There is little information available on the study of the relation between the physics community and individuals involved in the study of humanities and social sciences. However, the available studies show a strong association between physics and time, and a weak correlation between physics and aging. Research shows a significant association between the field of physics and the study of the physiological, social and psychological elements of human aging (gerontology). The two fields examine the concept of time. Their correlation is also emphasized by the universalism of the phenomenon of death, which is considered as one of the forces of nature. Physics is closely associated with the laws of nature, and more so, in the Second Law of Thermodynamics. This law argues that all living organisms experience a steady increase in entropy, which takes them closer to death. This paper looks at the notion of time with regard to physics, the “arrow” of time and its connection to the Second Law of Thermodynamics.
Time in classical physics
Time is a key element in physics. Theoretical physics has a different view of time from experimental physics, which uses instruments to obtain an accurate value of time. The common definition of time, even for a physicist, is that it refers to a quantity that is measured on a clock. One of the flaws of this definition is that the clock can, in turn, be defined as an instrument that measures time. The challenge posed by that definition involves circularity between the definitions of time and the clock. The second flaw of the definition of time based on the clock is that it responds to a quantitative aspect of the measurement of time, and not the meaning of the term. Consequently, physicists suggest that theoretical physics lacks the fundamental and non-temporal notions necessary to accurately define time. The definition of time can only be arrived at by those involved in the philosophy of physics, or metaphysics. A proper definition of time is based on the notion that all events can be ordered in an organized whole. This implies that the element of time can be defined on the basis of temporal events such as “earlier than,” “later than,” or “simultaneous with.” Taking E to represent earlier events and F to represent a later event, then the notions stated earlier can be presented as
E <F, E> F and E ~ F.
The relation between physics, time and aging depend on the definition of systems as classical particles that are immutable, non-destructible elements of matter that are not capable of aging. The systems are also ascribed to a quantity that tracks the passage of time, or clock variables. The quantity used for free moving particles is its displacement while that used for free-falling bodies due to the gravitational pull is velocity. While there appears to be appropriate measures of different systems, the use of these clock variables to measure the age of the system is troublesome in theoretical physics. Part of the challenge is attributed to the passage of a system through the same state at different times of its evolution, which makes the process ambiguous.
The Arrow of Time
The phrase “Time’s Arrow” was coined by Eddington in order to point out the deficiencies of physics in identifying various aspects of time. Some of these include the concept of time being continuous, the irregularity between past and future, the difference between being and becoming, and the unchangeable nature of various physical processes.
One of the vital aspects of time expressed in the phrase is the notion of passage of time. Uffink suggests that human experience is based on the assumption that time is continuously moving further from the past towards an unknown future. This notion is expressed using scale A and scale B by McTaggart. Scale A uses a one-dimensional continuous ordering for the same events while scale B is a one-dimensional continuum where all events are ordered based on a date. Scale A shifts along scale B, and applies time terms like ‘now’, ‘yesterday’ and ‘next month’, among others.
The phrase can also be interpreted as portraying different ontological status to the events that occur in different times. For instance, the phrase can imply that past events are not actual and that the present events are the only ones that are real. The phrase can also be used to imply that the future is not actual, but is open. In this regard, the passage of time is identified with an ontological transition that is defined by the onset or realization of events. Prigogine suggests that Newton’s conception of absolute time, which states “time flows equably and of itself” has no limit to the occurrence of the event in the past, present or future. Consequently, scale B provides a basis for the physical theory while ontological divisions define the metaphysical roles.
Uffink suggests that tenses can only be used in the context of a physical description if imposed from an external source. He defines the correlation between tenses and physics using a physicality and symmetrical rationale. Based on the physicalistic viewpoint, Uffink states that the physical notion of reality can be perceived as a literally true description of reality. While this point of view supports the non reality of tenses, contradicting arguments suggest that physics is an enterprise that portrays characteristics that make it limited and abstract. This view holds that physics pertains to real aspects that can be expressed in terms of general laws and repeatable events. As a result, all matters that are accidental and non-repeatable or the aspects that lack evidence are considered to be unreal and have no basis in physics.
Another factor relating physics and tenses examines the element of symmetry under time reversal. The ability of an inverted sequence, such as that of a film that is played backwards, to look the same indicates time symmetry. Horwich defines time symmetry as the ability of a class of processes to retain their symmetry with time. He further states that there exists a censor in physics that is responsible for banning films containing scenes that violate the theory for either direction of play. Time reversal in this sense refers to non-physical theory, whereby symmetry is a property of the processes. Consequently, two different theories can perceive one process as both time symmetric and time asymmetric at the same time. The concept of time reversal is explored by Maxwell (187), whereby he states
“… If every motion great & small were accurately reversed, and the world left to itself again, everything would happen backwards. The fresh water would collect out of the sea and run up the rivers and finally up to the clouds in drops which would extract heat from the air and evaporate, and afterwards, in condensing, would shoot out rays of light to the sun and so on. Of course, all living things would regrede [sic] from the grave to the cradle, and we should have memory of the future but not of the past” (Maxwell 187-188).
Horwich suggests that all fundamental physical theories are time symmetric when measured on a microscopic scale. Hence, the world portrayed in Maxwell’s statements is accurate and physically possible. However, a large number of the macroscopic physical laws such as the Second Law of thermodynamics, Fourier’s heat equation and the diffusion equation are not time symmetric.
