Alvin, 66, was deep in the woods in Louisiana, last December when a broken balloon caught his eye. Attached was a piece of paper decorated with sparkly star stickers. It read “Dear Santa, my name is Luna. I am four years old. I live in Liberal, Kansas. This year I have been nice. I would like candy, Spider-Man ball, Frozen doll, puppy. With love, Luna.”

Alvin’s heart hammered in his chest. Ever since he was a child, he had dreamed of this very scene. He believed this was his childhood wish coming true. And he decided to make Luna’s wish come true too. So he posted the Christmas list on his Facebook page, asking for help locating the sender.

Meanwhile, Leticia, the mother of four-year-old Luna, had no idea that such an effort was underway. It had been a hard year for them. On a particularly tough day last December, Leticia told Luna to send her wishes to Santa by balloon. The girl was excited. Leticia helped her write down her wishes, put the note into a Christmas red balloon and took her out to release her wishes on the chilly windy morning.

One day in January, a friend called Leticia, “Someone found Luna’s balloon.” Her jaw dropped. Then she logged on to Facebook and saw Alvin’s post and more netizens trying to help. Leticia was deeply touched and called Alvin. When Alvin told her how much it would mean to him to fulfill the girl’ wishes, she agreed to let him meet Luna. Back in Louisiana, Alvin got busy collecting toys from his newfound Facebook community.

On a morning in April, just as chilly and windy as the day when Luna waved goodbye to her balloon, Alvin made a trip to their house. He presented all the gifts, including a puppy. Luna cried with delight. Later, they sat down together to share homemade breakfast. They all felt as if they had known each other forever. Having received so much generosity, Leticia and Luna expressed their gratitude and intended to pay it forward.

Hawking died early Wednesday at his home in England at the age of 76. Throughout his career as one of the world’s most recognizable cosmic（宇宙的） thinkers, he regularly threw himself into pop culture’s comedic ring with cameos（客串）on programs such as The Simpsons and Late Night with Conan O’Brien.

These appearances defined（使明确） Hawking’s personal life as much as his universe-shaking theoretical work. Humor, however, was not just one side of his personality, but a key to overcoming the disease he struggled against since 1963.

“Keeping an active mind has been vital to my survival, ashas been maintaining a sense of humor,” Hawking said in a 2013 documentary. “I am probably better known for my appearances on The Simpsons and on The Big Bang Theory than I am for my scientific discoveries.”

At 21, Hawking was diagnosed with a condition similar to amyotrophic lateral sclerosis（肌萎缩性侧索硬化症）, also known as Lou Gehrig’s disease. According to the ALS Association, “Half of all people affected with ALS live at most three or more years after diagnosis. Twenty percent live five years or more; only ten percent will live more than ten years.”

The disease would eventually shut down Hawking’s motor functions, making him speechless and unable to move without a wheelchair. Doctors initially（最初） said he would be dead in two years. His condition, however, proved to be a rare slow-acting version.

But Hawking fought through his worse physical state, rising to a position as a celebrated professor of mathematical at the University of Cambridge and altering the popular conception of physics with his 1988 bestseller, A Brief History of Time.

“When I turned 21, my expectations were reduced to zero,” he said in a TV show. He added, “It was important that I came to appreciate what I did have. It’s also important not become angry, no matter how difficult life is, because you can lose all hope if you can’t laugh at yourself and at life in general.”