  Life is a complex biological phenomenon represented by numerous chemical,
physical and biological processes performed by a biothermodynamic
system/cell/organism. Both living organisms and inanimate objects are subject
to aging, a biological and physicochemical process characterized by changes in
biological and thermodynamic state. Thus, the same physical laws govern
processes in both animate and inanimate matter. All life processes lead to
change of an organism's state. The change of biological and thermodynamic state
of an organism in time underlies all of three kinds of aging (chronological,
biological and thermodynamic). Life and aging of an organism both start at the
moment of fertilization and continue through entire lifespan. Fertilization
represents formation of a new organism. The new organism represents a new
thermodynamic system. From the very beginning, it changes its state by changing
thermodynamic parameters. The change of thermodynamic parameters is observed as
aging and can be related to change in entropy. Entropy is thus the parameter
that is related to all others and describes aging in the best manner. In the
beginning, entropy change appears as a consequence of accumulation of matter
(growth). Later, decomposition and configurational changes dominate, as a
consequence of various chemical reactions (free radical, decomposition,
fragmentation, accumulation of lipofuscin-like substances...).
