Jim Baen's Universe

Quarks to Quasars:The Science of Science Fiction

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Human Immortality

Written by Ben Bova

Do you want to live forever? Maybe you will.

Several avenues of biomedical research are leading toward significant extensions of our lifespans. Insurance actuaries (no wild-eyes SF fans they!) now tell us that a baby born in the United States this year could have a life expectancy well beyond 100. And that’s before any of the new research efforts reach clinical practice.

Over the past century average life expectancy in the United States has doubled, to about 80 years. Yet our maximum lifespans have not increased. While there are more than 50,000 Americans aged 100 or more, no one has lived past 120. That’s going to change, though.

The doubling of average life expectancy came about through better nutrition, better health services, and better public sanitation. Pretty prosaic, but very important. Most infectious diseases—ailments caused by microbes invading our bodies—were brought under control in the twentieth century, thanks largely to penicillin and other antibiotics. When I was a kid growing up in South Philadelphia, children died of whooping cough and diphtheria. That’s a rarity today.

Today we live long enough for genetic diseases to become major threats: cancer, Parkinson’s Disease, Alzheimer’s and other diseases that manifest themselves mainly in our later years are caused by breakdowns in our genes, not from invasion by foreign microbes. Geneticists and cellular biologists are working to understand these diseases and their causes. Other lines of research are investigating the underlying causes of aging itself and the possibilities of regenerating cells and tissues that have been damaged by disease or injury.

Stem Cells and Regeneration

Suppose you’ve been hit by a heart attack. Why not replace the damaged cells of your heart with new, healthy cells? Why not, if necessary, grow an entire new heart right there in your chest—out of your own cells, so there’s no need for surgery and no fear of rejection?

You started life as a single cell, a fertilized ovum. In the genes of that one cell was all the information needed to build you. That information is still locked inside the genes of every one of the hundred trillion cells of your body. You could grow a new heart, or replace any damaged organ and even regrow an arm or leg lost to injury, if we knew how to unlock the information that’s coded into the genes of your cells.

Some jargon: A fertilized egg is called a zygote. As the single cell divides and grows, it is referred to as an embryo. Once the human body form is apparent, after the third month of gestation, the embryo is called a fetus.

When a fertilized ovum—a zygote—begins multiplying into two, then four, then more cells, those cells are totipotent. That is, they have the ability to grow any kind of cell the body needs: muscle, nerve, skin cells, heart cells, liver cells, toenails, hair, the “little gray cells” of your cerebral cortex—the works.

But as the embryo develops, its cells become more restricted. They are pluripotent: they have the capacity to produce a large number of different kinds of cells, but not all the different kinds that the earlier totipotent cells could produce.

And once the embryo’s cells differentiate into specific types of cells—heart, liver, bone, nerve and so on—they lose even their pluripotency. The cells have specialized and they will remain specialized. A muscle cell, for example, will not change into a nerve cell. It cannot. The cells of the lungs will not suddenly transform themselves into red blood cells.

You can see why this must be. Imagine trying to run a business organization where each day each employee decided which job he or she would do. Chaos. The same principle applies in your body. Specialized cells stick to their jobs. Once the cells have specialized (or differentiated, in the technical jargon) they cannot change into another type of cell.

However, each and every cell still carries in its nuclear DNA the genetic blueprint for the entire body. All those genes reside in each cell, although most of them are restricted from acting once the cell has differentiated. At that point most of the cell’s genes are turned off. Only the genes necessary for the cell’s specific, specialized job remain active. All the other genes go dormant.

Unless bioscientists learn how to activate them.

The goal is regeneration, and the means toward that goal was—at first—stem cells harvested from human fetuses. Such stem cells are still pluripotent; they haven’t differentiated into specialized cells as yet. But using fetuses for their stem cells caused an uproar among those who felt it morally wrong. People who felt that a fetus is entitled to all the rights of a living human being decried the idea of “taking a life to save lives.”

President George W. Bush felt those qualms, but he was the first President to allow any federal funding for stem cell research. President Barrack Obama has widened the scope of allowable stem cell research. Still, there are strong objections to using fetal cells, even though the fetuses themselves have been tossed away by fertility clinics and will never become true human beings.

But scientists are smart. They have found working stem cells in adult bodies. They have also discovered stem cells in placental blood. They have even learned how to take ordinary skin cells and “regress” them to the point where they re-acquire pluripotency.

Cell regeneration is on the way. Regeneration therapy is already reaching clinics around the world.

If you can grow new organs to replace failing ones inside your own body, using your own cells, how long will you be able to live? Immortality is beckoning.

Telomeres and the Hayflick Limit

Moreover, bioscientists are investigating the very causes of aging.

The American cell biologist Leonard Hayflick found in the 1970s that each type of cell in the human body will reproduce itself a certain number of times, and then stop. Once a cell reaches its Hayflick limit, it no longer reproduces. It becomes senescent and eventually dies.

As the different types of cells of your body reach their various Hayflick limits you begin to exhibit the symptoms of aging; your skin wrinkles, your muscles weaken, your limbs stiffen, etc. When enough of your cells reach their Hayflick limit, you die.

