# Entropy over Time | Physics Homework Questions

• Niles
In summary, the conversation is discussing a question about calculating the entropy over long time scales. The question is asking for the entropy to be calculated over all possible macrostates, rather than just one. This takes into account the increasing number of macrostates as time goes by.
Niles

## Homework Statement

Hi all, please take a look at this:

Nr. 2,4, the last question. What do they mean by: "Also compute the entropy
over long time scales."?

## The Attempt at a Solution

I simply don't understand the question. I know that the entropy, S, can be written as:

S = k*ln(omega),

but how does time come into this?

Last edited by a moderator:
In the first part, you are caculating the entropy of a specific macrostate (ie. the most likely and the least likely). What the question is asking (I believe) is to calculate the entropy over all possible macrostates. The idea is that, as time goes by, more macrostates are theoretically possible so you need to take into account all of the macrostates as opposed to just one.

As least, I'm pretty sure that's it...=)

## 1. What is entropy over time?

Entropy over time is a measure of the disorder or randomness in a system as it changes over time. It is a concept in thermodynamics and statistical mechanics that describes the tendency of systems to move from a state of order to a state of disorder.

## 2. How is entropy over time calculated?

The change in entropy over time can be calculated using the formula ΔS = Q/T, where ΔS is the change in entropy, Q is the heat transferred, and T is the temperature at which the heat is transferred. This formula is based on the second law of thermodynamics, which states that the total entropy of a closed system will always increase over time.

## 3. What factors affect entropy over time?

The factors that affect entropy over time include temperature, pressure, and the number and types of particles in a system. Higher temperatures, higher pressures, and more particles generally lead to an increase in entropy, while lower temperatures, lower pressures, and fewer particles lead to a decrease in entropy.

## 4. Can entropy over time be reversed?

In isolated systems, entropy over time cannot be reversed. This means that the overall trend is always towards an increase in disorder. However, it is possible for localized decreases in entropy to occur, such as in living organisms that maintain a high level of order and organization in the face of the overall increase in entropy in the universe.

## 5. How does entropy over time relate to the concept of time's arrow?

The concept of time's arrow refers to the idea that the past is different from the future, and that time only moves in one direction. Entropy over time is closely related to this concept because it demonstrates that the universe is constantly moving towards a state of maximum disorder, and this movement is irreversible. This explains why we only experience time moving forward and not backward.

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