I recently gave Stephen Hawking a boomerang1. It was an odd2 gift to give the worlds most famous scientist, but Stephen immediately understood its significance.

When I gave it to him, he flashed me the same wise, slightly mischievous grin that I had sought—and was occasionally rewarded with—when I was a rather intimidated young doctoral candidate under his supervision at Cambridge nearly 30 years ago.3

What I discovered about Stephen back then, and what I still admire now, is that his intellect and stamina are rivalled only by his irrepressible sense of humour.4

Hence the boomerang. It was an inside joke nearly three decades in the making. To understand its punchline5, we must boomerang ourselves back to 1983.

In the late fall of that year, I nearly dropped out of my physics studies at Cambridge, fully convinced I was going to flunk6 my freshman year anyway. But after my father summarized my prospects as a dropout—flipping7 burgers back home in Quebec, as he put it—I decided to give my studies one last shot.

It was gruelling8. I studied around the clock, depriving myself of any semblance9 of a social life. Apart from my once-weekly bicycle ride around Cambridge, I was practically an invisible man.

But someone, it turned out, had noticed me. The day our final exam scores were revealed—in a Draconian10 ritual during which all students test scores were read aloud in a courtyard for all to hear—a classmate approached me. “Professor Hawking would like to see you,” he said.

My stomach flip-flopped11. “Prof. Hawking,” I thought, “wants to see me?” This was a terrifying development.

The world at large had not yet learned of Stephens genius, but we Cambridge students were certainly aware of it, and unanimously in awe of it.12 As I slowly descended the stone staircase toward his office, I was certain hed be able to hear my knees nervously knocking together.

Stephen, it seems, had got wind that my exam scores were at the top of the class, and he wanted to see if Id make a good doctoral candidate to take under his wing.13

I dont remember much about the conversation that ensued14, but what I do recall is that Stephen gave me a list of books and papers to read over the summer and said hed see me in the fall.

You bet I read those books and papers, and thus began my year with Stephen—a year that forever changed who I am as a scientist, and as a person.

He put me straight to work that fall. He had recently hypothesized that, in a contracting15 universe, time would go in reverse. My job was to mathematically prove it.

I dove right into the assignment, but there was a hitch: The math just didnt add up.16 No matter which way I sliced the problem, time continued its eternal forward march, even when the universe itself made an about-face.17

Imagine my trepidation18 at the prospect of telling Prof. Hawking—the Stephen Hawking—he was wrong.

And he wasnt easily convinced. Countless afternoons were spent with me at the blackboard and him insisting I must have oversimplified19 something, or failed to consider some other thing.

That was around the same time that Stephens health went into serious decline. It was heart-wrenching20 to see a man of such energy betrayed by his own body. As his students helped him accomplish the kind of everyday tasks most of us take for granted, we forged a bond that ran far deeper than any teacher-student relationship.21

Stephen wasnt about to let his illness interfere with his academic life, and our blackboard sessions quickly resumed. After months of debate, and with the assistance of postdoctoral fellow Don Page, I convinced Stephen that, contracting universe or not, time soldiers22 ahead, forever clockwise. Little did I know this cosmological tidbit would find its way into A Brief History of Time, the book that made Stephen a scientific superstar.23

When I left Cambridge a few years later, Stephen personalized my copy of the book with a printed note inside the front cover. It reads: “To Raymond, who showed me that the arrow of time is not a boomerang. Thank you for all your help. Stephen.”

I still smile when I look at that dedication24. It so nicely captures the quick wit and warmth Stephen always exuded, even after ALS robbed him of his mobility and his voice.25

I learned a lot about the universe from Stephen, but I believe I learned even more about spirit. He taught me as much about courage and humility as he did about black holes and quantum mechanics26. Its a debt I fear Ill never be able to repay.

But make him chuckle27—that I could do.

In 2010, Stephen spent a summer in Waterloo, Ont., home of the University of Waterloos Institute for Quantum Computing, of which I am executive director.

I invited him to drop by the institute, an invitation he happily accepted. He spent the day visiting labs, meeting researchers and, I think, learning some new things about quantum information science. His scientific curiosity remains voracious and insatiable.28

The grad students who met him in Waterloo that day were as awestruck29 and inspired as I was in my Cambridge days.

At the end of his visit, I gave him the boomerang, a nice wooden one with smooth curves and a gleaming varnish.30

Yes, the boomerang was a silly inside joke, but it was more than that. It was a way of saying that, although time is indeed an arrow, it has a way of bringing our lives—and the people most important to us—full circle.

1. boomerang: 回力棒，回飛棒（扔出去能飛回的彎曲棒）。

2. odd: 古怪的，奇怪的。

3. mischievous: 惡作劇的，好搗亂的；intimidated: 緊張的，害怕的。

4. stamina: 耐力，持久力；rival: 比得上，可與……媲美；irrepressible: 壓抑不住的，控制不了的。

5. punchline: （笑話、演說或幽默故事中的）點睛妙語，關(guān)鍵語。

6. flunk:〈口〉（考試）不及格，沒通過（考試）。

7. flip: （使）快速翻轉(zhuǎn)。

8. grueling: 累人的，讓人筋疲力盡的。

9. semblance: 少量某物。

10. Draconian: 嚴厲的，殘忍的。

11. flip-flop: 翻轉(zhuǎn)。

12. the world at large: 全世界；unanimously: 全體一致地。

13. wind: 風聲，消息；under sb.s wing: 在某人的庇護下。

14. ensue: 接著發(fā)生。

15. contract: 收縮，縮小。

16. dove: dive的過去式，全身心投入，探究；hitch: （不嚴重的）問題，故障；not add up:不合情理。

17. eternal: 永恒的；about-face:（朝反方向的）倒轉(zhuǎn)。

18. trepidation: 恐懼，緊張，惴惴不安。

19. oversimplify:（使）過于簡單化。

20. wrench: 扭傷。

21. forge: 建立；bond: 親密的聯(lián)系。

22. soldier: 繼續(xù)下去。

23. cosmological: 宇宙學的；tidbit: 趣聞，花絮；A Brief History of Time: 《時間簡史》，是由英國偉大的物理學家、黑洞理論和“大爆炸”理論的創(chuàng)立人斯蒂芬·霍金撰寫的一本有關(guān)宇宙學的經(jīng)典著作，是一部將高深的理論物理通俗化的科普范本。

24. dedication: 題獻，獻辭。

25. exude: 充分顯露（某種特質(zhì)）；ALS: amyotrophic lateral sclerosis的縮寫，肌萎縮性側(cè)索硬化。

26. quantum mechanics: 量子力學。

27. chuckle: 輕聲地笑，暗自笑。

28. voracious: 渴求的；insatiable: 不知足的。

29. awestruck: 充滿敬畏的。

30. gleam: 閃爍；varnish: 清漆，罩光漆。