霍金，飞
Hawking, Flight
一、零
二十一岁。一个人刚到剑桥不久，正在读博士。他想知道宇宙从哪里来。医生开始告诉他，他自己的时间可能不多了。
1963年，斯蒂芬·霍金被诊断患有运动神经元疾病。据后来的记述，当时的预后大约只有两年。
两年。
从确诊算起，他又生活了约五十五年。
多年后，他把二十一岁时的期望形容为降到了零，把后来得到的生活看作额外所得。
这句话很容易被做成一张海报。海报上只有病和胜利，中间没有时间。
可是一个人不是每天早晨醒来，都已经知道自己会活到七十六岁。他醒来时，仍然是那一天。问题还没算完。身边的人还要生活。下一年会不会来，下一项工作能不能完成，并没有人预先保证。
零不是一种幸福。零是未来忽然缩小以后，眼前还剩下的一页纸。
他没有等到纸上重新印出五十五年的保证，才开始写。
二、身体关掉了
他的行动能力逐渐减少。走路、书写、说话，这些原先可以直接完成的事，越来越需要别的办法。
1985年，一场肺炎之后，他接受了气管切开术，失去了原来的声音。最初，别人指着拼字卡上的字母，他用眉毛的动作作出选择。后来，沃尔特·沃尔托兹提供的 Equalizer 程序让他能够用手中的开关选词，再交给语音合成器说出来。再往后，手部控制继续衰退，脸颊动作与眼镜上的传感器接过了开关的工作。
门在关。但门不是自己又打开的。
有人做手术，有人照料起居，有人写程序，有人调整设备，有人等他把一句话说完。他与简·怀尔德在1965年结婚，后来有了三个孩子。家庭、同事、学生与照护团队，不是放在一位独行天才身后的布景。
一张拼字卡。一个开关。一段等待。
他并不是因为不能走，就不再需要世界；也不是因为不能说，就从此不受琐事打扰。困难没有替他清空生活，供他专心思考。困难占用了时间，耗费了力气，需要别人付出劳动。
然而，借助这些劳动，他仍然能够选择那个词，而不是另一个词。能够同意，能够反对，能够改掉屏幕上的一句话。
机器发出声音。句子由他决定。
三、黑洞会发光
1974年，霍金发表《黑洞爆炸？》。第二年，更完整的计算以《黑洞的粒子创生》发表。
黑洞不是完全黑的。
在经典图景里，事件视界是一条单向边界：里面的光不能再传到遥远的外部。可是一旦把量子场纳入计算，远处观察者所描述的情形就变了。黑洞具有温度，会产生热辐射；在向外辐射超过吸收时，它会损失质量。
这是一项理论计算。贝肯斯坦此前已经提出黑洞熵的问题；霍金接过这个问题，把计算继续往前推。
大众叙述常把它画成一对粒子：一个落进去，一个逃出来。那幅小图可以帮助想象，却不能代替推导，更不等于普通信号已经能从事件视界内部爬出来。蒸发的最后阶段，也不能仅凭这幅小图就宣布全部解决。
计算改变了一堵墙的含义。它没有取消所有的墙。
你以为一件事已经被最后一句话说完，后来发现，那句话还得重写。
黑洞只能吞进去吗？在什么理论里？把什么遗漏了？
他不是靠愿望让黑洞发光。他把计算做到了旧答案不再够用的地方。
四、他和罗斯福
两个使用轮椅的人。
富兰克林·罗斯福的公开形象经过安排，轮椅通常不出现在正式照片里，站立则需要支架与协助。并不是没有轮椅照片留下；他的身体也不是靠镜头的角度恢复了行动能力。
霍金的轮椅和电子声音，却成为公众辨认他的一部分。
两张照片，隔着不同的年代，也隔着不同的公众期待。我们会先注意那把椅子：藏起来了，还是露出来了。可照片之外还有一天一天的生活，有坐在上面的人想做的事。镜头没有拍进去的，也属于他。
2007年4月26日。霍金六十五岁。他参加了改装波音727飞机的失重飞行。
飞机沿抛物线飞行，在短暂的近似自由落体阶段，舱内出现失重体验。地球的引力没有消失。他的病也没有消失。
可是，他离开了轮椅，飘在机舱里。
