The next sound you will hear in Tate Modern's turbine hall is a lot of very excited screaming. I always thought the space would make a great adventure playground and that is pretty much what it is becoming now. For the next Unilever installation, German artist Carsten Holler has built five enormous, stainless steel slides swooping down into the hall, including one that falls five storeys from the top floor. He says it is impossible to go down a slide without smiling so he hopes to see a lot of happy faces. But he also hopes that even people who have no desire to go down the slides will still enjoy looking at them as sculpture. And they are lovely - silver arabesques swooping through the cavernous gloom.
Normally, the Tate tries to conceal whatever is being installed in the turbine hall, but visitors have been able to see the slides under construction for some weeks now. Holler says he had no desire to keep them secret (and anyway it would be quite difficult to conceal a five-storey slide) - 'I don't like the idea of surprise really. The surprise will be how it looks and how it appeals to people, both people watching and people going down. There is a lot of fun in watching other people.'
The problem with the turbine hall is its vast size, but also the awkwardness of the space, approached, as it is, by a long ramp and bisected by a dark bridge and stairs. Some artists, such as Rachel Whiteread and Louise Bourgeois, have decided to ignore the ramp and confine their work to the area behind the bridge which makes it easier, but possibly less dramatic.
Anish Kapoor used the whole length of the hall for his Marsyas and solved the ramp problem by suspending it from the roof. Bruce Nauman solved it by working only in sound. But probably the most successful of the Unilever commissions so far, in terms of popularity at least, was Olafur Eliasson's Weather Project, a giant sun at the end of the hall that had whole families and school groups sprawled on the ramp as if sunbathing in the park. Visitors seemed to know what to do with a giant sun, whereas they weren't so sure what to do with previous installations. Presumably Holler's slides will have the same effect.
Holler admits that the turbine hall is daunting and gets more so for every artist who attempts it because nobody wants to copy what has gone before. 'You cannot work with sound because Nauman has done it; you cannot make a big light at the end because Eliasson has done it. I decided right from the beginning that I wanted to work with the height of the hall, not so much the length. And I was confident with slides because I have done them before. But the bridge is a problem, in the middle of everything. For Rachel Whiteread's Embankment, for instance, it was somehow in the way. But we will have all the slides landing under the bridge, to wake up this space. At the moment, it looks as though the architect forgot about it, but I will make it very special.'
The slides are quite wide (wide enough for me, anyway) and roofed with translucent polycarbonate acrylic glass. For the higher slides, you will have to don a cotton sack, because there is a danger that heavy people, especially if wearing acrylic clothes, can go too fast and burn themselves. Everyone will have to get a ticket with a time slot to avoid queuing and there will be guards top and bottom to move people along.
Is Holler worried about accidents? 'Yes, I do worry. We have to make sure that from the construction point of view that they're as safe as we can possibly make them and we know from other slides that they are very safe. They are much safer than stairs; stairs are quite dangerous. These are built to German safety standards which the British inspectors are very happy with because they have the reputation of being the best in the world.'
Holler seems an unlikely progenitor for this giant's playground. Bespectacled and geeky, with a bulging forehead, even at 44, he looks like the sort of boy who was always called Brains at school. Or, actually, he looks like what he was in a previous life - Dr Carsten Holler, leading research entomologist. His doctoral thesis was on aphid hyper-parisitoids and demonstrated that a plant infested by aphids can send out a smell that attracts aphid predators, almost like a cry for help.
He only gave up scientific research in 1994 when his career as an artist took off. Nowadays, he says he doesn't like being called Doctor - 'That is my past life.' His life is full of these sharp disjunctions. He grew up in Brussels because his father worked for the EU, then studied agriculture at Kiel and worked as a scientist in Germany. When he became an artist, he lived for some years in Cologne, but then married a Swedish artist, Miriam Backstrom and moved to Stockholm. Now he is building a house in Ghana, to avoid the Swedish winters. It will have a slide.
Much of his work is playful. Apart from slides, he has made goggles through which you see the world upside down, carousels and rooms with amanita mushrooms growing down from the ceiling. He likes to play with perception, to disconcert the viewer, to shake them out of their normal certainties and induce what he calls 'radical doubt'.
He came to fame in 1990-93 with an exhibition of devices for catching and killing children; one, for instance, was a swing fixed to the roof edge of a high-rise building. Was he really such a paedophobe? 'Well, now I have a daughter I've changed my mind! I never hated children, but I hated the idea of making children, the whole reproductive process. There's no freedom if you cannot get rid of the biological machinery that makes us decide to do this thing and not that thing. I thought very much about how you could break that chain. I was determined and convinced that I would not have children.'
So what happened: did he fall in love? 'I fell in love all the time! Very much so, even more, because I would not have children. But I think once you have really explored a certain conviction, it is time to give it up. I don't think you should go on holding it for the rest of your life. So I thought it was time to have a child, to see if I was right or wrong. And I found I was both right and wrong.'
He was always keen on slides, ever since his boyhood in Brussels, because every day on the way to school he passed an old people's home that had four fire escape slides coming out of the top and he always longed to go down them. So when he became an artist, he made an exhibition based on slides and was then commissioned to build a slide for Miuccia Prada's office in Milan: 'It goes right through the building, so as she goes down she has a very quick glimpse of what everyone is working on. Then it makes a big curve outside the building and lands exactly where her driver is waiting to drive her home.' Has it changed her life? 'She hasn't said so, but you can see it in the fashion she does. I think she does great work and part of the success story of Prada is using my slide.'
'Most people,' he goes on, 'associate slides with children's playgrounds. But there is no reason why they should be for children only. You could have slides to cross town. [He has designed a system of slides to use in Stratford town centre, as part of the 2012 Olympic Village project.] They are very environmentally friendly and it's like introducing a slight element of madness into your everyday life. I think slides would make everyone happy. It's virtually impossible to go down a slide without smiling. There is something peculiar with a slide. It does something to you that is not easily forgotten, almost like a strange dream that stays in your head a long time.
'I think a slide can change our perception of space and speed. Our brain structure is obviously affected by this vertigo effect and things that seem to be organised in a certain way can be reorganised and experienced in another order.' Will people scream? 'Oh they will, yes. Not because they're scared, but because they are let loose. They are finally free.'
· The Unilever Series: Carsten Holler opens at Tate Modern on Tuesday and runs until 9 April 2007