2nd Law and Open / Closed Systems

I wanted to make this post in the Post your short questions here. No need to start a thread everytime. thread, but it seems to be mostly about moderation and site maintenence. I am hoping to get more of a "concept check" from other, more knowledgable members."The second law of thermodynamics ... is an expression of the fact that over time, differences in temperature, pressure, and density tend to even out in a physical system that is isolated from the outside world." Wikipedia"Every energy transfer or transformation increases the entropy of the universe." Biology 7ed. Campbell, Reece. 2005If the universe is slowly falling into disorder as I understand the 2lotd to mean, does this concept impact the ideas of an ever expanding / neutral / or "Big Crunch" universe? What I mean to say is - does the 2lotd contradict the idea of Neutral or "Big Crunch"?If the universe is supposed to always have a net result of disorder how could it eventually collapse back into a singularity? or even remain neutral?This is not an "EvC" related question, but its 5 a.m. and questions like this pop up and ruin my chances for sleep!

Thread moved here from the Proposed New Topics forum.

Hi, Vacate. The problem, I'm afraid, is your understanding is wrong. The Second Law of Thermodynamics has little to do with order/disorder.This is a very common misconception, by the way, so there is no cause for embarrassment. There is a commonly told example that uses the disorder of a room as an analogy to explain conceptually the statistical mechanics definition of entropy, but that example itself has little to do with actual entropy.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

Thats what I expected. Though I have read quite a bit about it here on EvC I must say that I have never really thought about it.

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Spontaneous changes tend to smooth out differences in temperature, pressure, density, and chemical potential that may exist in a system, and entropy is thus a measure of how far this smoothing-out process has progressed.

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Entropy WikipediaSo entropy is the attempt to reach equilibrium but this does not nessesarily mean any form of disorder?The article writes about "free energy" and "useless energy" in regards to its ability to do work. I still am having trouble understanding if this is a conflict with the "Big Crunch" theory - doesn't this mean that the "useless energy" is no longer useless?

Think of it this way. The laws of conservation of energy state that in an ideal environment that energy just transforms from one type to another. Kinetic becomes potential becomes kinetic.We can also include matter now with Einstein's e=mc^{^2}But we are not in an ideal environment, there is always some friction, some stray particles, some loss to the systems.Thus if you were able to total all the useful energy at the end of every day in your hypothetical systems, you would have a little less each day, but all the activity, processes and interactions would still be going on ... but just a little bit less of it.Enjoy.

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I don't think that there's a connection between the two. Think of it this way: if you toss a book into the air, it will fly up and then it'll drop back to the floor. Period. Entropy really doesn't enter into it at all.Similarly (except that we would need to know General Relativity), if the mass density of the universe is large enough, it will halt the expansion of the universe and initiate a contraction. I don't think that entropy really enters into it.Edited by Chiroptera, : oops

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

Funny how a simple analogy can help change a way of thinking.I have read what you and Razd have told me and while attempting to better convey my thoughts - I have read a lot on the subject and jumped further into a topic than expected. This is what I was thinking of, but with incorrect ideas about what entropy and the 2lotd says. Each time I come up with a question regarding cosmology I find the subject is infinitely more vast than I had thought.

Usually if I post on a cosmological issue Cavediver will pop in to correct me, so I figure the best way to get this question answered properly is for me to attempt to answer it.Thermodynamic issues are a key consideration for the Big Bang and cosmological expansion/contraction. Many scientists believe that the thermodynamic requirement of non-decreasing entropy in an isolated system is somehow related to time's arrow, though we don't yet understand how this is so since the equations of our current models work equally well with time running either backward or forward.One of the key questions of a cyclical universe (which we don't appear to live in) is the origin of low entropy. The singularity of the Big Bang possessed extremely low entropy, and the entropy of the universe has been increasing ever since. If at some point gravity halted cosmological expansion and caused the universe to again contract into a singularity with low entropy, that would violate the 2nd Law of Thermodynamics. I don't know if an answer to this puzzle was ever devised, but it seems a key problem for the cyclical universe.But we live in a universe that is not only expanding, but is expanding ever faster and faster, and we don't know why. Perhaps the expansion is a cosmological imperative driven by the thermodynamic requirement of increasing entropy. Perhaps it is cosmological expansion that drives the arrow of time.One thermodynamic question about the expanding universe that pops up frequently in creation/evolution discussions asks how suns (which have very low entropy) formed from a relatively uniform distribution of matter (less than .001% difference in density between different regions of the young universe) that already has very high entropy.This actually has a simple answer. In an isolated system where gravity considerations are not important, such as a gas in a laboratory experiment, the gas equally distributed has higher entropy then the gas clumped into small regions of high density, hence the gas is very unlikely to become clumpy. But gravity *is* an important consideration when considering the universe, and when gravity is taken into account, a clumpy universe has higher entropy than a uniform-density universe.Well, hopefully that's enough uninformed meanderings to draw Cavediver's attention.--Percy

Questions will do that. In most subjects.

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I've done everything the Bible says, even the stuff that contradicts the other stuff! -- Ned Flanders

First of all you need a working definition of Entropy, there are several. Some are more appropriate to different areas, however I'll use the statistical/generic one as it emphasises how entropy is not the same as disorder.Basically entropy is a measure of how generic a state is. To explain this, let's take a pair of dices as an analogy.
I will write the numbers on each dice as {a,b}, so a roll of 3 on the first dice and 4 on the second is written as {3,4}.Let's say I roll the dice and I am a being who, for some reason, can only perceive the total of the dice roll. However I am still aware that what I perceive is due to combining the scores on each dice. So I roll the dice and get a result of 2. I roll it again and get a result of 7.Now the role of 2 can only be the result of a roll of {1,1}.
However a role of 7 could be a result of {1,6} ,{2,5} ,{3,4} ,{4,3} ,{5,2} ,{6,1}. So 7 is more generic. There are more dice states that produce it.Similarly, let's say I have a little cloud of gas confined to one corner of a room. There is only a small number of gas molecule states that will produce such a confined little cloud. This is a very special/highly non-generic state. However let's say the gas is instead spread all over the room, then there are several possible arrangements of molecules which can produce this.
The state of a gas filled room is much more generic. We call this "genericness" entropy.From this point it's very easy to explain why entropy always increases. Basically the second law says that as a system evolves it will find itself in increasingly generic states as time goes by.
This makes perfect sense because at any given time you're more likely to be in a generic state than a special state simply because special states are rarer.I recommend Penrose's "The Road to Reality" Chapter 27 (Section 4 in particular) if you enjoyed my explanation.