Keith Mack
The Second Law of Thermodynamics, which states that the entropy of an isolated system will always increase over time, has been considered one of the most fundamental laws of the universe. It is a powerful concept that has wide-ranging applications in scientific and engineering analysis, providing insights into energy quality, physical phenomena, and performance evaluation. However, despite its longstanding status as a cornerstone of physics, researchers have recently posited a potential loophole, suggesting that it may be possible to locally circumvent the Second Law on a microscopic scale. This discovery opens up new avenues of exploration and challenges our understanding of the fundamental principles governing the universe.
| Characteristics | Values |
|---|---|
| Status | For more than a century and a half, the Second Law of Thermodynamics has been considered as close to inviolable as any law in physics. |
| Description | The Second Law of Thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. |
| Entropy | The Second Law states that entropy always increases and that the state of entropy of the entire universe, as an isolated system, will always increase over time. |
| Cyclic Process | The Second Law can be regarded as a cyclic process, where energy is passed from a high-temperature source (the sun) to a lower-temperature sink (radiated into space). |
| Living Organisms | Living organisms' ability to grow and increase in complexity is not opposed to the Second Law but is consistent with it, as an increase in entropy can lead to an increase in complexity. |
| Reversibility | The Second Law states that certain processes are forbidden, even if they obey the requirement of energy conservation, and that heat energy cannot be converted to mechanical energy with 100% efficiency. |
| Perpetual Motion | The Second Law declared the impossibility of perpetual motion machines, which attempt to extract the internal energy of the environment to power the machine. |
| H-Theorem | The Second Law is underpinned by the H-theorem, which describes how two rooms, one hot and one cold, will eventually settle into lukewarm equilibrium. |
| Quantum Information Theory | Applying quantum information theory to condensed matter physics has led to a possible avenue for violating the Second Law on a microscopic level. |
| Maxwell's Demon | In 1867, James Clerk Maxwell proposed a hypothetical scenario where the Second Law could be violated, involving a small being that controls the speed of particles between two rooms. |
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What You'll Learn
The second law of thermodynamics and evolution
The second law of thermodynamics, which states that entropy always increases, has been regarded as close to inviolable. This law is based on the H-theorem, which states that if a door is opened between two rooms, one hot and one cold, they will eventually reach a lukewarm equilibrium. However, the fundamental physical origins of the H-theorem are not fully understood, even with advancements in quantum mechanics.
The second law of thermodynamics has implications for the theory of evolution, as critics claim that the increase in order and complexity of species through evolution contradicts the second law. This objection is based on the misunderstanding that the second law of thermodynamics applies to all systems, including living organisms. In reality, the second law is only valid in closed systems with no external sources of energy. The Earth, for example, is not an isolated system as it receives continuous energy from the Sun.
Evolutionary theory claims that organisms become more ordered over time, which contradicts the second law's notion of increasing disorder. However, this contradiction is resolved by understanding that the second law applies only to thermally isolated systems that are not in equilibrium. A thermally isolated system is one in which energy is not being added or subtracted. The Earth, as a system, does not meet this criterion due to the constant input of solar energy.
Furthermore, the ability of living organisms to grow and increase in complexity is not opposed to the second law. In some definitions, an increase in entropy can result in an increase in complexity. This is consistent with the concept of biological evolution, where the formation of correlations with the environment, in the form of adaptation and memory, leads to increased complexity in organisms. Therefore, the second law of thermodynamics does not disprove evolution but rather provides a framework for understanding the increase in complexity and order observed in biological systems.
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Entropy and the feasibility of processes
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. It predicts whether processes are forbidden despite obeying the requirement of conservation of energy as expressed in the first law of thermodynamics. The second law also provides the necessary criteria for spontaneous processes. For instance, the first law allows a cup to fall off a table and break on the floor, as well as allowing the reverse process of the cup fragments coming back together and 'jumping' back onto the table, while the second law allows the former and denies the latter.
Entropy is a scientific concept most commonly associated with states of disorder, randomness, or uncertainty. It is described by two principal approaches: the macroscopic perspective of classical thermodynamics and the microscopic description central to statistical mechanics. The classical approach defines entropy in terms of macroscopically measurable physical properties, such as bulk mass, volume, pressure, and temperature. The statistical definition of entropy defines it in terms of the statistics of the motions of the microscopic constituents of a system.
The second law of thermodynamics states that the entropy of an isolated system left to spontaneous evolution cannot decrease with time. As a result, isolated systems evolve toward thermodynamic equilibrium, where the entropy is highest. This is also known as the H-theorem, which says that if you open a door between two rooms, one hot and one cold, they will eventually settle into lukewarm equilibrium; the hot room will never end up hotter. The H-theorem is based on quantum information theory, which is applied to condensed matter physics.
The role of entropy is critical in determining the feasibility of chemical reactions. The overall entropy of the system tends to increase as chemical processes progress. High energy states with low entropy undergo reactions with low energy states with high entropy. According to the second law of thermodynamics, high entropy indicates high disorder and low energy. Entropy increases when a chemical process occurs. For example, the entropy of a liquid state is higher than that of a solid state for a given substance, and the entropy of a gas is higher than that of a liquid.
The feasibility of a chemical reaction can be determined by the Gibbs free energy equation, where ΔS represents the entropy change of the system. The reaction is feasible if the value of ΔG is less than 0. ΔS could be either positive or negative, depending on the combination of ΔH and ΔS. For instance, if ΔH is negative and TΔS is positive, then the reaction will be feasible at all temperatures. However, if ΔH is positive and TΔS is negative, the reaction won't be feasible at low temperatures, but increasing the temperature can make it feasible by making ΔG negative.
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Irreversible processes and entropy
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. It predicts whether processes are forbidden, despite obeying the requirement of conservation of energy as expressed in the first law of thermodynamics. The second law allows for a cup to fall off a table and break, but it denies the reverse process of the cup fragments coming back together and jumping back onto the table. This law also states that the entropy of isolated systems left to spontaneous evolution cannot decrease and that they will always tend toward a state of thermodynamic equilibrium where the entropy is highest at the given internal energy.
The second law of thermodynamics is consistent with Max Planck's blackbody radiation energy and entropy formulas, which state that blackbody radiation emission represents the maximum emission of entropy for all materials with the same temperature. Thermodynamic systems can be categorized by the four combinations of either entropy (S) up or down, and uniformity (Y) – between the system and its environment – up or down.
In thermodynamics, an irreversible process is one that cannot be undone. All complex natural processes are irreversible, although a phase transition at the coexistence temperature (e.g. melting of ice cubes in water) is well approximated as reversible. A change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state without expending energy. A system that undergoes an irreversible process may still be capable of returning to its initial state, but it is impossible to restore the environment to its own initial conditions. An irreversible process increases the total entropy of the system and its surroundings.
In a reversible process, every intermediate state between the extremes is an equilibrium state, regardless of the direction of the change. In contrast, an irreversible process is one in which the intermediate states are not equilibrium states, so the change occurs spontaneously in only one direction. As a result, a reversible process can change direction at any time, whereas an irreversible process cannot. For example, when a gas expands reversibly against an external pressure, such as a piston, the expansion can be reversed at any time by reversing the motion of the piston. Once the gas is compressed, it can be allowed to expand again, and the process can continue indefinitely.
In the physical realm, many irreversible processes are present, to which the inability to achieve 100% efficiency in energy transfer can be attributed. For example, the friction of solids, conduction of heat, and diffusion are irreversible processes. Many biological processes that were once thought to be reversible have been found to be a pairing of two irreversible processes. For instance, while a single enzyme was once believed to catalyze both the forward and reverse chemical changes, research has found that two separate enzymes of similar structure are typically needed to perform what results in a pair of thermodynamically irreversible processes.
