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But time is like a river in another way.
不過時間似流水還有另一層含義
It flows at different speeds in different places.
其在不同地點有著不同速度
And that is the key to traveling into the future.
而這正是穿梭于時間的關鍵所在
The idea was proposed by Albert Einstein
這一概念在100多年前
over 100 years ago.
由阿爾伯特·愛因斯坦提出
He realized that there should be places where time slows down
他認為時間在一些地方會減慢
and others where time speeds up.
而在另一些地方則會增快
He was absolutely right,
這話可是千真萬確
and the prove is right above our heads, up in space.
證據就在我們頭頂的那片太空中
This is the Global Positioning System, or GPS.
這是全球定位系統，又叫GPS
A network of 31 satellites
是由繞地球軌道運行的
in orbit around the earth.
31顆衛星形成的網絡
The satellites make satellite navigation possible.
正是這些衛星使衛星導航變為可能
But they also reveal that time runs faster up here
但同時也表明
than it does down on earth.
在這里時間流逝得比地球上快
Inside each spacecraft is a very precise clock.
每個航天器內都有一個十分精確的時鐘
But despite being so accurate,
盡管已經十分精確
they all gain around
但他們每天都大約會走快
a third of a billionth of a second every day.
十億分之一秒的三分之一
The system has to correct for the drift.
系統必須更正這一偏差
Otherwise that tiny difference would upset the whole system,
否則這細微的差異會擾亂整個系統
causing every GPS device on earth
致使地球上所有GPS設備
to go out by about six miles a day.
每天出現約6英里的誤差
You can just imagine the mayhem that would cause.
其引起的混亂可想而知
The problem doesn't lie with the clocks.
問題并不在于時鐘
They run fast because time itself runs faster here than
時鐘走得快是因為在這里時間本身
it does down below,
就比在地球上快
and the reason for this extraordinary effect
產生這種奇異現象的原因
is the mass of the earth.
在于地球的巨大質量
Einstein realized that matter drags on time,
愛因斯坦意識到，物質滯延時間
slows it down like the slow part of a river.
像河流的緩流部分那樣令時間減速
The heavier the object, the more it drags on time,
物體越重，滯延時間越長
and this startling reality
這一驚人的事實
is what opens the door to the possibility of time travel to the future.
打開了一扇穿越未來的希望之門
I admit this is a difficult concept to understand,
我承認這個概念很難理解
so let's take a simple example.
所以讓我們來看一個簡單的例子
This is the Great Pyramid of Giza.
這是吉薩的大金字塔
It weighs over 40 million tons,
重達4000多萬噸
and like all heavy things,
與其他所有沉重的物體一樣
it's actually slowing down time.
它會減慢時間
The effect is small,
不過影響微弱
billions of times smaller than that of the earth.
只及地球影響力的幾十億分之一
But if we exaggerate it drastically,
但是如果大幅放大這種影響
You can see the principle at work.
就能看到這種原理在起作用