照片上，他在笑。画面里还有照护和保护他的手。有人护住头部，有人照看身体的位置。飞起来的不是一个终于摆脱身体的灵魂，而是这个具体的人，穿着飞行服，在一架具体的飞机里。
支撑并没有败坏那一刻的轻盈。支撑使那一刻发生。
这也不是一张要求所有病人振作起来的通知。他没有义务代表所有人赢过疾病。他只是想体验一次失重，而这一次，他体验到了。
几十年里，他在研究引力。那一天，他还想知道暂时不被座椅托住，是什么感觉。
五、时间的形状
1988年，《时间简史》出版。它在英国《星期日泰晤士报》畅销书榜上停留了237周。
一本关于宇宙的书，到了本来不会翻物理论文的人手里。
写作跨过了他失声前后不同的交流方式；出版前的修订阶段，他使用手控开关的计算机系统。编辑、解释、重写，也是这本书到达读者所经过的路。
书里的问题却没有因此变小。时间有没有开端？宇宙是否有边界？如果我们坚持问开端之前发生了什么，那个“之前”一定有意义吗？
1983年，詹姆斯·哈特尔与霍金发表关于宇宙波函数的论文，提出后来著名的无边界方案。它尝试用量子宇宙学中的边界条件来描述宇宙，而不是在通常的时间开端之外，再摆一个等待宇宙启动的时钟。
霍金常用南极作比方。你一路向南，到了南极，还能不能继续向南？不是前面砌着一道禁止通行的墙，而是这个方向在这里不能照原样延长。
这是一种帮助理解提案的比喻。它不等于观察已经证实了宇宙的初始形状，也不是对一切宇宙模型发布的“从来没有之前”的裁决。
但它使一个平常的词变得陌生：之前。
我们太习惯时间像一条永远铺好的路。事情可以没有发生，路总应该在。霍金和哈特尔问的却是：那条路本身是不是也需要解释？
时间也许有形状。而形状，不一定是我们先画好的那一条直线。
六、他和费曼
费曼在这个系列里带着鼓。霍金带着轮椅。
两个人都生活在身体里，也都依靠语言、数学、同伴和工具。
他们之间还存在一条比性格相似更实际的线。费曼发展的路径积分，把量子演化写成对可能历史的振幅求和。霍金在讲解他与哈特尔的宇宙学工作时，明确借用了这个办法。
鼓声不会变成方程。但一个人的数学方法，确实可以进入另一个人的宇宙。
费曼写下的那些计算，到了霍金和哈特尔的纸上，又伸向了一个新的问题。翻过一篇，看见下一个人；上一页并没有因此合上。
霍金也喜欢把严肃的问题摆成一个玩笑。他曾为时间旅行者准备聚会，却把邀请留到聚会以后才公布。没有客人赴约。
笑话的好处，不是它会替你解决难题。它让难题不必变成一张永远紧绷的脸。
费曼可以敲鼓。霍金可以安排一场迟发邀请的聚会。两个人不需要用同一种方式，才能把好奇心保留下来。
他们也没有把宇宙全想明白，再回来向大家报告。他们把已经想明白的一部分，和仍然卡住的地方，一起交了出来。
鼓声之后还有问题。电子声音停下以后，也还有。
七、那把椅子
2018年11月8日，佳士得拍卖了一把霍金用过的电动轮椅。成交价296,750英镑。
这件拍品约制于1988年，是他先后使用过的多把轮椅之一，拍卖所得用于支持斯蒂芬·霍金基金会与运动神经元疾病协会。
椅子是会磨损的。设备要换，零件要调。一个人的身体条件改变，原来合适的位置就可能不再合适。
拍卖目录可以列出制造者、尺寸和出处，却装不下这些调整中经过的全部日子。
在这个系列的画面里，我们曾把奥本海默、罗斯福和霍金放在不同的椅子上：一把朝向洛斯阿拉莫斯，一把朝向公共事务，一把朝向宇宙。
霍金这把真正留下来的椅子，先是一件让他移动、工作、见人和出门的工具。
可是有人坐在这里，把关于宇宙的问题交给了椅子以外的人。
如今椅子留了下来。问题没有随它停止移动。
八、牛顿的椅子
还有一把不是家具的椅子。
剑桥大学卢卡斯数学教授席位。牛顿曾经担任的职位。1979年至2009年，霍金在这个席位上工作了三十年。
同一个名称，不同的时代。
