Is time travel possible? - Colin Stuart

時空旅行能否成真？ - 科林‧史嘟華

譯者: 瑞文Eleven 林Lim 審譯者: Adrienne Lin

Have you ever daydreamed about traveling through time,

你曾經幻想過

來一趟時空旅行嗎？

perhaps fast forward in the centuries and seeing the distant future?

或者穿越到幾百年後，

一窺遙遠的未來？

Well, time travel is possible,

讓我告訴你，穿越時空是有可能的。

and what's more, it's already been done.

而且更棒的是，

它已經被實現了。

Meet Sergei Krikalev,

有請謝爾蓋.克里卡列夫

the greatest time traveler in human history.

史上最偉大的時空旅行家，

This Russian cosmonaut holds the record

這位俄羅斯太空人創下了

for the most amount of time spent orbiting our planet,

環繞地球時間最久的記錄。

a total of 803 days, 9 hours, and 39 minutes.

長達803天9小時39分鐘。

當他在太空的時候，

During his stay in space,

he time traveled into his own future

他穿越時空

回到自己0.02秒後的未來。

by 0.02 seconds.

Traveling at 17,500 miles an hour,

時速接近三萬公里

he experienced an effect known as time dilation,

他經歷了一種稱為

時間膨脹的效應

and one day the same effect

有一天這個效應

將會讓穿越時空的時間更持久，

might make significant time travel to the future commonplace.

並在未來變得稀鬆平常。

To see why moving faster through space affects passage of time,

如果想瞭解為何在空間裡的快速運動

會影響時間流逝的速率，

we need to go back to the 1880s,

我們得回到1880年代，

when two American scientists,

當時兩位美國科學家：

Albert Michelson and Edward Morley,

阿爾伯特‧邁克生和愛德華‧莫立，

were trying to measure the effect of the Earth's movement around the Sun

他們嘗試測量

地球繞太陽

on the speed of light.

對光速有什麼影響。

When a beam of light was moving in the same direction as the Earth,

他們以為，當一束光

與地球往相同方向移動時，

他們預測光速會變快。

they expected the light to travel faster.

And when the Earth was moving in the opposite direction,

當兩者方向相反時，

they expected it to go slower.

光速會減慢。

But they found something very curious.

結果令他們很好奇，

The speed of light remained the same no matter what the Earth was doing.

不論地球往哪邊走，

測出的光速都相同。

Two decades later, Albert Einstein was thinking

20年後，愛因斯坦開始思考

about the consequences of that never-changing speed of light.

此一實驗的結果：

光速保持恆定不變。

And it was his conclusions,

他的結論寫在他的“相對論”中，

formulated in the theory of special relativity,

that opened the door into the world of time travel.

開啟了

時空旅行的大門。

Imagine a man named Jack,

試想，一個名為傑克的人，

standing in the middle of a train carriage,

站在一輛火車上，

traveling at a steady speed.

以等速率移動，

傑克覺得很無聊，

Jack's bored and starts bouncing a ball up and down.

開始在地板上拍球，

What would Jill, standing on the platform, see through the window

這個時候站在月臺上的吉兒，

當火車鳴笛經過，

透過窗戶會看到什麼？

as the train whistles through?

Well, between Jack dropping the ball and catching it again,

在傑克扔下球

和接球之間，

Jill would have seen him move slightly further down the track,

吉兒會看到傑克

和火車一起向前移動，

resulting in her seeing the ball follow a triangular path.

結果她看到的球，

是沿三角形的路線移動。

This means Jill sees the ball travel further than Jack does

這意味著，吉兒看到的球

在同一時段裡，

比傑克所看到的移動得更遠。

in the same time period.

And because speed is distance divided by time,

因為速率等於距離除以時間，

所以吉兒所看到球 比傑克看到的移動得更快。

Jill actually sees the ball move faster.

But what if Jack's bouncing ball is replaced with two mirrors

但如果我們把傑克的球

用兩面鏡子代替，

which bounce a beam of light between them?

有一束光在鏡子之間來回反射。

Jack still sees the beam dropping down

傑克依然會看到光束射下，

and Jill still sees the light beam travel a longer distance,

而吉兒還是會看到該光束

只是移動得更遠，

except this time Jack and Jill cannot disagree on the speed

不同的是，這次兩人

會測出相同的光速。

because the speed of light remains the same no matter what.

這是因為光速

無論如何都是固定不變的。

And if the speed is the same while the distance is different,

如果速率相同

而距離不一樣，

this means the time taken will be different as well.

