Immortality is the ability to live forever, or put another way, it is an immunity from death. It is unknown whether human physical (material) immortality is an achievable condition —biological forms have inherent limitations which may or may not be able to be overcome through medicalinterventions or engineering. And even should human biological immortality be achieved, people could still continue to die from unforeseeabletraumatic events.
In religious (typically Christian) contexts, immortality is often stated to be among the promises by God (or other deities) to human beings who show goodness or else follow divine law (cf. resurrection). Moreover, only God is regarded as truly immortal, hence it is only through God's resources for resurrection and salvation that human beings may transcend death and live eternally.
Certain scientists, futurists, and philosophers, have theorized about the immortality of the material human body, and advocate that human immortality is achievable in the first few decades of the 21st century, while other advocates believe that life extension is a more achievable goal in the short term, with immortality awaiting further research breakthroughs into an indefinite future. Aubrey de Grey, a researcher who has developed a series of biomedical rejuvenation strategies to reverse human aging (called SENS), believes that his proposed plan for ending aging may be implementable in two or three decades. The absence of aging would provide humans with biological immortality, but not invulnerability to death by physical trauma.
The Epic of Gilgamesh, one of the first literary works, dating back at least to the 22nd century BC, is primarily a quest of a hero seeking to become immortal. What form an unending human life would take, or whether an immaterial soul exists and possesses immortality, has been a major point of focus of religion, as well as the subject of speculation, fantasy, and debate.
Eternal life can also be defined as a timeless existence, which 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."
Definitions
Physical
Definitions
Physical
The persistence of life itself across time is a form of immortality, insofar as leaving surviving offspring or genetic material is a means of defeating death. Life extension technologies promise a path to complete rejuvenation. Cryonics holds out the hope that the dead can be revived in the future, following sufficient medical advancements. While, as shown with creatures such as hydra andplanarian worms, it is indeed possible for a creature to be biologically immortal, it is as of yet unknown if it is possible for humans.
Mind uploading is the concept of transference of consciousness from a human brain to an alternative medium providing the same functionality. Assuming the process to be possible and repeatable, this would provide immortality to the consciousness, as predicted by futurists such as Ray Kurzweil.
Spiritual
The belief in an afterlife is a fundamental tenet of religions, including Hinduism, Sikhism, Christianity, Zoroastrianism, Islam, Judaism, and the Bahá'í Faith; however, the concept of an immortalsoul is not. The "soul" itself has different meanings and is not used in the same way in different religions and different denominations of a religion. In the Bible the soul (Hebrew, ne'phesh; Greek, psykhe') is a person or an animal or the life that a person or an animal enjoys. The soul is not something with a separate existence. It can and does die (see Ezekiel 18:4)
Physical immortality
Physical immortality is a state of life that allows a person to avoid death and maintain conscious thought. It can mean the unending existence of a person from a physical source other than organic life, such as a computer. In the early 21st century, physical immortality remains a goal rather than a current reality. Active pursuit of physical immortality can either be based on scientific trends, such as cryonics, digital immortality, breakthroughs in rejuvenation or predictions of an impending technological singularity, or because of a spiritual belief, such as those held byRastafarians or Rebirthers.
Causes of death
There are three main causes of death: aging, disease and trauma.
Aging
Aubrey de Grey, a leading researcher in the field, defines aging as follows: "a collection of cumulative changes to the molecular and cellular structure of an adult organism, which result in essential metabolic processes, but which also, once they progress far enough, increasingly disrupt metabolism, resulting in pathology and death." The current causes of aging in humans are cell loss (without replacement), DNA damage, oncogenic nuclear mutations and epimutations, cell senescence, mitochondrial mutations, lysosomal aggregates, extracellular aggregates, random extracellular cross-linking, immune system decline, and endocrine changes. Eliminating aging would require finding a solution to each of these causes, a program de Grey calls engineered negligible senescence. It has also been researched that aging is not driven by genes, and that it is driven by random events. Everything in the world changes or ages without being driven by a purpose. There is also no direct evidence that proves that age changes are governed by a genetic program. There is also a huge body of knowledge indicating that change is characterized by the loss of molecular fidelity. This leads to the fact that there is no longer a chance for repair and turnover, increasing the vulnerability to pathology or age-associated diseases.
