Last week I gave a lecture at a workshop on global foresight. I was asked to describe what will happen to the world in the next half century.

I did not tell them the truth, which is that I have little idea what happened last year or this year, less idea what will happen next year, and beyond that anyone's guess is as good as mine.

Instead, I cheated. Rather than looking forward fifty years, I looked back one hundred.

It happens that my mother was born a century ago, in 1902. She is still alive, I'm glad to say, and enjoys life provided that it includes at least one Scotch whiskey and 7-Up every day. When she came into the world, there were plenty of forecasts as to what the twentieth century would bring. Those predictions were wrong, not because of what they included - which were mostly linear projections from the world of 1902 - but because of what they left out. And it was what was left out that most changed the world.

On the abstract side, no one expected relativity, quantum theory, the expansion of the universe, holography, subatomic structure, the conversion of matter to energy, solid state physics devices (such as transistors), information theory, black holes, the molecular structure of DNA, retroviruses, genome mapping, and the theory of finite state automata.

Still less did anyone expect the torrent of practical applications, with their massive social fallout, that would follow from the new theories: television and telephones in almost every home (I am tempted to say every room) of the developed world; widespread air travel, humans to the Moon, and observing equipment to the planets; lasers, genetic engineering, video recorders, antibiotics, CAT scans, nuclear energy plants and nuclear bombs; artificial satellites in regular use for communications, weather, and monitoring of the Earth's surface.

No one in 1900 imagined that by 2000 the automobile would be absolutely central to many people's lives, as the principal means of transportation, recreation, and even courtship. No one in 1902 imagined even one computer, still less the hundreds of millions used in people's homes to conduct business, play games, send and receive mail, and wander at will through a world-wide information network.

Then I became personal with my audience. I will do the same with you. Think of yourself, and think of today. Did you waken to the buzzing of an alarm clock? Did you turn on an electric light? Did you take milk or orange juice from a self-cleaning refrigerator? Did you heat something in a microwave oven, or a pop-up toaster? Did you watch the news on television, or the weather channel to see what satellites offer as weather patterns? Did you use a toothpaste containing fluoride? Did you drive an automobile at least part of the way here? Did you run a yellow light, or use a parking meter? Did you use a cell phone to send a message home or to your office? Did you check your e-mail?

I invite you to sit down and list the number of devices that you depend on every day that did not exist a hundred years ago. Look at your watch. Certainly, it may have old-fashioned hands and numbers and look like clockwork; but you can bet that at its heart lies a computer chip and digital logic.

Let me become more personal yet. Do you wear contact lenses, or a hearing aid? Have you had surgery to repair a joint, clear a clogged artery, or put in a pacemaker? Have you had dental work to fill or straighten teeth, or replaced eye lenses suffering from cataracts. Have you had a polio shot? Have you had (you can tell me, I won't pass it on) some form of cosmetic surgery, anything from hair transplants to face lifts to liposuction? Have you ever used antibiotics, or had blood tests, a Pap smear, a CAT scan, an MRI?

If you say no to all these things, you are most unusual. All the elements that I have mentioned affect our lives personally. Some of them affect us to the point of keeping us alive, when a century ago we would surely have died. And not one of them was predicted in 1902.

That might seem the end of the story. Forget prediction of science and discovery. The twentieth century demonstrates that such prediction is impossible.

However, let us now examine the past hundred years from a different point of view. In 1902, no one predicted World War One. No one predicted Nazi Germany and World War Two, or the rise and rapid collapse of communism. No one gave a thought to global warming. No one foresaw the problem of vanishing topsoil, resulting from the over-grazing and deforestation activities of humans. No one predicted diminishing fossil fuel supplies, when reserves of oil and gas appeared endless. No one worried about the pollution of fresh water sources and the lowering of water tables. No one concerned themselves with species die-out by the thousands or even millions, with plants and animals vanishing forever from the Earth. No one saw in advance the pandemic of influenza that followed World War One, or today's scourge of AIDS. No one expected international terrorism. No one predicted a world population in excess of six billion (Thomas Malthus, writing in the first decade of the nineteenth century, foresaw population outstripping food production; but he did not dream of the rate at which population might increase).

And now to my main point: all the worst disasters of the previous hundred years, except for influenza and AIDS, and even these are debatable, arose as the direct result of human actions. The same will assuredly be true of the next half-century, and the next century.

The problems that face humans can't be solved by predicting the future of science, or predicting the social effects of scientific discoveries. This is just as well, because if the last century has proved anything, it is that such prediction is impossible.

The real problem is quite different. As the Nobel-Prize-winning physicist, Denis Gabor, remarked in a book written forty years ago, "The future cannot be predicted; but futures can be invented."

The future is not a given; it is, except for unavoidable natural disasters, largely what humans decide to make it. The real task in the next half century is not simple, but it is simply defined: we humans must invent and bring into existence our own better future.

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