Death



Death, therefore, the most awful of evils, is nothing to us, seeing that, when we are, death is not come, and, when death is come, we are not. It is nothing, then, either to the living or to the dead, for with the living it is not and the dead exist no longer. And I am not frightened of dying, any time will do, I don't mind. Why should I be frightened of dying? There's no reason for it, you've gotta go sometime.

Death is the end of life and is conceptually easier to understand than life. Everything that is not alive is dead, even if it never lived to begin with, like a piece of quartz. We measure life with thermodynamics, defining it as decreasing internal entropy while increasing it externally. Death is when the same physical and chemical processes carry on but increase entropy both internally and externally.

In humans
Death is a complicated subject for humans since we are subject to death at any time. And it is not so much a singular event, but like the beginning of life, is a sequence of events best described as a process rather than a single occurrence. For the sake of pragmatism, treating it as an event remains useful. Various conventions have existed to make a legal or medical decision regarding whether a person has "died."

This topic is crucial because doctors (and lawyers) need to know how to define death: when is it okay to stop trying to save someone's life, when can the organs be harvested for transplants, and when is it safe to say that someone has killed or been killed, and so on. Thus, death is a point where certain things stop happening.

Clinical death
Before heart-lung machines were available, the persistence of a pulse was the main factor when considering whether someone was alive or not. If someone's heart stops beating, their cells lose access to oxygen and nutrients carried in the blood, and they can't get up and walk. Neurons in the brain will begin to starve after ten seconds of oxygen deprivation, leading to loss of consciousness. Circulatory arrest exceeding 3 minutes may cause irreversible brain damage. This window corresponds to the time cells exhaust their ATP when unsustained, as Phagocytes can no longer work. Unable to clean up rogue enzymes and destroy decomposers, the body starts decaying after minutes.

"Clinical death" refers to the absence of a pulse. Notably, while clinical death often leads to brain death, it is not the same thing. Stories of people "coming back from the dead" or "being dead for three minutes" come from being clinically dead but not suffering irreversible brain failure. Tales of near-death experiences (NDEs) are always good for a book deal or a stint on Coast to Coast AM. The universality of the experiences across cultures suggests a biological explanation, like perhaps the reaction of any human brain to mortal trauma.

Unless there is some active intervention by modern medical technology, the entire process described below is an inevitable consequence of clinical death. In other words, if your heart stops, you will turn to mush.

Brain death
More recently, brain death has become a more relevant landmark. Although it depends on the presence or absence of brain activity, it can be difficult to assess, as an EEG will not necessarily show low levels. Although a lack of a pulse is a good indication that someone isn't going to make it, their consciousness may still work, if only for a few minutes. Brain death occurs when the brain is starved of oxygen, usually after the heart stops beating. Unlike the heart, though, brain death is currently irreversible. This definition can prove very controversial in cases where it's the other way around. Consciousness can fail perpetually, but the rest of the body can persist due to unconscious processes. Such was the case with Terri Schiavo, who unfortunately got tossed around like a political football. Various political conservatives tried to score points with fundamentalist Christians.

Cellular death
The whole idea of defining "death" becomes more complicated by cellular death. Even if someone's heart stops and their brain ceases to function, the chemical and biological processes inside each cell will go on. They will continue respiring, producing proteins, and replicating until they run out of energy in the form of food and oxygen. Cells are not intelligent or aware (even if the organism they form is), so they don't know that they're part of someone who has died. You could theoretically clone a pig from fresh sausages because many of the cells inside them are still alive (think about that next time you buy a string from the butcher's!).

However, a many-celled organism is an emergent entity arising from when cells join together and organize into tissues and organs to function together. Multi-cellular entities die when the cells fail to coordinate because the brain fails to monitor the entity's actions (brain death) or nutrients go astray (clinical death).

An issue with people who claim life begins at a cellular stage as an argument against abortion or birth control emerges here. To avoid special pleading, they should also conclude it would end at the cellular stage despite the infeasibility of tracking every last decomposing cell. No one says that "death" happens at cellular death.

