MARCH 12, 2050.
I HAVE been riding commercial jet-rocket flights for more than 10 years now, but it still takes my breath away when I soar into outer space.

This is my granddaughter Jennifer's first trip and we watch the brilliant turquoise sky over New York turn a gorgeous deep maroon as we leave the atmosphere and begin to orbit Earth.

"Grandpa, where exactly are we?" Jennifer asks, squirming in her seat.

"Let's ask that question of Molly," I say. I take out our portable holoscreen, place it on the tray in front of us and a hologram of Molly, a 3-D image about 10cm tall, with artificial intelligence, springs to life on the screen.

"Molly, Jennifer wonders where we are."

"Well, Jennifer, let's see," says Molly. "I've locked onto the global positioning satellites." Molly disappears from the screen and is replaced by a 3-D map of the US.

"The Aerospace plane is 85.6km over Earth," says Molly. "By the way, Michio, it's time for me to check your health. Let me scan the computer in your bloodstream."

I had forgotten that a tiny computer, no bigger than a human cell and using the latest in nanotechnology, was injected into my blood last year. On the holoscreen a 3-D image of my body appears, with a bright red dot, representing the computer, floating swiftly through my heart and organs. No more jabbing you with needles.

"Scientists have sent probes into outer space and now we're sending probes into inner space," I tell Jennifer. "The computers in my clothes monitor my blood pressure and heartbeat, and the computer in my blood does the rest."

Molly reports: "I've picked up telltale proteins from a tiny colony of cancer cells, maybe 100 cells. Left unchecked, they might kill you in 10 years. But no problem. I'll zap them with some smart molecules when we get back to Earth."

"Cancer? What's that?" Jennifer asks, puzzled.

"It's a rare disease, but one that terrorised people in the last century," I say. I shuddered to think of the barbaric procedures once used to treat cancer, such as radiation and chemotherapy.

Molly adds: "Jennifer, we can also grow body parts in the laboratory. About 15% of your grandfather's organs were grown in a test tube."

"Jennifer," I say, "when you were born, the doctor took some stem cells from you, so we can grow new livers, kidneys, hearts and lungs for you as they wear out. Like spare parts."

"Grandpa," Jennifer blurts out, "just how old are you?"

"Well, I'm over 100. But that's about average now. Hardly anyone dies of diseases these days."

"So, Molly, how long will I live?" Jennifer asks, with a curious look.

"Well, let me first check your genes, Jennifer." The holoscreen is filled with all 100,000 genes in Jennifer's genome. "Hmmm, I see about eight genetic defects, but nothing to worry about. You'll live to a ripe old age," says Molly.

"And by the time you hit 30, you may decide to cruise at that age for a few decades," I add.

Molly says: "The fountain of youth is not just one type of therapy but a mixture of several."

"Yes, I remember the breakthrough," I nod. "It was back in 1998, when scientists showed that the enzyme telomerase can make human skin cells divide for ever; that is, become immortal."

"And," Molly says, "since then scientists have isolated scores of other genes and enzymes that slow down the ageing process. And now that everyone's DNA sequence is on file we can comb through the genes of people who live exceptionally long lives to find new age genes."

"And don't forget," I add, "that all the age genes in the world won't replace an arm or leg lost to disease. I remember back in 2010 when the first liver was grown in the lab. It created a sensation and prolonged the lives of thousands. With all these developments and hormone and antioxidation therapy to keep our cells vigorous and vibrant, scientists think we might be able to live to be several hundred years old."

"But Grandpa," Jennifer protests, "you didn't answer my question. How long will I live?"

"That's hotly debated. Your children may well live several hundred years, to be as old as Methuselah. And some scientists claim that your children might live to be immortal."

Jennifer looks puzzled: "But won't we run out of space with all these people living for ever?"

"Well, not quite," says Molly." The populations in rich countries have been collapsing for decades. If you are a poor peasant, you need to have 12 kids, hoping a few of them will survive. But if you are middle-class, you want to have just two kids and enjoy life. The world's great birth-control method is called prosperity."

"But Grandpa, if scientists can do all that, couldn't you have made me taller, or given me a bigger nose? Or made me smarter?" Jennifer was always complaining about her nose.

