# Increasing entropy vs groundstate

• Jim Kata
In summary, entropy theory says that all states of a system are equally likely, but this is only true in an isolated system.
Jim Kata
Atoms and molecules like to be in their ground state, that is its most probabilistic for them to be in the ground state, but the entropy of an isolated system is always increasing. Which implies, to my understanding, all states should be equally likely. There is something I'm definitely missing. How do I reconcile these two concepts?

Here's an interesting link on the concept of a negative entropy source (the Sun):

http://www.digital-recordings.com/publ/publife.html

I recall a similar description in the book A Brief History of Time.

My problem with entropy theory is that, if my brain recognizes a pattern, I call it "order" and if it doesn't, I call it "chaos" or "disorder." So the line between the two is perhaps not a property of the universe, but perhaps a natural limit on the power of pattern recognition.

Jim Kata said:
Atoms and molecules like to be in their ground state, that is its most probabilistic for them to be in the ground state, but the entropy of an isolated system is always increasing. Which implies, to my understanding, all states should be equally likely. There is something I'm definitely missing. How do I reconcile these two concepts?

Not "always increasing" just "practically never decreasing".

Consider: there are only a few "ways" for an atom (with a particular amount of energy) to be in an excited state. This system can decay into a photon and a ground state atom, and then there will be an infinite range of "ways" that those two could be arranged. (The thermodynamic microstates correspond to all those "ways"/arrangements of the entire system, not to the atomic electron states by themselves; the latter doesn't even correspond to a closed system.)

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Jim Kata said:
Atoms and molecules like to be in their ground state, that is its most probabilistic for them to be in the ground state, but the entropy of an isolated system is always increasing. Which implies, to my understanding, all states should be equally likely. There is something I'm definitely missing. How do I reconcile these two concepts?
When an atom drops into its ground state, it gives off a photon. The entropy of the photon makes up for the entropy loss of the atom itself, so that the total entropy always increases. Remember that once the atom gives off that photon, it's not isolated.

(cesiumfrog was right, though, it technically is "almost never decreases" rather than "always increases." But the probability of seeing entropy decrease in a real system is astronomically low, i.e. we have every reason to expect that it's never happened.)

Jim Kata said:
Atoms and molecules like to be in their ground state, that is its most probabilistic for them to be in the ground state, but the entropy of an isolated system is always increasing. Which implies, to my understanding, all states should be equally likely. There is something I'm definitely missing. How do I reconcile these two concepts?
Atoms and molecules only like to be in the ground state, when their are not an isolated system. You are right that if they were isolated, then all states would be equally likely. However atoms are in thermal contact with the environment. All state of the combined system enviroment+atom are indeed equally likely. One can derive that this is equivalent to saying that the free energy of the atoms is the smallest possible.

## 1. What is entropy and why does it increase?

Entropy is a measure of the disorder or randomness in a system. According to the Second Law of Thermodynamics, the overall entropy of a closed system will always increase over time. This is because the random movement and interactions of particles within a system will naturally lead to a more disordered state.

## 2. How does increasing entropy relate to the concept of groundstate?

The groundstate of a system is the state with the lowest possible energy. As entropy increases, the system moves away from its groundstate and towards a higher energy state. This is because increasing entropy means an increase in the number of microstates (possible arrangements of particles) which are available to the system.

## 3. Can entropy ever decrease?

The Second Law of Thermodynamics states that the overall entropy of a closed system will always increase. However, on a microscopic level, there may be localized decreases in entropy. For example, when a chemical reaction occurs, the entropy of the reactants may decrease while the overall system entropy still increases.

## 4. How does the concept of entropy apply to the universe?

The concept of entropy is relevant to the universe as a whole because it is a closed system. This means that the total amount of energy and matter within the universe is constant, and the overall entropy will continue to increase as the universe expands and particles interact and move randomly.

## 5. Can entropy be reversed or decreased?

While entropy can decrease on a localized level, it cannot be reversed on a macroscopic scale. This is due to the fact that it would require a highly improbable and organized event to occur, which goes against the natural tendency towards disorder and randomness. However, it is possible to decrease entropy in a system by adding energy and decreasing its disorder, but this would increase the entropy of the surrounding environment.

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