白云千载空悠悠.

Your wisdom and generous spirit still guide us, especially now.

Xiaxi turns 20 today!

Hi David,

Today is the last day of the year of tiger and I have thought about you when sending 红包 today in a wechat group.

It has been close to 7 years now I am in China. My interaction with you, although short, was very influential in shaping my life in the last seven years and many decisions I have made. I am grateful that I met you.

I ended up leaving academia by the way, but I am sure you would not mind. You would even probably encourage it. I am happy and as you said to me once that is what matters the most.

Happy new year, I am gonna drink some for you too tonight!

终于下定决心换个赛道开始新的征程…

多么希望能与您分享我现在的思考和打算。

Miss you so much

I visited the site of a favorite boulder of David and myself in Los Alamos yesterday. We often sat there, looked at the views across the Rio Grande, and discussed science projects. Sadly the spot has been built on recently. All things pass -- but wonderful memories remain. Peace!

I cannot believe it has been 5 years since David's untimely passing.  I often think what his comments would be about these days' unsettling events. Also, when I try to solve scientific problems and don't know what to do, I keep thinking that David would know ... He was a very special person.

如果上帝不存在 你已經隨風而逝 如果真的有上帝 你一定是在天堂

上帝把你這麼早帶離這個世界的原因到底是什麼 我能猜到最好的理由是：他看你在這個世上太累了 所以讓你去天堂休息

以你的個性 看到今日的中美貿易科技戰和隱然的軍事對峙 恐怕晚上睡不著覺了

你好好休息 這些事讓我們來處理

在中美對抗的大背景下 中國政府認知到科研的重要性 加上中國的綜合國力持續提升 自然科學研究院蓬勃發展 你的一切努力和付出都沒有白費 我很為你感到高興 你在天有知 也必感欣慰

五年了，时间过得好快。时常会想起以前讨论问题的时光，美好，却又触不可及。

经历的人和事情越多，就越能体会到您看问题的深刻、您与众不同的人格魅力以及对理想的坚守和执着追求。

Five years passed, still remember the great lesson by you. We are on the track of the direction you wished us to go. RIP.

Missing you.

会牢记您当年的教诲，不忘初心。学生很想念您。

最近工作上遇到了一些瓶颈，十分想念以前能与您探讨的日子。

Some updates from Earth.

2022 Nobel Prize of Physics went to quantum entanglement. Since then, previously ridiculed quantum mind theory (actually proposed by another Nobel winner) has resurfaced with an quatum entanglement twist, saying that somewhere in the universe exists a entangled soul receiving one's life experience on earth. These words are coming from some established physicists...
There's another weird thing I stumbled upon. The University of Virginia's medical school has a "Division of Perceptual Studies" that focuses on research of near-death experience and reincarnations. The results (discounting cases of pure illusions) can surely make me superstitious if the handling of data (suprisingly abundant) is indeed scientifically rigorous as the lead psychologists said. They also published a few peer-reviewed papers and books but I haven't got time to check their validity.
No harm in believing right, any comment?

Anyway, miss you.

经历得越多，就约深刻地体会到您当年对我们的教导多重要。

很怀念能与您畅谈人生的经历。

Miss you so much.

您离开我们五年了，想念您。

It has been 4 years already, but the memory of David and his generous spirit is still strong. 

Also, belated Happy 18 to Xiaxi

Cai LaoShi: I can feel but still don't understand death after recently losing an old friend. What does it mean for us scientists? What did it mean to you, and what will it mean to me?

Perhaps a neuroscientific paradigm of the process of death (hopefully, based on computation) can be developed one day. I would be more than interested to read that paper.

---A little student you met six years ago, now writing in Courant

Today is a good day in Shanghai and a good day to memorialize an old friend.

四年了，第一次梦中看到了你曾经的身影，一切都是那么清晰可见。

Miss you so much

Xiaxi turns 18 today.

三十五年前的九月初秋，我在埃文斯顿校园里第一次见到你。你英俊的身姿，潇洒的举止，至今在我的脑海里历历在目。如今又是初秋九月，我带着孩子们重回故地，特在此告慰你在天之灵并祈求你的保佑。 想你，爱你。家林

To Cai's family

Andy Majda and I were not aware of this Tribute site - not until Andy died on March 12, 2021 after a long battle with Parkinson's and his students set up a forevermissed Andrew J. Majda website. So, sorry we didn't know. I come late to write my condolences to you all and let you know how much David Cai meant to us, how close a friend he has been for so many years, how we traveled with him through his illness and still shared many fun moments during his visits to Andy's office during his illness.

Andy and I met you all the first time at the train station in Shanghai upon our return with David from Xian. It was only for a very short time, but I remember it as if it was yesterday. It was such a pleasure to finally meet David's family. The second time we met Jack and David's eldest son at the memorial to David Cai at NYU Courant Institute.

