# The Naked Scientists Forum

### Author Topic: What is entropy?  (Read 2872 times)

#### @LifeSWITCH1

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##### What is entropy?
« on: 26/09/2011 22:01:02 »

What exactly is entropy?

What do you think?
« Last Edit: 26/09/2011 22:01:02 by _system »

#### Soul Surfer

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##### What is entropy?
« Reply #1 on: 27/09/2011 00:19:05 »
Entropy is quite a complex concept and rather different depending on what you are talking about. and it is most definitely not EXACTLY anything

Firstly it originates as part of the differential equations of thermodynamics  where the change in the quantity of heat in a body is less than or equal to the temperature times the change in entropy in the body if the change is reversible this becomes an equation.

The fact that this is a differential equation means that it does not dal fully with the absolute entropy of anything only how it changes  as conditions change.

In thermodynamics the second law states that in all thermodynamic interactions entropy always increases.  This is a bit like saying that water always runs down hill.  OK there are several devices that allow water to move up hill but it always needs a lot more water running downhill to make them work.

Over the years there has been an attempt to get some idea of what absolute entropy would be like described by the amount of "disorder" or the number of indistinguishable states in any closed system but this is only a figurative expression  for example the crystallisation of a liquid into an ordered crystalline solid seems to be an increase in order and not a decrease but this is not the case because you have not taken into account any heat flow and its consequences
« Last Edit: 27/09/2011 00:22:35 by Soul Surfer »

#### damocles

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##### What is entropy?
« Reply #2 on: 27/09/2011 04:17:12 »
for example the crystallisation of a liquid into an ordered crystalline solid seems to be an increase in order and not a decrease but this is not the case because you have not taken into account any heat flow and its consequences

I am a little lost on this one, Soul Surfer. The process of going from melt to solid results in release of heat (associated with a positive latent heat of fusion). This is a general result for most (all?) liquids. Release of heat on crystallization is exactly consistent both with a decrease in entropy and an increase in order. I completely fail to see why a crystallization process does not match the order/disorder view of entropy.

#### Geezer

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##### What is entropy?
« Reply #3 on: 27/09/2011 05:27:36 »

#### Soul Surfer

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##### What is entropy?
« Reply #4 on: 27/09/2011 09:27:43 »
The point is damocles, that in any closed system entropy always INCREASES and our universe is always progressing from an ordered state to a disordered one!!  The ordered crystallisation state of the solid is more than matched by the disordered heat released as it does it.

Black holes have the highest possible entropy for their mass because once one thing has dropped into it it is completely indistinguishable from any other thing that has dropped into it.   The final state of our universe (and probably any other universe) is just black holes slowly evaporating into incredibly cold nothingness.

#### Geezer

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##### What is entropy?
« Reply #5 on: 27/09/2011 18:48:52 »
The point is damocles, that in any closed system entropy always INCREASES and our universe is always progressing from an ordered state to a disordered one!!  The ordered crystallisation state of the solid is more than matched by the disordered heat released as it does it.

Ah yes! The tricky thing with thermodynamics is properly defining the system boundaries (as I have found out to my cost on many occasions.)

#### yor_on

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##### What is entropy?
« Reply #6 on: 02/10/2011 23:01:19 »
I think of it as socks. The entropy of my room rise as they disappear, and they always disappear? I get them all neatly packaged from the store and then, as I use them, they seem perfectly happy? But the next day at least one of them has left? And it's the same every time I wake up. I'm starting to suspect that they hide behind the wallpaper, snickering at me..

#### Bored chemist

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##### What is entropy?
« Reply #7 on: 03/10/2011 07:17:27 »
Boltzmann would be spinning in his grave.
S=K log (w)

#### Johann Mahne

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##### What is entropy?
« Reply #8 on: 03/10/2011 10:16:27 »
Quote
The point is damocles, that in any closed system entropy always INCREASES and our universe is always progressing from an ordered state to a disordered one!!
According to the Big Bang theory, the early universe was a soup of particles. Galaxies then started to form as well as planetary systems.
Galaxies that collide may seem disordered, but then can form spiral galaxies.
Is this not a progress into more order?

#### damocles

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##### What is entropy?
« Reply #9 on: 03/10/2011 11:06:06 »
It is very difficult to see or speculate about the second law of thermodynamics on a cosmic scale; it is certainly effective on a scale up to solar systems. One of the issues in the big bang and the early days of the universe is that although the condensation of energy into matter, and the gathering of matter due to gravitational effects may seem to be producing order, there are (at least) two sources of disorder that probably outweigh it: the fact that the galaxies are becoming increasingly lost in an expanding universe, and the fact that local gravitational accumulation of matter is accompanied by huge increases in the temperature (relative kinetic energy) of that matter.

