加速流逝的时间

你是否记得，当你还小的时候，暑假似乎永远不会结束。对我的两个孩子来说，一年似乎是一段长到无法想象的时间。相比之下，随着我们年龄的增长，时间似乎以惊人的速度流逝，几天像滚雪球一样变成几周，再变成几个月，最后都成为过去。当我循例每周与我70多岁的父母聊天时，他们给我留下的印象是几乎没有时间接我的电话，而是奔波于他们日程表中的活动。然而，当我仔细询问他们如何度过一周时，我发现对我来说，他们一周完成的活动我似乎在一天之内就能搞定。我由此知道与时间赛跑的压力有多大：我得照顾两个孩子，做一份全职工作，还要好好写一本书。

然而，我不应该对我的父母过于苛刻，因为随着我们变老，时间的流逝看起来确实越来越快，我们也越发感到时间不够用。 ^[30] 在1996年进行的一项实验中，一群年轻人（19~24岁）和一群老年人（60~80岁）被要求在头脑中默数3分钟。平均来说，年轻组的用时差不多是3分3秒，而老年组的用时是3分40秒。 ^[31] 在其他类似的实验中，参与者被要求估计他们执行任务的用时。 ^[32] 与年轻组相比，年老的参与者对他们的用时估计一直较短。比如，时间已经过去了两分钟，而老年组觉得只过去了50秒，而且他们都很困惑其余的1分10秒去了哪里。

我们对时间感知的加速，与我们挥手告别无忧无虑的青春时光并且开始承担成年人的责任之间没有多大关系。事实上，对于为什么随着年龄的增长我们对时间的感知会加速这个问题，存在着很多不同的解释。一种理论认为这与人类的新陈代谢随着年龄的增长而减缓的事实有关，时间加速是为了和我们的心跳和呼吸减慢相匹配。 ^[33] 正如秒表被设置为快速运行那样，这些“生物钟”的儿童版本运行得更快。在固定的时间段内，小孩会经历更多个生物起搏器的周期（比如呼吸或心跳），使他们感觉已经过了很长时间。

一个与之不同的理论表明，我们对时间流逝的看法取决于我们从环境中获得的信息数量。 ^[34] 新的刺激越多，大脑花在处理信息上的时间就越长，在回忆的时候，相应的时间段似乎也会显得更长。这个观点可用于解释为何在事故发生前的瞬间，我们的大脑会像放电影一样以慢动作播放事故的全过程。对受害者来说，由于其遭遇的事故是完全陌生的场景，因此信息量非常大。在事故发生期间，对事故的回忆可能会减慢，因为大脑会根据它所收集的大量数据形成更详细的记忆。针对受试者进行的自由落体实验证实了这一看法。 ^[35]

这个理论与我们为何会感受到时间加速流逝可以很好地契合。随着年龄的增长，我们越来越熟悉自己的生活环境和经历。那些曾经漫长而富有挑战性的旅途不再有吸引力，那些在我们转错弯的路口会邂逅的风景也变得日渐熟悉。现在，我们的人生就是自然而然地往前走，失去了发现新风景的动力。

但是，儿童的世界是充满了未解之谜的奇妙之地。青少年时期的我们不断重建关于周围世界的模型，这需要精神上的努力，所以从他们的角度看，时间的流逝似乎比成年人更慢。我们对日常生活中的各类经历越熟悉，我们就会越快意识到时间的流逝，而且一般来说，随着年龄的增长，这种熟悉度会不断增加。这个理论表明，为了让我们感知到的时间变得更长，我们应该用丰富的新体验把我们的生活填满，避免平庸单调。

但上述两种观点都无法解释我们对时间的感知似乎在以相同的速率增加。随着年龄的增长，我们对某个时间段的感知似乎会持续减少，这表明时间在以指数方式加速。当我们需要测量在大范围内变化的量值时，通常会采用指数尺度，而不是传统的线性尺度。最常见的例子是声音或地震活动等能量波的测量尺度。在地震单位里氏震级中，从10级到11级意味着地壳运动的强度增加了10倍，而不是像线性尺度那样增加了10%。里氏震级能够捕捉到墨西哥城在2018年6月的低能级震颤，当时墨西哥球迷正在世界杯足球比赛上庆祝墨西哥队对德国队的一粒进球。里氏震级也能够记录下智利瓦尔迪维亚1960年发生的9.6级地震，它释放的能量相当于25万颗在广岛投下的原子弹。

如果一段时间在我们感知中的长度与我们的年纪成比例，指数模型就是有意义的。作为一个34岁的人，一年占据我的生命将近3%，这些年我的生日似乎过得太快了。但对一个10岁的孩子来说，等待下一次生日礼物却需要很大的耐心。对我4岁的儿子来说，他在等待他的下一个生日到来期间仿佛度过了1/4的生命那么漫长，这几乎让他无法忍受。在这个指数模型中，一个4岁大的孩子在相邻两个生日之间感知到的时间流逝，相当于一个40岁的人过到50岁时感知到的时间流逝。从这个角度看，时间随着年龄的增长而加速流逝的说法似乎是成立的。

将我们的人生以10年为计量单位来划分是非常常见的：无忧无虑的20岁，认真负责的30岁……这表明对人生的每个时期应该给予相同的权重。然而，如果时间确实以指数方式加速，那么我们人生中时间跨度不同的阶段就可能有着相同的感知时间。在指数模型下，年龄从5到10岁、10到20岁、20到40岁、40到80岁可能看起来同样长（或短）。不要急于给自己的人生立下太多目标，在指数模型下，从40岁到80岁之间的40年（包括中年和老年的大部分时间）可能会像你5岁到10岁之间的5年那样飞快地消逝。

福克斯和查尔莫斯因为实施“给与拿”金字塔计划而被捕入狱，监狱生活的例行程序或感知到时间的指数式加速应该使她们感觉到服刑时间过得很快，这对她们而言也不算坏事。

共有9名女性因参与该计划而被判刑。虽然有些人也被判偿还他们在该计划运作期间赚取的部分钱款，但投入的数百万英镑中能收回的只是少数。无法获得偿还的投资者因为低估了指数增长的力量而失去了一切。

从核反应堆爆炸到人口爆炸，从病毒传播到病毒式营销，指数增长和指数衰减在普通人的生活中发挥着至关重要的作用。对指数行为的探索催生了科学分支的形成，有些技术可以用来给罪犯定罪，有些技术会摧毁世界。缺少指数思维的思考方式可能像不受控的核链式反应一样，会造成不可预料的后果。此外，以指数增长的技术进步促进了个人化医疗时代的到来，现在，任何人都能以可承受的代价对自己的DNA（脱氧核糖核酸）进行测序。只要现代医学背后的数学框架能得到应有的完善，这种基因组学革命就有可能为我们的健康指标提供前所未有的洞见，我们将在下一章讨论这一点。

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[3] 1盎司 ≈28.3克。——编者注

[4] 1英寸= 2.54厘米。——编者注

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[28] 1公顷 = 10 000平方米。——编者注

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