Never say die: Who wants to live forever?

It's one of the most ghoulish sound bites of the First World War.

Frontline troops in France, waiting to climb the ladders out of the trenches and advance across the no-man's-land of mud, craters and barbed wire to almost certain death from enemy machine guns, would be encouraged to go over the top by pistol-wielding NCOs shouting, "Come on lads – you don't want to live forever, do you?"

Do we? Of course we do. At least, we want to live on. Most of us, when terminally ill, would hope to be spared to live one day longer – a week if possible, a year, or three, or 10. And as medical science discovers how to cheat once fatal diseases, as many over-fifties take chemical measures to conceal the appearance of ageing, and as the human genome project promises to identify and eliminate every negative tendency in our DNA, our thoughts turn to the ultimate triumph of mankind over nature: staying alive indefinitely.

"I don't want to achieve immortality through my work," Woody Allen memorably observed. "I want to achieve it by not dying." Allen is now 75 and, though clearly a little frail, shows no sign of cutting down his remarkable work-rate of directing a movie every year. Would we be surprised if he made it to 100? Not terribly. Our head of state, now 85, is confidently expected to receive, as it were, a telegram from herself on her 100th birthday, as her mother did before her.

The rock n' roll generation, who like to break the rules of age-appropriate behaviour, disdains the idea of retiring, resting, slowing down, giving up, ceasing to strive. Mick Jagger could be found in South Africa last Saturday evening, high-fiving Bill Clinton when the United States scored a penalty in the match against Ghana, and the next afternoon looking crestfallen as England were trounced by Germany. He wore the same scarf round his throat at both matches, a minimal sign that he might be susceptible, at 66, to chills and sniffles. His bandmate Keith Richards, having abused his liver, heart, lungs and other vital organs for 50 years with the enthusiasm of a medieval flagellant, sails gracefully on into old age with his tight jeans, his batik shawls, his skull rings and vodka-and-orange cocktails. To a certain generation it's inconceivable that either of them – four years away from their Biblical span of life – could die. And, taking our cue from them, it's inconceivable that we won't go on for umpteen years too.

We're probably deluding ourselves – but it's a fact that there are more centenarians stalking the earth now than ever before. Their number increases by 7 per cent each year, and doubles every 10 years. In 1980 there were 15,000 centenarians in the US; in 2000 the figure had risen to 77,000. America is only just ahead of Japan when it comes to the ratio of 100-year-olds to the main population. In Okinawa, whether it's the low-carbohydrate diet or the spirituality of the inhabitants, there are 34.7 centenarians among every 100,000 inhabitants – a world record.

In the next couple of decades, centenarians will be counted in millions, worldwide. Super-centenarians, as 110-plus oldsters are called, will become commonplace. The oldest woman whose life was fully documented was Jeanne Calment who died in 1997 at 122 years and 177 days; it won't be long before that record is broken, many times over. A generation from now, someone will celebrate his 150th birthday by telling astonished listeners what life was like in the days when phones had to be plugged into the wall. And what if it didn't stop there?

Could we cheat death indefinitely? There are just three things that make the human body pack up and die: ageing, disease and trauma. If we halt the degenerative processes of age, body-swerve the onset of disease through preventative medicine, and avoid physical or mental trauma by nanotechnology or brain-transfer, what is to stop us continuing to live for hundreds, no thousands, no millions of years?

While young readers imbibe a modern flood of fictions in which immortality is central – in Stephenie Meyer's Twilight saga and its myriad offshoots – early 21st-century scientists are exploring ways of bringing it about in real life. They examine the biology of ageing, the constant subdivision of cells that leads to their decay (it's exciting to report that they've discovered an immortal species – the Turritopsis nutricula jellyfish, which can transform itself from mature adult to childish polyp and repeat the process indefinitely.) They look into the system called "mind-uploading", in which your personality and memories, as well as your consciousness, can be loaded onto a computer or a new-born baby's mind.

Some rich patients flirt with Cryonics, in which their bodies, before death, will be frozen at temperatures which stop them from getting older or decaying, to be held in this chilly equilibrium until future medical technology becomes sophisticated enough to sustain their unfrozen forms. Sir Martin Rees, the Astronomer Royal, who gave this year's Reith Lectures, should theoretically be a fan of such far-seeing, time-transcending science. But in his third lecture he remarked: "For my part, I would much rather end my days in a Wiltshire churchyard than a Californian refrigerator."

