A important property of all systems in thermodynamics and statistical mechanics. Entropy characterizes the degree to which the energy of the system is *not* available to do useful work
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Nonextensive statistical mechanics
I know that the Tsallis($S_q$) entropy is called nonextensive information measure in the sense that if $P$ and $Q$ are two probability distributions then $S_q(P\times ...
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How is thermodynamic entropy defined? What is its relationship to information entropy?
I read that thermodynamic entropy is a measure of the number of microenergy states. What is the derivation for $S=k\log N$, where $k$ is Boltzmann constant, $N$ number of microenergy states.
How is ...
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220 views
Simple question about a gas in a box with a moving wall
David Albert is a philosopher of Science at Columbia. His book "Time and Chance" includes this example (p 36).
A gas is confined on one side of a box with a removable wall. "Draw the wall out, ...
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334 views
Restrictions on defining microstates (Entropy)
If we have an isolated system $Sb$ with thermodynamic entropy $Eb=X$
(and growing by the 2nd law of thermodynamics),
we could define an abstract system $Sa$ (containing the system $Sb$) but define ...
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2answers
366 views
Does entropy apply to Newton's First Law or does “acted upon” always require an external factor?
First law: Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force. This means that in the absence of a non-zero net ...
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Explaining Arrow of Time with Entropy
WARNING: Possibly a naive post.
Hi guys. I just watched on BBC, [some show] yesterday (sunday) where the host talked about Arrow of Time, where by 2nd law of thermodynamics states that "nature" is ...
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744 views
Best example of energy-entropy competition? [closed]
What are the best examples in practical life
of an energy-entropy competition which favors entropy over energy?
My initial thought is a clogged drain -- too unlikely for the
hair/spaghetti to align ...
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0answers
238 views
How does lifting an object effect its entropy
I have figured out that:
When photons leak out from a container, the entropy of the photon collection increases, because each photon has a different escape time.
Photons that have leaked out from a ...
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128 views
Do all closed systems, only considering kinematic/mechanical principles, exhibit time reversal symmetry?
It makes a lot of sense to me to imagine a cannonball flying through space as not so much experiencing a macroscopic non-conservative drag force, but as pushing a bunch of air molecules and giving ...
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2answers
412 views
Energy of unmixing
Mixing of two different fluids is associated with an increase of entropy. Conversely, separation of two gases must be associated with a decrease of the entropy of the two fluids.
Is there a minimum ...
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5answers
2k views
Why was the universe in a extraordinarily low-entropy state right after the big bang?
Let me start by saying that I have no scientific background whatsoever. I am very interested in science though and I'm currently enjoying Brian Greene's The Fabric of the Cosmos. I'm at chapter 7 and ...
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3answers
652 views
How to understand temperatures of different degrees of freedom?
So I'm reading this book, where after the preface and before the models there is a section called General Notions and Essential Quantities, which introduce some things I don't understand. They regard ...
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203 views
Defining Orderly/Chaotic states in terms of entropy?
I'm trying to properly understand the meaning of entropy, and how the universe is moving from an orderly state to a chaotic one.
If a glass of wine (for example) only has meaning to a human, what ...
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1answer
200 views
What is the current science on entropic gravity?
In the past couple of years there has been some buzz about 'entropic gravity', including here on stackexchange in Jan 2011. Many say that there is no way that gravity can be entropic, while others ...
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3answers
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Second law of thermodynamics and a bunch of magnets
Say I put a bunch of powerful square magnets on a nearly frictionless table in a disordered fashion. The second law of thermodynamics states that the system shall spontaneously get more disordered, ...
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6answers
661 views
How can it be that the beginning universe had a high temperature and a low entropy at the same time?
The Big Bang theory assumes that our universe started from a very/infinitely dense and extremely/infinitely hot state. But on the other side, it is often claimed that our universe must have been ...
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0answers
382 views
Is this a known entropy formula?
While playing around with a variant of the one-dimensional Ising model with periodic boundary conditions I came up with a formula, let's call it $F$, whose form looks suspiciously like an entropy ...
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1answer
349 views
Does the heat death of the universe really imply a maximum entropy state *all* of the time? Or most of the time?
Statistically speaking, you're going to still encounter deviations from equilibrium, even though the expected value is equilibrium. But these rare deviations from equilibrium - which are inevitable - ...
