Eight leading thinkers ponder how the world will change in eight crucial areas over the next 50 years

* MATT RIDLEY on disease

Aids, mad-cow disease, the Ebola virus: it sometimes seems as if we live in an age of terrifying new fatal epidemics. From the hubris of the 1960s many people have swung to despairing pessimism. Nature seems to be taking its revenge on an overcrowded and rapacious species, unleashing lethal viruses. Old diseases come back to haunt us. Diseases that we never considered infectious turn out often to have parasitic microbes at their roots.

There is no end to the struggle with disease. Infection will never be defeated entirely, however well we organise our governments, invent ingenious new cures or stop interfering with nature. It is not in the nature of a war of attrition between parasites and host for either side to declare victory or accept defeat.

That is not to say that the third millennium will be punctuated by plagues. Even in the developing world, death from infection will become rarer and rarer: not because of medical technology alone, but because of changing lifestyles. Our well-spaced, mosquito-free, sanitary, urban, individualistic lives give most diseases little purchase: they find it hard to travel by insect, sewer or direct contact. Only coughing and sex remain efficient methods of transmission - and these, with a few exceptions, are better suited to mild infections than virulent ones. We will survive, but we will sneeze.

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Matt Ridley is science editor and Washington correspondent of The Economist.

* STEPHEN TUMIN on crime and punishment

The great majority of prisoners are male and young, uneducated and with little family support. At least half of the young men in prison have a history of truancy. Their crimes usually involve drink, drugs or cars, and the average sentence to be served is around a year.

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So how can we reduce crime by these young men? The answer is with education. From the moment he goes into prison, a young man of this kind should be prepared for release. He should learn reading, writing, arithmetic and computer skills -Jand how to behave morally and socially in the outside world. The objection is that we would be giving more expensive training to the criminal than to those who have survived our educational system.

Prisons can reduce crime. I have visited a number, in the Cayman Islands and in Cyprus, where they actually do so. I predict that -once the failures of the American system of cramming more and more men into undisciplined workhouses are more clearly understood -Jwe will use prisons essentially for educating the majority of inmates.

There will always be a minority, the mad and very bad, who must be kept securely in custody and treated with humanity. I also predict, following the success of electronic tagging for petty offenders, that the number of inmates will fall.

Sir Stephen Tumin is principal of St Edmund Hall, Oxford.

* CONOR GEARTY on terrorism

This month the home secretary will issue a white paper on terrorism. Until recently people like Jack Straw were passionate opponents of the Prevention of Terrorism Act. Old Labour held to its civil libertarian principles despite terrible paramilitary violence and the contemptuous ridicule of the right. Now Labour plans not to expunge the PTA but to do what not even the Tories dared - make it permanent.

Mr Straw will want us to worry collectively about serious crime in the hope that debate is conducted solely on his own alarmist terms. But counter-terrorism is about using the fear of political violence as a means of controlling political freedom.

A new permanent anti-terrorism law risks making suspects, in the way that the PTA has done to the Irish, of all those whose commitment to political change is outside the narrow confines set by Parliamentary debate. Will the environmental activist, the animal rights advocate and the leader of a radical ethnic group henceforth trigger the attention of M15 and the Special Branch? Will the world's tyrants be able to rely on the British police to control dissenters lucky enough to have made it to our liberal shores?

None of this is inevitable. The future of terrorism depends on public opinion. Either terrorism is consigned to history as an offshoot of the political turmoil of the last quarter of the 20th century, or it becomes the alibi through which hard-won freedoms are casually but effectively and permanently eroded. Britain's response to Mr Straw's upcoming plans will be an early sign of the direction in which the next century will be moving.

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Conor Gearty is professor of law, King's College, London.

* FRANCOIS HEISBOURG on welfare

Future warfare will witness a growing paradox. "Surgical strikes" will become a rule rather than an exception: information technology makes it possible to single out and destroy targets with minimum damage to bystanders. Nato's 1995 bombing operations in Bosnia exemplified the discriminate application of effective firepower with no significant "collateral damage'' - the heedless killing of civilians and the gratuitous destruction of physical assets. Modern surveillance systems, notably satellites, give high-tech warriors ever-greater battlefield "situational awareness'', dissipating much of the traditional fog of war. State-of-the-art command, control, communication, computation and intelligence systems vastly increase the ability to conduct major complex operations from a distance and with little delay between decision and execution.

But war will not cease to be a contest of wills entailing extremes of physical violence. In many instances, war aims will imply the savage treatment of civilians. Even when war aims are limited, determined foes will not give up in the face of an antagonist neither ready to resort to massive violence, nor willing to run the risk to bear casualties. Saddam Hussein's defeat in the Gulf war has neither broken his willingness to cause mischief nor broken his grip on power. Technology can make war "cleaner''. But war, by definition, is not a game: clean war is an oxymoron.

Francois Heisbourg was formerly director of the Institute of Strategic Studies in London.

