Thermodynamics and the Destiny of the Universe
© Copyright mAY 2012—August 2014,
Document created mAY 8, 2012
In this brief piece I give little explanatory detail; see Thermodynamics and the Destiny of the Universe for details.
Thermodynamics concerns study of heat and work interactions for systems. It refers to a macroscopic level at which molecular motion is not apparent and systems are described in terms of bulk properties that do not refer to molecular (or other particle) properties and energy and motion. The molecular level is of course present but enters into thermodynamic description only implicitly. Thus the gross energy of a system includes molecular energy (kinetic and potential) and energy transfer includes mechanical work and heat (which is work of molecular interactions that are not included in mechanical work).
The first law is a form of the principle of conservation of energy.
Conservation implies that energy available must be the energy of some source.
We know this: we know for example that fossil fuel energy reserves will run out; and we know that we cannot build an engine that uses no resources; further this can be made quantitative: to get a certain amount of energy output at a certain efficiency of conversion we need a proportional amount of fuel (if the efficiency is 100% the energy supplied must be the energy of the fuel; if the efficiency is 50% twice the amount of fuel is needed to supply the same amount of energy). From these thoughts we conclude that conservation and efficiency are important.
Because energy is important, we sometimes tend to ignore other resources such as materials and human resources. Materials are important because they too can run out and there use requires energy. Human resources are important as well but as such they are (obviously) not the subject of thermodynamics .
We also sometimes forget that ‘renewable’ resources are not free. For example, solar energy requires land and materials (solar energy panels, photovoltaic cells). Land has rent; and the materials decay and must be replaced: therefore there they are not mere one time costs.
At the level of the Universe, energy budgets have significance to its fate. It is also interesting that a non conserving cosmos might be deflationary and non livable or inflationary and too energy intense to be livable.
According to the First Law the energy of the Universe, since it is not in interaction with any other system (there is no other system) is constant. If the Universe were to achieve a state in which all useful energy is used up (e.g. it is at uniform pressure, temperature etc) there would be no other source of usable energy.
In expansion, as energy of motion goes into overcoming gravity and is stored in the gravitational field the energy of motion must decrease. I.e., the rate of expansion must slow down (unless other forces supply more energy than is stored in the gravitational field).
The Second Law is the assertion that the entropy of an isolated system must increase (or at best in an ideal case cannot decrease).
The prosaic consequences include (1) Limits on ideal efficiency of heat engines (2) Further limits on real engines that result from dissipation (necessarily present per the Second Law) and other contingent leaks and other requirements such as materials.
The limit on ideal efficiency is useful knowledge because understanding it shows how to improve efficiency. These considerations show that high combustion temperatures and low exhaust temperature improve efficiency in heat engines. Materials and size considerations set limits on these temperatures. In the real situation actual is usually significantly less than ideal. The ideal energy limit does not apply to direct energy conversion, e.g. as in a fuel cell or simple mechanical drives that do not have heat production as an intermediate step. However, mechanical drives require an energy source and fuel cell and other direct energy conversion devices have practical limits, especially dissipation, as well as materials and perhaps other (e.g. land) requirements.
While thermodynamics had origins in concerns with energy generation, its final formulation is in the form of general scientific laws. These laws, the first and the second, have implications for science and its disciplines.
The Second Law suggests that the Universe will ultimately arrive at a state called heat death. Per the Second Law entropy of isolated systems (those systems that do are not interacting with others) must increase in real processes; and since entropy is a measure of disorder isolated systems tend to disorder until disorder and entropy are at a maximum and are unable to further generate structure, life, or useful ‘work’. Since the Universe is isolated this is true of the Universe if the Second Law is applicable at the scale of the Universe.
There is a sense in which the ‘limits’ are not true limits but limits on what we used to or might imagine.
It should be added that an ideal Universe, e.g. one without dissipation might not be livable, e.g. though friction is dissipative it is also essential in many ways.
However, it is useful to imagine ‘overcoming’ the laws of physics at least because it may give us insight into the laws and the Universe (this may be fun). Further, we may learn something of practical interest.
We would ‘overcome’ the First Law if there were an inexhaustible energy source, e.g. a box which had no input but gave out energy eternally.