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103 views
Use of escort distribution in nonextensive stat. mech
In some of the articles which I read recently, I happen to see the following statement.
In Nonextensive statistical physics, it is inappropriate to use the original distribution $P=(p_i)$ ...
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Can a single classical particle have any entropy?
recently I have had some exchanges with @Marek regarding entropy of a single classical particle.
I always believed that to define entropy one must have some distribution. In Quantum theory, a single ...
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Entropy of two expanding and mixing ideal gases
I am currently stuck with the following problem:
...
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2answers
335 views
The entropic cost of tying knots in polymers
Imagine I take a polymer like polyethylene, of length $L$ with some number of Kuhn lengths $N$, and I tie into into a trefoil knot. What is the difference in entropy between this knotted polymer and ...
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2answers
464 views
Entropy of an empty universe
After watching the first episode of wonders of the solar system, one question came up which is not explained.
Bryan Cox says that ultimately the universe will be devoid of matter, so not even a ...
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3answers
379 views
How bright can we make a sun jar?
A sun jar is an object that stores solar energy in a battery and then releases it during dark hours through a led.
Assume:
a $65cm^2$ solar panel
a 12h/12h light/dark cycle
insolation of ...
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1answer
548 views
Why it is said that Universe is an isolated system?
I have read in many places
"Entropy of an isolated systems never
decreases"
And as a corollary:
"As Universe is an isolated system(I) then its entropy is constantly increasing(II)"
I) ...
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1answer
253 views
Relation between classical and quantum information
It is known that for a classical system the amount of information needed to store its state is the same as the amount of information that can be stored in that system. This amount is equal to ...
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1answer
186 views
If 100% of the energy from the sun is reflected back into space
100% of the energy from the sun is reflected back into space, it's just shifted from a low-entropy state to a high-entropy state, and from a high frequency (ultraviolet) to a low frequency (infrared). ...
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1answer
424 views
Entropy and how it applies to everyday activities like eating food
So I was eating a plate of food one day and thought of entropy. As I understand the definition of entropy, it is the logarithm of the number of arrangements or states the object in question can be in, ...
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1answer
146 views
Can the entropy of a subsystem exceed the maximum entropy of the system in quantum mechanics?
Quantum mechanics has a peculiar feature, entanglement entropy, allowing the total entropy of a system to be less than the sum of the entropies of the individual subsystems comprising it. Can the ...
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1answer
492 views
Why is there an absolute entropy?
Why is there an absolute entropy? Given any non-discrete probability distribution, we don't really have an absolute entropy because the entropy depends on the parametrization of the distribution ...
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7answers
795 views
Is there a four-dimensional definition of entropy?
It seems odd that entropy is usually only defined for a system in a single 'slice' of time or spacelike region. Can one define the entropy of a system defined by a 4d region of spacetime, in such a ...
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1answer
310 views
The full entropy quote
What is the full text (and possibly the source) of the summary of the 3 laws of thermodynamics that goes something along the lines of "Can't break even, can't win and can't even stop playing the ...
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1answer
240 views
How to vizualize a heat pump microscopically?
Hey guys,
while learning thermodynamics i wondered how a the principle of a heat pump would look at a microscopic level, not on a quantum mechanical level.
I learned that when a hot and a less hot ...
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3answers
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Why does the low entropy at the big bang require an explanation? (cosmological arrow of time)
I have read Sean Carrol's book. I have listened to Roger Penrose talk on "Before the Big Bang". Both are offering to explain the mystery of low entropy, highly ordered state, at the Big Bang.
Since ...
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2answers
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Experiments that measure the time a gas takes to reach equilibrium
If you take two ideal gases at different temperatures, and allow them to share energy through heat, they'll eventually reach a thermodynamic equilibrium state that has higher entropy than the ...
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4answers
617 views
What are the arguments towards the Life-and-Entropy relation?
I've heard it from a few people, and I've seen it popup here in the site a couple of times. There seems to be speculation (and studies?) towards this idea, and this is what I've picked up so far:
...
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3answers
754 views
How efficient is a desktop computer?
As I understand it (and admittedly it's a weak grasp), a computer processes information irreversibly (AND gates, for example), and therefore has some minimum entropy increase associated with its ...