Can we prevent cells from reaching their Hayflick limits? Some scientists believe that telomeres hold the answer.

Inside the nucleus of each cell, the genes are strung together on long filaments called chromosomes. At the ends of these chromosomes are telomeres, little endcaps, sort of like the aglets at the ends of shoelaces. Each time the cell reproduces, the telomeres shrink a little. When the telomeres are reduced to a certain critical length, the cell stops reproducing. It has reached its Hayflick limit and is on its way to cellular death.

If something could stop the telomeres from shrinking, would the cells stay youthful and vigorous?

Scientists have injected cells with telomerase, an enzyme that promotes telomere growth. And the cells don’t die! Cell samples treated with telomerase have lived more than twenty times their normal lifespan.

If the normal human lifespan is roughly 100 years, and telomerase can increase that span by a factor of twenty, human lifespans could stretch to 2000 years. Shades of Mel Brooks!

Seriously, scientists pursuing the telomerase option have a long way to go. Making cells in a Petri dish virtually immortal is a step forward, but only the first step. At present they need a different version of telomerase for each different type of cell in the body. And there are still many unknowns: for example, would telomerase therapy lead to uncontrolled cell growth, to tumors and cancer?

But science fiction enthusiasts are accustomed to taking the long view. Perhaps telomerase therapy will allow humans to live for millennia. And if you live that long, think of the new discoveries that will be made in your lifetime. Human immortality, indeed.

Realize that you won’t be living as a feeble, pain-racked, helpless old wreck. You will remain youthful, vigorous, and healthy. For centuries. For millennia.

Therapeutic Nanomachines

Another avenue toward possible immortality lies in the development of nanotechnology.

Nanomachines, as envisioned by K. Eric Drexler and others, have become a staple of science fiction. Drexler predicted building machines the size of viruses, on the order of a billionth of a meter (a nanometer). Teeny.

Nobel physicist Richard K. Feynman, in a talk he gave in 1959 titled “There’s Plenty of Room at the Bottom,” asked, “What would happen if we could arrange atoms, one by one, the way we needed?” He offered prizes of $1000 apiece to the first person who could shrink the information on a printed page to twenty-five thousandths of its original size (which would allow you to put the entire Encyclopedia Britannica on the head of a pin) and to the first person who could make a working electric motor no larger than a cube one sixty-fourth of an inch on a side—about the size of the period at the end of this sentence.

Within a few years Feynman had to pay off on both prizes.

Drexler proposed building nanometer-sized machines that could manipulate matter one atom or molecule at a time. Take a pile of soot and build a starship out of its carbon atoms.

In the human body therapeutic nanomachines could serve as a purposeful super-immune system, destroying invading microbes, cleansing arteries of dangerous plaque buildup, strengthening bone and muscle.

Nanotechnology is inching forward (pardon the pun) and may indeed eventually allow us to make the human body virtually invulnerable to disease and injury.

Social Consequences

What happens to society when people can live for centuries? For millennia? When the death rate plummets close to zero?

Kiss goodbye to Social Security and other retirement plans, for one thing. But who will retire when they are youthful and vigorous, despite their calendar age?

Birth control will become crucially important. Unless the birth rate comes down to match the death rate, we will overpopulate ourselves into poverty, famine, war and extinction.

Maybe we will produce a society in which children are truly treasured, because they are rare. Maybe people will have children because they want to, rather than for their own egos or to satisfy their relatives or some other extraneous reason.

Slowboat to the Stars

Or maybe we won’t control our birth rate. Maybe we’ll expand out to the stars, instead. One of the possible consequences of life extension could be, at last, to give us the stars.

We know that other stars harbor planetary systems, although no Earth-like planets have yet been found. That will change, though, and probably quite soon.

But even if there are zillions of Earth-like planets waiting to be colonized, they are so far away that it seems unlikely we will ever reach them.

The distances to the stars are truly staggering. Proxima Centauri, the nearest star to our solar system, lies 4.3 light years away. It takes light, traveling at 183,000 miles per second, slightly more than four years to span the distance between us and Proxima. And nothing in the universe moves faster than light.

Science fiction stories use space warps or star drives that propel star ships faster than light, but in the real world nothing moves faster than light. There are good physical reasons to believe that nothing can, or ever will.

Which means that star travel will be restricted to “generations ships,” taking tens, hundreds, thousands of years to reach another star system. Far beyond a single human lifetime.

Oh really? If and when we can extend human life spans to centuries and millennia, the path to the stars lies open to us—even though we may be stuck with the universe’s speed limit of 186,000 miles per second.

Virtually immortal humans could travel through the universe on “slow boats.” Bring some good books!

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A SHORT HISTORY OF MEDICINE

Medical breakthroughs may seem miraculous, but it’s sobering to realize that medical practice has a long and interesting history.

“Doctor, I have an earache.”

200 BC: “Here, eat this root.”

100 AD: “That root is heathen. Say this prayer.”

1850 AD: “That prayer is superstition. Drink this potion.”

1940 AD: “That potion is snake oil. Swallow this pill.”

1985 AD: “That pill is ineffective. Take this antibiotic.”

2000 AD: “That antibiotic is artificial. Here, eat this root.”

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