See C. J. Caes, Beyond Time: Ideas of the Great Philosophers on Eternal Existence and Immortality (1985); P. and L. Badham, Death and Immortality in the Religions of the World (1987).
As immortality is the negation of mortality—not dying or not being subject to death—it has been a subject of fascination to mankind since at least the beginning of history. The Epic of Gilgamesh, one of the first literary works, dating back at least to the 22nd century BCE, is primarily a quest of a hero seeking to become immortal. What form an unending human life would take, or whether the soul exists and possesses immortality, has been a major point of focus of religion, as well as the subject of speculation, fantasy, and debate.
It is not known whether human physical immortality is an unachievable phenomenon or not. Biological forms have inherent limitations — for example, their fragility and slow adaptability to changing environments, which may or may not be able to be overcome through medical interventions, engineering, etc. On the other hand, biological immortality already exists among some simple, but multicellular life-forms.
Some scientists, futurists, and philosophers, such as scientists Aubrey de Grey and Ray Kurzweil believe that human immortality is achievable in the next few decades. Others are somewhere in the middle of these two extreme viewpoints, thinking that immortality is achievable in some period of time longer than 20-30 years, but not impossible.
Biological immortality is what life extension advocates feel is likely in decades to come. Specifically this refers to the abscence of aging of the body due to baseline biological human limitations, but acknowledgement that complete immortality in a human form is unlikely due to the fact that even when you remain biologically young, once every few hundred years individuals will get killed in an accident (4.4% of U.S. deaths now) or by other means .
Ultimately, a timeless existence is also not known for certain to be achievable, or even definable, despite millennia of arguments for eternity. Wittgenstein, in a notably non-theological interpretation of eternal life, writes in the Tractatus that, "If we take eternity to mean not infinite temporal duration but timelessness, then eternal life belongs to those who live in the present."
The speed and quality of paramedic response remains a determining factor in surviving severe trauma. A body that could automatically treat itself from severe trauma, such as speculated uses for nanotechnology, would mitigate this factor.
Being the seat of consciousness, the brain cannot be risked to trauma if a continuous physical life is to be maintained. Therefore, it cannot be replaced or repaired in the same way other organs can. A method of transferring consciousness would be required for an individual to survive trauma to the brain, and this transfer would have to anticipate and precede the damage itself.
Biological immortality is an absence of aging, specifically the absence of a sustained increase in rate of mortality as a function of chronological age. A cell or organism that does not experience aging, or ceases to age at some point, is biologically immortal.
Biologists have chosen the word immortal to designate cells that are not limited by the Hayflick limit, where cells no longer divide because of DNA damage or shortened telomeres. Prior to the work of Leonard Hayflick there was the erroneous belief fostered by Alexis Carrel that all normal somatic cells are immortal. By preventing cells from reaching senescence one can achieve biological immortality; telomeres, a “cap” at the end of DNA, are thought to be the cause of cell aging. Every time a cell divides the telomere becomes a bit shorter; when it is finally worn down, the cell is unable to split and dies. Telomerase is an enzyme which rebuilds the telomeres in stem cells and cancer cells, allowing them to replicate an infinite number of times. No definitive work has yet demonstrated that telomerase can be used in human somatic cells to prevent healthy tissues from aging. On the other hand, scientists hope to be able to grow organs with the help of stem cells, allowing organ transplants without the risk of rejection, another step in extending human life expectancy. These technologies are the subject of ongoing research, and are not yet realized.
Modern theories on the evolution of aging include the following:
Mutation accumulation is a theory formulated by Peter Medawar in 1952 to explain how evolution would select for aging. Essentially, aging is never selected against, as organisms have offspring before the mortal mutations surface in an individual.
Antagonistic pleiotropy is a theory proposed as an alternative by George C. Williams, a critic of Medawar, in 1957. In antagonistic pleiotropy, genes carry effects that are both beneficial and detrimental. In essence this refers to genes that offer benefits early in life, but exact a cost later on, i.e. decline and death.
The disposable soma theory was proposed in 1977 by Thomas Kirkwood, which states that an individual body must allocate energy for metabolism, reproduction, and maintenance, and must compromise when there is food scarcity. Compromise in allocating energy to the repair function is what causes the body gradually to deteriorate with age, according to Kirkwood.
