Siddhartha Chaibub’s suspicions that the Earth wasn’t really round were first aroused when he stumbled across a YouTube video while living in Brazil’s capital, Brasília.

“I was always very sceptical about things,” said the 35-year-old freelance designer, who soon dived deep into the flat Earth universe: reading, watching videos and joining a dedicated WhatsApp group.

By the end of 2015, he was convinced. “The model that is imposed on us – that the Earth is spherical – is full of contradictions,” he said.

Today, his YouTube channel Professor Terra Plana (Flat Earth Professor) – featuring videos such as “25 examples that prove Nasa is a fraud” and “gravity doesn’t exist” – has nearly 29,000 subscribers.

Like Britain and the United States, Brazil is seeing a revival of flat Earth theory: 7% of the population – 11 million Brazilians – believe that the Earth is flat, according to the polling firm Datafolha. The poll noted believers were more likely to be religious or poorly educated.

Last week, Chaibub and three of his flat Earth fellows got their biggest break yet when they appeared on the country’s most-watched talkshow, The Night, to promote Brazil’s first ever flat Earth convention this Saturday in São Paulo.

The location of the event will only be disclosed on the day, organizers say, for security reasons. “There is a lot of prejudice,” said Chaibub

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Accusations of links to the flat Earth movement have dogged Bolsonaro’s government.

In January, the science minister, Marcos Pontes – South America’s first astronaut – said that he felt a “knot in the stomach” when he heard suggestions that the Earth is flat.

But just a few months later, Olavo de Carvalho – a former astrologer who is considered the intellectual guru of Bolsonaro and his inner circle – prompted outrage and ridicule when he tweeted: “I didn’t study the subject of the flat Earth. I just watched a few videos of experiments that show that aquatic surfaces are flat – and so far I haven’t found anything to refute them.”

Carvalho – who has also claimed Pepsi was sweetened with aborted foetuses and that oral sex can cause cancer – dined with Bolsonaro and Steve Bannon in Washington during the Brazilian president’s state visit to the US in March.

When questioned about flat Earthism, the foreign minister, Ernesto Araújo – an Olavo disciple who believes climate change is a Marxist plot – also seemed sympathetic to the movement, saying: “For me, the Earth is round. But it’s important to have this spirit of questioning,”