Irreversibility is a primary element in understanding the arrow of time. The term refers to processes that cannot be totally undone. Such processes cannot regain their initial state once they have occurred, despite the involvement of various auxiliary apparatus. Such processes include erosion, corruption, decay and aging. Plank suggests that all processes in the world are irreversible, due to the Second Law of Thermodynamics. According to Bridgman, the Second Law of thermodynamics holds that all systems in an equilibrium state are characterized by a quantity known as entropy. In addition, all transitions that the system undergoes in adiabatic isolation result in another state of equilibrium, whereby the entropy does not reduce (Maxwell 97).
Uffink (322) suggests that the confusion involving the interpretation of this law has led to numerous modifications in order to make it applicable to more general types of systems and situations. Alterations of the Second Law of Thermodynamics have led to new theories such as “generalized” thermodynamics, “extended” or “rational” thermodynamics, thermodynamics of irreversible processes, non-equilibrium thermodynamics, and continuum thermodynamics, among others. One of the modifications of the theory, by Prigogine, suggests that open dissipative systems are in a state of non-equilibrium. The theory holds that the systems undergo a change in entropy that is governed by both internal entropy production, di S, and an exchange of entropy, de S, with the surrounding. This yields equation (1).
dS = di S + de S…………………………………………………(1)
The law also holds that internal entropy production is never negative as indicated in equation (2) below
di S > 0………………………………………………………….(2)
The status of the Second Law of Thermodynamics in physics has been controversial over history, despite its success with regard to principles suggesting that there is a minimal level of entropy produced by a body. Another success of the law was its incorporation in the Onsager relation.
Some of the shortcomings of the law involve the resolution of entropy as the sum of internal entropy and change in entropy. Uffink (332) suggests that equation (1) holds irrespective of whether one of the values is negative and the other positive. However, an absolute value of entropy can be obtained by enhancing the definition of the law. The conventional interpretation of the Second Law of Thermodynamics assumes that internal entropy has a positive value at all times. However, this assumption is not applicable in non-equilibrium systems, though the assumptions are applied in some alterations of the law. Modifications of the Second Law of Thermodynamics make use of ordinary differential calculus, which makes their differential inequalities meaningless. However, there is still a correlation between the law and physics.
The Second Law of Thermodynamics
Uffink (152) suggests that living organism can be viewed as open thermodynamical systems in a steady state. Consequently, the system can be considered as having an entropy S, whose change is under the control of an internal entropy production, as well as, exchange with the surrounding. A steady state implies that the two terms neutralize their effects, whereby internal entropy production is compensated by an equivalent quantity of entropy that is lost to the surrounding. This yields the equation (3).
dS = di S + de S = 0……………………………(3)
Yates (99) offers an alternate comparison between living organisms and entropy production, arguing that the former cannot sustain a steady state of operation. Yates (102) states that “the internal thermodynamical engine cycles are not perfect, being themselves subject to the Second Law”. This implies that dS > 0 as indicated in equation (4).
di S > de S…………………………………………(4)
The buildup of entropy in the system causes disorder and eventually, death. This defines aging in thermodynamic terms as the increase in entropy with age (Yates 22). Uffink (153) identifies various faults in the interpretation by Yates of the Second Law of thermodynamics. According to Uffink, both living and non-living organisms experience a loosening of various elements with time, such as wear and tear, which are accompanied by a rise in entropy. However, Uffink (153) suggests that the constraints are not loosened, but altered through either addition or subtraction of constraints.
Another argument against the interpretation by Yates is that there is no relation between the accumulation of entropy in living organisms and aging. For instance, it is possible to prevent the build-up of entropy by increasing the rate of exchange with the surrounding. An example of such a scenario is locking a living organism inside a freezer without increasing its insulation. The organism would experience and increase in entropy that is less than the heat lost from the body to the surrounding, giving equation (5).
di S < de S……………………………………………………………………..(5)
While equation (5) varies from equation (4) due to the decrease in total entropy, the expression does not contradict the Second Law. However, this does not imply that the organism experiences negative aging. Additionally, the life of the organism may not be preserved, but instead, die from the cold. This implies that death cannot be equated to a state of maximum entropy as indicated by Yates, which means that there is no relation between death and thermodynamics. The condition of maximum entropy is achieved when organisms decay or cremate. As a result, human aging cannot be interpreted in terms of an increase or decrease of a one-dimensional physical attribute (Horwich 143).
In conclusion, the attempt to relate physics with aging uses the concept of human beings as physical systems. This aspect does not disregard the complex relationships of humans as psychological and social beings. However, the study of aging in physics requires a consideration of human beings as physical systems, instead of spiritual, rational agents. Despite the contradicting arguments, the study shows that living organisms, including human beings, are subject to the laws of thermodynamics. While all living organisms can be considered as open thermodynamic systems, human beings do not age the same way as microbes or inanimate objects. The study also shows that the concept of aging requires a deeper study of physical concepts, as well as, human biological, psychological and social make-up. In conclusion, it is true to say that physics can be related to time and the concept of age as a variable of a thermodynamically open system (Uffink 317).
Horwich, Paul. Asymmetries in time. Cambridge, MA: MIT Press, 1987. Print.
Maxwell, Clerk. Maxwell on heat and statistical mechanics. Bethlehem: Lehigh University Press, 1995.
Uffink, Jos. “Bluff your way in the second law of thermodynamics.” Philosophy and History of Modern Physics 32.1 (2001): 305-394. Print.
Yates, Eugene. “The dynamics of aging and time: How physical action implies social action.” Emergent theories of aging 3.12 (1988): 90-117. Print.