Immortality

Immortality is the concept of eternal life and permanent resistance to death from natural causes. It is a subject that spans the realms of religion, science, and philosophy.

People have long wondered about the nature of unending existence. Some explore whether immortality is a spiritual state involving an immaterial soul. Others investigate whether it is a physical state that can be achieved through technology. This concept remains a major point of focus for human thought and speculation.

In religious contexts, immortality is often viewed as a promise from divine beings.

Ancient Mesopotamian and Greek traditions held that gods possessed physical bodies that were immortal. These religions also suggested that gods might grant physical immortality to certain humans. In Christianity, many followers believe in the resurrection of the flesh at the end of time. Other groups, such as Rastafarians or Rebirthers, also hold beliefs regarding physical immortality. These traditions often link eternal life to following divine law or performing virtue.

Historically, humans have pursued physical immortality through various legends and methods.

Ancient cultures spoke of the Fountain of Youth or the Peaches of Immortality. In the 16th century, alchemists sought to create the Philosopher's Stone to achieve life extension. Modern science has introduced new, speculative theories for reaching this goal. One idea is digital immortality, which involves uploading a human mind to a computer. Another is cryonics, which is the hope that the dead might be revived by future medical advancements.

Biological immortality refers to an absence of aging in a living organism.

Specifically, it is the absence of a sustained increase in mortality as a function of chronological age. Biologists use this term for cells that are not limited by the Hayflick limit. This limit occurs when cells stop dividing due to DNA damage or shortened telomeres. Telomeres are protective caps at the end of DNA strands. Every time a cell divides, the telomere becomes shorter. When it is worn down, the cell dies. The enzyme telomerase can rebuild these caps, allowing for infinite replication.

Some species demonstrate this biological immortality in nature.

Bacteria are considered essentially immortal because they reproduce through binary fission. A parent bacterium splits into two identical daughter cells, and this process repeats. The jellyfish *Turritopsis dohrnii* can transform itself from an adult back into a polyp. This process, called transdifferentiation, allows for an indefinite lifespan. The genus *Hydra* also possesses biological immortality. However, these organisms are physiologically very different from humans, and it is unknown if humans could achieve similar results.

To achieve human physical immortality, several major causes of death must be overcome.

The first is natural aging, which researcher Aubrey de Grey defines as cumulative molecular and cellular changes. These changes disrupt metabolism and result in pathology. To stop aging, one would need to solve issues like DNA damage, cell senescence, and mitochondrial mutations. The second challenge is disease, which is an abnormal condition affecting the body. While genetics and stem cell research offer hope for curing diseases like Parkinson's or cancer, many ailments remain.

Even if aging and disease are solved, other threats persist. Physical trauma from accidents or catastrophes remains a danger to a continuous physical life. A person would also need to survive environmental changes and resource limitations. Death through starvation or hypoxia is still possible if resources are unavailable. Some mathematicians suggest that if risks are mitigated enough, the probability of death over an infinite horizon might be less than certainty. This concept is related to achieving what is known as actuarial escape velocity.