Benjamin Franklin: I wish it were possible... to invent a method of embalming drowned persons, in such a manner that they might be recalled to life at any period, however distant; for having a very ardent desire to see and observe the state of America a hundred years hence, I should prefer to an ordinary death, being immersed with a few friends in a cask of Madeira, until that time, then to be recalled to life by the solar warmth of my dear country! But... in all probability, we live in a century too little advanced, and too near the infancy of science, to see such an art brought in our time to its perfection.

—Letter to Jacques Dubourg, April 1773

Eternal life may come within our reach once we understand enough about how our knowledge and mental processes are embodied in our brains. For then we should be able to duplicate that information — and then into more robust machinery. This might be possible late in this century, in view of how much we are learning about how human brains work — and the growth of computer capacities.

However, this could have been possible long ago if the progress of science had not succumbed to the spread of monotheistic religions. For as early as 250 BCE, Archimedes was well on the way toward modern physics and calculus. So in an alternate version of history (in which the pursuit of science did not decline) just a few more centuries could have allowed the likes of Newton, Maxwell, Gauss, and Pasteur to anticipate our present state of knowledge about physics, mathematics, and biology. Thenperhaps by 300 AD we could have learned so much about the mechanics of minds that citizens could decide on the lengths of their lives.

I'm sure that not all scholars would agree that religion retarded the progress of science. However, the above scenario seems to suggest that Pascal was wrong when he concluded that only faith could offer salvation. For if science had not lost those millennia, we might be already be able to transfer our minds into our machines. If so, then you could rightly complain that religions have deprived you of the option of having an afterlife!

Do we really want to lengthen our lives?

Woody Allen: I don't want to achieve immortality through my work. I want to achieve it through not dying.

In discussing this prospect with various groups, I was surprised to find that the idea of extending one's lifetime to thousands of years was often seen as a dismal suggestion. The response to my several informal polls included such objections as these: "Why would anyone want to live for a thousand hundred years? What if you outlived all your friends? What would you do with all that time? Wouldn't one's life become terribly boring?"

What can one conclude from this? Perhaps some of those persons lived with a sense that they did not deserve to live so long. Perhaps others did not regard themselves as having worthy long term goals. In any case, I find it worrisome that so many of our citizens are resigned to die. A planetful of people who feel that they do not have much to lose: surely this could be dangerous. (I neglected to ask the religious ones why perpetual heaven would be less boring.)

However, my scientist friends showed few such concerns: "There are countless things that I want to find out, and so many problems I want to solve, that I could use many centuries." I'll grant that religious beliefs can bring mental relief and emotional peace—but I question whether these, alone, should be seen as commendable long-term goals.

The quality of extended lives

Anatole France: The average man, who does not know what to do with his life, wants another one which will last forever.

Certainly, immortality would seem unattractive if it meant endless infirmity, debility, and dependency upon others—but here we'll assume a state of perfect health. A somewhat sounder concern might be that the old ones should die to make room for young ones with newer ideas. However, this leaves out the likelihood that are many important ideas that no human person could reach in, say, less than a few hundred well focused years. If so, then a limited lifespan might deprive us of great oceans of wisdom that no one can grasp.

In any case, such objections are shortsighted because, once we embody our minds in machines, we'll find ways to expand their capacities. You'll be able to edit your former mind, or merge it with parts of other minds — or develop completely new ways to think. Furthermore, our future technologies will no longer constrain us to think at the crawling pace of "real time." The events in our computers already proceed a millions times faster than those in our brain. To such beings, a minute might seem as long as a human year.

How could we download a human mind?

Today we are only beginning to understand the machinery of our human brains, but we already have many different theories about how those organs embody the processes that we call our minds. We often hear arguments about which of those different theories are right — but those often are the wrong questions to ask, because we know that every brain has hundreds of different specialized regions that work in different ways. I have suggested a dozen different ways in which our brains might represent our skill and memories. It could be many years before we know which structures and functions we'll need to reproduce.

(No such copies can yet be made today, so if you want immortality, your only present option is to have your brain preserved by a Cryonics company. However, improving this field still needs further research — but there is not enough funding for this today — although the same research is also needed for advancing the field of transplanting organs.)

Some writers have even suggested that, to make a working copy of a mind, one might have to include many small details about the connections among all the cells of a brain; if so, it would require an immense amount of machinery to simulate all those cells' chemistry. However, I suspect we'll need far less than that, because our nervous systems must have evolved to be insensitive to lower-level details; otherwise, our brains would rarely work.

Fortunately, we won't need to solve all those problems at once. For long before we are able to make complete "backups" of our personalities, this field of research will produce a great flood of ideas for adding new features and accessories to our existing brains. Then this may lead, through smaller steps, to replacing all parts of our bodies and brains — and thus repairing all the defects and flaws that make presently our lives so brief. And the more we learn about how our brains work, the more ways we will find to provide them with new abilities that never evolved in biology.