed the world forever.

這一想法最終徹底改變了世界。

The boy's name was Albert Einstein.

男孩的名字叫阿爾伯特-愛因斯坦。

So what really was that thought?

那麼，這種想法到底是什麼呢？

And how could one thought change the world so thoroughly?

一個念頭怎麼能如此徹底地改變世界？

Well in this video we're discussing Einstein's theory of relativity and more importantly how he got there.

在這段視頻中，我們將討論愛因斯坦的相對論，更重要的是他是如何達到這一境界的。

We cannot start talking about Einstein without discussing classical physicist Sir Isaac Newton.

談到愛因斯坦，就不能不討論古典物理學家艾薩克-牛頓爵士。

In 1687, Newton published his book Mathematical Principles of Natural Philosophy.

1687 年，牛頓出版了《自然哲學的數學原理》一書。

In the book, he described history, laws of motion, and the law of gravity.

在書中，他描述了歷史、運動定律和萬有引力定律。

His book is considered one of the most important writings in the history of mankind.

他的著作被認為是人類歷史上最重要的著作之一。

After watching an apple fall, he asked himself a question.

看著蘋果掉下來，他問了自己一個問題。

If the apple falls, does the moon also fall?

如果蘋果掉下來，月亮也會掉下來嗎？

These questions led him to discover the law of gravity.

這些問題促使他發現了萬有引力定律。

According to his law of gravitation, every object in the universe enacts its own force of attraction on another object.

根據他的萬有引力定律，宇宙中的每一個物體都會對另一個物體產生自己的吸引力。

And this force is the reason why we are stocked on earth, why the moon orbits the earth, and indeed why the universe exists.

這種力量是我們在地球上生存的原因，也是月球圍繞地球運行的原因，更是宇宙存在的原因。

But that didn't answer all of Newton's questions, like why do objects attract each other, what is the source of gravity, and why does Mercury's orbit jiggle?

但這並沒有回答牛頓的所有問題，比如物體為什麼會相互吸引，萬有引力的來源是什麼，水星的軌道為什麼會抖動？

The rest remained a mystery until the era of Albert Einstein.

在愛因斯坦時代之前，其餘部分一直是個謎。

In 1915, Einstein published his theory of general relativity, or in other words, his In this theory, Einstein explained gravity and its source.

1915 年，愛因斯坦發表了他的廣義相對論，或者換句話說，在這一理論中，愛因斯坦解釋了萬有引力及其來源。

He answered all the questions that Newton couldn't, like Mercury's precession.

他回答了牛頓無法回答的所有問題，比如水星的躔度。

Let's take a step back to 1905 to truly grasp where these different pieces of the puzzle come to life.

讓我們回到 1905 年，真正瞭解這些不同的拼圖是如何形成的。

This year, Einstein published his theory of special relativity.

這一年，愛因斯坦發表了狹義相對論。

It deals with the speed of light and the motion of objects.

它涉及光速和物體的運動。

It was fine with non-accelerating objects, but the theory did not apply when gravity was present, or if the object was accelerating.

這對非加速物體沒有問題，但如果存在引力，或者物體正在加速，該理論就不適用了。

He couldn't quite figure the rest out until one fine day in 1907.

直到 1907 年的一個晴朗的日子，他才弄清了其餘的事情。

He was observing a window washer on a ladder and had an epiphany.

他在梯子上觀察一個擦玻璃的人時，頓悟了。

He thought about what he would be experiencing while falling.

他想到了自己在墜落時會經歷什麼。

He imagined himself there and realized that while falling, the ground would not be pushing him so he would be in a free fall.

他想象著自己在那裡，並意識到在下落的過程中，地面不會推動他，是以他將處於自由落體狀態。

That put some of the pieces together, but still he wasn't fully finished.

這使一些碎片拼湊在一起，但他仍然沒有完全完成。

He began to think about falling again.

他開始考慮再次墜落。

This time he imagined himself in a room with no windows.

這一次，他想象自己在一個沒有窗戶的房間裡。

On the surface of the earth, you would weigh whatever your weight is now.

在地球表面，你現在的體重是多少，你就會有多重。

But imagine if the room was in a spacecraft, moving in an upward direction with the same 9.8 meters per second squared as here on the ground.

但是想象一下，如果這個房間是在宇宙飛船中，以與地面上相同的每秒 9.8 米的速度向上移動。

In that moment, if you were to weigh yourself, you would weigh the same as you do on earth.

在那一刻，如果你稱一下自己的體重，你的體重與你在地球上的體重是一樣的。

Einstein realized that the observer would not be able to tell if he's on a spaceship or on the surface of the earth.

