Death
From RationalWiki
Death was a metal band from Florida is the end of life.
As a concept it is easier to define and apply to multicellular animals, since many plants and single-celled lifeforms are capable of dividing (mitosis), budding, or sprouting into what can become independent organisms which are genetic clones of the original critter.
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[edit] The moment of death
The exact moment of death is difficult to determine. Like the beginning of life, death has many points and can be best described as a process rather than a single point, but for many reasons, it's convenient to think of it as an event. Various conventions have been established to make a legal or medical decision regarding whether a person has died. This is very important because doctors (and lawyers) need to know how to define death; when is it okay to stop trying to save someone's life, when it is safe to say that someone has killed or been killed, and so on. Thus, death is defined as a point where certain things stop happening.
Before heart-lung machines were available, the persistence of a pulse was the main factor when considering if someone was alive or not. If someone's heart stops beating, then they cannot be supplied with oxygen from the blood and they are not going to get up and walk about. More recently, brain-death has been considered to be a more relevant point. This is demonstrated by the presence or absence of certain brain waves that can be measured - although the lack of a pulse is a good indication that someone isn't going to make it, their consciousness may still be working normally, if only for a few minutes. Brain death occurs when the brain is starved of oxygen, usually after the heart stops beating, but unlike the heart, the brain cannot be restarted. This definition can prove very controversial in cases where it is the other way around. Consciousness can stop (or at least be reduced so that any meaningful consciousness is lost), but the rest of the body can still continue. This was the case with Terri Schiavo, who was unfortunately tossed around like a proverbial political football by various political conservatives trying to score points with fundamentalist Christians.
[edit] Clinical death
When the pulse stops, this is referred to as "clinical death". It is important to note that while clinical death often leads to death, it is not the same thing. Stories of people "coming back from the dead" or "being dead for three minutes" are the result of people being classed as clinically dead but who haven't suffered irreversible brain failure. Tales of near death experiences (NDEs) are always good for a book deal, or a stint on Coast to Coast AM, but the universality of the experiences across cultures suggests a biological explanation, perhaps the reaction of any human brain to mortal trauma.
[edit] Cellular death
The whole idea of defining "death" becomes slightly more complicated by the idea of cellular death. Even if someone's heart stops, and their brain ceases to function, the chemical and biological processes inside each cell will continue. 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 that they form is) so don't know that they're part of someone who has died.
It is claimed that you could clone a pig from sausages if they're fresh enough, because many of the cells inside them are still alive (think about that next time you buy a fresh string from the butchers). So as cells live on, could a person be classed as still alive? Not necessarily, as a "person" or "being" (or whatever you prefer to say) is an emergent entity composed of these cells when they function together correctly. The death of the person is when these cells cease to function together to produce the emergent phenomena. This leads to a slight issue with people who claim that life begins at a cellular stage as an argument against abortion or birth control; as logically they should also conclude that if life begins at this cellular stage, it would also end at the cellular stage. As far as most people are aware, no one says that "death" happens at cellular death.
[edit] Chemical
Although not a "death" in any way by most definitions, it is best to cover the very final step. This is because the form of a body will still exist after death and often beyond even cellular death (although it may not look too good at this point). At a chemical level, the previously living body stops resisting entropy and comes to equilibrium with the environment. Usually this is through being consumed by a variety of other. still-living. organisms in a process termed decomposition. Even the greatest hair-splitters in the world wouldn't want to push back the "point" of death further than this.
[edit] Note
It should be noted that, unless there is some active intervention by medical technology, the entire process described above is an inevitable consequence of clinical death. In other words, if your heart stops, then you will turn to mush.
