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For the controllers of the GPS, time is everything.
对于GPS的控制者来说，时间是关键。
'US naval observatory master clock,
美国海军天文台的主时钟，
'at the tone, mountain daylight time, 18 hours, 48 minutes, five seconds...'
基本对时，山区夏令时，18点48分5秒……
'US naval observatory ma...'
美国海军天文台的主时钟……
For the global positioning system to work,
为了GPS正常运作，
the clocks on board the satellites have to be exactly synchronised with time on Earth.
卫星上的时钟必须严格地与地球上的时钟同步。
But for the satellites, orbiting 18,000 kilometres above our planet,
然而对于卫星来说，运行在地球1.8万英里的上空，
Einstein predicts something very strange.
爱因斯坦预言过一些很奇怪的现象。
He predicts that in orbit, time itself runs at a different speed to that on the Earth's surface.
他预言处在轨道上，时间本身的流逝的速度不同于地球表面。
It's incredible for anyone to suggest that time goes at a different rate on the ground than it does in space.
谁都不会想到地面上与太空中相比，时间的速度不同。
What's the difference?
不同在哪里？
Well, the difference is gravity, the closer you are to the Earth, the stronger the gravitational field
不同在引力，你越靠近地球，引力场就越强，
the further you are up into space the weaker the gravitational field.
你越深入太空，引力场就越弱。
What Einstein said was that the stronger the gravitational field, the slower time ticks.
爱因斯坦称引力场越强，时间的流逝就越慢。
The weaker it is, the faster time ticks.
引力场越弱，时间的流逝就越快。
The link between the speed of time and the strength of gravity
时间速度与引力强度之间的联系，
is all down to Einstein's prediction that the Earth distorts the space time.
都囊括在了爱因斯坦的地球弯曲了时空的预言里了。
If you put something heavy in space like a planet, a star, the Earth,
如果你将一些大的物体放到空间里，比如行星、恒星、地球，
then that heavy thing bends the space, it curves the space.
那么那些大的物体就会弯曲空间，扭曲空间。
But space and time are intimately linked.
但是空间与时间是紧密联系在一起的。
So, does the Earth also bend time?
那么地球也弯曲了时间？
Well, yes, it does.
啊，是的。
In the reduced gravity up in orbit, time really does tick a bit faster than time on Earth.
处在引力减少的轨道上，时间真的要比地球上走得快一点。
To keep everything in sync, the controllers have to dial-in a time correction.
为了始终保持同步，控制者必须进行时间校准。