牛顿力学为许多运动提供了可以计算的秩序。但“知道初始条件便能知道一切”，不是一张覆盖所有物理问题的无限通行证，更不意味着每个复杂系统都容易预测。
到了霍金这里，问题越过了经典描述独自能够处理的范围：引力、量子理论、热、信息，怎样在同一幅图景里相处？
不是牛顿铺的地板忽然都成了废料。许多地方，它仍然承重。只是走到极端处，人开始看清它的适用范围，开始问，下面还需要什么。
霍金没有从那下面带回一套已经完成的万有理论。他留下了结果，也留下了仍需工作的接缝。
2018年6月15日，他的骨灰安葬于威斯敏斯特教堂，靠近牛顿和达尔文的墓。
一个职位传下去，一些方程留下来，后来的人继续检查：这里还稳吗？那里是不是还有问题？
椅子可以有继任者。问题不保证按任期结束。
九、飞
2018年3月14日。剑桥。霍金在家中去世，七十六岁。
约五十五年，从那个二十一岁的年轻人算起。
有些日子在工作，有些日子在医院。有别人的时间，有机器的故障，有论文上的修改。有一次，他穿着飞行服，离开轮椅，漂浮在空中。
传记到这里停下。这个系列的桥还在。
桥头又多了一个人。他坐着。
先让轮椅落在桥面上。让路有足够的宽度。让等待他说完话的人，不抢走他还没有说出的那半句。
在桥头的想象里，椅子慢慢离开了地面。
苏格拉底站在空地上。柏拉图蹲着画图纸。休谟守着双陆棋盘。叔本华看桥底下。克尔凯郭尔已经跳了。图灵看苹果。契诃夫靠着栏杆。康托尔看天上。哥白尼放下书走了。萨特转来转去。波伏瓦举着镜子。蒯因说了一句话。
特斯拉听嗡嗡声。爱迪生拿着灯泡。海森堡的位置不确定。玻尔拿着没寄出的信。托尔斯泰拿着药方。莎士比亚不在。斯宾诺莎手里有玻璃粉。亚里士多德蹲着铺地板。法拉第蹲着掀地板。麦克斯韦站着写方程。
贞德带着火，飘在上方。王尔德站得很好看。拉马努金从缝隙里冒出半个身子。奥本海默背着灰。夏洛蒂·勃朗特拿着笔。艾米莉·勃朗特在荒原上。玻尔兹曼抱着石头。梵高身上有颜料。狄更斯站在裂缝上面。丘吉尔背着旗。罗斯福坐在轮椅上，手边有一截坡道。薛定谔抱着猫。费曼在碎片上跳舞打鼓。
现在，霍金也在上方。
贞德带着火。霍金带着一个尚未想完的宇宙。
她往下看。他往上看。
费曼抬起头，鼓声停了一下。他等着霍金把那句话说完。问题已经到了另一人手里，回答还没有来。桥上一时只听见风，鼓仍搁在他的膝上。
远处，康德还站着。
通向目的王国的路，不该先问一个人能不能站起来。走过去，坐着过去，被协助着过去，不能因此分成不同等级的人。
在这幅画里，霍金的轮椅缓缓向前。桥没有因为他升起来就变得多余。照护没有因为他能思考就变得多余。有人铺路，有人接线，有人等候，而方向不是由他们替他指定。
身体的限制，没有替他说完生命的全部。
他在空中。
托住他的手，也在。
注释
[1] 生平与交流工具参遗产官网、2017年NHS演讲、Intel及科学博物馆资料。手控开关与后来脸颊传感器属于不同阶段；“期望降到零”为2004年访谈的间接转述。
[2] 黑洞辐射依据1974、1975年理论工作；粒子对仅为示意。1983年哈特尔—霍金无边界方案仍是理论提案。失重飞行、轮椅拍卖及教席资料见下列影像记录、佳士得与剑桥来源。
[3] 桥头飞行是文学想象，现实失重飞行中霍金离开了轮椅并得到工作人员协助。照护与辅助技术支持他的选择，不意味着疾病制造天才，或成就决定一个人是否值得照护。
I. Zero
At twenty-one, he had barely arrived at Cambridge. He was beginning a doctorate and asking where the universe had come from. Then his own future became the urgent question.
