Name: 愛因斯坦的狹義相對論｜時間真的會變慢嗎？ (Einstein’s Special Relativity Theory | Does Time really Slow down)
Uploaded: 2024-11-25T21:00:57.000Z
Duration: 13 min 15 s

To us, it appears that time doesn't stop or slow down for anyone in this universe.

在我們看來，這個宇宙中的任何人的時間都不會停止或減慢。

It's always running forward without waiting for anyone or anything.

它總是向前奔跑，不等待任何人或任何事。

程度副詞

Special relativity theory tells us that time is really not like this.

狹義相對論告訴我們，時間其實並非如此。

Time is not the same for all across the whole universe.

在整個宇宙中，所有人的時間都是不一樣的。

Different observers feel different times at different places.

不同的觀察者在不同的地點感受到不同的時間。

Einstein's special relativity theory starts with two basic ideas.

愛因斯坦的狹義相對論始於兩個基本思想。

The first postulates that the laws of physics are the same in all frames of reference.

第一個假設是，物理定律在所有參照系中都是相同的。

Imagine your friend is standing at the platform of a train station and you are in a train traveling at a constant velocity.

想象一下，你的朋友站在火車站的月臺上，而你在一列勻速行駛的火車上。

Constant velocity means an object is moving in a fixed speed and fixed direction.

勻速運動是指物體以固定的速度和方向運動。

This motion doesn't have any acceleration, deceleration, and does not change direction.

這種運動沒有任何加速度、減速度，也不改變方向。

From his perspective, he is at rest and you are heading forward.

從他的角度來看，他在休息，而你在前進。

But from your perspective, who is traveling at a constant speed, does not feel any motion.

但從你的角度來看，以恆定速度行進的你並沒有感覺到任何運動。

是以，你也可以說自己是在休息。

The rest of the world can appear to be running towards you.

世界上的其他事物似乎都在向你奔來。

If the train windows are closed, there is no outside reference point.

如果火車窗戶關閉，就沒有外部參照點。

是以，你認為自己處於靜止狀態。

As all the laws of physics will apply to both your friend and you, both of you can be considered to be at rest.

由於所有物理定律都適用於你和你的朋友，所以你們都可以被視為處於靜止狀態。

To explain more simply, let's take a look at a mosquito in a flying plane.

為了更簡單地解釋，讓我們來看看飛行飛機上的蚊子。

Now that the mosquito is sitting on the back seat, it wants to fly to the pilot room.

現在蚊子坐在後座上，它想飛到駕駛室去。

If the laws of physics is not the same for a moving plane, it must travel above the flight speed.

如果物理定律對飛行中的飛機來說不一樣，那麼它的飛行速度一定高於飛行速度。

But there is nothing like that and the mosquito feels at rest on a moving plane.

但是，沒有這樣的感覺，蚊子在移動的飛機上感覺是靜止的。

So the normal effort is enough to reach the pilot's room.

是以，正常的努力就足以到達駕駛室。

Now let's come back to the train scenario.

現在讓我們回到火車上的情景。

You are in a moving train and your friend is on the platform.

你在一列行駛中的火車上，你的朋友在站臺上。

Whatever your friend is doing on the platform, you can also do in the moving train.

無論你的朋友在站臺上做什麼，你都可以在動車上做。

However, the speed is not the same for all observers.

然而，所有觀測者的速度並不相同。

Let's say the train is moving at a constant speed of 100 km per hour and you throw a football at the speed of 20 km per hour.

假設火車以每小時 100 千米的速度勻速行駛，而你以每小時 20 千米的速度投擲足球。

From your perspective, the ball is traveling 20 km per hour because you are at rest inside the train.

從你的角度看，球的時速為 20 公里，因為你在火車內處於靜止狀態。

But from your friend's perspective who is on the platform watching the train, he feels the ball is traveling at a whopping 120 km per hour.

但從你朋友的角度來看，他在站臺上看著火車，他覺得球的時速高達 120 公里。

Let's say you have another friend who is running on the track towards your train at 10 km per hour.

假設你有另一個朋友，他正在軌道上以每小時 10 公里的速度向你的火車跑來。

Now if he measured the ball speed, he would judge it to be 130 km per hour.

現在，如果他測量球速，就會判斷為每小時 130 公里。

How can the same moving object be showing different speeds?

同一個運動物體怎麼會有不同的速度？

Because speed is relative, it can vary from one to another.

因為速度是相對的，所以會因人而異。

Different observers can measure different speeds on the same moving object.

不同的觀察者可以測量出同一運動物體的不同速度。

Special Relativity's other postulate is that the speed of light is the same for all observers.

狹義相對論的另一個假設是，所有觀測者的光速都是相同的。

The speed of light is constant and it always shows the same value for all frames of reference.

光速是恆定的，它在所有參照系中始終顯示相同的值。

You and your friend are standing opposite each other.

He has a flashlight and your friend flashes the light.

他拿著手電筒，而你的朋友在閃燈。

If you could measure the speed of light quick enough, you would measure it at around 300,000 km per second.

如果你能足夠快地測量光速，你就能測出它的速度約為每秒 30 萬公里。

No surprises yet, as you are both at rest.

還沒有驚喜，因為你們都在休息。

But now you are running towards your friend at the phenomenal speed of 10,000 km per second and he flashes the light.

但現在，你正以每秒一萬公里的驚人速度向你的朋友跑去，而他卻閃了一下光。

You would measure it still showing the same value of 300,000 km per second instead of showing 310,000 km per second.

你測量到的數值仍然是每秒 30 萬公里，而不是每秒 31 萬公里。

This is due to the fact that the speed of light is constant.