"About 30 years ago, when it became possible to alter our genes, there were so many abuses that they passed the Genetics Law banning designer children. But even today there is a thriving black market. Some parents will pay anything to create perfect children."

"But Grandpa, what's wrong with choosing what your baby is going to look like?"

"Because, Jennifer, in the past, many peasants chose to have only male children. They killed the female ones. They considered being female to be a genetic defect. Would you like that, a world of only boys?"

"Oh no," she says, looking a bit frightened.

Molly interrupts. "Michio, I detect a message from the university. They are having an urgent meeting and want you to attend."

"Molly, download the meeting from the Internet and send it through my glasses. I'll teleconference from there."

I put on my glasses. A laser beam scans the retina and iris of my eye to confirm my identity. The security check complete, I can see the video of the conference in the lens of my glasses, with my colleagues sitting around a table.

"Michio, terribly sorry to interrupt you on your holiday. But we think we've made some headway on the Orion Project and want your advice."

The Orion Project! A chill goes down my spine. Years ago, the International Space Agency replaced largely ceremonial manned space missions in favour of building robotic bases on the planets and asteroids. One of these uncovered a piece of metal debris with ancient writing on it and traces of some kind of alien DNA. It was apparently millions of years old.

The writing was placed on the Net, and now thousands of scientists are scrambling to crack what appear to be mathematical equations. Alien mathematics.

"Michio, we've deciphered a few of the equations. You were right about one thing. It appears that some of these equations are related to your special subject: superstring theory."

Ever since I was a child, I have dreamt that my equations, if they were truly universal, would be duplicated by alien creatures. After conferring with my colleagues, I conclude that the aliens seem to use the unified field theory to power their machines. After the meeting I try to take a nap, but then the Internet connection in my watch begins to ring. I hear Michelle, my daughter, calling us, so I put her image on the holoscreen. I can see she is cleaning the attic and speaking into the wall screen there.

"Jennifer, sweetheart. How's everything in outer space? By the way, Dad, I was cleaning your room and came across a dusty old copy of your book Visions. I was reading some of the predictions you made 50 years ago."

"I was afraid of this. Did you laugh?"

"Oh, no, Dad. I guess physicists do see a bit farther than the rest of us, like you always say. So, which prediction was your biggest blooper?"

I think a bit. "I guess I underestimated the power of human stupidity and folly. Remember that prediction I made about our one day becoming a Type I civilisation? A truly planetary civilisation, with a planetary language, economics and culture?"

"Yes, Dad. And a Type II civilisation uses the power of a star, and a Type III civilisation is galactic," adds Michelle.

"Well, even with all our technology, the world is aflame with cruel civil wars and ethnic conflicts. You know, our technology has conquered most diseases and suffering, but the worst suffering is self-inflicted. Our brain is identical to the savage mind that emerged from the forest 100,000 years ago, except now that savage brain can kill millions of fellow humans with weapons. You know, there is no cure for sheer stupidity."

"So Dad, what do you predict for the solar age?"

"I thought we would be well into the solar age by now. But I underestimated the power of the oil companies. They fought the transition to solar and fusion power. Because of this, only in the past few years have a solar/hydrogen economy and fusion power come into their own. And now that cheap oil is only a distant memory, this transition did not come a moment too soon."

"So the delay aggravated global warming?"

"Undoubtedly. For decades the greenhouse effect has turned the weather upside down, creating super-hurricanes, flooding coastal cities, turning growing areas into deserts. And I shudder to think what might happen if the South Pole continues to break up, raising sea levels."

I look out of the window again. From 320km out in space, I can see the greatest achievements, and the foulest disasters, of nine billion people living on Earth. I can see the flames of civil wars flaring out of control. I can see acrid smoke belching from forest fires that are incinerating many of Earth's plant and animal species. But I can also see vast potential.

"Michelle, one prediction I made still holds. I predicted that it would be a race against time, a race between the forces of unification and the forces of darkness. As I predicted, it's going to be close."

Michio Kaku is professor of theoretical physics at City University, New York. His book Visions: How Science Will Revolutionize the 21st Century and Beyondis published by OUP at £8.99.