那花的時間也將不相同。

Thus, time must tick at different rates for people moving relative to each other.

所以，當人們相對他人運動時，

時間會以不一樣的速率流逝。

Imagine that Jack and Jill have highly accurate watches

試想如果傑克和吉兒 都有非常精確的手錶，

that they synchronize before Jack boards the train.

並在傑克上火車前校對好時間，

在實驗當中，傑克和吉兒會看到

During the experiment, Jack and Jill would each see

their own watch ticking normally.

自己的手錶正常地走，

但是如果他們在實驗結束後再相遇，

But if they meet up again later to compare watches,

比對彼此的手錶時，

less time would have elapsed on Jack's watch,

他們會發現傑克的手錶走得較慢一些，

balancing the fact that Jill saw the light move further.

因此解釋了

「吉兒看到的光移動得更遠」的事實。

This idea may sound crazy,

這聽起來很詭異，

but like any good scientific theory,

但是，就像任何一個完善的科學理論一樣，

it can be tested.

它是可以被檢驗的。

在1970年代，

In the 1970s, scientists boarded a plane

科學家們校對了一些 非常精確的原子鐘，

with some super-accurate atomic clocks

that were synchronized with some others left on the ground.

一些帶到飛機上，一些留在地面，

當飛機環球飛行之後，

After the plane had flown around the world,

他們發現飛機上的原子鐘

the clocks on board showed a different time

顯示的時間與地面的不一樣。

from those left behind.

Of course, at the speed of trains and planes,

當然，以火車與飛機的速率，

the effect is minuscule.

所產生的時間膨脹效應十分微小，

But the faster you go, the more time dilates.

但是行駛的速率越快、 時間膨脹越明顯。

For astronauts orbiting the Earth for 800 days,

如果太空人環繞地球800天，

it starts to add up.

其影響就很明顯了。

But what affects humans also affects machines.

而且，影響人類的也會影響機器。

Satellites of the global positioning system

全球衛星定位系統(GPS)的衛星，

are also hurdling around the Earth

持續環繞著地球飛行，

at thousands of miles an hour.

且時速高達數千哩(1哩約為1.6km)，

So, time dilation kicks in here, too.

因此，此速率下在也會顯出時間膨脹效應。

In fact, their speed causes the atomic clocks on board

事實上，GPS衛星的飛行速率導致

飛行中的原子鐘

to disagree with clocks on the ground

與地上的原子鐘之間，

by seven millionths of a second daily.

每天產生7百萬分之一秒的差異。

Left uncorrected,

如果不進行校正的話，

this would cause GPS to lose accuracy

將會使GPS因此失去準確性，

by a few kilometers each day.

每天產生幾公里誤差 。

So, what does all this have to do with time travel

那麼，這些與穿越時空

to the far, distant future?

回到未來有什麼關係呢？

Well, the faster you go, the greater the effect of time dilation.

當你的速率越快，

時間膨脹的效應也越明顯。

If you could travel really close

如果你的速率真的能夠接近光速的話，

to the speed of light, say 99.9999%,

比方說，以光速的99.9999%，

on a round-trip through space

繞太空來回一圈，

for what seemed to you like ten years,

對你來說可能像過了10年，

you'd actually return to Earth

但是當你回到地球時，

around the year 9000.

將是差不多9000年後了。

Who knows what you'd see when you returned?!

到那時候，誰知道你回來後會看到什麼？

Humanity merged with machines,

人類與機器分不開？

extinct due to climate change or asteroid impact,

人類因全球暖化

或小行星撞擊而滅絕？

or inhabiting a permanent colony on Mars.

又或是人類已在火星定居了。

But the trouble is,

但問題是，

先不提太空飛船，

getting heavy things like people, not to mention space ships,

單要把像人一樣重的東西，

up to such speeds requires unimaginable amounts of energy.

加速到達接近光速，

將需要無法想像的巨大能量。

It already takes enormous particle accelerators

龐大的粒子加速器

like the Large Hadron Collider

如大強子對撞機，

to accelerate tiny subatomic particles to close to light speed.

已能把次原子粒子(如質子、電子)加速

到接近光速了。

But one day, if we can develop the tools to accelerate ourselves to similar speeds,

如果有一天我們能發明一些工具，

可以讓我們自身加速到如光速般，

then we may regularly send time travelers

到那時候，我們可能 隨時可以把時空穿越者

into the future,

送到遙遠的未來，

bringing with them tales of a long, forgotten past.

並帶著我們古老、被遺忘的故事去。