Swerve with verve: Oscar Niemeyer, the architect who eradicated the straight line

One of the things that strike you on arriving at Oscar Niemeyer's studio on the top floor of a Rio de Janeiro apartment block is that it is a smoking zone. He and several of his associates enjoy small cigars – "I used to smoke very little, but now I smoke more, when I'm working, between one problem and another..."

There is also a grand piano, some of the architect's doodles on the walls, and a stunning vista of Copacabana beach, the Sugar Loaf and Rio's other mountains. At 102 years old, Niemeyer still comes to work every weekday. Instead of having to walk up the stairs from the top landing to his studio, he uses a specially installed lift, but there are few other concessions for the man who, some seven decades ago, broke the stranglehold of the right angle and the straight line on Western architecture.

"In our work, we are always looking to surprise. Because that Bauhaus idea that architecture has to be purely functional was absolute nonsense. Architecture can be both practical and beautiful. It can amaze. Our buildings set out to meet the required specifications, but people also want something a little inventive, that will confound their expectations. The aim is to turn architecture into a work of art, the main features of which are generating emotion and astonishment. That's what gives me the greatest pleasure. We're seeking an architecture that's lighter and freer, with few supports, so that it becomes more daring and creates a more generous space, where people can behave in a new way."

Niemeyer talks in a deep, sonorous voice, and for someone who learnt his trade with Le Corbusier in the 1930s and almost single-handedly designed the monumental buildings of the new capital, Brasilia, in the late 1950s, is remarkably unassuming. "Our concern is political too – to change the world," he says. "Architecture is my work, and I've spent my whole life at a drawing board, but life is more important than architecture. What matters is to improve human beings."

Though brought up in a devout Catholic family, Niemeyer joined the Brazilian Communist Party (PCB) in 1945, and a picture of Luiz Carlos Prestes, the historic leader of the party, hangs on his studio wall. "We are asking for so little. We want people to be equal, in accordance with each person's capabilities," he says. "We want people to regard each other fraternally, without looking for faults. We're all in the same boat – we should be living with our hands joined."

For the past five years, Niemeyer and his colleagues have had a weekly visit from a physicist who leads seminars on philosophy, history and the cosmos. "We emerge from a session on the cosmos feeling smaller, more modest, that we're really not so important. But we should at least be loyal, and keep faith with others. Why so much fighting? Human beings are full of good qualities and foibles, and our weakness in the face of the universe should make us more conscious, more humble, more supportive of each other. But young people grow up, they don't read anything but only learn about subjects relevant to the profession they choose, and they turn into specialists. One talks only about architecture, another only about engineering, another about medicine..."

Indeed, Niemeyer is scathing about higher education in Brazil. "When students leave college, they are like children who know nothing about the problems of life, and don't have a political stance." He and his second wife – Vera Lucia, who had been his secretary of 14 years when they married in 2006, following the death in 2004 of his wife of 76 years, Annita Baldor – have launched a magazine, Nosso Caminho (Our Path), to try to counteract this specialisation. "It is ostensibly about architecture, but takes in literature, philosophy and many other things with the aim of making young people more idealistic, showing them that they live in a selfish world and should try to improve it."

Niemeyer's own contribution has been to dream up an array of buildings that reject the concept of monotonous architecture and challenge the status quo – often, too, the laws of gravity. "In architecture today you can make use of all the possibilities of reinforced concrete. There is no reason to design buildings that are more basic and rectilinear, because with concrete you can cover almost any space." He is currently working – as always, in close collaboration ' with a structural engineer – on a design for an arts complex in Asturias, Spain, including a 40m dome which can be erected in a matter of days, with concrete poured into an inflatable mould. "It's like magic."

The sinuous curves of Niemeyer's buildings, some with improbable exterior walkways suspended in mid-air, are often coloured his trademark white. They reflect his aim to convey beauty and harmony through the simple geometry of the structure itself, rather than adornment and decoration. As he has famously said: "What attracts me is the flowing, sensual curve. The curve which I find in the mountains of my country, in the body of a favourite woman, the clouds in the sky and the waves on the sea. The whole universe is made of curves – Einstein's curved universe."

Niemeyer first made a splash designing audacious buildings in Pampulha, a suburb of Belo Horizonte, in 1940 for the city's mayor, Juscelino Kubitschek. Nearly two decades later, when Kubitschek was president of Brazil, they renewed their collaboration to conjure Brasilia out of a strategically located area of scrubland. "It was the success of Pampulha that gave us courage to build Brasilia. The problems were bigger, but there was the same idea of wanting to create something useful."