* BERNARD LEWIS on the Middle East

The Arab-Israel peace process will probably survive for the reasons it began - both sides realise their wars are unwinnable, and great power rivalries no longer sustain the conflict. The process will suffer delays and even reverses, but it will continue until it succeeds or the circumstances that produce it change. Other less publicised conflicts will persist, and may produce other wars, both between and within countries. The latter are likely in autocratic states with mixed populations and no clear rule of succession.

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Without real peace, the economy will deteriorate. The world will tire of a fuel that pollutes the environment and is at the mercy of capricious rulers; it will find other sources of energy. In almost all the countries of the region water will be scarce and contested.

There will be increasing polarisation between democratic and theocratic ideas. The existing democracies, Turkey and Israel, are both challenged by theocratic forces at home; the major theocracy, Iran, by a democratic opposition. Both trends exist, in varying strengths, in the Arab world.

The Middle East today confronts alternative futures: one leads through peace to freedom and prosperity, the other through conflict to poverty and oppression. The peoples or governments of the Middle East must choose. If they fail, the region may again become the arena of clashing interests, perhaps between a resurgent Russia and the emergent powers of Asia.

Bernard Lewis was professor of the history of the Middle East at the School of Oriental and African Studies, London.

* HUGH THOMAS on Europe

The future will be one where the nation state will seem less and less an appropriate frame for political activity. Most successful states will merge sections of their sovereignty to participate in associations leading to greater security, health, prosperity and understanding of neighbours. States that prefer splendid isolation will see their possibilities narrowing, The structure of Europe will no doubt continue with a basically confederal model, with some federal elements. I expect to see a common currency, and suspect many British subjects will have euro accounts. Most political questions will continue to be dealt with at national levels, but something like a European defence community will at last come into being. I would expect that Europe's regionalisation will continue, even making headway in France, with Burgundy, Aquitaine and Normandy reappearing. I expect Europe to encompass all the Baltic states, most of the Balkans, but not Ukraine, Russia, Turkey or any of the states of north Africa. I suspect that, in one more gesture towards the memory of Rome, there will be officials named consuls who, ruling for only a year, will be responsible for overall management of policies in the EU.

Lord Thomas of Swynnerton was formerly professor of history, University of Reading.

* ANDREW GOUDIE on climate

In the 1970s, scientists, scientific journalists and even authors of airport novels were predicting the imminent arrival of an Ice Age. How different the situation appears following the recent Kyoto conference on climate change. Many scientists now predict an era of greater warmth, with a whole suite of impacts on the environment and society. They have attracted the support of some politicians and the ire of the so-called fossil-fuel lobby.

What is certain is that climate is always uncertain and always varying. Natural forces much more powerful than humans will, whatever humans do, continue to change our climate in coming decades, centuries and millennia. A great volcanic eruption could trigger an Ice Age tomorrow. Equally, if there were to be no major volcanic eruptions in coming decades, and a slight increase in the output of the Sun's energy, the human-accelerated greenhouse effect could be accompanied by natural warming, causing change even greater than that which the scientific establishment predicts.

We need to be cautious in our predictions of future climate change, but if the present consensus is correct, and if the expanding emissions of greenhouse gases are not controlled, we will move into a world where there will be enormous upheavals. To be sure, there will be winners and losers from such changes, but all change can destabilise. Do we know enough to know who the winners and losers will be?

Andrew Goudie is professor of geography, University of Oxford.

* JOHN CLARKE on population

Demographers are getting better at forecasting population changes. They are reasonably confident that the rate of world population growth will continue to slow down, so that by 2030 the world total will be about eight billion, much lower than previous forecasts. The cause is a "reproductive revolution" in which fertility decline has become part of the global belief system. It should persist in most parts of the world, although much will depend on the rising status of women.

Mortality is generally easier to predict than fertility. Widespread future reductions in mortality may be expected, but once again progress will be very uneven. Any future reduction in the marked inequalities in economic development between different regions of the world would have a vital effect on mortality decline.

One certainty is that most populations will have increasing proportions of old people. By contrast, mobility and migration are the least predictable of population phenomena, past flows being an unreliable guide to future flows. Yet they will play an even greater role in population changes at local level. We can be sure of several things: that political boundaries will continue to constrain human movement; that refugees will still be numbered in their millions; that average travel distances will get longer; that, for several decades at least, the relationship between residence and workplace will become increasingly dysfunctional despite mercurial improvements in communications; and that most migration streams will still be up the economic ladder.

The world's population will also become even more polarised on a small part of the earth's surface. In general, it looks as if we are facing more of the same.

John Clarke is emeritus professor of geography, University of Durham.

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The Predictions series looking forward to the next 50 years was launched byWeidenfeld and Nicholson on December 29. Twelve titles, including all eight above,were published on December 29, with 12 more to come in March. Each of the titles costs Pounds 2.