In 1907 a young Albert Einstein was looking for a way to extend his special theory of relativity to include acceleration.It took him eight years to come up with the mathematical solution that we know as the General theory of relativity. 1907年，年轻的爱因斯坦在寻找一个可以将狭义相对论推广到包括加速参考系的理论。他花了长达八年时间想出了一个数学上的解释，也就是我们现在熟知的广义相对论。 It tells us that we all live in a 4-dimensional spacetime.We can move up and down,left and right,backwards and forwards,Thats three physical dimensions,but we also move in time-in the direction of the future,Thats dimension number four. 广义相对论认为 我们都生活在一个四维时空中,我们可以上下 左右 前后的运动,这是三维实体空间，但我们还能在时间维度上朝着未来前进。这就是第四个维度。 One consequence of Einsteins theory is that space-time can be stretched,a bit like a rubber sheet,He found out that mass,or energy,tells the 4 dimensional space-time how to deform,and vice versa,that deformation tells matter How to move. 爱因斯坦理论的结论之一就是：时空有点像橡胶，可以扭曲。他发现质量或者能量可以令四维空间形变，反之，形了变的空间又能影响物质的运动。 Its way easier to think about if we consider less dimensions,Lets cut one out and limit ourselves to two spatial dimension,When we put in the Earth,its mass curves the space-time and our apple falls towards it,And this is what we call gravity.We can make it even simpler still,and remove another spatial dimension. 在低维度上思考会简单很多，我们可以剪出一个维度，并把自己限制在这个两维度空间里，然后把地球放上去，它的质量会弯曲时空并且令苹果滚向它，这就是我们所说的重力。我们可以让继续简单地探讨一下，再去掉进一个空间维度. Here we are,you,me,the apple all falling towards Earth,While we can clearly see and feel the attraction from something really massive and nearby,Like the earth,the effect of things that are further away is harder to notice, 看吧！你，我还有苹果都掉到地球上。尽管我们可以清楚地看到并感受到，来自附近很大质量物体的吸引，比如地球，但远处物体的影响就很难察觉了。 For example,the influence we feel from the moon is pretty weak,And the main effect we can observe is when parts of the ocean fall into the space-time curvature.That the moon causes,Most people like to call this effect tides.Its the gravity of the sun that holds our planet in its orbit,but we can barely feel this effect at all.This is because the gravitational force decreases with the square of the distance,So it becomes weak really quickly the further away you go. 例如，月球引力带给我们的感觉就很微弱，我们所能观察到的现象就是：受时空弯曲影响而跌宕的海水，这就是由月球造成的。大部分人称之为潮汐，太阳的引力将地球困在其轨道中运转，但我们几乎感觉不到这种力，这是因为引力会随距离的增大按其平方值递减，所以随着距离增加，力会迅速地减小。 In the end gravity may be a weak force,but while electric charges cancel each other out in large objects,that cant happen with gravity,Over large distances gravity always wins and will even allow us to perceive the universein a completely new way.While all modern astronomy sees the Universe,Einsteins general relativity predicts that: We can also hear the Universe with Gravitational waves. 最终 引力也许会变成一个很小的力，大物体里面的电荷会互相抵消，但引力不会在大尺度上，引力总是胜利的，它让我们以一种全新的方式认识宇宙，虽然所有的现代天文学都在观察宇宙，但爱因斯坦的广义相对论预言说：我们还能通过引力波聆听宇宙的声音. These ripples in space-time are the sound of the universe and travel at the speed of light,They are emitted by the most extreme objects and are detectable from really really far away.This is pretty awesome,because soon the effects of gravity might be more to us than just the means by which stuff sticks to the ground.It will also provide us with a whole new way of observing our Universe and all the incredible objects that is contains. 这些在时空中以光速传播的涟漪就是宇宙之声，它们是由最极端的物体产生的 可以在极远处被接受到，这真的非常神奇，因为不久之后，引力的影响，将不仅意味着东西会被吸到地面上。它将让我们一种完全新的方式来观察这个宇宙和宇宙中所有不可思议的物体。