The first law of thermodynamics
The universe encompasses an enormous amount of phenomena and events. Some of them have been discovered and successfully described in the past, while others remain unknown, waiting there to be unveiled.
Among these occurrences, there are certain rules that the universe invariably seems to obey “no matter what”. These are called laws, and as their name suggests, they are always fulfilled. It does not matter what is the instance under study, the laws of the universe are always satisfied. These laws distinguish between occurrences that are possible in our reality and those that are inconceivable.
For example, an object at rest cannot spontaneously start moving in a random direction without an external force. Similarly, liquid water cannot exist at temperatures above 100°C under moderate pressure conditions anywhere in the universe.
Rather than imposing mere restrictions, the implications of these laws shape the universe as we know it. They endow our reality with a well-defined basis to exhibit ordered patterns. Without such laws, the universe would not only be “funny” as a cartoon, but it could be potentially unstable, as to prevent the formation of planets and galaxies, and by all means life.
To account for this, we can say that among the many laws that we could discuss, there is one in particular that can be the simplest one and also the foundational basis for many others. Namely, the first law of thermodynamics.
The first law of thermodynamics concerns the conservation of matter and energy. Basically, they cannot be created or destroyed, they can only change their form.
For example, in real-life if you buy a portable battery at the airport, the amount of energy that you will be able to transfer to your phone is bounded by the amount of stored energy available in the portable battery. Moreover, that energy had to be stored there before, by previously charging the portable battery from electricity that was supplied by a utility. The utility itself also had to get the energy from a generator whose spinning is induced, most of the times, by the work produced by burning a fossil fuel, which was also “charged” through actually millions of years, by concentration of organic material driven by the power of the sun.
This may seem like common sense. If we want something we have to pay for it, including all the people involved in the whole supply chain. From the workers in charge to extract the fossil fuel, to the guy that sold the portable battery at the store.
There could be an open debate and even controversy about many aspects of physics, but there is no question about the validity of the first law of thermodynamics. It is so fundamental, that failing to satisfy this law, at least one time, would overthrow all the understanding that we have about the universe where we live.
Things would not be as we would expect, at all…
For instance, in the previous example of the portable battery, imagine if, miraculously, some “extra energy” spontaneously appeared. Who paid for that? That would not be only the end of a well-established energy market, but would be also dangerous.
If energy was not a conserved quantity and could be spontaneously created:
— What would prevent objects with kinetic energy from suddenly moving faster? This includes a tree leaf that increases its weight, in the form of the force with which it hits the ground, or the head of an unfortunate pedestrian.
— What would prevent our planet from starting to move faster, abruptly pushing everything on earth including us, into an involuntary motion due to the acceleration.
— What would prevent the sound of ants walking near us, to be suddenly amplified as to damage our eardrums?.
The latter are events derived from a sudden creation of energy, but sudden destruction is equally catastrophic. For example, consider what would happen if the energy stored in our cells suddenly disappeared; the result would be fatal. Consider what would happen if the heat radiated by the sun sometimes vanished on its way to Earth. It would be a catastrophe.
At this point, we can possibly agree that the first law of thermodynamics is necessary to keep an adequate equilibrium in the universe. Energy can pass through different processes and transformations, but it always remains constant. This is due to the fact that applying energy to a process has only two possible outcomes: 1) it generates work, or 2) it produces heat.
Energy supply rate = Work + Heat.
Applying energy results in work, which involves a change in energy over time (“dynamics”). Or it will produce energy dissipation as heat (“Thermo-”). — Energy supply rate can be measured in terms of the power delivered to perform a physical process.
— Energy supply rate can be measured in terms of the power delivered to perform a physical process.
— Work is the rate of change of energy with respect to time, it has to do with dynamics such as motion and transfer of energy.
— Heat is produced in the form of dissipation, that is released from the process to the environment.
The above is probably the most accurate way to describe the first law of thermodynamics, since it permits to avoid confusion, especially in those cases that seem paradoxical.
For example, imagine that you connect a refrigerator inside a hermetic room, which prevents the exchange of heat with the outside world. Then you leave the refrigerator door open.
What would happen with the room temperature? Will it get hot or cold? The possibly surprising answer is that it will get hot. The reason is that the energy supplied to the refrigerator (in this case by electricity) must find a possible outcome as work and/or heat. But work cannot take place since there is no transfer of heat to the outside world and then there is no exchange of energy changing with time.
Consequently, the only possible outcome is that the energy supplied is transformed into heat dissipation. Moreover, unlike many other processes in physics, the process of heat dissipation is irreversible, but that matter has to do with another law that deserves more space for elaboration, i.e., the second law of thermodynamics.
Jonathan Mayo