Technological immortality is the prospect for much longer life spans made possible by scientific advances in a variety of fields: nanotechnology, emergency room procedures, genetics, biological engineering, regenerative medicine, microbiology, and others. Contemporary life spans in the advanced industrial societies are already markedly longer than those of the past because of better nutrition, availability of health care, standard of living and bio-medical scientific advances. Technological immortality predicts further progress for the same reasons over the near term. An important aspect of current scientific thinking about immortality is that some combination of human cloning, cryonics or nanotechnology will play an essential role in extreme life extension. Robert Freitas, a nanorobotics theorist, suggests tiny medical nanorobots could be created to go through human bloodstreams, find dangerous things like cancer cells and bacteria, and destroy them. Freitas anticipates that gene-therapies and nanotechnology will eventually make the human body effectively self-sustainable and capable of living indefinitely, short of severe trauma. This supports the theory that we will be able to continually create biological or synthetic replacement parts to replace damaged or dying ones.
However, other futurists argue that it is impossible to move consciousness from one body to another, but that any successful attempt would be duplication, as the original would still exist, creating two independent consciousnesses.
Long before modern science made such speculation feasible, people wishing to escape death turned to the supernatural world for answers. Examples include Chinese Taoists and the medieval alchemists and their search for the Philosopher's Stone, or more modern religious mystics, who believed in the possibility of achieving physical immortality through spiritual transformation.
Individuals claiming to be physically immortal include Comte de Saint-Germain; in 18th century France, he claimed to be centuries old, and people who adhere to the Ascended Master Teachings are convinced of his physical immortality. An Indian saint known as Vallalar claimed to have achieved immortality before disappearing forever from a locked room in 1874.
Rastafarians believe in physical immortality as a part of their religious doctrines. They believe that after God has called the Day of Judgment they will go to what they describe as Mount Zion in Africa to live in freedom for ever. They avoid the term "everlasting life"' and deliberately use "ever-living" instead.
Another group that believes in physical immortality are the Rebirthers, who believe that by following the connected breathing process of rebirthing they can physically live forever.
Until the late 20th century, there were no creditable scientific forecasts that physical immortality was obtainable. As late as 1952, the editorial staff of the Syntopicon found that in their compilation of the Great Books of the Western World, "The philosophical issue concerning immortality cannot be separated from issues concerning the existence and nature of man's soul." Thus, the vast majority of speculation regarding immortality before the 21st century was regarding the nature of the afterlife.
Spiritual immortality, also known as the immortality of the soul, is the unending existence of a person from a nonphysical source, or in a nonphysical state, such as a soul.
It is a belief that is expressed in nearly every religious tradition. In both Western and Eastern religions, the spirit is an energy or force that transcends the mortal body, and returns to: (1) the spirit realm whether to enjoy heavenly bliss or suffer eternal torment in hell, or; (2) the cycle of life, directly or indirectly depending on the tradition.
The world's major religions hold a number of perspectives on spiritual immortality.
Hindus believe in an immortal soul which is reincarnated after death. According to Hinduism, people repeat a process of life, death, and rebirth in a cycle called samsara. If they live their life well, their karma improves and their station in the next life will be higher, and conversely lower if they live their life poorly. Eventually after many life times of perfecting its karma, the soul is freed from the cycle and lives in perpetual bliss. There is no eternal torment in Hinduism, temporal existence being harsh enough, although if a soul consistently lives very evil lives, it could work its way down to the very bottom of the cycle.
According to the philosophical premise of the Buddha, the initiate to Buddhism who is to be "shown the way to Immortality (amata)", wherein liberation of the mind (cittavimutta) is effectuated through the expansion of wisdom and the meditative practices of sati and samādhi, must first be educated away from his former ignorance-based (avijja) materialistic proclivities in that he "saw any of these forms, feelings, or this body, to be my Self, to be that which I am by nature".
Thus, desiring a soul or ego (ātman) to be permanent is a prime consequence of ignorance, itself the cause of all misery and the foundation of the cycle of reincarnation (saṃsāra). Form and consciousness being two of the five skandhas, or aggregates of ignorance, Buddhism teaches that physical immortality is neither a path to enlightenment, nor an attainable goal: even the gods which can live for eons eventually die. Upon enlightenment, the "karmic seeds" (saṅkhāras or sanskaras) for all future becoming and rebirth are exhausted. After biological death an arhat, or buddha, enters into parinirvana, an everlasting state of transcendental happiness.
The Hebrew Bible speaks about sheol (שאול), the underworld to which the souls of the dead depart. The doctrine of resurrection is mentioned explicitly only in although it may be implied in several other texts. Later Judaism accepted that there would be a resurrection of all men (cf. ) and the intertestamental literature describes in more detail what the dead experience in sheol. By the second century BC, Jews who accepted the Oral Torah had come to believe that those in sheol awaited the resurrection either in comfort (in the bosom of Abraham) or in torment.