愛因斯坦意識到，觀察者無法分辨自己是在宇宙飛船上還是在地球表面。

That is because he would be moving at the exact same rate of acceleration.

這是因為他將以完全相同的加速度運動。

There would be no way to tell the difference.

根本無法分辨。

This phenomenon is called the equivalence principle, which states that an object that is accelerating free of any gravitational pull is essentially no different than the same object that is stationary but affected by gravity.

這種現象被稱為 "等效原理"，即一個物體在沒有任何引力的情況下加速，與靜止但受引力影響的物體沒有本質區別。

In other words, something moving in space with no gravity has the same mass as something on earth that is not moving.

換句話說，在沒有重力的情況下，在太空中運動的物體與地球上不動的物體具有相同的品質。

In his special theory of relativity, he could only deal with non-accelerating objects and the speed of light.

在他的狹義相對論中，他只能處理非加速物體和光速。

Let's pause here for a second.

讓我們暫停一下。

This means that at that point, he knew how to unify his theory of special relativity with gravity.

這意味著，此時他已經知道如何將狹義相對論與萬有引力統一起來。

Luckily, he didn't stop there.

幸運的是，他並沒有就此止步。

He did another thought experiment.

他又做了一個思想實驗。

This time he imagined what would happen if he pointed a laser beam from one side of the room towards the other.

這一次，他想象著如果把激光束從房間的一側對準另一側，會發生什麼。

If the room were in a spaceship that was moving upwards with the same acceleration rate as earth, the height of the beam would slightly be lower on the other side of the room.

如果房間是在一艘飛船中，飛船以與地球相同的加速度向上運動，那麼房間另一側的光束高度會稍低一些。

As the floor moved up, it curved the light and caused it to bend down.

當地板向上移動時，它彎曲了光線，導致光線向下彎曲。

But this principle only applied in space.

但這一原則只適用於太空。

When he thought about the same experiment on earth, the light would appear to be straight.

當他在地球上做同樣的實驗時，光線看起來是直的。

Of course, these two scenarios only happened in his brain.

當然，這兩種情況只發生在他的大腦中。

Let's just take a brief moment to appreciate how brilliant he is to be able to conduct that experiment, all of that, in his brain.

讓我們花一點時間來欣賞一下他是多麼的聰明，能夠在自己的大腦中進行這樣的實驗。

Back to the topic.

言歸正傳。

Einstein wasn't convinced though, as this violated the principle of equivalence.

但愛因斯坦不以為然，因為這違反了等效原理。

The acceleration of the room on the spaceship was the same as under the influence of gravity.

飛船上房間的加速度與重力作用下的加速度相同。

The height should be the same in both cases.

兩種情況下的高度應相同。

He realized that the only possibility could be that the light beam must be bending under the influence of gravity.

他意識到，唯一的可能就是光束在重力作用下發生了彎曲。

But how could this be?

但這怎麼可能呢？

What does this bending of light mean?

光的彎曲意味著什麼？

Well, thanks to his incredible imagination and deep thinking, he came up with an answer.

好吧，多虧了他驚人的想象力和深入的思考，他想出了一個答案。

He considered that maybe the light was following the shortest and straightest path that it could, but that in space, there was no visual, objective straight path and maybe there was an inherent curvature.

他認為，也許光線是沿著它所能達到的最短、最直的路徑前進的，但在太空中，並不存在直觀、客觀的直線路徑，也許存在著固有的曲率。

This idea revolutionized the entire course of scientific history.

這一思想徹底改變了整個科學史的進程。

That space somehow gets curved in the presence of gravity and it creates an illusion that the light beam is being curved.

在萬有引力的作用下，空間會發生某種彎曲，從而產生光束被彎曲的錯覺。

He hypothesized that whenever matter or energy present in space, it creates a curvature.

他假設，只要空間中存在物質或能量，就會產生曲率。

There's one really popular video on YouTube.

YouTube 上有一段非常受歡迎的視頻。

Imagine a trampoline with two types of masses, a heavy chunk of metal and a piece of marble.

想象一下，在蹦床上有兩種品質，一塊重金屬和一塊大理石。

When the metal is placed on the trampoline, it bends it.

當金屬放在蹦床上時，它就會彎曲。

Then the piece of marble is rolled on the surface.

然後在表面滾動大理石。

It orbits the heavy chunk of metal.

它圍繞著這塊沉重的金屬運轉。

In this scenario, we can see that no force is acting on the piece of marble, but it is still revolving around the heavy metal.

在這種情況下，我們可以看到沒有力作用在這塊大理石上，但它仍然圍繞著重金屬旋轉。

Einstein went even further and said that the same thing happens when the earth is orbiting the sun.

