entropy and expansion of universe

theoretically full equilibrium will never be reached.

 

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Oh. I should think about this!! I thought exactly opposite of what you said!! I would have confused Q-reeus's answer.Thank you!!

 

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I am confused.....:bawl:

 

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Notice eram used the words not always. Things have to be taken in a total context. Take the example of entropy of a perfect crystalline solid I dealt with in #29. As an isolated system, yes entropy tends to zero as T goes to zero for just that solid. But in order for T to drop it cannot be an isolated system. In order to extract thermal energy in an otherwise uniform room temperature environment, some refrigeration cycle involving a larger system must interact with it, and the total entropy of the combined system will always have increased - Carnot cycle. Following article may be useful:
http://www.everyscience.com/Chemistry/Physical/Entropy/b.1307.php

Getting back to the universe as a whole, I suggest to study this Wiki article:
http://en.wikipedia.org/wiki/Heat_death_of_the_universe

 

When does decreasing temperature mean decreasing entropy?

 

An example would be the freezing of water.

 

I agree, and I will add that in the past, as far back in time as you look, there was never a time when the process of increasing entropy started. Just like full equilibrium will never be reached, so too did the process of increasing entropy never have a beginning.

 

If water freezes on its own it is increasing entropy. If water is forced to freeze it required power, which increased entropy, so you're wrong on both counts.

 

Expounding on my earlier claim that disorder isn't that useful a notion in systems at equilibrium.

Thermodynamics partitions a system so that as the partitions get smaller, the average kinetic energy of each approaches the same value. That means, regardless which partition you measure the temperature of, you get the same value. So every partition is randomized 'identically' (i.e. has the same 'Maxwellian' distribution of energies over all particles in a partition).

This is analogous to having a set of strings of characters, where each string is a random arrangement of the set of characters; so the set of strings is like the set of partitions, and each string has an identical measure of randomness (which is the information entropy). Equilibrium then corresponds to the disappearance of strings with 'structure'; each string contains an identical 'random' message. . .

 

that's an interesting concept. but I guess that whatever order that has been dissipated into disorder can dissipate even further.

 

I am confused!! just answer this question. Is Entropy the measure of disorder? Does Increasing Entropy mean decreasing usable Energy? Which has High Entropy? Comparatively hot or cold objects?

 

The explanation is not so straightforward.

You could try watching this, though it's in Portuguese.

[video=youtube;2iCJ-T_IHTM]http://www.youtube.com/watch?v=2iCJ-T_IHTM[/video]

 

C'mon!! How can i understand Portuguese??

 

I couldn't find the English version. It used to be online, but all were taken down. Anyway what's your mother tongue? I think arauca is Spanish.

 

What about you?

I am an Indian.

 

Entropy has many definitions such as a measure of disorder. However, defining entropy as only disorder is somewhat misleading, since two daughter cells from one mother cell, will increase the entropy, even though both daughter cells retain the order needed for life.

As such, although disorder is an important aspect of entropy, this definition does not include all entropy situations. A better definition for entropy is connected to information, with an increase in entropy implicit of an increase in information needed to define the new system. Disorder will require more information to define, than will order, since order has repeat patterns. While two cells from one cell now needs double the information to keep track of both.

Since time moves to the future, in our universe, that alone adds more information/entropy to everything, since it adds information associated with a building history time-line. The expansion of the universe, not only occurs in time but it also expands distance, thereby increasing the information needed to define the universe.

The expansion of space-time, by speeding up time, also speeds up the rate at which entropy will increase. One way to see this is consider two twins, each working in a factory on identical machines, which produce one defect per hour, on the average. The defect represents an entropy increase, since it adds new information to the redundancy of the desired uniform product.

One twin is in our reference, while the other twin we will have traveling near C, where time slows relative to the first twin. If we compare the machines (side-by-side) the reference with the slower time reference will generate defects slower than the machine on the stationary earth reference. Side-by-side the stationary reference makes defects faster because time is faster. The expanding universe, since it cause time to speed up (expanding space-time) speeds up rate of entropy increase.

For entropy to increase, the system needs to absorb energy. This is why entropy is often associated with the inefficiencies in machines; wasted heat due to friction. Or if we boil a liquid into a gas, the increase of entropy to get the higher gases, needs to absorb the heat of vaporization. If we assume dark energy is causing the expanding universe, and the expansion of space-time is increasing the rate of entropy increase, the amount of dark energy in the universe needs to be lowering as it is absorbed into entropy. The energy within the dark energy is conserved within the entropy/information.

If you look at gravity, gravity will lower entropy. This can be inferred from GR, with the increasing gravity causing time to slow. Using the twin factory workers, the slowing of time due to gravity and the contracting space-time well slows the rate of defects, therefore slows entropy. The loss of entropy releases energy. This means entropy needs to accelerate elsewhere with energy being recycled for this purpose.

I would guess the universe is integrated and that gravity, using the substance of matter, by lowering the entropy rate in time via GR, and with universal entropy having to increase, will necessitate the expansion of universal space-time to speed up the rate of entropy increase elsewhere to compensate. Dark energy, in this case, would be connected to an energy output from gravity/GR due to the decrease in entropy; energy is recycled.

 

Yes. Of course.

 

Entropy can be defined as an increase in disorder.

 

In order for work to be accomplished in a duration of time (power=work/time) there had to be a "fuel" for that work. All fuel is derived from extracting energy from evolving mass to space. Want to burn a log and get warm? Then convert the log into heat! Want to walk down the sidewalk? Turn the pizza you ate into heat! Want to push an earth away from you (the sun)? Then convert some of your mass into heat!

All physical process stems from converting mass into energy. That process can be referred to as entropy. There are no free rides, so if you want to freeze something, you are gonna have to make some heat first!