Lots of people disagree. Immortality has intrigued the human race ever since Neanderthal man gazed at his dead parents and wondered if he could stop the same fate overtaking him. It's an awe-inspiring notion, that has lodged in the head of everyone raised in the great religions, where the concept of eternity is always aired, mostly in relation to our post-mortem residence in Hell or Paradise.

I was brought up by staunch Catholics, who believed in the resurrection of the body after the Final Judgement. My mother used to tell me what a lovely time we'd have in heaven, reconnected with our physical being and swanning around with the rest of the resurrected faithful.

"But Mum," I'd say, "Would you want to have your body back in the condition it was in when you died? Heaven would be full of old people, groaning from arthritis or cancer, and looking wrinkled and terrible."

"It won't be like that at all," she reassured both of us, "We'll get our bodies back looking like we did in our prime." "What, we'd all look about 35 or 40?" I said. "Without any sign of youthfulness or maturity? Would that be ideal? So I could walk past your parents and grandparents, and they'd all be 40 and fit-looking – how would I know they were my ancestors?"

"Don't be so stupid, John," she said, "Sure, wouldn't I introduce you?"

There lies one of the many crucial questions in the small print of immortality. If you lived for-ever, would all your friends do so too? Would you become a superannuated glee club of pals aged 350 or 550 years? Would you be subject to the usual attrition of the human body, so that, by the age of only 200, your once-lovely face resembles late-period WH Auden, or Seamus Heaney's Tollund Man, dug up from the turf-bogs of pre-history?

Who would want that? If you didn't, and couldn't, die, would you become progressively more infirm and enfeebled, your skin like parchment, your mouth like ashes, your sex life a wholly faded memory, your memory itself a thing of only spasmodic reliability, briefly flickering into life and going out again like a defective fridge bulb?

We may remember with horror Philip Larkin's pitiless poem about ageing: "What do they think has happened, the old fools,/To make them like this? Do they somehow suppose/It's more grown-up when your mouth hangs open and drools,/And you keep on pissing yourself, and can't remember/Who called this morning? Or that, if they only chose,/They could alter things back to when they danced all night,/Or went to their wedding, or sloped arms some September?/Or do they fancy there's really been no change,/And they've always behaved as if they were crippled or tight,/Or sat through days of thin continuous dreaming/Watching the light move? If they don't (and they can't), it's strange;/Why aren't they screaming?"

No, it's too awful. Let's assume that medical science will find a way to keep us all evergreenly gorgeous and youthful, or, failing that, at least in our prime. We won't die or become ill, we won't rot away, we'll just go on, greeting the daylight every morning for decades and centuries, admiring the purple hedgerows flashing by the car on summer drives and the carpets of snow on the silent metropolis in winter. We will continue to make friends until our social acquaintance numbers in millions. Our interest in the news will continue, sharpened by the long perspectives on history to which we have personal access. We will become wiser, cleverer, better informed – won't we?

But I can't pursue this happy picture without thinking of the Struldbrugs. Remember them? In Gulliver's Travels, Gulliver encounters them in Book Three. Struldbrugs are immortal beings who are born from time to time, with a red spot over their left eyebrow, and who will live forever. Gulliver exclaims what a wonderful thing it must be to be "born exempt from that universal Calamity of human nature, [to] have their minds free and disengaged, without the Weight and Depression of Spirits caused by the continual Apprehension of Death."

Were he able to live forever, he tells his friends, he'd spend 200 years becoming the richest man in the kingdom, then apply himself to studying the arts and sciences in order to excel all others in learning. Finally, by observing every change in politics, public affairs, customs, language and fashion, he would become "the Oracle of the Nation". With a brotherhood of Immortals, he would contemplate the progress of revolutions and discoveries, and teach future generations the uses of virtue. He would befriend a few Mortals, secure in the knowledge that, when they died, he would note their passing with equanimity, "just as Man diverts himself with the annual Succession of Pinks and Tulips in his Garden".

Gulliver soon gets a wake-up call. Struldbrugs, he is told, spend most of their lives morose and dejected: "They were not only opinionative, peevish, covetous, morose, vain, talkative; but uncapable of friendship and dead to all natural affection, which never descended below their grandchildren. Envy and impotent desires are their prevailing Passions." They envy, Gulliver learns, the vices of youth and cannot hear of a funeral without lamenting that someone else has gone to a place of rest forever denied them. They have no memory of anything that happened after they were 30. After 80, they're treated as though dead, their land inherited by heirs. They are held to be incapable of working or holding office. They lose their teeth, hair and their sense of taste, and cannot read because their memory won't let them remember the beginning of a sentence by the time they've reached its end. They lose the elasticity of language until they can't communicate with their neighbours. They are ancient, silent, useless, hopeless individuals, with nothing to enjoy, no hope of relationships, looking fruitlessly for just one thing: death.

