Frank Wilczek

弗兰克·维尔切克是麻省理工学院物理学教授、量子色动力学的奠基人之一。因在夸克粒子理论（强作用）方面所取得的成就，他在2004年获得了诺贝尔物理学奖。

一个物理学家的游乐园体验报告

作者 | Frank Wilczek

翻译 | 梁丁当

校对 | 秋水

配音 | 李娜（蔻享学术）

在课堂里学F=ma（力等于质量乘以加速度）是一回事，坐过山车则是另外一回事。和物理学来一次亲密接触是非常令人振奋的，比方说，在游乐园里。最近我就畅游了一个漂亮的游乐园。

F=ma (force equals mass times acceleration) is one thing, a roller-coaster ride is another. It’s bracing to encounter physics in visceral ways—for example, in an amusement park. Recently I went to a beautiful one.

1986年，当我第一次访问斯德哥尔摩时，我一眼就注意到了绿色隆德（Gröna Lund）游乐园。它具有古典的帝沃力风格[1]，坐落在斯德哥尔摩水系的大动脉，索特斯翰（Saltsjön）湾。远远看着绿色隆德游乐园，听着不时传来的诱人的尖叫声，我想起了我在纽约长岛度过的童年时光，想起了那些小小的游乐园和流动的狂欢节。

In 1986, when I first visited Stockholm, Gröna Lund was one of the first things I noticed. It is a classic, Tivoli-style amusement park, situated on Saltsjön bay, the aorta of Stockholm’s watery arteries. Seeing Gröna Lund from a distance, and hearing the lusty shrieks and squeals it inspired, summoned up happy memories of the comparatively paltry amusement parks and mobile carnivals of my Long Island childhood.

此后，去这个游乐园游玩成了我一个小小的心愿。2004年12月，当我回斯德哥尔摩领取诺贝尔物理学奖的时候，我对绿色隆德游乐园满怀期待--但令人失望的是，它不在冬季开放。

A visit to the park has been on my bucket list ever since. When I came back to Stockholm in December 2004 to receive the Nobel Prize in Physics, I looked wistfully toward Gröna Lund—but sadly, it was closed for the season.

几周前，我终于如愿以偿来到了绿色隆德游乐园。斯德哥尔摩的夏日阳光灿烂，白日漫长，我完全放松，像孩子一样尽情游玩了几乎一整天。不过偶尔有几次，我还是会像物理学家一样思考一番。

A few weeks ago, I finally got there. For most of a gloriously long Stockholm summer day, I went with the flow, being like a kid again. But a few times, I got to thinking like a physicist.

游乐园的趣味屋提供了一个有趣的应用物理谜题。它的入口在二层，你必须通过一对运动的扶梯才能达到。常见的自动扶梯是把你的身体或上或下运到某处，但这对运动的扶梯不是这样。它们是想把你的思维从日常的模式中运出去。趣味屋的扶梯在不停地变化--一会儿向上几步，一会儿向下几步。如果你站在某级台阶上不动，你不会有任何进展。如果这些台阶间隔合理，你完全可以忽略它们的运动，踏着它们直接上去。但这些台阶的间隔很大，令人进退维谷。

One intriguing puzzle in practical physics was posed by the park’s funhouse. The entrance is on the second floor, and you access it through a pair of movable stairways. Normal escalators are designed to transport your body somewhere, either up or down. But this pair is different. They’re designed to transport your mind elsewhere, out of everyday routine. The funhouse stairways vacillate—a few feet up, then a few feet down. If you stand still on a step, you’ll make no progress. If the steps were reasonably spaced, you could just walk up them, basically ignoring their motion. But the distance between the steps is quite large, so that’s awkward.

为了前进，你必须利用两个扶梯是反向运动的这一事实：一个向上另一个就向下。此处的诀窍是逆直觉而动（你行动前最好花点时间想一下行动方案）。

Instead, you can exploit the fact that the two stairways are out of sync: When one goes up, the other goes down. The smart thing to do is counterintuitive. (You might take a moment to try to figure it out.)

