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It's perfectly obvious the time has a direction
时间有方向，这是理所当然的。
All we mean by that is that the past is different from the future in lots of different ways
我们说这的意思是：过去与未来很不同。
We were younger in the past, we will be older in the future
以前我们比较年轻，未来的我们也相应地会比现在老。
We remember the past, we don't remember the future
我们能记得的是往事，记不了未来的事情。
The surprise is that that difference between past and future
令人感到惊讶的是，过去和未来的区别
is nowhere to be found in the deep down laws of physics
并不能在物理的定律找到
Time is actually a lot like space if you're out in a space suit flying around
其实时间和空间很相似，如果你穿着太空服在外空中漂浮，
there will be no difference between up, down, left, right
上、下、左、右， 不会有任何差别。
likewise, there is no intrinsic difference between the past and the future in the laws of physics.
相应的，过去与未来在物理定律没有实质的分别。
Now that's not completely a mystery to us
这并非是一件不可思议的事。
we know that what actually happens in the real world
我们知道在现实世界里，真正的是
is that you're not just made of one or two particles bumping into each other,
你不但只是从一个、两个微粒碰撞而组成的，
you're a very very complicated collection of many many particles and they're becoming more disorderly with time.
你实际上非常复杂，是从很多很多的微粒组成的。而且这些微粒随时间变得更混乱。
this is just saying that entropy increases.
这等于说熵在增加。
The interesting thing is that every difference between the past and the future
有趣的是，过去和未来的每一个差别，
will utimately be traced to the fact that the entropy was lower in the past and is growing.
都是因为过去的熵会比较未来低，而且在持续地增加。
That's the Second Law of Thermodynamics
那就是热力学的第二定律。
The universe was orderly, it's becoming more disorderly
世界本来是有秩序的，它变得越来越不条理。
That's not a surprise. There is more ways to be disorderly than to be orderly.
但这并不奇怪，不条理的形态比条理的多。
The suprise is that the universe was ever low entropy to begin with.
奇怪的是世界里的熵一开始已经不低。
If we go all the way back to the Big Bang, 13.7 billion years ago, the universe began in a highly ordered state.
如果我们一直追溯到137亿年前的大爆炸，宇宙开始处于高度有序的状态。
So, modern cosmologists are trying to understand right now why the early universe was in a such precise state.
所以，现代宇宙学家现在正试图理解为什么早期宇宙处于如此精确的状态。
why it was so low entropy.
为什么宇宙的熵那么的低。
Once we understand that,
一旦我们理解了这一点，
it will make perfect sense to us why the arrow of time stretches as it does from the past to today all the way toward the future.
我们就会明白为什么时间的箭头从过去一直指到今天，一直指向未来。