Disease
Disease is theoretically surmountable via technology. In short, it is an abnormal condition affecting the body of an organism, something the body shouldn't typically have to deal with its natural make up. Human understanding of genetics is leading to cures and treatments for myriad previously incurable diseases. The mechanisms by which other diseases do their damage are becoming better understood. Sophisticated methods of detecting diseases early are being developed. Preventative medicine is becoming better understood. Neurodegenerative diseases likeParkinson's and Alzheimer's may soon be curable with the use of stem cells. Breakthroughs in cell biology and telomere research are leading to treatments for cancer. Vaccines are being researched for AIDS and tuberculosis. Genes associated with type 1 diabetes and certain types of cancer have been discovered allowing for new therapies to be developed. Artificial devices attached directly to the nervous system may restore sight to the blind. Drugs are being developed to treat myriad other diseases and ailments.
Trauma
Physical trauma would remain as a threat to perpetual physical life, even if the problems of aging and disease were overcome, as an otherwise immortal person would still be subject to unforeseen accidents or catastrophes. Trauma is an experience which is related to both the subjective and objective components of a situation. "It is not merely a situational phenomenon, but a socio-psychological process which develops in time and follows a course." Longevity researchers would prefer to mitigate the risk of encountering trauma. Taking preventative measures by engineering inherent resistance to injury is thus relevant, in addition to entirely reactive measures more closely associated with the paradigm of medical treatment.
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. Without improvements to such things, very few people would remain alive after several tens of thousands of years purely based on accident rate statistics, much less millions or billions or more.
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.
If there is no limitation on the degree of gradual mitigation of risk then it is possible that the cumulative probability of death over an infinite horizon is less than certainty, even when the risk of fatal trauma in any finite period is greater than zero. Mathematically, this is an aspect of achieving "Actuarial escape velocity".
Biological immortality
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. The first and still most widely used immortal cell line is HeLa, developed from cells taken from the malignant cervical tumor of Henrietta Lacks without her consent in 1951. Prior to the 1961 work of Leonard Hayflick and Paul Moorhead, 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.
Biologically immortal species
Life defined as biologically immortal is still susceptible to causes of death besides aging, including disease and trauma, as defined above. Notable immortal species include:
- Turritopsis nutricula, a jellyfish, after becoming a sexually mature adult, can transform itself back into a polyp using the cell conversion process of transdifferentiation. Turritopsis nutricularepeats this cycle, meaning that it may have an indefinite lifespan. Its immortal adaptation has allowed it to spread from its original habitat in the Caribbean to "all over the world".
- Bacteria (as a colony) – Bacteria reproduce through Binary Fission. A parent bacterium splits itself into two identical daughter cells. These daughter cells then split themselves in half. This process repeats, thus making the bacterium colony essentially immortal.
A 2005 PLoS Biology paper suggests that in a bacterial colony, every particular bacterial cell may be considered to eventually die since after each division the daughter cells can be identified as the older and the younger, and the older is slightly smaller, weaker, and more likely to die than the younger. - Bristlecone Pines are speculated to be potentially immortal; the oldest known living specimen is over 4800 years old.
- Hydra is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa.
As the existence of biologically immortal species demonstrates, there is no thermodynamic necessity for senescence: a defining feature of life is that it takes in free energy from the environment and unloads its entropy as waste. Living systems can even build themselves up from seed, and routinely repair themselves. Aging is therefore presumed to be a byproduct of evolution, but why mortality should be selected for remains a subject of research and debate. Programmed cell death and the telomere "end replication problem" are found even in the earliest and simplest of organisms. This may be a tradeoff between selecting for cancer and selecting for aging.
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.
Life-extending substances
There are some known naturally occurring and artificially produced chemicals that can dramatically increase the lifetime or life-expectancy of a person or organism, such as resveratrol. Future research might enable scientists to increase the effect of these existing chemicals or to discover new chemicals (life-extenders) which might enable a person to stay alive as long as the person consumes them at specified periods of time.
Scientists believe that boosting the amount or proportion of a naturally forming enzyme, telomerase, in the body could prevent cells from dying and so may ultimately lead to extended, healthier lifespans. Telomerase is a protein that helps maintain the protective caps at the ends of chromosomes. A team of researchers at the Spanish National Cancer Centre (Madrid) tested the hypothesis on mice. It was found that those mice which were genetically engineered to produce 10 times the normal levels of telomerase lived 50% longer than normal mice.
