BEIJING (XINHUA) - Many elderly Chinese spend their retirement looking after grandchildren or travelling the world, but Mr Bai Wuming, 62, reignited his career by popularising science.
Retiring after a 40-year career in geophysics, Mr Bai has presented more than 800 lectures on earth science in schools across the country, including remote rural areas.
He likes to open with the words, "science is all around us", before lighting up his talk with small experiments.
To show how volcanoes erupt, Mr Bai invites a student to pour sugar in a bottle of beer. The sugar produces carbon dioxide that makes the beer spray up immediately.
"I remember my high school textbook also mentioned volcanoes, but my teacher did not do that experiment," says Mr Zhang Hao, a graduate student.
Mr Bai is one of 60 members of Senior Scientists Public Lectures, an organisation under the Chinese Academy of Sciences. Established in 1997, the team of speakers mainly comprises retired researchers in fields including astronomy, physics, chemistry and biology.
The oldest member is aged 90, but their average age is 68.
Mr Zhong Qi, founder of the original team of just eight, says most of the team had little previous experience of popularising science despite dedicating their careers to their research.
"I remembered my teenage years in the 1950s, which were a crucial time for me to develop my mind and body," Mr Zhong recalls. "If we senior scientists can communicate with people and arouse their interest in science and inspire them to explore the unknown world in their youth, I think it would be good for them and our work."
These senior scientists still take a rigorous attitude when selecting retirees who apply to join the team.
Regardless of titles and awards, all applicants must deliver a report and rehearsal. If the audience feels the lecture is difficult to understand, the application can be declined. Those expecting to find fame will be rejected, too.
"You have to make your lectures interesting. It can be difficult trying to explain a formula clearly to the public. So I don't think popularising science is easier than doing research," says geologist Xu Wenyao.
To ignite audience interest, Mr Xu always makes a music analogy in his lectures.
"There are two tenors. Can you tell which one sings better?" Mr Xu asks. "Musicians say each has his merits, beyond description. But we scientists can use data, curves and equations to analyse their voices."
It's a winning formula.
"Many students get a headache when it comes to sciences, especially maths, physics, and chemistry. I am always thinking how to make these subjects accessible," Mr Xu says.
The retirees also expect their young audiences to learn the spirit and method of scientific research. They also keep learning. They have mastered making PowerPoint presentations and videos, as well as writing jokes, stories and lyrics that fill lecture rooms with laughter.
By 2017, the association had delivered 23,000 lectures mainly in primary and high schools to a total audience of 8.2 million. They also lectured to people at community events, in jails, the military and temples.
They have crossed hills and rivers, braved freezing cold and extreme heat to reach remote rural schools.
"I remember once I lectured in a playground, because the rural primary school did not have an auditorium. But the pupils listened carefully, without any distractions," recalls Mr Xu.
"It's an opportunity to communicate with scientists in school," says Mr Yang Xinghua, head of Tangshan Oriental International School, in north China's Hebei Province.
Chinese President Xi Jinping has described scientific innovation and popularisation as "the two wings for realising innovation-driven development".
More public figures and organisations have emerged in recent years, working on science popularisation through social media, but the retired scientists hope more researchers will take up the cause.
Mr Bai says their advantage lies in their years of research. "The content of our lectures is based on the research we have done, which was real and scientific. We don't allow our speakers to download content from the Internet."
He says the team is especially looking for experts in emerging subjects such as artificial intelligence and ocean science.