#### CPT ArkAngel

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##### What is entropy?
« Reply #10 on: 03/10/2011 11:42:23 »
The entropy of a system can be seen as the complexity of the information necessary to describe it.

The universe we see and we know was at its lowest entropy state just before the BigBang. Entropy is simply the expansion of energy in space, or spacetime if you prefer. This is certainly linked to electromagnetic radiation loss (photons loss).

#### Johann Mahne

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##### What is entropy?
« Reply #11 on: 04/10/2011 03:58:43 »
Quote
one of the issues in the big bang and the early days of the universe is that although the condensation of energy into matter, and the gathering of matter due to gravitational effects may seem to be producing order, there are (at least) two sources of disorder that probably outweigh it: the fact that the galaxies are becoming increasingly lost in an expanding universe, and the fact that local gravitational accumulation of matter is accompanied by huge increases in the temperature (relative kinetic energy) of that matter.

If entropy is seen as the amount of dispersal of energy, then you are right. As space expands so energy dispersis.
But if you think of it as only disorder then i'm not so sure.

The latest theories on the expansion of space time says that local groups of galaxies do not experience this expansion because their gravity stabilises their local space time. So they are not, in themselves, becoming disordered by being "lost in space". Even if they freeze over, they will still have some order.

« Last Edit: 04/10/2011 04:01:06 by Johann Mahne »

#### yor_on

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##### What is entropy?
« Reply #12 on: 04/10/2011 05:11:48 »
Entropy is about the way our universe work, disorder and statistics. We can see that when mixing warm water with cold, the water becomes lukewarm. When we mix a strong color into a water-filled container we see that color weaken as it gets diluted and dissolves. All of that involves some sort of work, and a 'timely direction' involving a transformation.

So we might define it such as there is two qualities in the universe, work, and work done. We also defines SpaceTime as being closed, nothing ever gets lost in it, it only transforms. That one is a old revelation existing in different varieties, but mainly referred to as coming from the experiments of Antoine Lavoisier, around the time of the French revolution. In a open system things get disordered too, like my socks did as I have a door opening to other rooms. But there you will have problems defining the boundaries for your system, and also the possibility of those socks being 'lost' forever, not only 'transformed', if you see what I mean. So we want to have clear demarcations for any entropic system, and when work is done inside SpaceTime and energy transformed from 'useful work' to 'work done' then whatever it transformed into still must be contained inside SpaceTime.

Modern entropy is about describing the probabilities involved as it transforms. It uses what is called 'micro states' for defining what probability a system has for arranging itself into a defined order, aka its 'macro state'. Micro states may be the molecules or atoms.

It is also about disorder. When you have order in a system the entropy is low, as with my socks when I first got them, neatly packaged. But as they disappear the entropy raises. The Second Law is about the irreversibility of it, stating that the entropy must increase in all processes, begetting a greater disorder. So, at the Big Bang there was a great amount of 'order' and so a low entropy and as the universe cooled and started to create stars and planets the disorder grew and entropy raised. And how that later disorder can come from order is a subject where people still don't agree. But it is also about a equilibrium as a balance where nothing more will change.

And yes, it's hard to encompass it, there seem to be so much involved in it. I agree that entropy can be defined and treated statistically for a closed system, but it all seem to depend on your definitions of how such a system should be considered. The modern way is to treat it statistically from the probability of those micro states turning out into some defined configuration.
==

But then we come to 'energy', and that one is so very difficult to define. Where is that 'energy' that drove your car, some of it became transformed into water and some as other 'substances' but some of it must have 'disappeared'. Otherwise we just could mix those subjects together again in a closed system and get ourselves a perpetual motion machine. And that's 'work done, whatever that is. The difference between being able to use something versus reusing it. some stuff we can reuse, but there is always some level from where we can't get any more 'useful energy' from it. And where did it go? In a closed SpaceTime it still has to be here, somewhere?
« Last Edit: 04/10/2011 06:03:34 by yor_on »

#### Geezer

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##### What is entropy?
« Reply #13 on: 04/10/2011 06:12:33 »
Entropy is greatly overrated.

It really isn't "anything". It's just a way of balancing the books so you don't get something for nothing.

#### The Naked Scientists Forum

##### What is entropy?
« Reply #13 on: 04/10/2011 06:12:33 »