Stephen Hawking was diagnosed with motor neurone disease in 1963. Later accounts describe a prognosis of about two years.
Two years.
He lived for roughly fifty-five years after the diagnosis.
Looking back, he described his expectations at twenty-one as having fallen to zero, and the life that followed as something extra.
Put that on a poster and the story becomes wonderfully simple. Illness at one end. Triumph at the other. No time in between.
But he did not wake every morning knowing that he would reach seventy-six. He woke into that particular day. There was unfinished work. There were other people with lives of their own. Nobody had promised the next year, or the completion of the next calculation.
Zero is not a form of happiness. It is a page left in front of you when the future has suddenly become smaller.
He did not wait for a guarantee of fifty-five more years before making a mark on it.
II. The Body Shut Down
Movement became harder. Walking, writing, speaking: activities that had once been direct began to require another route.
After pneumonia and a tracheostomy in 1985, Hawking lost his natural speaking voice. For a time, another person pointed to letters on a spelling card; he selected them by moving his eyebrows. Walt Woltosz's Equalizer software subsequently enabled him to choose words with a hand-operated switch and send them to a speech synthesiser. Much later, as hand control deteriorated, a sensor on his glasses detected movements of his cheek.
Doors were closing. They did not reopen by themselves.
There were operations, care, software, adjustments, and the time somebody spent waiting for a sentence. Hawking and Jane Wilde married in 1965 and had three children. Family, colleagues, students, and carers were not scenery behind a solitary mind.
A spelling card. A switch. A pause long enough for someone else to grow impatient.
Being unable to walk did not release him from needing the world. Losing speech did not conveniently protect him from small talk. Disability consumed time and effort; it did not clear his diary for cosmology.
Yet with assistance he could still choose this word rather than that one. Agree. Object. Delete a sentence on the screen.
The sound came from a machine. The sentence was his to decide.
III. Black Holes Glow
In 1974 Hawking published “Black hole explosions?” A fuller calculation appeared the following year as “Particle creation by black holes.”
Black holes were not entirely black.
In the classical description, an event horizon is a one-way boundary: light inside cannot reach distant observers outside. Add quantum fields to the calculation and the picture changes. A black hole has a temperature and emits thermal radiation. When it loses more energy than it absorbs, its mass decreases.
This was a theoretical result. Jacob Bekenstein had already raised the question of black-hole entropy; Hawking carried the calculation further.
Popular explanations often offer a little picture of two particles, one falling in while the other escapes. A useful picture is not a derivation. It does not mean that ordinary messages have found a route from inside the horizon to the outside, or that the last instant of evaporation has thereby been explained.
The calculation changed what a boundary meant. It did not abolish every boundary.
Something seems settled by a final sentence. Then the sentence has to be written again.
Black holes can only take things in? Within which theory? What has been left out?
Hawking did not make them glow by wishing. He carried the calculation to a place where the previous answer was no longer enough.
IV. Hawking and Roosevelt
Two men who used wheelchairs.
Franklin Roosevelt's public appearances were carefully arranged. His wheelchair generally stayed out of official photographs; standing required braces and assistance. Some wheelchair photographs nevertheless survive. A camera angle did not restore his mobility.
Hawking's wheelchair and electronic voice, by contrast, became part of his public recognisability.
Two photographs, separated by their periods and by what the public expected to see. Our eyes go first to the chair: hidden, or visible. Outside the frame, though, are ordinary days and things its occupant wants to do. What the camera leaves out belongs to his life too.