Chemical death
Although not a "death" by any sensible definition, it is best to cover the final step. The shape of a body will still exist after death and often beyond even cellular death, although it may not look too good. At a chemical level, the previously living body stops resisting entropy and comes to equilibrium with the environment. Usually, this occurs through the influence of other still-living organisms via decomposition. Even the greatest hair-splitters in the world wouldn't want to push back the "point" of death further than this. It's not even clear how death is at any point after everything once in the body is scrambled out of existence from decomposition and erosion.

Information-theoretic death
Coined by people discussing cryonics, this concept describes brain annihilation so complete that no hypothetical technology could fix it, no matter how advanced it is. Due to how chemical death works, we can infer that the former implies the latter once it spreads to the whole body (barring infinitesimally improbable time travel). As even brain death remains irreversible, this concept lacks current practical uses.

Immortality
Immortality is the ability to never die. It currently remains hypothetical, and any real immortal being would eventually still have to deal with end-of-universe scenarios like the or, , etc. Immortality is common in religions; most gods are believed immortal, and most religions promise eternal paradise or torment.

Afterlife
See our main article on this subject.

An afterlife is a speculative concept that one's disembodied consciousness will magically leave the body post mortem. In the Good Old Days, it became trendy to worry about death - meaning the quality of one's putative afterlife. (Religious establishments fostered and played on such fears.) In depraved secular modern times, the average punter has transferred concerns about death to fixating on popular-media portrayals of murder.

Biological
One of the more immediately relevant obstacles to immortality is aging. Individual cells can only reproduce so many times before they accrue so much damage that they commit suicide via programmed cell death. This phenomenon appeared in animals as a "safety mechanism," lest some of those mutations make the cell cancerous.

As stated at the beginning of the article, single-celled creatures and plants often reproduce asexually, making "immortality" difficult to define for them. Is the growth of aspen trees "immortal" if nothing happens to them?

Biological immortality is immunity to aging; one's likelihood of dying doesn't change no matter how old one is. However, it does not imply a chance of 0%. You can still get eaten, starved, asphyxiated, exploded, or otherwise killed. "Immortality" is not synonymous with "invulnerability." It just means things won't break down as you age.

Biologically immortal creatures include:
 * Hydra, a genus of simple fresh-water animals possessing radial symmetry. All cells continually dividing allows defects and toxins to dilute among daughter cells. How hydrae keep their telomeres from shortening from replication is unknown.
 * Turritopsis nutricula, a 1/5-inch-long species of jellyfish that uses a process called transdifferentiation to replenish cells after sexual reproduction. As such, the life cycle of the immortal jellyfish goes from egg to planula (larval stage of stinging animals) to a polyp (sessile creature rooted to a substrate) to medusa (jellyfish), then back to a polyp, back to medusa, et cetera, ad infinitum. This cycle can potentially repeat indefinitely, rendering it biologically immortal. Unfortunately, the immortal jellyfish is zooplankton ("plankton" simply referring to any marine life that can't move against the current) and gets eaten a lot. The species originated in the Caribbean Sea but has since become cosmopolitan.
 * Both sexual and asexual planarian flatworms (class Turbellaria) appear to live indefinitely and have "apparently limitless [telomere] regenerative capacity fueled by a population of highly proliferative adult stem cells." A planarian can regenerate from as little as 1/279th of the original. Science!

Research
The metaphorical quest for the holy grail has been in people's minds for at least a few thousand years, not satisfied with merely a promising of spiritual agelessness, it has been attempted by people unscientifically. Many might be familiar with the story of the Chinese Emperor Qin Shi Huang. On his fifth tour, after a comet had struck, prophecies had informed him that he would die, and after becoming ill he had taken efforts to seek a cure for his mortality, his court alchemists handed him mercury, leading to his death, at least so the story goes. Along the years of history to the present, you can find many other stories of alchemists and magicians that had tried to find their immortality, all across the world. Today, a more empirical approach surfaced to genuinely start asking the questions of how we die in the first place, in a biological sense, and in doing so, maybe even find a way to prevent those mechanisms taking place and prolong our lives.

Today, anti-ageing research is a multi-billion dollar industry. Very rich people are very serious about solving this using the scientific method, and although you can find an absolute plethora of opportunistic quacks, there is a real body of researchers doing genuine work in that field. As of today, there is no known 'cure' for growing old, even though it is being worked on, claims to the contrary should probably be met with a dose of scepticism.