Primer Home / Entropy / Summary on entropy
Summary on entropy
Topic: Entropy
by Matthew, 2018 Cohort
Note: This entry was created in 2018, when the task was to “summarise a key reading”, and so may not represent a good example to model current primer entries on.
the tendency for a system to move towards equilibrium
Entropy is often used within a scientific context. This primer will look at defining Entropy in a technical context but also look at its wider applications, uses in other areas, and relation to complexity. This is a topic which is simple in theory but has a lot of nuance (and is surprisingly hard to explain).
What is entropy?#
Entropy can be complex to explain because it has different meaning based on the context. It is both “the tendency for a system to move towards equilibrium” and a measure of disorder in a system. In physics we use entropy as a quantitative measure of disorder in a system by looking at its energy distribution. A low entropy system is relatively ordered. Whereas a high entropy state is very disordered. Maximum entropy is reached when it is at equilibrium as the system has a uniform distribution of energy.
In simple terms, entropy says that energy must be used to keep a system ordered. Otherwise the system deteriorates, becoming increasingly disordered. A simple example is tidying your bedroom. If you start with a clean room (low entropy state) but never tidy or clean, the room will quickly become disordered and cluttered (high entropy state). We must continually apply energy to the system (i.e. tidy and clean) to keep the system ordered. The process of cleaning is reducing the entropy for that part of the system.
The Second Law of Thermodynamics This leads us to one of the fundamental laws of the universe, the second law of thermodynamics. It states that “the entropy in a system can never decrease”. While some local parts of the system can decrease entropy, the global entropy must increase. This has huge ramifications outside of keeping your room clean and has application everywhere. For example, a refrigerator cools the items inside of it, reducing entropy, but also outputs significant heat such that the total entropy is still increasing. Famously, this law is the driving force behind the heat death of the universe. In which all the energy in the universe will be uniformly distributed, reaching it maximum entropy, but also ending any life in the universe as the temperature will approach absolute zero (-273.15C).
How is entropy linked to complexity?#
Entropy is inherently linked to complexity. It is this increasing disorder which allows for more complex systems to develop. Such as the emergence of galaxies, life, and complex cells. In other words, increasing complexity can never be avoided and is a fundamental part of our universe.
The concept of “systems becoming disordered over time” has been encompassed by many disciplines other than physics. With application in social and economic contexts. In these contexts we attempt to reduce entropy by applying rules, laws or new processes. For instance, social entropy looks at evaluating social behaviour based on the disorder and inequality in the distribution of wealth. As over time, the distribution of wealth becomes more disordered (rich get richer) we must apply corrections in the form of taxes, and laws.
While there are many applications of entropy, its use in the physical world is the easiest to observe. From adding milk into your tea, the burning of fossil fuels, and the erosion of land, the increasing disorder in the world is all around us. By understanding this it can help us achieve some insights into why complex systems behave in particular ways.
References
- Lineweaver, Charles H., Paul CW Davies, and Michael Ruse, eds. Complexity and the arrow of time. Cambridge University Press, 2013.
- Arieh Ben-Naims, Discover Entropy and the Second Law of Thermodynamics, Chapter 1.
- Social Entropy: A Paradigmatic Approach. http://www.nexialinstitute.com/social_entropy.htm;
- https://en.wikipedia.org/wiki/Entropy_(order_and_disorder)
- https://en.wikipedia.org/wiki/Second_law_of_thermodynamics
- Entropy: Embrace the Chaos! https://www.youtube.com/watch?v=ZsY4WcQOrfk;
- https://en.wikipedia.org/wiki/Thermoeconomics
Disclaimer#
This content has been contributed by a student as part of a learning activity.
If there are inaccuracies, or opportunities for significant improvement on this topic, feedback is welcome on how to improve the resource.
You can improve articles on this topic as a student in "Unravelling Complexity", or by including the amendments in an email to: Chris.Browne@anu.edu.au