Christian theology holds that Adam and Eve lost physical immortality for themselves and all their descendants in the Fall of Man, though this initial "imperishability of the bodily frame of man" was "a preternatural condition."
According to the book of Enoch, the righteous and wicked await the resurrection in separate divisions of sheol, a teaching which may have influenced Jesus' parable of Lazarus and Dives. Christians believe that every person that believes in Christ will be resurrected; Bible passages are interpreted as teaching that the resurrected body will, like the present body, be both physical (but a renewed and non-decaying physical body) and spiritual.
Specific imagery of resurrection into immortal form is found in the Pauline letters:
Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed,
In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.
For this corruptible must put on incorruption, and this mortal must put on immortality.
So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.
O death, where is thy sting? O grave, where is thy victory?
The sting of death is sin; and the strength of sin is the law.
But thanks be to God, which giveth us the victory through our Lord Jesus Christ.
Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord. —
In Romans 2:6-7 Paul declares that God "will render to every man according to his deeds: To them who by patient continuance in well doing seek for glory and honour and immortality, eternal life", but then in Romans 3 warns that no one will ever meet this standard.
After the Last Judgment, those who have been born again will live forever in the presence of God, and those who were never born again will be abandoned to never-ending consciousness of guilt, separation from God, and punishment for sin. Eternal death is depicted in the Bible as a realm of constant physical and spiritual anguish in a lake of fire, and a realm of darkness away from God. Some see the fires of Hell as a theological metaphor, representing the inescapable presence of God endured in absence of love for God; others suggest that Hell represents complete destruction of both the physical body and of spiritual existence.
After the final judgment, it is expected that the righteous will receive eternal life and live forever in an earth turned into a paradise. Another group referenced as "the little flock" of 144,000 people will receive immortality and go to heaven to rule as Kings and Priests. Jehovah's Witnesses make the distinction that those with 'eternal life' can die though they do not succumb to disease or old age, whereas immortal ones cannot die by any cause. They teach that Jesus was the first to be rewarded with heavenly immortality, but that Revelation 7:4 and Revelation 14:1, 3 refer to a literal number (144,000) of additional people who will become "self-sustaining," that is, not needing anything outside themselves (food, sunlight, etc.) to maintain their own life.
In Mormon theology, there are three degrees of glory which are the ultimate, eternal dwelling place for nearly all who lived on earth. Joseph Smith, Jr., the founder of the Latter Day Saint movement, provided a description of the afterlife based upon a vision he reportedly received, recorded within the Mormon canonical writings entitled Doctrine and Covenants. According to this section of LDS scripture, the afterlife consists of three degrees or kingdoms of glory, called the Celestial Kingdom, the Terrestrial Kingdom, and the Telestial Kingdom. The few who do not inherit any degree of glory (though they are resurrected) reside in a state called outer darkness, which, though not a degree of glory, is often discussed in this context. The only ones who go there are known as "Sons of Perdition".
Critics of the Latter Day Saint Movement argue that Joseph Smith used the ideas of Emanuel Swedenborg to formulate the theology surrounding the three degrees of glory.
Some sects who hold to the doctrine of baptismal regeneration also believe in a third realm called Limbo, which is the final destination of souls who have not been baptised, but who have been innocent of mortal sin. Souls in Limbo include unbaptised infants and those who lived virtuously but were never exposed to Christianity in their lifetimes. Christian Scientists believe that sin brought death, and that death will be overcome with the overcoming of sin.
Instances from other religions include the Buddhist concept of eternal rebirth, which considers that rebirth is caused by ignorance, an essentially undesirable condition that is to be overcome.
Physical immortality has also been imagined as a form of eternal torment, as in Mary Shelley's short story "The Mortal Immortal", the protagonist of which witnesses everyone he cares about dying around him. Jorge Luis Borges explored the idea that life gets its meaning from death in the short story "'The Immortal"; an entire society having achieved immortality, they found time becoming infinite, and so found no motivation for any action.
Physical immortality is considered desirable over its counterpart, death, which to date has been inevitable for all human beings. This presumes tolerable living conditions as an incentive for perpetual life, as the prevalence of suicide demonstrates.
There are numerous symbols representing immortality. Pictured here is an Egyptian symbol of life that holds connotations of immortality when depicted in the hands of the Egyptian deities and pharaohs who were seen as having control over the journey of life, the ankh (left). The Möbius strip in the shape of a trefoil knot is another symbol of immortality. Most symbolic representations of infinity or the life cycle are often used to represent immortality depending on the context they are placed in. Other examples include the Ouroboros, the Chinese fungus of longevity, the ten kanji, the phoenix, and the colors amaranth (in Western culture) and peach (in Chinese culture).