# Questions about entropy

1. May 2, 2012

### infinitylord

Hi guys! I'm new to the forum and had several questions about entropy. I am a bit of a physics newbie by a lot of standards but I understand a lot of it and love physics. I can understand the basics of entropy that it is (correct me if I'm wrong) basically just disorder, that it is always increasing except if it is at absolute 0. It creates an arrow of time in the way that we can't go back on what has happened and bring the order back just as we can't reverse time to stop a volcanic eruption. Now I get the principles of it but how is it calculated and what does it mean when it is? there are the more basic forumula's for thermodynamics but I was referring to
S=-k·Σ[Pilog(Pi)]. So I know what most of it means,
k=boltzmann constant,
Σ = sigma,
in the brackets = the probability that a particle will be in a certain nanostate * by the logarithm of the same probability.
but how is this applicable? I want an example. I tried to do one by myself but i was most likely horribly wrong on what to do.
So i'd like an example with the math written out and what it means really. how do you know the probability of a particle being in a nanostate? once you have the number whats the unit in... J/K^-1? and what does it mean if you have a higher entropy?
sorry for the bombardment of questions... I'm just trying to wrap my head around this

2. May 2, 2012

3. May 3, 2012

### infinitylord

Thanks a ton.. this really helped!

4. May 3, 2012

### Whovian

Sorry about reviving, but I've thought of entropy as, well, sort of information.

5. May 3, 2012

### infinitylord

yeah... i've got a better handle on it now. One good definition I read was "the amount of energy needed to complete a system." that's where it all just clicked for me I guess

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook