Thermodynamics Essay, Research Paper
You arrive at your office and unpack your breakfast. The piping-hot tea and chilly orange juice you purchased just minutes ago are now both lukewarm. Why can t the tea steal heat from the juice to stay hot? Why does even the most state-of-the-art car operate at a mere 30 percent efficiency? Why can t some genius create a perpetual motion machine? The answers lie in the field of thermodynamics. Thermodynamics is the study of the mechanical action or relations of heat. It turns out that the flow of heat from the tea into the air- or from any body into a cooler one, for that matter- defines the flow of time itself. Earlier is, by definition, the time when the cup was hot, later the time when it is cool (Von Baeyer xiv). This idea is what gave scientists the concept of real and imaginary time. Stephen Hawking says, Imaginary time is indistinguishable from directions in space. If one can go north, one can turn around and head south; equally, if one can go forward in imaginary time, one ought to be able to turn around and go backward (Hawking 182). Real time on the other hand follows certain arrows, or directions in space. This is where the difference between past and future comes from. This is why we remember the past but not the future. In his book Maxwell s Demon, Von Baeyer explains how without this arrow of time provided by thermodynamics, we would be living in a reversible world, in which time could flow forward, backward, or not at all (Von Baeyer xiv). In this essay I will explain further how the flow of heat, or increase in disorder of the universe, is intimately related to the forward progression of the time that we experience.
If an arrow is drawn arbitrarily, and if as one follows this arrow, he finds more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases, the arrow points towards the past (Fraser 100). Stephen Hawking described these arrows of time in his book The Illustrated A Brief History of Time. He says, there are at least three different arrows of time. First there is the thermodynamic arrow of time, the direction of time in which disorder or entropy increases. Then there is the psychological arrow of time. This is the direction in which we feel time passes, the direction in which we remember the past but not the future. Finally there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting (Hawking 184-5).
Now that we ve given time the property of direction, we can begin to try to understand the thermodynamic progression of time. Assuming that the universe has no boundary, it can be argued that all of Hawking s arrows point in the same direction. He says the psychological arrow is determined by the thermodynamic arrow, and that these two arrows necessarily always point in the same direction. [And] There must be well-defined thermodynamic and cosmological arrows of time, but they will not point in the same direction for the whole history of the universe it is only when they do that conditions are suitable for the development of intelligent beings (Hawking 186).
As far as humans are concerned, the thermodynamic arrow of time gives rise to the laws of thermodynamics. The First Law of Thermodynamics is the law of conservation of energy. It states that energy cannot be created or destroyed. Instead it is converted from one form to another, such as from work to heat, from heat to light, or from chemical to heat, or such. As the universe expands, energy tends towards unordered states, but it is not increased or decreased in total relative amount. The Second Law of Thermodynamics has several variations. One version says that some heat is always wasted when converting heat into mechanical energy. Another states that heat normally flows from high to low temperatures.
So why do hot cups cool off? The answer lies in the fact that the universe itself is expanding. Say the universe started off infinitely small and infinitely dense, then expanded at an exponential rate as fluctuations in density increased, eventually forming galaxies. This explanation of the universe would explain the existence of the thermodynamic arrow of time. Because the universe is expanding, disorder is increasing. It can t be stopped. No one and nothing is powerful enough to break the laws of thermodynamics, no one that is, besides Maxwell s Demon.
Albert Einstein once said, thermodynamics is the only physical theory of general nature of which I am convinced that it will never be overthrown. If you want to know what s going on in the physical world, you simply have to follow the heat. In Maxwell s Demon: Why Warmth Disperses and Time Passes, physics professor Hans Christian Von Baeyer tells the story of heat through the lives of the scientists who discovered it, most notably James Clerk Maxwell. He took his inquiries to the atomic scale and used his demon to explain the concepts of energy conservation and heat flow as we observe them. An intelligent, microscopic gremlin that could sort atoms as they flew by, the demon could, in theory, reverse heat flow. Because this great feat of the demon broke the laws of thermodynamics, the question of why these phenomenom weren t observed in nature could only be answered by the fact that the direction in which time was progressing wouldn t allow them to be.
To understand the forward flow of time, Hawking asks us to suppose that God decided that the universe should finish up in a state of high order but that it didn t matter what state it started in (Hawking 187). This would mean that disorder would increase with time. One could observe a broken bottle gathering itself together on the floor and jumping back up onto the table. Such beings would have a psychological arrow of time that is backward. This means that I could take a warm beer, set it on the counter, and in some mysterious way, the colder particles in the room would become ordered, or congregate around the bottle, making the beer cold! This makes the second law of thermodynamics almost trivial. Disorder increases with time because we measure time in the direction in which disorder increases. You can t have a safer bet than that.
Why don t we see broken things gathering themselves together, or slices of pizza jumping out of our stomachs and into our hands? Taking into consideration the two universal metaphysical beliefs concerning irreversibility and time, it is assumed that there must exist at least one physical process that is truly irreversible. [and] Once such a process has been identified it will either itself be found responsible for the one-wayness of our experience of time or it will lead us to the physical process which really is (Fraser 109). What is a necessary condition to define irreversible, is that nature has to have such a preference for a final state that the reverse process becomes meaningless. After all, although a process may not normally run backward, the initial conditions could somehow be stored. Time moves forward and heat dissipates in our universe because a time- reverse process of life is meaningless (Fraser 111).
The laws of science do not distinguish between the forward and backward directions of time, it is the arrows of time that distinguish the past from the future. The big bang theory of the universe says that the universe started off in a smooth and ordered state which began to expand or become disordered. The strong thermodynamic arrow of the expanding universe is necessary for the existence of intelligent beings. For example, in order to live, people have to eat food, which is an ordered form of energy, and convert it into heat, which is a disordered form of energy.
So, is time infinite? The answer to this question is not clear. It all depends on the future of the universe. As long as the universe continues to expand, we will witness the forward progression of time. If, however, the universe were to contract in the future time would run in reverse, slowly at first, then with increasing speed. As explained before, because the time reverse process isn t suitable for the development of life, we wouldn t be around to witness any of this, however there isn t any evidence against it.
Most would probably think it absurd that a cup of tea cooling off determines the flow of time, but water runs and stones roll downhill, and this tends in the long run to flatten out the high spots and fill in the low ones. Heat moves from hotter bodies to cooler ones as time progresses. In infinite other ways, also, nature tends toward mediocrity- a dead level of uniformity and quiescence (Russell 4). The conclusion is unpleasant, but is supported by the tremendous weight of the law of averages. It is much more likely that something be in one of its infinite numbers of disordered states rather than its one ordered one. With regards to the future, the universe bids fair by an overwhelming probability to become gradually less and less interesting (Russell 6). Reading this paper has probably taken you about five minutes. During this time you will have increased the amount of ordered information in your brain. However, during the same time, the heat released from your body will have had a much greater effect increasing the disorder in the rest of the universe. I suggest you stop reading now. (Hawking 195).
Fraser, J.T. The Genesis and Evolution of Time. Amherst: The University of
Massachusetts Press, 1982.
Hawking, Stephen. The Illustrated A Brief History of Time. New York: Bantam Books,November 1996.
Russell, Henry Norris. Time Scale of the Universe. Time and its Mysteries: SeriesThree. New York: New York University Press, 1949.
Von Baeyer, Hans Christian. Maxwell s Demon: Why Warmth Disperses and Time
Passes. New York: Random House, 1998.