Question

According to the second law of thermodynamics, systems always spontaneously move toward a condition of greater entropy. Yet life and ecosystems on Earth represent local systems where negative entropy is continuously being generated. What conditions allow this apparent paradox to exist?

Short answer

Life reduces entropy locally using energy from the Sun, but the universe's total entropy increases, resolving the paradox.

Step-by-step solution

Understanding Entropy and Thermodynamics

Entropy is a measure of disorder or randomness in a system. According to the second law of thermodynamics, the total entropy of an isolated system can never decrease over time. Systems naturally evolve toward a state of maximum entropy or disorder.

Identifying Life's Local System Behavior

Living organisms and ecosystems are not isolated systems; they are open systems. This means they can exchange energy and matter with their surroundings, allowing for local decreases in entropy (increased order) within the system.

Role of Energy Input from the Sun

The Earth receives energy from the Sun, which powers photosynthesis in plants. This process converts solar energy into chemical energy, decreasing entropy by creating complex organic molecules from simpler ones.

Balancing Entropy on a Global Scale

While life on Earth maintains order locally, the entropy of the surrounding environment increases. For instance, animals eating plants release heat and waste, increasing entropy outside the system, leading to a net increase in the total entropy when considering the Earth and surroundings.

Reconciling the Paradox

Life reduces entropy locally by utilizing external energy sources, like solar energy, to create order. However, the overall entropy of the universe still increases, aligning with the second law of thermodynamics, due to the energy exchanges and waste heat generated in processes.

Key concepts

Second law of thermodynamics

The second law of thermodynamics is a fundamental principle governing the behavior of energy in our universe. It states that in any isolated system, the total entropy, which is a measure of disorder, will never decrease over time. This means that systems naturally tend to evolve towards more randomness and disorder.
However, this law speaks specifically to isolated systems, which are systems that do not exchange energy or matter with their surroundings. Most real-world systems, like ecosystems or living organisms, are not isolated but are open, allowing for complexity and order to arise locally while still abiding by the second law on a universal scale.

Open systems

Open systems are systems that interact with their environment by exchanging both energy and matter. Unlike isolated systems, these systems have the unique ability to achieve decreases in entropy, or increases in order, within themselves.
Living organisms are prime examples of open systems. They continuously take in energy (such as through food or sunlight) and matter (such as nutrients and gases) from their environment to maintain internal organization and perform work. This intake allows them to build and sustain complex structures and processes, despite the universal trend towards disorder prescribed by the second law of thermodynamics.

• Import energy and materials.
• Export waste to maintain local order.
• Dependence on environmental exchanges for survival.

Solar energy input

Solar energy input is the driving force behind much of the life and order we observe on Earth. The Sun provides a continuous influx of energy to our planet, which is used by plants and other photosynthetic organisms.
By capturing sunlight, these organisms initiate the process of photosynthesis, where light energy is converted into chemical energy, stored in the bonds of glucose and other organic molecules. This transformation is crucial as it allows for the building of complex molecules from simpler ones, effectively decreasing local entropy and fostering life.

• Powers photosynthesis in plants.
• Facilitates the energy flow through ecosystems.
• Essential for sustaining life forms on Earth.

Photosynthesis

Photosynthesis is a remarkable process conducted primarily by plants, algae, and some bacteria, where sunlight is transformed into chemical energy. This process not only fuels plant growth but also underpins the energy foundation of most ecosystems.
During photosynthesis, plants absorb carbon dioxide from the air and water from the soil. Using the absorbed solar energy, they convert these into glucose and oxygen.
This conversion is vital as it builds biomass, supporting plant life and providing food and energy for other living organisms.

• Transforms solar energy into chemical energy.
• Produces oxygen as a byproduct.
• Forms the basis of the food chain.