2nd Law of Thermodynamics Question

[JacobEvans]

In the "Brief History of Time" Hawkins says that the 2nd Law arises from the fact that there are always more disordered systems than ordered ones.

I guess I'm asking... How does entropy increasing over time arise from the fact that there are more disordered systems than ordered systems?

I have a basic understanding of both concepts just not how they connect.

 

[aeroeng314]

From what I remember from statistical thermo each microstate has essentially the same probability. The fact that there's more disordered microstates than ordered microstates means it's much more likely to see disorder.

Of course someone will come and explain this better than I did and probably correct me. I never was much of a fan of thermodynamics or statistics...mixing them together formed a subject I was destined to not be interested in.

 

[Master_Ghost_Knight]

The second law of thermodynamics is extremely miss concieved if looked at it with our sense of order or desorder. In fact the second law of thermodynamics has no say in the macroscopic order.

First you need to know what is heat and temperature at the microscopic scale. Temperature at the microscopic scale is simply the ammount of activity of a given molecule that remains in a vabrational state do to the simple implications of conservation of many other propreties such as energy and momentum.
2 bodies are said to be at the same temperature if they have the same activity, in this state there is no net energy is transfered between them. if 2 bodies are at different temperature the most active one when interacting with the less active one will transfer cinetic energy at the microscopic level, and to that energy transfer we call heat. (note same activity doesn't mean same ammount of energy per particle). But sense we can neither see activity or cinetic energy transfer at the microscopic scales, with replace the with macroscopic propreties such as temperature and heat (that we can esaily measure) that represent the microscopic state in which the molecules of the body is in. The microscopic models of this gives by far a clearer picture of the situation, but it generaly implies the use of quantum mechanics, there is allot that can be said about this but for the purpouse of your question I think it is suficient.


The second law of thermodynamics arrises from the simple fact that heat flows naturaly from hoter bodys to colder ones and not the oposite.
We can evaulate this proprety in a quatifiable method trough the propretie of increment of entropy that is basicaly the reason between the heat transfer and the change of temperature, sense heat only passes naturaly from hoter bodies to colder bodies this mean that it can only be a positive figure. From this there are several difrent implication, but for the purpouse of this topic is the ammount of micro states in wich a particle can be. As it also happens that entropy is closely related to the ammount to the ammount of microstates in which the molecules can be in (due to their activity; and thus arriving to the latin sense of entropy which means the ammount of possible states).
You can call this increase of possible states as a disorder (as what the macroscopic interpretation might sugest), but it has nothing to do with what we know about disorder in that we observe at the macroscopic scale.

It is a bit harder to understand if you don't have the backgrounf of it all, and I'm sory if I wasn't clear enough, this is generaly one of the things that is only well understood after a long semester.

 

[JacobEvans]

Could someone explain to me a microstate?

 

[Master_Ghost_Knight]

Unfrotunatly I'm not that able to explain what exactly do we mean by microstate, we would need to go into quatum physics which is an area where I'm not totaly confortable with.
Maybe some one with more knowledge in statistical or quatum thermodynamics is able to give you a better answer then I could.

 

[Artsysiridean]

By the explanation Master_Ghost_Knight said, this makes the 2nd law seem less of a law in league with the zeroith and first and more an excuse for others to believe that everything's going to end with some scruples.

I'm interested to hear more.

 

[Dumbfounded]

I think Hawking is probably referring to entropy as defined by Boltzmann: S = k log W, where k is the Boltzmann constant and W is the number of microstates equivalent to the macrostate. But I'd have to read the quote in context to understand what he was getting at.

 

[Master_Ghost_Knight]

By the explanation Master_Ghost_Knight said, this makes the 2nd law seem less of a law in league with the zeroith and first and more an excuse for others to believe that everything's going to end with some scruples.

I'm interested to hear more.

The 2nd law of thermodynamics is as much of a law in the league of the 1st law. The premisses may seam simple or plain for those who have other expectatives from it, the 1st law is simpler still (the 2nd law is by far a much more complicated subject). But non of the less do not underestimate it's importance, they have an authentic universe of implications under their aparent aspect.

 

[ImprobableJoe]

One of the issues I have with using the 2nd Law of Thermodynamics to reference anything besides heat and energy is that it gets rather confusing and imprecise. When you are talking about entropy to discuss available or "motive" energy, it is relatively straightforward. When you start talking about order and disorder, it gets muddy and less coherent. The universe tends to go from a state of order to disorder? Or does it really go from a state of disorder to order? In truth, a state of 100% entropy is a state of highest "order"... "from a certain point of view." Go Obi-Wan! :lol:

 

[JacobEvans]

By order to disorder I'll explain what I mean using Hawking's example.

Imagine a pool table with the balls placed out before the first shot in the game. The state of order would be the balls in that position and any variation from that is disorder. It's almost impossible to shoot the cue into the balls and have them reorganize to their original position, so disorder is almost guaranteed to arise from this situation.


It's always more likely that a system of order will become disordered, than a system of disorder will return to a state of order.

While order is relative, when looked at from one specific reference point, we will always notice the above mentioned outcome.