Now that medical science can add 12 months to life expectancy every year and sustain that rate of progress, the potential for immortality arrives. It is an intriguing, if unlikely, prospect - the stuff of science fiction.But could it ever happen?

Some at the cutting edge of nanotechnology think so.

At the Foresight Institute, the nanotechnologists are all excited by President Clinton's announcement earlier this year that he is putting $500m into their pet projects in the hope that they will lead to a leap forward comparable to the industrial revolution.

But what is nanotechnology? At its simplest it involves rearranging matter at the atomic level to create new or different molecules. It is the solution to the alchemists' quest for a means of changing base metals into gold, carbon into diamonds.

What the nanotechnologists want to do is to develop nanomachines capable of going that one step further - constructing new enzymes capable of spinning a fine diamond fibre 50 times stronger than the same weight of aluminium, for example.

They foresee the day when we will have nanocomputers - not a daft idea when you consider that the average computer occupied an entire room 25 years ago and barely had the intelligence to cope with a health authority's monthly pay cheques.Nanocomputers open up the possibility of all sorts of 'smart' substances.

And then, of course, there is the real philosopher's stone: nanomedicine.Nanoguru Ralph Merkle's Nanotechnology and Medicine foresees fleets of molecular machines floating freely through our bodies to extend life and stamp out ageing.They could remove obstructions in the circulatory system or even kill cancer cells. Just as today we have the artificial heart, so in the future we could have the artificial mitochondrion, he suggests.

Of course, not even nanomedicine will be able to abolish NHS waiting lists.But they won't be as big.

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