愛因斯坦更進一步說，當地球繞太陽運行時，也會發生同樣的情況。

The sun acts like a chunk of metal and creates a curvature in space.

太陽就像一大塊金屬，在太空中形成了一個曲率。

The same can be applied to all objects in the universe.

同樣的道理也適用於宇宙中的所有物體。

So according to Einstein, matter and energy warp space-time, making nearby objects fall towards it.

是以，根據愛因斯坦的觀點，物質和能量會扭曲時空，使附近的物體向它墜落。

Another remarkable part of his theory is that it doesn't just include the three dimensions of space, but also time.

他的理論的另一個顯著特點是，它不僅包括三維空間，還包括時間。

This is why we use the term space-time.

這就是我們使用時空一詞的原因。

But how does time come into play?

但時間是如何發揮作用的呢？

Well, it comes from his previous theory, the theory of special relativity.

這來自於他之前的理論，即狹義相對論。

The speed of light is the same for the observers in any frame of reference.

在任何參照系中，觀察者的光速都是相同的。

Either the object is moving or in a state of rest.

物體要麼在運動，要麼處於靜止狀態。

Again, imagine a light beam traveling from point A to point B.

同樣，想象一束光從 A 點射向 B 點。

If we place a massive object like our sun between these two points, the sun will curve the path and the distance from point A to point B will increase.

如果我們在這兩點之間放置一個像太陽這樣的大品質物體，太陽就會彎曲路徑，從 A 點到 B 點的距離就會增加。

So it will take more time for light to move from A to B than in the absence of the sun.

是以，與沒有太陽時相比，光從 A 處移動到 B 處需要更多時間。

But that concept violates the theory of special relativity, which says that the speed of light is independent of the frame of reference.

但這一概念違反了狹義相對論，因為狹義相對論認為光速與參照系無關。

This means that regardless of whether the light beam is traveling freely or under the gravitational field, it must take the same time for it to travel from A to B.

這意味著，無論光束是自由傳播還是在引力場作用下傳播，它從 A 到 B 所需的時間都是相同的。

So for special relativity to be valid, time must slow down.

是以，為了使狹義相對論成立，時間必須變慢。

In other words, time moves slowly when you are near a massive object like in space, and moves faster when you are away from it.

換句話說，當你靠近像太空這樣的大品質物體時，時間會緩慢流逝，而當你遠離它時，時間會加速流逝。

For example, time for us on Earth is slower than the astronauts on the ISS, which has been directly confirmed through many experiments.

例如，我們在地球上的時間比國際空間站上的太空人慢，這已經通過許多實驗得到了直接證實。

This phenomenon is called gravitational time dilation.

這種現象被稱為引力時間膨脹。

Back a century ago, no one was taking Einstein's ideas seriously.

一個世紀前，沒有人認真對待愛因斯坦的觀點。

But just four years after the publication of his general theory of relativity, astronomer Sir Arthur Eddington performed an experiment to test it out.

但是，就在他的廣義相對論發表四年後，天文學家阿瑟-愛丁頓爵士做了一個實驗來驗證他的理論。

If the general relativity was correct, then the sun would warp the space around it, causing the light beams to bend and the position of the stars behind the sun to change.

如果廣義相對論是正確的，那麼太陽就會扭曲它周圍的空間，導致光束彎曲，太陽背後恆星的位置也會發生變化。

Eddington followed this principle, and he found that Einstein was right.

愛丁頓遵循了這一原則，他發現愛因斯坦是對的。

That phenomenon is now called the gravitational lensing.

這種現象現在被稱為引力透鏡。

This was the first proof of Einstein's theory, and it took the world by storm.

這是愛因斯坦理論的第一個證明，它在世界範圍內掀起了一場風暴。

Today we have found lots of evidence that proves his theory.

今天，我們找到了很多證據來證明他的理論。

The predictions made by his theory a hundred years ago are now being confirmed today.

一百年前他的理論所做的預測如今得到了證實。

They have created a new window to look into the universe.

他們創造了一個觀察宇宙的新窗口。

Thank you so much for watching this video.

非常感謝您觀看本視頻。

I'm Harry and I'm so glad you made it to the end.

我是哈利，很高興你能堅持到最後。

If you like this type of content, please subscribe.

如果您喜歡這類內容，請訂閱。

If you want to, follow us on Instagram at Beyond Ideas.

如果您願意，請在 Instagram 上關注我們的 Beyond Ideas。

I'll see you again next week for more curiosity videos.

下週再見，我們將為您帶來更多精彩視頻。

Bye bye.

再見