It's the same for all the observers, no matter where that observer is at rest or in motion.

無論觀察者處於靜止還是運動狀態，對所有觀察者來說都是一樣的。

In order to maintain the constant nature of the speed of light, space and time experience weird features.

為了保持光速的恆定性，空間和時間會出現一些奇怪的特徵。

Even today we still don't know exactly what time is, but we do have some basic understanding.

即使在今天，我們仍然不知道時間到底是什麼，但我們已經有了一些基本的認識。

We've all agreed that all the clocks in our world tick at the same rate.

我們都同意，世界上所有的時鐘都以相同的速度滴答作響。

We've all agreed on how long some things take to happen and what things happen at the same moment.

我們都同意，有些事情需要多長時間才能發生，有些事情會在同一時刻發生。

These basic things of time we experience in our everyday life.

我們在日常生活中體驗到這些基本的時間。

But the constant nature of light says that it's all wrong.

但光的恆定性表明，這一切都是錯誤的。

Imagine there are two nations, nation A and nation B, and they want to sign an agreement.

設想有兩個國家，A 國和 B 國，他們想要簽署一項協議。

The problem is that they both want to sign the agreement at the same moment, and they found the procedure too.

問題是，他們都想在同一時刻簽署協議，而且他們也發現了這一程序。

The procedure is that the leader of both nations need to sit at the opposite sides of the table, with a light bulb fixed over the middle of the table.

程序是，兩國領導人需要坐在桌子的兩邊，桌子中間固定一個燈泡。

Turn on the light bulb, and when the light reaches both leaders' eyes, they can both sign simultaneously, because they already know that light always travels at the same speed.

打開燈泡，當光線到達兩位領導者的眼睛時，他們可以同時做出手勢，因為他們已經知道光總是以相同的速度傳播。

Both nations' leaders decide to sit exactly the same distance from the bulb.

兩國領導人決定坐在距離燈泡完全相同的位置上。

They turn on the light, and the light reaches both leaders at the same moment.

他們打開燈，燈光在同一時刻照亮了兩位領導人。

The agreement is signed simultaneously by leaders, and everyone is happy with the result.

雙方領導人同時簽署協議，結果皆大歡喜。

A few months later, they decide to sign another agreement, but this time, both leaders want to do it differently.

幾個月後，他們決定簽署另一份協議，但這一次，雙方領導人都希望以不同的方式行事。

Even though they have many different options, both leaders have an extreme love of trains.

儘管他們有很多不同的選擇，但兩位領導人都對火車情有獨鍾。

So they set up the same scenario in a moving train.

於是，他們在一列行駛中的火車上設置了同樣的場景。

The light flashes and goes to each leader, reaching them simultaneously.

燈光閃爍，同時照射到每個領導者身上。

They sign, and again everybody in the train is happy with the result.

他們簽了字，火車上的每個人再次對結果感到滿意。

But the people standing on the platform started fighting, because the people from nation B complained that nation A leader signed the agreement first.

但是，站在平臺上的人們開始爭吵，因為 B 國人抱怨 A 國領導人先簽署了協議。

How did they come up with that conclusion?

So they saw that the flash first reached leader A, because he was moving towards the flash.

是以，他們看到閃光首先到達了領導者 A，因為他正朝著閃光移動。

They already know that light always travels at constant speed.

他們已經知道光總是以恆定的速度傳播。

Leader B was moving away from the flash, so it took a longer time to reach leader B compared with leader A.

領導者 B 正在遠離閃光燈，是以與領導者 A 相比，到達領導者 B 所需的時間更長。

From the perspective of those watching the event from the platform, both leaders didn't sign at the same moment.

從站臺上觀看活動的人的角度來看，兩位領導人並不是在同一時刻簽署的。

But from the leader's perspective, who were in the moving train at constant velocity, claimed that they signed at the same moment.

但從領導者的角度來看，他們在勻速行駛的列車上，聲稱他們是在同一時刻簽字的。

We already know that when an object travels at a constant speed from the perspective or frame of reference, it can claim it is at rest.

我們已經知道，當一個物體從視角或參照系中以恆定的速度運動時，它可以聲稱自己處於靜止狀態。

Now let's move on from the platform perspective.

現在，讓我們從平臺的角度出發。

讓我們做一個簡單易懂的活動。

We will draw a line when the flash takes place, and draw a line when the flash reaches leader A versus leader B.

我們將在閃光發生時畫一條線，並在閃光到達領導者 A 和領導者 B 時畫一條線。

So from this line, we can clearly see that the flash reaching leader B needs to travel a longer distance compared to leader A.

是以，從這條線上我們可以清楚地看到，與領隊 A 相比，到達領隊 B 的閃光需要走更長的距離。

If it has to travel further, it takes a longer time.

如果要走得更遠，則需要更長的時間。

The leaders inside the train or the people watching from outside?

是列車內的上司，還是列車外的觀眾？

The constant nature of speed of light means that the events take place at the same time even though from the perspective of one group of people, the events don't take place at the same time as from the perspective of other groups.

光速的恆定性意味著事件發生在同一時間，即使從一組人的角度來看，事件發生的時間與從其他組人的角度來看並不相同。

One group of people don't realize any time difference and the other group of people witness a time difference on the same event.

一組人沒有意識到任何時差，而另一組人則目睹了同一事件的時差。

The thing that happened from one person's perspective does not happen at the same moment as from the other person's perspective if they are in relative motion.

如果兩個人處於相對運動中，從一個人的角度看發生的事情與從另一個人的角度看發生的事情並不在同一時刻。