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The second law and living organisms
The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. It states that entropy always increases and the universe tends towards disorder. Living organisms, however, seem to resist this law by growing, increasing in complexity, and adapting to their environments. This apparent contradiction can be explained by understanding that living organisms are not closed systems.
The second law of thermodynamics applies specifically to closed systems, where the entropy of the isolated total system must not decrease. The only known closed system is the entire universe. Living organisms, on the other hand, are open systems that constantly exchange energy and matter with their surroundings. They obtain energy from outside their system, using it to combat entropy and maintain their structure and functionality. This is made possible by the information contained in their DNA, which allows them to interact with their environment and obtain the necessary energy to sustain themselves.
The growth and increase in complexity observed in living organisms can be understood through certain definitions of entropy. Under some definitions, an increase in entropy can lead to an increase in complexity and correlations with the environment. This is consistent with the ability of living organisms to adapt and form memories. The second law, therefore, does not contradict the existence and behaviour of living organisms but provides a framework for understanding their interactions with their surroundings.
While living organisms do not directly violate the second law, they showcase interesting behaviours within its framework. By exchanging energy and information with their environment, they maintain their internal order despite the universal tendency towards disorder. This exchange is facilitated by the H-theorem, which describes how two systems at different temperatures will eventually reach equilibrium. Living organisms, by utilizing external energy, can temporarily resist the universal increase in entropy, highlighting the intricate balance between the laws of physics and the dynamics of living systems.
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Heat energy and mechanical energy
The second law of thermodynamics is a physical law based on universal empirical observation concerning heat and energy interconversions. It establishes the concept of entropy as a physical property of a thermodynamic system. Entropy is the total heat content of a system, equivalent to the system's internal energy plus the product of volume and pressure.
The second law of thermodynamics also deals with the direction taken by spontaneous processes. Many processes occur spontaneously in one direction only, meaning they are irreversible under a given set of conditions. For example, heat flows spontaneously from hotter to colder regions of matter, and not the other way around. This is because, in any spontaneous process, the net transfer of energy will always be from the hot object to the cold object.
The second law also states that it is impossible to convert heat energy to mechanical energy with 100% efficiency. For instance, in an engine, gas is heated to increase its pressure and drive a piston. However, as the piston moves, there is always leftover heat in the gas that cannot be used for any other work. This leftover heat is wasted and must be discarded, for example, by transferring it to a heat sink or, in the case of a car engine, by exhausting the used fuel and air mixture into the atmosphere.
Mechanical energy, such as kinetic energy, can be completely converted to thermal energy by friction. However, the reverse is not true. This is because the second law of thermodynamics also states that it is impossible to get a continuous supply of work by cooling a body to a temperature lower than its surroundings.
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Frequently asked questions
The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time. It also states that the changes in the entropy in the universe can never be negative.
The Second Law of Thermodynamics has been considered as close to inviolable as any law we know. However, researchers from the U.S. Department of Energy's Argonne National Laboratory have recently posited a way to locally circumvent the law on a microscopic level.
The H-theorem is a principle that underpins the Second Law of Thermodynamics. It states that if you open a door between two rooms, one hot and one cold, they will eventually settle into lukewarm equilibrium; the hot room will never end up hotter.
Some critics claim that evolution violates the Second Law of Thermodynamics, as organization and complexity increase in evolution. However, the Second Law only refers to isolated systems, and the Earth is not an isolated or closed system. The Earth receives constant energy increases from the sun, so while order on Earth may be becoming more organized, the universe as a whole becomes more disorganized as the sun releases energy and becomes disordered.
The Second Law of Thermodynamics provides a number of benefits over energy analysis alone in scientific and engineering analysis. It provides the basis for determining energy quality (exergy content), helps us understand fundamental physical phenomena, and improves performance evaluation and optimization.
