The second law of thermodynamics states that the entropy of an isolated system tends to increase over time. Entropy is often associated with disorder or randomness in a system. While it is not possible to decrease the entropy of an isolated system without violating the second law, there are a few scenarios where the local decrease of entropy is observed, while the overall entropy of the universe continues to increase. These scenarios include:
Local Decrease with Energy Input: It is possible to decrease the entropy of a system locally by supplying energy and performing work. For example, consider a refrigerator. It extracts heat from the inside, lowering the entropy locally, and expels it to the surroundings, increasing the overall entropy of the system (refrigerator + surroundings). The key is that the total entropy, including the surroundings, always increases.
Self-Organization and Information: Systems can exhibit self-organization and increase their internal order or complexity while still adhering to the second law. This is possible because the decrease in entropy within the system is offset by an even greater increase in entropy elsewhere. A common example is biological systems, where living organisms can maintain and increase their internal organization by consuming energy and dissipating heat to the surroundings.
Entropy Transfer: Entropy can be transferred between different parts of a system or between different systems, resulting in local decreases and increases. For instance, in a chemical reaction, one reactant may decrease in entropy while another increases, but the overall entropy change is positive. Similarly, heat transfer from a hot object to a cold object results in a decrease in entropy for the hot object and an increase in entropy for the cold object, leading to an overall increase in entropy.
It's important to note that while local decreases in entropy are possible, they are typically accompanied by larger increases in entropy elsewhere, ensuring that the second law of thermodynamics is upheld. The overall entropy of an isolated system or the universe as a whole will always increase or remain constant over time.