If the world had such sources in sufficient quantity it might become too hot to be livable (a definite possibility even without inexhaustible energy supply).
As we noted above, without conservation the Universe might be inflationary or deflationary.
This is part of one approach to understanding energy conservation. In a Universe with many cosmological systems, the hyper-conservative ones might be unstable and the hypo-stable ones insufficiently productive to support variety and life.
The two laws are consequences at the bulk level of microscopic constituents of matter (atoms, molecules, vibrating fields etc). The First Law is a necessary consequence while the Second Law is a statistical consequence. The Second Law is in fact violated for short periods for very small regions (the violations are fluctuations). However, over sensible regions the fluctuations are insignificant. In fact there is probability that there will be gross violations but that probability is generally so low as to be effectively zero.
However, there are experimental confirmations of such violations and there may be practical applications in the future.
Further the Second Law pertains to what is called equilibrium and this opens up the possibility of its violation ‘far from equilibrium’. Still, many so-called far from equilibrium cases of spontaneous order are not violations because they involve open systems in which order is the result of low entropy sources and is not a violation; but even though that is true, the case may be suggestive.
1. Because the Second Law is statistical one could simply wait a long time. Experience suggests that on practical scales this is immensely unlikely to reveal significant or useful violations. However, on the scale of the Universe it might provide a loophole from heat death and or increasing entropy of a later manifestation from a ‘big crunch’.
2. Open systems and system far from equilibrium. I must research this. I don’t know much about practical situations but on the scale of the Universe this may have significance.
3. Anti-dissipative forces. The source of Universal increase in entropy and disorder is that of dissipation. Most if not all finite rate processes (and there are no zero rate processes except in conceptual though useful idealizations) are dissipative and so there seems to be no way around this. However it seems possible that in a universal gravitational big crunch gravity may be sufficiently powerful to be ordering. Here, too, I don’t know enough to evaluate this intuition.
4. Expanding Universes. In an expanding Universe the maximum entropy might increase (as suggested in modern physical cosmology) and the increase might exceed increase in entropy due to dissipation and so heat death might lie ever over the ‘horizon’.
5. Although our cosmos is or very close to conservative at the fundamental level there is no guarantee that this is its destination. There may be ways in which hyper-conservative forces enable entropy decrease in the Universe (cosmos) and other isolated systems.
The scenario for immediate technical ‘anti-thermodynamic’ is limited except perhaps regarding thermodynamic fluctuations.
The case for the necessity of thermodynamics is hardly weakened. However, we have learnt something about the nature of that necessity: it is cosmological rather than universal. This is after all a weakening but apparently not one of immediate consequence.
The fate of the Universe is an open issue. Perhaps the ordering in a crunch is the mechanism of greatest significance (however it is not distinct from the far from equilibrium case and it appears to speed up process so that the normal wait would not be practically eternal).
What is the significance to mortals of a practical eternity? It is nothing material if we are truly finite. If however the Universe is ‘ergodic’ (i.e. that all possible states will recur over sufficiently long periods) then the consequences are significant. They include first that the Universe will revisit all its states and this includes, second, that all its inhabitants will recur. What is the meaning of a recurrence? In this life I am not aware of any other occurrences so that unawareness would also obtain in recurrences. However, (1) I may be aware of other occurrences but this may be subconscious, e.g. in terms that normal consciousness does not recognize and (2) There may be higher forms that integrate the separate ones (for me, this is speculation).
Finally, I have not given voice to the metaphysics of Journey in being-detail and related documents at http://www.horizons-2000.org which requires such recurrence (and much more: the metaphysics which is not in violation of science shows, subject to evaluation of its demonstration, that while the valid regions of science are necessary, the ‘standard scientific universe’ is infinitesimal in comparison to the Universe and that this infinitesimal nature refers at least to extension, duration, and variety of Being).
A project first of imagination, then of reasoning and quantitative analysis.
Far from equilibrium where the nature of entropy is in question (if it exists at all) and far from equilibrium statistics of mechanical systems (‘statistical mechanics’) are interesting but immensely difficult and, it seems, under-appreciated topics.