Entropy Definition and 999 Threads

I understand entropy as a movement from order to less order and that the universe's entropy is increasing. So I was wondering, life takes molecules and organizes them into organisms, so isn't life a reversal of entropy?

When trying to describe why the entropy goes up for a irreversible process, such as gas expanding into a vacuum, it seems fairly easy at a high level. the valve between the two chambers opens, the free expansion occurs, the pressure drops proportional to the volume change and the temp remains...

I'm reading Brian Greene's latest book 'Until the End of Time' (I'll pause here while you finish groaning at yet another layperson reading popularist physics books.) In it, he's describing entropy in a way I've never heard before and it clarifies something that's always stuck on my craw about...

Hi, I'm new to PF and not really sure which forum may be the most appropriate to find people with an interest in probability and entropy. But the title of this forum looks promising. If you share an interest in this topic would be delighted to hear from you.

Thinking of the common language notion of "entropy" as "uncertainty", how can running a simulation based on a probability model implement entropy increasing? After all, the simulation picks definite outcomes to happen, so (intuitively) there is less uncertainty about the future as definite...

Question --- So I've done a calculation which seems to suggest if I combine the system of a measuring apparatus to say an experimenter who "reacts" to the outcome of the the measurement versus one who does not. Then the change in entropy in both these situations is bounded by: $$ \Delta S_R...

I thought that would be something like, using similar counts from Einstein solid, ##S = kln(\frac{(q+N-1)!}{q!(N-1)!})## Where q is ##hv## v is frequency But the results are not similar, so i am little stuck

Can you reverse entropy without using energy?

I am struggling to understand Callen's explanation for stability, I understand that the concavity of S(U) must be negative because otherwise we can show that this means that the temperature increases as the internal energy decreases (dT/dU<0) but I cannot understand equation (8.1) which...

I am a little confused why does the temperature was took out of the integration, is there an error in the solution?

Not sure whether this is the right category but bear with me.I've seen graphics where the information increase with time of evolution is projected like the one in the link below from Carl Sagan's book https://www.researchgate.net/figure/Page-from-the-book-of-Carl-Sagan-21_fig2_322153131 Now I...

The following paper appeared earlier this year on arxiv, entitled "Islands in Schwarzschild Black Holes": https://arxiv.org/pdf/2004.05863.pdf First, a bit of background: this paper appears to be part of a larger research effort aimed at resolving the black hole information paradox by showing...

In special relativity, observers can disagree on the order of events - if Alice thinks events A, B and C are simultaneous, Bob can think A happened before B which happened before C, and Carlos thinks C happened before B which happened before A - provided A, B and C are not causally connected, of...

Is it 0 K for a substance to have no entropy?Sorry. Just had to get that off my chest.

i consider a pair of two level particles which can be up or down. this pair is described in the tensor product by the unitary vector (cos(\theta) (du + ud) + sin(\theta) (dd + u)) /\sqrt 2 i take its density matrix , trace it on one of the two particles and find the density matrix of each one...

The conclusion of my attempt I am listing below is that there do exist entropies for both but I am not sure. $$dU=TdS-pdV$$ $$dS=\frac{dU}{T}+\frac{p}{T}dV$$ Therefore, gas A: $$S=\frac{{\Delta}U}{T}+\alpha_A(\frac{-N}{{\Delta}V})$$ Gas B...

So I've answered the first question and I got a final temp of 42.06 Celsius. Now for this second one, I don't know why I am getting it wrong: Im doing 0.215*ln(315.06/291.46) + 1*ln(315.06/319.91) But it says I am wrong. What about my process is faulty?

(not a paradox nowadays, but it was an issue for years) https://en.m.wikipedia.org/wiki/Gibbs_paradox It's not a question about a formula. I don't understand the motivation in physics to claim Gibbs mixing "paradox", the discontinuity point. What bothers the physicist to ask for a continuous...

Maxwell's demon measures the position and velocity of the particle. How can it do that when it violates the uncertainty principle? Does that mean uncertainty principle is unavoidable otherwise we will violate II law of thermodynamics as in the case of Maxwell's demon?

Actually i am trying to see what the first equation to the entropy means, maybe N1 remets to the part 1 (the left suppose) of the system? (or the molecules type 1?) I am not sure about the equations i will do below, probably it will be wrong, anyway. ∂S/∂U1 = 1/T1 = 3NR/2U1 Okay, it will give...

There is five physically possible entropy to exist, and five entropy which can't be real, find it all. I could found just four entropy, what is the another? B, H and J: S(λU,λV,λN) ≠ λS(U,V,N) D: ∂S/∂U < 0 what is the another? (another or other??)

We need to find the system's entropy variation. I don't think i understood pretty well what is happening in this process, can someone help me how to start?

I came upon a realization recently. The early universe is always described to have begun in a state of extremely low entropy and it's been increasing ever since. But the same amount of stuff exists now as it did back then. Only thing that's changed is how big the universe is now vs then. So...

Sketch a qualitatively accurate graph of the entropy of a substance as a function of temperature, at fixed pressure. Indicate where the substance is solid, liquid, and gas . Explain each feature of the graph briefly. What you think about?: dU = -P*dV + Q*dS (1) V = C*T => dV = C*dT Nfk*dT/2 +...

