Did you know that the Earth receives an astounding amount of energy from the sun every second? It’s about 90 petajoules, which is enough to meet all human energy needs thousands of times over! However, the Earth also sends almost the same amount of energy back into space as heat. This balance might make you wonder how we manage to use energy for anything at all.
The key isn’t just energy itself but rather useful energy. Energy is considered useful when it comes in a low-entropy form. In any closed system, the total amount of energy remains constant due to the law of conservation of energy. However, the usefulness of that energy can vary.
Imagine the water behind a dam. It holds useful energy because it can flow and do work until the water levels equalize. Similarly, hot tea can melt an ice cube until they reach a medium temperature. You never see the reverse happening spontaneously because that would require energy to become more useful on its own, which doesn’t happen naturally.
Useful energy is low-entropy energy that can perform work, like turning a turbine or pushing a piston. On the other hand, useless energy is high-entropy energy, like waste heat or noise, which can’t be harnessed to do work. For example, gasoline and air contain low-entropy energy. When burned together, they power a car, converting chemical energy into high-entropy heat and noise. The energy remains, but it’s no longer useful for powering more cars.
The sun provides us with energy in a convenient, low-entropy form, primarily as visible light photons. This energy is absorbed and used on Earth, eventually being radiated back into space as high-entropy infrared photons. For every visible photon received, about twenty infrared photons are emitted, increasing the entropy of the energy significantly.
The sun is a source of useful energy because it stands out as a hot, bright spot against the cold, dark sky. If the entire sky were as hot as the sun, the Earth would reach a high-entropy equilibrium, making life as we know it impossible. In such a state, all energy would be equally useless, and time would lose its meaning.
This fascinating exploration of energy and entropy is part of a series on time and entropy, created in collaboration with physicist Sean Carroll. Supported by Google’s Making and Science initiative, the series aims to inspire people of all ages to engage with science. If you’re intrigued, you might want to check out Sean Carroll’s book, “The Big Picture: On the Origins of Life, Meaning, and the Universe Itself,” available online and in bookstores worldwide.
Engage in a simulation exercise where you model the flow of energy from the sun to the Earth and back into space. Use software like MATLAB or Python to visualize how energy is absorbed, transformed, and emitted. This will help you understand the balance of energy and the concept of entropy in a tangible way.
Conduct a simple experiment to observe entropy in action. Use a hot cup of tea and an ice cube to see how energy is transferred until equilibrium is reached. Document your observations and relate them to the concepts of low and high entropy discussed in the article.
Analyze a real-world case study on energy transformation, such as solar power plants or internal combustion engines. Discuss how these systems utilize low-entropy energy and the challenges they face in terms of efficiency and entropy increase.
Participate in a debate on the topic: “Is it possible to achieve a sustainable balance of energy use on Earth?” Use the concepts of useful energy and entropy to support your arguments. This will enhance your critical thinking and understanding of energy sustainability.
Create a presentation or video explaining the role of the sun in energy transformation and entropy. Use visuals and analogies to make the concepts accessible and engaging. Share your presentation with peers to foster a deeper understanding of the topic.
Energy – The capacity to do work or produce change, often measured in joules or calories. – In physics, energy can be transferred between objects and transformed from one form to another, such as from kinetic energy to potential energy.
Entropy – A measure of the disorder or randomness in a system, often associated with the second law of thermodynamics. – As a closed system evolves, the entropy tends to increase, leading to a state of maximum disorder.
Useful – Capable of being utilized effectively to achieve a desired outcome, often in reference to energy or work. – In thermodynamics, useful energy is the portion of energy that can be converted into work, as opposed to energy lost as heat.
Low-entropy – Describing a state of orderliness or organization within a system, often associated with high energy availability. – A low-entropy state is characteristic of a newly charged battery, where energy is readily available for work.
High-entropy – Describing a state of disorder or randomness within a system, often associated with low energy availability. – After a chemical reaction reaches equilibrium, the system is in a high-entropy state, with energy dispersed and less available for work.
Conservation – The principle that a particular measurable property of an isolated physical system does not change as the system evolves. – The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another.
System – A set of interacting or interdependent components forming an integrated whole, often studied in physics to understand energy and matter interactions. – In thermodynamics, a system can be defined as the part of the universe being studied, separated by boundaries from its surroundings.
Transformation – The process of changing the form, appearance, or structure of something, often referring to energy changes in physics. – The transformation of potential energy into kinetic energy is evident when a roller coaster descends from the top of a hill.
Photons – Elementary particles representing a quantum of light or other electromagnetic radiation, carrying energy proportional to the radiation frequency. – Photons are emitted when electrons in an atom transition from a higher energy level to a lower one, releasing energy in the form of light.
Physics – The natural science that studies matter, its motion and behavior through space and time, and the related entities of energy and force. – Physics provides fundamental insights into the workings of the universe, from the smallest particles to the largest galaxies.
