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Time travel was once considered scientific heresy.
时间旅行曾一度被当作科学邪说
I used to avoid talking about it
由于害怕被贴上科学怪人的标签
for fear of being labeled a crank.
我过去常常避免谈及此事
But these days, I'm not so cautious.
现如今，我不会再顾虑这些
In fact, I'm more like the people who built stonehenge.
实际上，我更像是建造巨石阵的那些人
I'm obsessed by time.
我对时间着迷了
If had a time machine
若我有台时间机器
I'd visit Marilyn Monroe in her prime
我想去拜访鼎盛时期的玛丽莲·梦露
or drop in on Galileo as
或者去拜访正用望远镜
he turned his telescope to the heavens.
眺望星空的伽利略
Perhaps I'd even travel to the end of the universe
我甚至想穿越到宇宙的尽头
to find out how our whole cosmic story ends.
去探寻宇宙的完整故事结局
To see how this might be possible,
要验证这些想法能否实现
we need to look at time as physicists do
我们需要像物理学家那样
as the fourth dimension.
以四维的角度看时间
It's not as hard as it sounds.
四维时空并不像听起来那样令人费解
All physical objects, even me and my chair,
所有的物体，甚至是我和我的椅子
exist in three dimensions.
都是三维的
Everything has a width and a height and a length.
任何事物都有宽度，高度和长度
But there is another kind of length -- a length in time.
但是还存在另一种维度，即时间维度
While a human may survive for 80 years,
与人类的80余年寿命相比
these stones will last much longer
这些石头延续得更久远
-- for thousands of years.
甚至长达数千年
And the solar system will last for billions of years.
而太阳系则能达到数十亿年
Everything has a length in time,
所有事物在时间上都有长度
as well as space.
在空间内同样如此
Traveling in time means
时间旅行意味着
traveling through this fourth dimension.
穿越第四维时空
To see what that means, let's do a bit of normal
为更好地理解，我们以日常旅行为例
everyday traveling just to get a feel for it.
来直观体会一下四维时空的含义
A fast car makes it a bit more fun.
一辆高速行驶的车能让实验变得更生动
Drive in a straight line, and you're traveling in one dimension.
在一条直线上行驶，是在一维空间内
Turn right or left, and you add the second dimension.
左转或右转，就增加了第二维空间
Drive up or down a twisty mountain road,
在蜿蜒的山路上下颠簸
and that adds height.
就增加了高度的维度
So that's traveling in all three dimensions.
这样就算是在三维空间内行驶了
But how on earth do we travel in time?
但我们究竟要怎样才能实现时间旅行呢
How do we find a path
怎样才能找到一条
through the fourth dimension?
通往第四维空间的路呢
Let's indulge in a little science fiction for a moment.
让我们用一个小小的科幻情节放松一下
