Stephen Hawking takes the stage at his 75th birthday celebration. (Facebook Live photo)

An auditorium erupted in a chorus of “Happy Birthday to You” followed by traditional cheers of the English “Hip Hip Hooray” on Sunday at a 75th-birthday celebration for famed physicist Stephen Hawking.

Following lectures by British physicist Brian Cox and gravitational-wave researcher Gabriela González, Hawking took the stage at Cambridge University in England to reflect on his past 75 years.

“Actually, for those keeping count, I am closer to 75 and a half, but that shouldn’t get in the way of a good celebration,” he joked, using his computer-generated voice.

Hawking’s birthday is actually in January, but Cambridge organized the conference as a belated birthday present.

The wheelchair-riding physicist put the jokes aside as he talked about his early life. The most emotional part of the talk came when Hawking recalled how he became aware of his disability as a young graduate student in 1962.

“At that time, it became clear something was not right with me,” Hawking recalled.

During the Christmas break, he stumbled while skating with his mother. “I fell over, and had great difficulty getting up again,” Hawking said.

That led to weeks of hospital tests, but his doctor left him in the dark about his condition, which turned out to be amyotrophic lateral sclerosis, a crippling neurodegenerative disease.

“At first, I became depressed. I seemed to be getting worse pretty rapidly,” he said. “There didn’t seem to be any point in working on my Ph.D. because I didn’t know if I would live long enough to finish it.”

But his story quickly turned into a tale of hope as he made progress on his work and started his family.

“After my expectations had been reduced to zero, every new day became a bonus, and I began to appreciate what I did have,” he said.

Hawking’s success continued to rise, proving that with technology’s help, he could continue his work and communicate with the world.

Now Hawking is worried about a new challenge having nothing to do with his medical condition or black holes: namely, climate change.

During a pre-conference interview with the BBC, he spoke out against President Donald Trump’s decision to pull out of the Paris climate agreement and said that global warming could become irreversible.

“Trump’s action could push the Earth over the brink, to become like Venus, with a temperature of 250 degrees and raining sulphuric acid,” he said.

Unless action is taken to curb industrial carbon dioxide emissions, the world will be at great risk in the years to come, he said. Hawking envisions future generations turning to space settlement as a cosmic insurance policy, and for that reason he’s a strong proponent of space exploration.

“I don’t think we will survive another 1,000 years without escaping beyond our fragile planet,” he said. “I therefore want to encourage public interest in space — and I’ve been getting my training in early.”

Like what you're reading? Subscribe to GeekWire's free newsletters to catch every headline

Job Listings on GeekWork

Find more jobs on GeekWork. Employers, post a job here.