As a science fiction writer it is my business to create imaginary pictures of different times and different worlds. This is common knowledge. What's less well recognised is that the imagination of any science fiction writer feeds on the past as much as on the future. ‘Those who refuse to learn from History will be condemned to repeat it’ (George Santayana): this is the aphorism on which much ‘scientific’ fiction is based, the writers being reasonably sure that the human race will never learn… No serious sf writer ever simply invents a future-world out of a vacuum. The effort involved, the sheer mass of interlocking detail required, would make that project highly uneconomic in terms of work hours and creative effort. Less than serious writers don't trouble themselves to invent anything much, and their year 2525 differs not at all from 198X in social mores, in lifestyle technology, in cultural and political infrastructure; except that in this relabelled present-day the galaxy has been colonised, immortality is available to all, and aliens of bizarre shapes and sizes mingle with the tourists on Oxford Street. Other writers, and I count myself among them, believe that technological change affects every aspect of people's lives, slowly in detail but sometimes in sudden leaps so dramatic that the passing generation can hardly recognise a world that is to their children as normal as if its gadgets and innovations had been there forever.

It should be noted that quantative change may be for the worse as well as for the better. Stocks in imaginary futures, as the standard warning goes, can go down as well as up. One short answer to the question ‘What will leisure be like in the year 2020?’ might be: there won't be any. We'll have bombed ourselves back into the stone age, and the rare pleasure of falling asleep with a full stomach will be the height of human entertainment experience.

But whenever the whole human environment has to be made over in order to present an ‘accurate’ picture of the future, the job will be quite impossible without some extremely trenchant short-cutting.