The cathedral in Brasilia, completed in 1970, is perhaps Niemeyer's most iconic building. I wonder whether, as a confirmed atheist, he had found it uncomfortable to design. "The Catholics in my family were very good, honest people, so I felt at ease because of that. And the project of a cathedral is fantastic – you can do what you like. You have the problem of light to resolve. I remember how much I enjoyed designing the cathedral, making those prefabricated curves and hanging them up. The challenge of a cathedral is very good for architectural inventiveness. I like talking to priests, to Catholics. Everyone has their beliefs. I've designed a mosque too [in Algeria] – they gave me the plan and I carried it out."

And, 40 years later, Niemeyer is still adding to the distinctive skyline of the Brazilian capital. "We've designed a new television tower more than 100m high. Halfway up there is a large information and lookout point. It's a new and different kind of tower – no one has built anything like it." He is also proposing a new central square for Brasilia to ease congestion around the nearby bus station and provide an attractive focal point for city events. It features a soaring triangular structure – also more than 100m high – that would make the square unique and memorable.

Such flamboyant designs have attracted some critics, but Niemeyer is no stranger to conflict. He was on a boat to France when, in 1964, the military seized power in Brazil. "They went to my studio and trashed it." His political affiliation forcing him into exile, Brazil's loss was France's gain, as the architect received special dispensation to work there, designing, among other buildings, the elegantly undulating French Communist Party (PCF) headquarters in Paris.

"The dictatorship was 20 years of misery and violence. I stayed in France several months, but when I returned to Brazil the police hadn't forgotten me. On my first day back I was taken to make declarations about this and that. Some of my friends were tortured, but I didn't suffer that. I was humiliated. A number of times I was detained for several hours. They would interrogate me in an enormous room full of tables and police officers. I was made to talk to all the officers, so they would know who I was. But fortunately things changed."

Niemeyer is positive about the current Workers' Party (PT) government led by President Luiz Inácio "Lula" da Silva. "Capitalism is crap, it's in decay, but we're living at a moment that allows us a certain hope. Our president is a worker, he's linked to the people and linked to the defence of Latin America, which has been under such threat. He is on the side of Fidel and Chavez. He is a fighter, and that pressure from the Americans which has threatened us all our lives is gradually coming to an end. We don't want to quarrel with anyone, but we do want our own laws and independence, our sovereignty." His view of Brazilian society at large is less rosy. "Everything is a fight over money. Today, the prevailing force is egoism, a lack of understanding of life, of how human beings can be fairer. And we badly need agrarian reform – the land belongs to everybody."

As for the future of the Earth, his vision is, well, apocalyptic. "I think the planet has grown tired. In the next 40 years, things are going to change a lot. The sea level could rise by more than two metres, and all the coastal cities will have to be moved. It may get so hot that people have to create gardens on the roofs of apartments, cover open spaces with vegetation. Then there is the problem of water..."

Despite his international prestige, Niemeyer charges architect's fees at the lower end of the professional scale, and chose to design Brasilia on a civil servant's wage. And although his work is "informed by protest and rebellion", he has always rejected the idea that flights of imagination should be geared to political commitment, or that his designs should be simplified and made more accessible. "Architecture is one thing. Politics is about creating a better world. The day when the people have more influence, architecture will be different. Houses will be more modest, and great human undertakings – theatres, stadiums and cinemas – will be even bigger because everyone will have access to them. At present, an architect has to work for governments and for the rich, while the poor are outcasts who have to look on from afar. The rich in Brazil – the ignorant elite – are cooped up in their luxury apartments, and poor people in the shanty towns are regarded by them with disdain, almost as enemies. But that is starting to change."

Niemeyer travels regularly to the town of Niteroi, across the bay from Rio, where he is designing a series of buildings along the scenic coastline. "It is a big effort for me to go there, but you have to try to set an example, and we want to make sure that the work is carried out well." While there, he takes the opportunity to talk to groups of architecture students who come from as far afield as São Paulo and Brasilia. His advice to them is to read widely. "You have to read to be informed. Everything is interconnected. It's no good being ignorant."

He still enjoys a full life, and has no remaining ambitions, but is busy with new projects – the latest a commission for a vast square in Kazakhstan. "Things are difficult. You get older and find yourself saying goodbye to people. Life doesn't make a lot of sense. But it's more meaningful if the will to be useful and to help your neighbour predominates. Human beings have to be realistic. We live, die and see others die – at the very least there should exist a spirit of solidarity."