So Gulliver is cured of his desire to live forever. But are we? I have not the slightest interest in dying. I am passionately keen to evade its icy tentacles for as long as possible. But if the alternative were to live on indefinitely, I'm not sure I could endure it. Of course I want to be around to see my three children grow up, have adventures, make fortunes, fall in love and spawn children of their own (this is a mixture of paternal devotion and incurable nosiness); but as we all get older together, I suspect my interest in the third or fourth generation of Walshes would suffer the law of diminishing returns. My love of nature, of yomping on the hillsides and riding on the South Downs, has never been as passionate as it might be, but I become sentimental about the arrival of flowers in May and the turning of leaves in October. And this sentimentality wouldn't exist unless the fear of oblivion – of there being a time when I will see these sights no longer – lay behind it.

I like to think I'm quite well read, but still feel terrible that I may never reach the end of 1,000 Books you Must Read Before You Die. (Must I read all of Thomas Mann's Joseph and His Brothers? Could I skip a chapter? Or a volume?) Having a finite time to digest them, I must be ruthless and selective, and read only the best, most entertaining ones. If I lived forever, of course, I could read them all – and might expire from boredom in doing so. Ditto music and movies: if I'd rather listen to early Prefab Sprout these days than Katy Perry and The MGMT; if I'd sooner watch old Powell and Pressburger movies on DVD than sit through The Dark Knight or the Matrix Trilogy, how responsive will I be to the contemporary art world when I'm 387?

Ditto travel. I haven't yet seen Machu Picchu, or Monument Valley or Neuschwanstein castle or the Florida Keys or the curve of the earth seen from space, or 100 other destination sights. I'd love to see them all, knowing that, at present, my chances of doing so are lessening all the time. But it's that lessening process that gives them an additional, far-off beauty, and my trip to see them an extra urgency. Give me all the time in the world, and I'll put off the travelling for, oh, centuries. I mean, what's the rush?

The rush, of course, is what makes life melancholy and beautiful in equal measures. Because you discover that although 70 years just isn't enough time to cram in all the living you'd like to do, not just the drinking cold wine and eating T-bone steak, all the travelling and swimming and riding and dancing, all the party-going and talking and singing and kissing and so forth, but also, of course, all the weeping and heartbreak and recriminations and false starts and second goes, and impassioned mistakes and lessons hard won, and the children you loved from the first moment, to whom you will one day say goodbye for always, and the friends who kept you going and the lovers who forgave you (eventually) for being an arse – although one human lifetime is hardly enough time to cram it all in, our very consciousness of a deadline, somewhere around the 70 mark, makes it all poignant, rather than simply episodic.

Martin Amis, speaking at the Hay Festival, said that, at about 40, you discover this wonderful thing called The Past, which you can inspect at leisure, marvelling at moments of triumph and despair, weeping about your callowness, laughing at your gauche close encounters with the real world.

I would say that, at 50, you discover something just as valuable – the Finite Future. To have what Swift called the "Weight and Depression of Spirits caused by the continual Apprehension of Death" may not be a basket of chuckles, but it concentrates the mind on what it must inevitably lose, and gives a sublime value to simple but touching things. Without the Grim Reaper lurking in the garden, we might notice the white roses, but we wouldn't enjoy them half as much.

Walter Pater, in the celebrated conclusion of The Renaissance, wrote eloquently about the search for beauty when time is short: "Not to discriminate every moment some passionate attitude in those about us...is, on this short day of frost and sun, to sleep before evening. With this sense of the splendour of our experience and of its awful brevity, gathering all we are into one desperate effort to see and touch, we shall hardly have time to make theories about the things we see and touch. What we have to do is to be forever curiously testing new opinions and courting new impressions..."

To be condemned to live forever is to lose all that excitement – to exchange the "awful brevity" of human life for an "awful longevity" in which the splendour of experience becomes dulled by repetition, and the appetite becomes decadent by trying everything. Like Heaven, eternity would become a place of excruciating boredom, where 1,000-year-old, enervated, louche Methuselahs chat to each other about the very [itals] very [italsoff] old days, play their old Emerson Lake and Palmer albums until they're deaf, and wish someone could finish them off, seriously, before they have to endure another million mushroom pizzas and another million TV repeats of The Great Escape and The Good, The Bad and the Ugly.