About our discussion of whether one can come back from the dead. Death as process:
Death in this context is now seen as less an event than a process: conditions once considered indicative of death are now reversible. Where in the process a dividing line is drawn between life and death depends on factors beyond the presence or absence of vital signs. In general, clinical death is neither necessary nor sufficient for a determination of legal death. A patient with working heart and lungs determined to be brain dead can be pronounced legally dead without clinical death occurring. Precise medical definition of death, in other words, becomes more problematic, paradoxically, as scientific knowledge and technology advance.
How to define death?
Death would seem to refer to either the moment at which life ends, or when the state that follows life begins. However, determining when death has occurred requires drawing precise conceptual boundaries between life and death. This is problematic however because there is little consensus over how to define life. Some have suggested defining life in terms of consciousness. When consciousness ceases, a living organism can be said to have died. One of the notable flaws in this approach is that there are many organisms which are alive but probably not conscious (for example, single-celled organisms). Another problem with this approach is in defining consciousness, which remains a mystery to modern scientists, psychologists and philosophers. This general problem of defining death applies to the particular challenge of defining death in the context of medicine.
Historically, attempts to define the exact moment of a human's death have been problematic. Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, but the development of CPR and prompt defibrillation have rendered that definition inadequate because breathing and heartbeat can sometimes be restarted. Events which were causally linked to death in the past no longer kill in all circumstances; without a functioning heart or lungs, life can sometimes be sustained with a combination of life support devices, organ transplants and artificial pacemakers.
Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death" to define a person as being clinically dead; people are considered dead when the electrical activity in their brain ceases. It is presumed that an end of electrical activity indicates the end of consciousness. However, suspension of consciousness must be permanent, and not transient, as occurs during certain sleep stages, and especially a coma. In the case of sleep, EEGs can easily tell the difference.
