In 1962, a cave explorer named Michel Siffre started a series of experiments
1962年，米歇尔·西弗雷，一名岩洞探险者，开始了一系列的试验，
where he isolated himself underground for months without light or clocks.
把自己封闭在地下数月，那里没有光也没有表。
He attached himself to electrodes that monitored his vital signs and kept track of when he slept and ate.
他通过连接的电极片来监测自己的生命体征，并记录下何时吃饭、睡觉。
When Siffre finally emerged, the results of his pioneering experiments
当西弗雷最终出关时，这一系列实验结果
revealed that his body had kept to a regular sleeping-waking cycle.
表明他的身体保持了规律的作息周期。
Despite having no external cues, he fell asleep, woke up, and ate at fixed intervals.
尽管没有外界的线索，他入睡、起床和吃饭都在特定的时间段。
This became known as a circadian rhythm from the Latin for 'about a day.'
这就是昼夜节律，源于拉丁文，意思是‘一日’。
Scientists later found these rhythms affect our hormone secretion,
科学家后来发现这个节律会影响激素分泌，
how our bodies process food, and even the effects of drugs on our bodies.
对食物的消化，甚至是药物对身体的药效。
The field of sciences studying these changes is called chronobiology.
研究这一领域的学科叫做时间生物学。
Being able to sense time helps us do everything from waking and sleeping
我们做任何事都离不开对时间的感知能力，比如起床和入睡
to knowing precisely when to catch a ball that's hurtling towards us.
以及判断何时接住呼啸而来的球。
We owe all these abilities to an interconnected system of timekeepers in our brains.
这些能力都归于我们脑中互联的计时系统。
It contains the equivalent of a stopwatch telling us how many seconds elapsed,
它集合了记秒的秒表，
a clock counting the hours of the day, and a calendar notifying us of the seasons.
报时的时钟，播报季节的日历于一身。
Each one is located in a different brain region.
每个计时器都处在大脑不同的区域。
Siffre, stuck in his dark cave, relied on the most primitive clock in the suprachiasmatic nucleus, or SCN of the hypothalamus.
困在黑暗的洞穴里，西弗雷依靠最原始的计时器，它们位于下丘脑的视交叉上核（SCN）中。
Here's the basics of how we think it works based on fruitfly and mouse studies.
基于果蝇和老鼠实验，我们认为其原理是这样的。
Proteins known as CLK, or clock, accumulate in the SCN throughout the day.
被称为CLK的蛋白，也读作clock，在一天中都在SCN中积累。
In addition to activating genes that tell us to stay awake, they make another protein called PER.
在激活那些让我们保持清醒的基因的同时，产生另一种被称为PER的蛋白质。
When enough PER accumulates, it deactivates the gene that makes CLK, eventually making us fall asleep.
当PER积累到足够的量，它会给制造CLK蛋白的基因一个负反馈，最终使我们进入梦乡。
Then, clock falls low, so PER concentrations also drop again, allowing CLK to rise, starting the cycle over.
之后，clock的浓度降低，PER的浓度也随之降低，使得CLK的浓度回升，开始了新一个轮回。
There are other proteins involved,
这一过程不乏其他蛋白质的参与，
but our day and night cycle may be driven in part by this seesaw effect between CLK by day and PER by night.
但我们的昼夜循环受到这样一个在白天的CLK和夜晚的PER之间跷跷板效应的驱使。

For more precision, our SCNs also rely on external cues like light, food, noise, and temperature.
为了变得更精确，我们的SCN也会依赖外界的线索，比如光、食物、噪音还有温度。
We called these zeitgebers, German for 'givers of time.'
我们把这些称作zeitgebers，德语中的意思是“时间之源”。
Siffre lacked many of these cues underground, but in normal life, they fine tune our daily behavior.
西弗雷在地下时缺乏这些线索，但在日常生活中，他们对我们的行为进行微调。
For instance, as natural morning light filters into our eyes, it helps wake us up.
比如说，一束晨光射到我们眼睛里，唤醒了我们。
Traveling through the optic nerve to the SCN, it communicates what's happening in the outside world.
穿过视神经传到了SCN，传达着外界正在发生的事情。
The hypothalamus then halts the production of melatonin, a hormone that triggers sleep.
下丘脑于是不再产生褪黑素，一种触发睡眠的荷尔蒙。
At the same time, it increases the production of vasopressin and noradrenaline throughout the brain,
同时，在大脑中，下丘脑增加对抗利尿激素和去甲肾上腺素的分泌，
which help control our sleep cycles.
如此帮助我们管控睡眠周期。
At about 10 am, the body's rising temperature drives up our energy and alertness,
早上10点左右，逐渐升高的体温促使我们的能量和警觉性提升；
and later in the afternoon, it also improves our muscle activity and coordination.
傍晚，我们的肌肉活力和协调性也得到提升。
Bright screens at night can confuse these signals, which is why binging on TV before bed makes it harder to sleep.
夜间的亮光会扰乱这些生物信号，这就是为什么在睡前长时间看电视会导致失眠。
But sometimes we need to be even more precise when telling the time,
然而有些时候我们需要更准确的知道时间，
which is where the brain's internal stopwatch chimes in.
这就是脑内秒表发挥作用的时候。
One theory for how this works involves the fact that
关于它的工作原理，一种臆测认为，
communication between a given pair of neurons always takes roughly the same amount of time.
任意一对神经元间的信号传递大致总是一个特定的时长。
So neurons in our cortex and other brain areas may communicate in scheduled, predictable loops
所以我们大脑皮层和其他区域的神经元，在一个设定的、可预测的环路传递信息，
that the cortex uses to judge with precision how much time has passed.
大脑皮层就从这一机制来精确判断过去了多少时间。
That creates our perception of time.
我们的时间概念由此产生。
In his cave, Siffre made a fascinating additional discovery about this.
在洞里时，西弗雷还有另一个有趣的发现。
Every day, he challenged himself to count up to 120 at the rate of one digit per second.
每天，他都会挑战自己，以每秒一个数字的速度数到120。
Over time, instead of taking two minutes, it began taking him as long as five.
随着时间的推移，从开始的用时2分钟，到后来用时可以长达5分钟。
Life in the lonely, dark cave had warped Siffre's own perception of time despite his brain's best efforts to keep him on track.
在孤寂、黑暗的洞穴中的生活，使得西弗雷的时间概念也扭曲了，尽管他的大脑很努力的使他保持正轨。
This makes us wonder what else influences our sense of time.
这就使得我们想知道还有什么会影响到我们对时间的感知。
And if time isn't objective, what does that mean?
如果时间不是客观的，这又意味着什么？
Could each of us be experiencing it differently? Only time will tell.
可不可能我们每个人对时间的感受都不同？只有时间会给出答案。