窍门如下：如果想往上，你应该往下走，在另一个扶梯向下周期快结束时踏上去，然后让它带你自动向上。按照这个方式，集中精神，你会毫不费力走上去。但是，我注意到几乎所有的人都在费力地抓住扶梯边的绳子狼狈地踉跄向上。我走了两遍：一次是利用我大脑的额叶（它掌控学习能力），按照那个逆直觉方案走；另一次是利用我的小脑（它控制运动能力），勉强地疾冲上去。

Here’s the trick: To go up, you should step down, catch a step near the bottom of its cycle and let the moving stairs do the work. If you keep your wits about you, the physical part is easy. But almost everybody I saw just blundered through, holding on to the side ropes and pulling. I did it twice—once the easy yet counterintuitive way, using my frontal lobes (which control problem-solving), and once by improvised scampering, using my cerebellum (which handles motor control).

游乐园里还有一个物理学家必玩的项目：“自由落体”，也叫雷克斯•路瑟[2]的死亡之坠 (Drop of Doom)。玩法很简单：坐在椅子里，系好安全扣，然后你被拉到80米高空--突然绳索打开，你开始下落。大约有四秒时间，你完全在自由落体。玩过的朋友警告我说这个非常吓人。我用爱因斯坦的引力理论来宽慰自己：“弗朗克，你就要完全顺从时空的安排，按最自然的方式运动了。”这个安慰对我还真管用了。

The park has another ride that’s a must for a physicist: Fritt Fall (Free Fall), also known as Lex Luthor’s Drop of Doom. The ride is simplicity itself. Strapped into a little cocoon, you are lifted to a height of 80 meters—then your cable suddenly cuts free and down you go. For about four seconds, you’re in free fall. Friends who had done the Drop of Doom warned me that it was terrifying. Channeling Einstein, I prepared by telling myself, “This is the natural state of motion, Frank: For once, you’re going to do what space-time wants you to do.” That worked for me.

当下落停止时，我瞬间感受到了一个三倍半的重力加速度，也就是说，觉得自己的体重达到了原有的三倍半。电影里常常有受难者在撞击的瞬间被超级英雄拉起，从而免受冲击的场面。我们物理学家会说，这非常“不物理”。无论你的减速是由路面、水面或超级英雄造成的，它都会对你造成伤害。

As the ride brought me to a stop, I briefly experienced a G-force of 3.5 gs—in other words, I felt 3½ times my normal weight. You know those movie scenes where the superhero saves a plummeting victim from impact by scooping them up at the last second? They are, as we say, “unphysical.” Whether it’s imposed by pavement, water or superhero, it’s the deceleration that gets you.

不过我最喜欢的项目还是“日食”。我悬在400英尺的高空，坐在一个金属条做成的秋千里，被一个26英尺长的链条带着以每小时40英里的速度旋转。刚开始，我有些不安。于是我提醒自己时间平移不变原理--物理规律是不随时间改变的--如果头10秒没问题我预测后面也不会有问题。我对离心力也非常信任，它把我牢牢摁在已经几乎垂直的椅子上。我似乎变成了一只鸟，轻松地飞翔在斯德哥尔摩上空。真爽！

But my favorite ride was the Eclipse. It takes you 400 feet in the air, where you rotate at more than 40 miles an hour, attached to bare-bones swings on chains that are 26 feet long. At first, I felt uneasy. But I reminded myself of time-translation symmetry—the principle that the laws of physics don’t change—and deduced that if the first 10 seconds of the ride went fine, the rest would too. I also trusted the phenomenon of centrifugal force, which kept me pressed to my nearly vertical seat. I flew over Stockholm with an easy mind, pretending to be a bird, high.

注释

[1] 帝沃力 (Tivoli)：意大利地名，在罗马附近。这里有因喷泉闻名世界的埃斯特别墅 (Villa d' Este)。18世纪末巴黎建了世界上最早的游乐园，以帝沃力命名。后来的游乐园多仿照它的风格。丹麦哥本哈根有一个著名的游乐园，就叫帝沃力乐园 (Tivoli Gardens)。

[2] 雷克斯•路瑟 (Lex Luthor)：一个超级反派角色，首次出现在《动作漫画》(Action Comics) 第23回中（1940年4月）。

声明：该文章曾于2016年--2017年间以专栏形式发表于《赛先生》公众号，后经作者授权发布于蔻享学术平台。

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