It is two weeks since I met Aida in her village, a few miles north of Kampala in Uganda. The earth there was red and the banana trees grew in dense clumps. It is two weeks since she showed me where she had hidden her mango plant.

I had gone to Kampala by car from the airport in Entebbe. Kampala is a cluster of hills, seven or eight, and tucked tightly between these hills dotted in elegant houses with large gardens was the town itself, with far too much traffic, far too many people.

Africa is always a conflict of opposites, of urban muddle and vast, empty regions.

I say Africa, but Africa can be divided into any number of parts. Some countries within this continent are the size of all of western Europe. There is no clear-cut, single entity that you can think of as Africa. This continent has many faces, but wherever I have been the dense urban muddle and vast, empty spaces have always been side by side.

Aida's village is like all the other African villages I know. The houses are made of clay or sheets of corrugated iron or the strangest mixture of materials that happened to be at hand for the builders. But all of the lived-in houses I saw in her village had a roof.

On the other hand, there were also abandoned houses that had collapsed. When I asked why this was so, I was told that the people who had lived there had died of Aids.

African houses often have a distinctive character. Perhaps you could say it is the equivalent of the Scandinavian passion for ornate carpentry at the end of the nineteenth century. In Aida's village two doors from an old American car make up the gate in a ramshackle fence round a house where a hairdresser is plying his trade. As we pass, he is cutting a customer's hair in the shade of a tree. Shortly before we came to Aida's house – or rather her mother, Christine's, house – I notice two men, their backs running with sweat, building a wall made of rusty pieces from old petrol drums between two corner-posts.

African houses in rural areas are a hymn to the imagination, if you like. But of course they are also an expression of poverty and destitution. Around the houses are small gardens, gravel roads meandering all over the place, and apologies for fences. Nearly all of the windows have broken panes with curtains flapping behind them.

Life proceeds at a leisurely pace in these villages. Haste is a human error that has not established very deep roots in the African countryside.

But none of this is important. I do not need to describe houses and roads, as if this were some sort of travelogue from a country in Africa. I have other reasons for being here.

In this very village, Aida's village, there is something else that all the other villages in the area have in common. Many of the villagers have Aids. Many are already dead from the disease. You can already see the big gap: lots of children, quite a few old people, but not many in between. Aids generally kills people from fifteen to twenty years old to those in their early fifties. The old people have to look after their grandchildren when their parents are no longer alive. When the old people die, the children are left to look after themselves. What that means is obvious to everybody. Children who have to be one another's parents have a pretty distorted start in life. They slip up.

Even if life goes on as usual, it is as if there is an endless silence all around them. Daily events, everyday events, take place under a cold shadow. Many people, too many people, are going to die. That shadow is not black, nor is it white. It is just not visible. It is like a cold gust of wind.

In Aida's village the silence was so tangible that it did not need to be visible.

There were various sorts of waiting among the people I met in Uganda. Those who knew they were infected and spent every day looking for symptoms. Those who didn't know, those who had refused to be tested, but nevertheless looked for symptoms every day, from the moment they opened their eyes.

But there is another kind of waiting. For the people who find themselves in the same position as Aida. She is only a child, she knows that she is not infected, but she will become mother to herself and her siblings the moment that responsibility is passed on to her.

And now I see her again in a dream. It is not a very long time since we were together. The last I remember of her, she is waving vigorously. Even when she could no longer see me nor the car, no doubt she went on waving.

We all do that when we hope against hope that somebody will change their mind, decide to do something different. Come back, break off the journey, stay behind.

But in the dream she's dead. Her face appears as an unfinished wooden sculpture. That upsets me. And it's not right. It must be somebody else, somebody who looks like her. She is not the one who is dead. It is others who are dying. Not Aida. She is alive. She hasn't grown thinner, she isn't covered in sores, she hasn't lost all her strength so that all she can do is lie on a bast-mat in the shade, staring up at the sky or at the big leaves of the banana trees.

The answer is obvious, of course. I'm mixing things up. Dreams do mix things up. The first thing that strikes me when I meet Aida is how much like her mother she looked. And Christine, her mother, is ill. She may well be dead by now. The same applies to Aida's aunt. Both of them could well be dead, even though it is only a couple of weeks since I was talking to them. Aida's face is there, out in the mist. She comes very close to me.

One windy day, in the middle of this most unstable June, just before I start to write down my story about Aida, about her mango plant, and all the people around her in Uganda waiting to die of Aids, I visit one of the many medieval churches on the island of Gotland. It doesn't matter which one. The darkness of these old stone-built churches is the breath they all breathe. Darkness has no individual identity. Darkness is eternal, and has no face, no name.

A lone man is tending a grave. The gate at the churchyard entrance is black and heavy. The handle is difficult to turn.

Somebody, a friend from the old days, once told me that dark churches made him afraid of death. It is precisely the opposite for me. In the darkness of a medieval church on Gotland, time ceases to exist. Or perhaps all time, the past, the present, the future – all of them are compressed into a shared moment. Going into certain churches you feel at peace the moment the door has closed behind you. Nothing else is needed. The church creates its own universe.