On 26 April 2007, aged sixty-five, Hawking took a flight aboard a modified Boeing 727.
The aircraft followed parabolic arcs, allowing brief periods of approximate free fall and the experience of weightlessness. Earth's gravity had not gone away. Neither had his illness.
But he left his wheelchair and floated inside the cabin.
In the photograph he is smiling. Other hands are visible too, protecting his head and attending to his position. This is not a soul finally released from a body. It is a particular person, wearing a flight suit, aboard a particular aircraft.
Assistance does not spoil the lightness of the moment. It helps make the moment possible.
The photograph is not an instruction to every ill person to try harder. Hawking had no obligation to defeat disease on anybody else's behalf. He wanted to experience weightlessness. On that day, he did.
For decades he had studied gravity. He also wanted to know what it felt like, briefly, not to be supported by a seat.
V. The Shape of Time
A Brief History of Time appeared in 1988. It remained on the Sunday Times bestseller list for 237 weeks.
A book about the universe reached people who were unlikely to open a physics journal.
The writing passed through different means of communication before and after he lost his voice. During revisions before publication, he operated the computer with a hand switch. Editing, explanation and rewriting were part of the book’s journey to its readers.
The questions did not become small. Did time have a beginning? Did the universe have a boundary? If we ask what happened before the beginning, must that “before” make sense?
In 1983 James Hartle and Hawking published their paper on the wave function of the universe. Their no-boundary proposal sought a quantum-cosmological description without simply placing another clock outside the conventional beginning and leaving it waiting for the universe to start.
Hawking liked the analogy of the South Pole. Travel south until you reach it. Can you then continue farther south? There is no wall across the route. The direction cannot be extended in the way your question assumes.
An analogy helps introduce a proposal. It is not an observation establishing the initial geometry of our universe, nor a verdict that every possible cosmological model must contain no earlier phase.
Still, an ordinary word has become strange: before.
We imagine time as a road already laid. Nothing may have happened yet, but surely the road must be there. Hartle and Hawking asked whether the road itself required an explanation.
Time might have a shape. And that shape need not be the straight line we drew before beginning to think.
VI. Hawking and Feynman
Feynman enters this series with a drum. Hawking arrives with a wheelchair.
Both lived in bodies. Both worked through language, mathematics, companions and tools.
There is a more substantial connection than a resemblance of temperament. Feynman's path-integral approach describes quantum evolution through a sum of amplitudes associated with possible histories. When explaining the cosmological work he developed with Hartle, Hawking explicitly invoked this method.
A drumbeat does not turn into an equation. But one person's mathematics can enter another person's universe.
Calculations Feynman had put on paper reach toward a new question on the pages of Hawking and Hartle. We turn to the next life. The preceding page has not quite closed.
Hawking also knew how to stage a serious question as a joke. He prepared a party for time travellers and withheld the invitation until afterwards. Nobody came.
Humour need not solve the difficulty. It can keep difficulty from demanding a permanently solemn face.
Feynman could play his drums; Hawking could arrange a party with a late invitation. Curiosity did not require them to perform the same gestures.
Nor did either first work out the entire universe and then return to tell everyone. They handed over things they had understood together with things they could not yet resolve.
Questions after the drumbeat. Questions after the electronic voice falls silent.
VII. The Chair
On 8 November 2018, a motorised wheelchair used by Hawking sold at Christie's for £296,750.
This one was made around 1988, one of several he used. The sale benefited the Stephen Hawking Foundation and the Motor Neurone Disease Association.
Chairs wear out. Equipment needs replacing; components require adjustment. As a person's requirements change, yesterday's workable arrangement may cease to work.
An auction catalogue can record dimensions, maker, and provenance. It cannot contain all the days that passed through those adjustments.
Within this series, three imagined chairs face in different directions: Oppenheimer's towards Los Alamos, Roosevelt's towards public affairs, Hawking's towards the universe.
The actual chair that survives was first of all equipment for moving, working, meeting people, and going out.
Someone sat there and gave questions about the universe to people beyond the chair.
Now the chair remains. The questions have not stopped travelling.
VIII. Newton's Chair
There was another chair, one that was not furniture.
