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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 aging can be effectively and completely prevented and treated. Such individuals would still be susceptible to accidental or intentional death by trauma, 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, especially in religious contexts, an inability to ever die.
Life expectancy increases slightly every year as treatment strategies and technologies improve. At present, more than one year of research is required for each additional year of expected life. Actuarial escape velocity occurs when this ratio reverses, so that expected years of remaining life actually increases each year.
The concept was first publicly proposed by David Gobel, founder of the Methuselah Foundation. The idea has been championed by biogerontologist Aubrey de Grey and futurist Ray Kurzweil. These two claim that that by putting further pressure on science and medical to focus research on increasing limits of ageing, rather than continuing along at its current pace, more lives will be saved in the future, even if the benefit does not immediately seem apparent.
Calorie restriction has been presented as a piece of the puzzle of reaching actuarial escape velocity.
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 "incapable of dying". "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, choosing to die, 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.
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 genetic engineering becomes safe and effective (and is not banned by opponents) within the relatively near future, it may be conceivable for some of those alive presently to attain indefinite lifespans.
Most 30+ year olds who wish to live longer, so that perhaps they reach a future where regeneration is possible, will concentrate on healthy living measures. An alternative that is on the horizon, and being explored on a number of disjointed fronts, is the concept of using a variation on hibernation or reversible, 'cut down' version of cryonics where human metabolism is reversibly stopped at low temperatures for short, perhaps 5 year episodes. Twenty-First Century Medicine for example, recently took a rabbit kidney down to minus 135ºC and brought it back viable. 'Skipping forwards' using some variation of hibernation or cryonics may be a viable approach to 'buying time' ,.
↑ 1.0 1.1 de Grey, Aubrey D. N. J. (June 15, 2004). "Escape Velocity: Why the Prospect of Extreme Human Life Extension Matters Now". PLoS Biol 2 (6): 723–726. doi:10.1371/journal.pbio.0020187. http://biology.plosjournals.org/perlserv/plosonline/%3Frequest%3Dget-document&doi%3D10.1371/journal.pbio.0000045?request=get-document&doi=10.1371/journal.pbio.0020187. Retrieved on 12 February 2007.