Indefinite lifespan

Indefinite lifespan is a term used in the life extension movement to refer to the longevity of humans, and other lifeforms, under conditions in which ageing can be effectively and completely prevented and treated. Such individuals would still be susceptible to accidental or intentional death (vehicular accidents, sporting injuries, murder, suicide, etc), but not death from aging. Their lifespans would be "indefinite," because protection from the effects of aging on health does not guarantee survival. The term "indefinite lifespans" is often considered to be technically correct by some life extensionists, as opposed to terms such as "immortality" which imply, as it were, an inability to ever die.

Actuarial escape velocity
The concept of actuarial escape velocity refers to a level of technological advancement at which indefinite lifespan can be achieved even though a complete cure for all aspects of aging, disease, and death is not currently foreseeable. Specifically, it refers to the situation in which the expected age at death is being advanced at more than one year per year. In that case, an individual's remaining life expectancy will actually increase rather than decreasing.

Current advancement is insufficient for this. However, as life extension research advances and results begin to become apparent to the public, it is hoped that funding will increase and research accelerate and younger individuals have greater chances of living indefinitely. When people begin to realise that it may be possible for them to achieve indefinite lifespans, or, even more effectively, if a person of more advanced age comes to realise that their life will probably end and that they will just "miss the window of opportunity" (thereby potentially making them one of the last people to die of aging), it will motivate large sets of the population to take a very serious interest in attaining the full range of benefits of the research as soon as possible. Soon, this will result in a large "buy-in" wherein everybody below a certain maximum age becomes almost certain of attaining indefinite lifespan as the rate at which breakthroughs and new techniques arrive begins to exceed the speed of the aging process in these individuals. Anybody older than that maximum age will probably be aging too rapidly already for the earliest treatments to be effective enough for them to survive to the next stage of treatments (assuming treatments decline in effectiveness the more advanced the aging process is), or the next stage after that, and so on. Therefore, life extensionists claim, it is important that we attempt to foster such buy-ins as soon as possible, because to not do so and continue on at the relatively leisurely pace of non-goal oriented research would be to allow massive numbers of people to simply drift past the threshold of actuarial escape velocity..

Immortality
The terms "immortality" and "eternal youth" are often used as synonyms for indefinite lifespan, but they carry connotations from their other contexts which science has deemed to be impossible. That is, immortality means "impervious to harm and incapable of dying", but from a scientific point of view, this is implausble due to the Law of Entropy. "Eternal youth" implies guaranteed existence for eternity, and in this context is also implausible because of entropy. Even if cures were found for all the degenerative diseases, and effective treatments were developed for all the processes of aging, so that bodies could be maintained as easily as cars can be repaired, people would still be killed in accidents, slain in wars, perish in natural disasters, etc. The term indefinite lifespan represents this more achieveable state of affairs, because it merely implies freedom from death by age or infirmity. The use of the term is also sometimes favoured for reasons of linguistic aesthetics, much like the term birth control is preferred to "birth prevention" or "birth elimination" which both imply, as does 'immortality', that the choice is one-time only and has permanent consequences, whereas the point of 'indefinite lifespans', like the point of 'birth control', is to gain the opportunity to lead one's life in a more conscious and deliberate manner.

Is indefinite lifespan possible?
This question is twofold. On the one hand it can be interpreted to mean, "Will a cure (or program of effective treatments) for aging ever be developed?" while on the other hand it could mean "Will the effective treatment of aging become available soon enough for those alive today to take advantage of it?" The answer to the first question is conditional on medical advancement: if medical science continues to advance in the fields of biogerontology and bioengineering, then some people hope the answer is "yes, that it will happen eventually, excepting if some event or series of events were to prevent the further advance of biological science" (see Nuclear warfare and the Doomsday Clock). Scientists researching this area at the moment do not agree. They see a problem in not just individual diseases but in failure of repair mechanisms alluded to above in the discussion of thermodynamic considerations.

While science is constantly advancing and technology is becoming ever more sophisticated, the human body and mind are finitely complex and have not changed significantly in one hundred thousand years, and the aging process has not, in that time, become any more damaging (which, in short, is why we live three times as long on average in the twenty-first century as we did ten thousand years before).

The answer to the second question depends on two factors: the first being how fast medical science advances, and the second being how well each person takes care of themselves (such as utilizing the best available life extension technology or not, and generally eating and behaving in a healthful and non-degrading way), both of which may affect whether or not a given person is still alive when the cure (or set of treatments) becomes available. This strategy is captured in the subtitle "Live Long Enough To Live Forever" of the popular life extension book Fantastic Voyage, by Ray Kurzweil and Terry Grossman M.D.

It should be noted that the second factor to the second question hinges on the first factor - no amount of healthy living will enable somebody alive today to reach the point of indefinite lifespan if medical science is curtailed significantly, or if aging turns out to be massively more complex than presently believed. However, if biomedical gerontology continues to improve, if somatic and germ line genetic engineering become safe and effective (and are not banned by opponents) within the relatively near future, it may be conceivable for some of those alive presently to attain indefinite lifespans.

Indefinite lifespan in fiction

 * The novel To Live Forever revolves around a grand prize of an indefinite lifespan given to the winner, as well as increased lifespans given to others.

Books

 * Fantastic Voyage: The Science Behind Radical Life Extension Raymond Kurzweil and Terry Grossman M.D., Rodale. 2004. 452pp.  ISBN 1-57954-954-3

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