The Lucasian Professorship of Mathematics at Cambridge: a post once held by Newton. Hawking occupied it from 1979 to 2009. Thirty years.
The same title, different times.
Newtonian mechanics made many kinds of motion calculable. But “know the initial conditions and you know everything” is not an unlimited passport through physics. Nor is every complex system straightforward to predict.
Hawking worked where a classical description by itself would not suffice. How could gravity, quantum theory, heat, and information inhabit a coherent account?
Newton's floor had not suddenly become useless rubble. In many places it still carried weight. At the extremes, however, its reach became visible, and with it the question of what further structure was needed.
Hawking did not return with a finished theory of everything. He left results, and joins at which there was still work to do.
On 15 June 2018 his ashes were interred in Westminster Abbey, near the graves of Newton and Darwin.
A post passes on. Equations remain. Other people return to inspect the work: does this still hold? What happens over there?
A chair can have a successor. A question need not respect the end of a term.
IX. Flight
14 March 2018. Cambridge. Hawking died at home, aged seventy-six.
Roughly fifty-five years from that twenty-one-year-old student.
There was work, and there were days in hospital. Other people's time. Equipment that needed attention. Revisions on a page. Once, there was a flight suit and the experience of floating outside his chair.
The biography stops. The bridge in this series remains.
Another person has arrived. He is sitting.
First put the wheels on the bridge. Leave enough room. Let the person waiting for a sentence refrain from taking away the half that has not yet been spoken.
In the bridge’s imagined world, the chair slowly rises.
Socrates stands in the clearing. Plato crouches over a plan. Hume is at his backgammon board. Schopenhauer peers below the bridge. Kierkegaard has jumped. Turing looks at an apple. Chekhov leans on the railing. Cantor looks upwards. Copernicus has put down his book and left. Sartre paces. Beauvoir holds a mirror. Quine has said something.
Tesla listens to a hum. Edison holds a light bulb. Heisenberg's position is uncertain. Bohr carries an unsent letter. Tolstoy holds a prescription. Shakespeare is absent. There is glass dust on Spinoza's hands. Aristotle lays the floor. Faraday lifts a board. Maxwell writes equations.
Joan of Arc floats above them with fire. Wilde stands beautifully. Ramanujan has appeared halfway through a gap. Oppenheimer carries ash. Charlotte Brontë holds a pen; Emily Brontë is on the moors. Boltzmann cradles a stone. Van Gogh wears paint. Dickens stands over a crack. Churchill carries a flag. Roosevelt sits in his wheelchair with a section of ramp beside him. Schrödinger holds a cat. Feynman dances on fragments and plays his drum.
Hawking is above them now.
Joan carries fire. Hawking carries a universe not yet thought through.
She looks down. He looks up.
Feynman raises his head. The drum falls silent while he waits for Hawking to finish his sentence. The question has changed hands; the answer has yet to come. For a moment there is only wind on the bridge, the drum still resting on his knees.
Far away, Kant is still standing.
The road towards a kingdom of ends should not begin by asking whether a person can stand. Walking, riding, arriving with assistance: these cannot be grades of personhood.
In this picture Hawking's chair moves slowly forward. The bridge has not become unnecessary because he rises above it. Care has not become unnecessary because he can think. Some lay a route, some connect a wire, some wait. They do not therefore acquire the right to choose his direction.
The limits of his body did not have the last word on his life.
He is in the air.
The hands supporting him are there too.
Notes
[1] Biography and communication equipment: the estate, the 2017 NHS speech, Intel and the Science Museum. Hand switches preceded the later cheek sensor. The remark about expectations is an indirect paraphrase of the 2004 interview.
[2] Radiation refers to the theoretical work of 1974–75; particle pairs are a heuristic image. The 1983 Hartle–Hawking no-boundary proposal remains a theoretical proposal. Flight, auction and professorship details are documented in the linked image records, Christie’s and Cambridge sources.
[3] The bridge’s flight is literary imagination. During the real weightless flight, Hawking floated outside his wheelchair with staff assistance. Care and technology supported his choices; illness does not create genius, nor does achievement determine entitlement to care.