Any deep-rooted physicists would tell all beings are immortal as their ideas and beliefs are tightly held with the concept that energy cannot be destroyed. However, for a non-physicist, the precise definitions of life and death are somewhat indecipherable, because medically speaking, we know exactly when a living organism is declared dead.
The video released by TED-Ed Original explains the what is true death or the moment when exactly you are dead. True death is not something like death resulting from cerebral or brain death or a person whose heart has stopped beating, because we have seen death resulting from such conditions to be brought back to life. True death is when there is no point of return or being resurrected.
The cells activity in living organisms is driven by the oxygen and the glucose that our bodies convert into Adenosine triphosphate (ATP) which biologists consider to be the energy currency of life, from the moment an organism develops.
Our bodies follow universal law of entropy; and entropy as expressed by the Second Law of Thermodynamics, the activity of the molecules in our body can be derived from a molecule only when that molecule interacts with another at a lower temperature. Any spontaneous process such as complex cellular process results in an increase of entropy and if not kept constantly checked, the result is death.
Emergency life-saving procedures such as cardiopulmonary resuscitation and defibrillation can preclude death, but once the cell refuses to keep entropy in balanced or has succumbed to entropy, resurrection is impossible. However, scientists believe that if the cells can survive entropy, then they may exceed the point of no return.