We were very sad loosing David. He was a unique person and dear friend and we often talked about him over the years since. David showed us China and taught us so much of its history, culture, cuisine and beauty that we fell in love with it. Our trip to Xian was a veritable history short course and so fantastic, we marveled how he knew so much of its history. He told us he learned if from his father. An earlier trip was to the Yellow Mountains, which is also unforgettable.

David and Andy were always close friends and enjoyed each other talking about anything from math to life to politics, to eating great food, of his family and kids and so much more. I want to share with you the many photos I've taken on those trips and hope they will be of some help to you.

If there is an afterlife, I would like to think that David and Andy can enjoy and continue their friendship.

Gerta

想念您。

每次站在人生的路口，心里总是无比想念您。

Miss you that much.

我是2020年刚入学的一名致远学院新生，初次听闻蔡先生大名还是在十周年院庆时，知道蔡先生为学院付出了许多的心血。没想到今日竟才听闻蔡先生已经过世！为您和您的家人感到惋惜。我和您虽然素未谋面，但从之前的留言中，我已经对您有了无比的尊敬，感谢您多年来为致远以及自然科学研究院做出的贡献，希望您在天堂一切安好，吾等后辈定不会辜负您对致远的期望。

May heaven have no pain

All of us, David's friends, miss his sparkling mind, gentle sense of humor, universal knowledge, and great generosity.  His spirit will forever be among us.

Also, belated Happy 17 to Xiaxi!

A memorable and fun-loving human. Thinking of him and keeping his name alive, in the name of chaos theory.

每年都要来看看您，也是想提醒自己不忘您当年对我们的教诲。

一个好朋友是人生中的巨大财富!

Xiaxi turns 17 today.

As a student in SJTU,I heard of David from my friends.I mourn for the fall of a star in the sky of physics.

2020.5/26 交大继续教育学院原院长/电信学院特聘教授，教育技术专家，计算机专家申瑞民也逝世了，享年53，比蔡老师还要早。

时间真快，转眼三年已快过去。跟您相识在2003年的暑期班。彼时，您白天穿一赤膊T恤授课，晚上请学生们一起去校外喝茶夜宵，畅聊各种北大趣事。十几年了，这些往年旧事历历在目，不知您在天堂是否还记得？

正值科研压力大的时候，脑海里却常常蹦出蔡老师曾经授课，与学生讨论的一幕幕。多想也拥有您那般的热情与希望。

David邻居回忆他规划致远学院的建设 眼中闪烁着光芒 让我想起Simone Severini分享的那张2011年办公室照片 我从未和David在中国见面 知道他忙 不敢去打扰他 在美国我未曾见过他眼中有如那张照片那样的光芒

有幸曾和蔡老师做邻居，那时候蔡先生应该是刚到交大不久。刚开始只知道这位对门家孩子的爸爸几乎不待家里，忙工作每天只睡4个小时。为了不打扰他休息，他在家的时候孩子们都到我家来玩。对门每几个月就有年轻人来住一段时间，这些都是他一位位从国外挖回来的人才，劝他们买房，直到他们找好住处。那年元宵节前和他在小区花园碰到，蔡教授随口出了很多谜语给孩子们猜，我惊讶之余，网上搜索才发现这是多牛的人：高考状元，数学，物理，生物都有建树，书画皆好，游刃有余。简直是人生偶像啊！记得蔡老师说起张杰校长拎着两个西瓜到他办公室和老师们共度中秋，规划志远学院的建设，眼中闪烁着光芒。春蚕到死丝方尽 蜡炬成灰泪始干。蔡先生千古！

老师，我想念您。

Hello David. My life has changed dramatically since I came to China about three and half years ago, especially in the last two years after you are gone. One thing that has not changed is I frequently remember you. You have left a great influence on my worldview and attitude towards life (and death) despite our very short term interaction.

I am forever grateful. Rest in peace.

David, time goes fast and it has been two years since you left us. Your impact on our life, however, becomes deeper and deeper.

时间过的真快，转眼两年了。时常会想起你的谆谆教诲，受益匪浅。希望你在天堂一切安好！

老师，我很想念你。

"Some people came into our lives and quickly go.
Some people move our souls to dance.
They awaken us to new understanding
with the passing whisper of their wisdom.
Some people make the sky more beautiful to gaze upon.
They stay in our lives for a while,
leave footprints on our hearts,
and we are never, ever the same."

Xiaxi turns 16 today! A handsome young man of 1.8m tall.

David, the Institute of Natural Sciences has just moved to the new Science Building, I will keep making progress and you are always a role model in my life. miss you.

老师，又是一年清明节，学生很怀念您，愿您在天堂一切都好。

意外点开这个网页，但祝蔡老师在另一个世界安好。

Dear David,
I want to let you know that I recently received the tenure-track faculty position offers from Columbia University and University of Chicago, among several others. I was so lucky to have you supervise my undergraduate research, and I can never forget your earnest teachings on how to do research, how to become a good researcher as well as how to enjoy life. As I launch my own academic career, I am driven to be as encouraging and generous with my future students as you was with me. It is a true pity that I cannot share my delight with you in person when receiving these offers. Wish you all the best in the other world!
Forever,
Haihao