In normal circumstances, without the presence of telomerase, if a cell divides repeatedly, at some point all the progeny will reach their Hayflick limit. With the presence of telomerase, each dividing cell can replace the lost bit of DNA, and any single cell can then divide unbounded. While this unbounded growth property has excited many researchers, caution is warranted in exploiting this property, as exactly this same unbounded growth is a crucial step in enabling cancerous growth. If an organism can replicate its body cells faster, then it would theoretically stop aging.
Embryonic stem cells express telomerase, which allows them to divide repeatedly and form the individual. In adults, telomerase is highly expressed in cells that need to divide regularly (e.g., in the immune system), whereas most somatic cells express it only at very low levels in a cell-cycle dependent manner.
Technological immortality
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 brain trauma. This supports the theory that we will be able to continually create biological or synthetic replacement parts to replace damaged or dying ones.
Cryonics
Cryonics, the practice of preserving organisms (either intact specimens or only their brains) for possible future revival by storing them at cryogenic temperatures where metabolism and decay are almost completely stopped, can be used to 'pause' for those who believe that life extension technologies will not develop sufficiently within their lifetime. Ideally, cryonics would allow clinically dead people to be brought back in the future after cures to the patients' diseases have been discovered and aging is reversible. Modern cryonics procedures use a process called vitrificationwhich creates a glass-like state rather than freezing as the body is brought to low temperatures. This process reduces the risk of ice crystals damaging the cell-structure, which would be especially detrimental to cell structures in the brain, as their minute adjustment evokes the individual's mind.
Mind-to-computer uploading
One idea that has been advanced involves uploading an individual's personality and memories via direct mind-computer interface.The individual's memory may be loaded to a computer or to a newly born baby's mind. The baby will then grow with the previous person's individuality, and may not develop its own personality. Extropian futurists like Moravec and Kurzweil have proposed that, thanks to exponentially growing computing power, it will someday be possible to upload human consciousness onto a computer system, and live indefinitely in a virtual environment. This could be accomplished via advanced cybernetics, where computer hardware would initially be installed in the brain to help sort memory or accelerate thought processes. Components would be added gradually until the person's entire brain functions were handled by artificial devices, avoiding sharp transitions that would lead to issues of identity. After this point, the human body could be treated as an optional accessory and the mind could be transferred to any sufficiently powerful computer. Another possible mechanism for mind upload is to perform a detailed scan of an individual's original, organic brain and simulate the entire structure in a computer. What level of detail such scans and simulations would need to achieve to emulate consciousness, and whether the scanning process would destroy the brain, is still to be determined.[30] Whatever the route to mind upload, persons in this state would then be essentially immortal, short of loss or traumatic destruction of the machines that maintained them.
Cybernetics
Transforming a human into a cyborg can include brain implants or extracting a human mind and placing it in a robotic life-support system. Even replacing biological organs with robotic ones could increase life span (i.e., pace makers) and depending on the definition, many technological upgrades to the body, like genetic modifications or the addition of nanobots would qualify an individual as a cyborg. Such modifications would make one impervious to aging and disease and theoretically immortal unless killed or destroyed.
Evolutionary immortality
Another approach, developed by biogerontologist Marios Kyriazis, holds that human biological immortality is an inevitable consequence ofevolution. As the natural tendency is to create progressively more complex structures, there will be a time (Kyriazis claims this time is now ), when evolution of a more complex human brain will be faster via a process of developmental singularity rather than through Darwinian evolution. In other words, the evolution of the human brain as we know it will cease and there will be no need for individuals to procreate and then die. Instead, a new type of development will take over, in the same individual who will have to live for many centuries in order for the development to take place. This intellectual development will be facilitated by technology such as synthetic biology, artificial intelligence and a technological singularity process.
Mystical and religious pursuits of physical immortality
Many Indian fables and tales include instances of metempsychosis—the ability to jump into another body—performed by advanced Yogis in order to live a longer life. There are also entire Hindu sects devoted to the attainment of physical immortality by various methods, namely the Naths and the Aghoras.
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 Vallalarclaimed 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 forever. 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.