Does increase the size of the solid body increase its entropy? I was thinking about it using the Einstein model of solid. S = k*lnΩ Ω = (q+n-1)!/((q)!(n-1)!) I am not sure how this question should be answer, i think if we talk about rigid bodies, the question don't even have sense, but about...

Sorry for being fuzzy here, I started reading a small paper and I am a bit confused. These are some loose notes without sources or refs. Say we start with a collection F of features we want to trim into a smaller set F' of features through information gain and entropy (where we are using the...

I read in a book "Quantum Space" by Jim Baggot, page 290, that the entropy of an object is inversely proportional to its temperature. (He was describing the temperature of a black hole. Does this statement only apply to black holes?) No doubt he is correct, but wouldn't an increase of energy...

How did you find PF?: random Brownian motion Is randomness real or is it simply defined as such due to our inability to perceive hyper complex order? Randomness is a troublesome word. I'd feel better if I knew it was an objective phenomenon and not merely a placeholder description of...

As a systems engineer I have thought a lot about entropy in trying to get a better intuitive sense for what it is, at a more macro level than it is usually discussed. I have some ideas and am looking for a forum to present and explore them with others. I wish to discuss more from an...

I am a biology undergraduate interested in abiogenesis. The entropic explanation for the origin of life is that life is allowed to exist because it increases universal entropy. I am curious about how far we can take this theory down. How can you explain the emergence of atoms and atomic...

If we know the molecular structure of a complex chemical (organic), can we calculate the dissociation energy for each and every bond somehow? Also, can we calculate the standard etropy of the same molecule? These information would be needed to calculate Gibbs free energy for reactions of a...

Previous of this problem, there was another problem. that is "What is the change in Temperature of van der Waals gas in free expansion?". I got them. It was C_V dT= -aN^2/V^2 dV Then, I got T=T0-aN^2/2VC_V So i knew that the Temperature is decreased by free expansion in adiabatic process. Then I...

Hello to everyone, I'm studying thermodinamics and I would like to understand better the meaning of entropy and how to calculate it. I know that if A and B are two possible states of a system, the equation whcih defines variation of entropy from A to B is...

Is there any particular reason why entropy could not be a measure of or proxy for the level of competition within a system?

I'm trying to relate an analogy from Brian Greene about entropy microstates/macrostates to the real world. In the analogy, you have 100 coins that you flip. The microstate is which particular coins landed heads up. The macrostate is the total number of coins that are heads up. So a low entropy...

Hi, I am currently reading Introduction to statistical physics by Huang. In the section of entropy, it reads But what if I choose ##R-P## as a closed cycle? Then in a similar process, I should have ##\int_{R} \frac {dQ} {T} \leq \int_{P} \frac {dQ} {T}## and ##S \left ( B \right ) - S \left (...

Attempt at a Solution: Heat Absorbed By The System By the first law of thermodynamics, dU = dQ + dW The system is of fixed volume and therefore mechanically isolated. dW = 0 Therefore dQ = dU The change of energy of the system equals the change of energy of the gas plus the change of energy...

The von Neumann entropy for an observable can be written ##s=-\sum\lambda\log\lambda##, where the ##\lambda##'s are its eigenvalues. So suppose you have two different pvm observables, say ##A## and ##B##, that both represent the same resolution of the identity, but simply have different...

I want to know what are the QFT topics that I need to understand in order to proceed in reading papers on entanglement entropy such as, Entanglement Entropy and Quantum Field Theory Entanglement entropy in free quantum field theory Entanglement entropy: holography and renormalization group An...

the entropy change for a reversible adiabatic process is zero as it remains constant. Is this a reversible process? assuming T1>T2: hot (h) water has mass M, temp T1 cold (c) water has mass nM, temp T2 let the final temperature be Tf if δQ=0 as the process is adiabatic, |Qh|=|Qc| so Qh=-Qc...

ΔU_A + ΔU_B = 0 (Is this because of isolated system am I right?) ΔU_A = CA * (T_final - T_A ) ΔU_B=CB * (T_final-T_B) And because of a very slow process : S=ln(T) T_final= (CA T_A + CB T_B)/(CA + CB) ΔS_final = CA*ln(T_f/TA) + ln(T_f/TB) * CB My QUESTION is : When we say No heat exchange...

In a shrinking universe heat will increase, but also volume available to place particles will decrease. What happens to entropy when the volume gets very small and the temperature is very high?

If ##N## is constant (per the partial derivatives definitions/ the subscripts after the derivatives) then ##G## is constant ##H - TS = constant## Taking the derivative of both sides with respect to ##T## while holding ##N,P## constant we get the following with the use of the product rule...

If it occurs spontaneously then it must increase entropy but the possible micro states reduce so what else is occurring to increase entropy

I was studying statistical mechanics when I came to know about the Boltzmann's entropy relation, ##S = k_B\ln Ω##. The book mentions ##Ω## as the 'thermodynamic probability'. But, even after reading, I can't understand what it means. I know that in a set of ##Ω_0## different accessible states...

In a (reversible) Carnot cycle the entropy increase of the system during isothermal expansion at temperature TH is the same as its decrease during isothermal compression at TC. We can conclude that the entropy change of the system is zero after a complete Carnot cycle. The mentioned textbook now...

##dmL_f= Q \; \; ##,##∆T=\frac{T(v_l-v_s)∆P}{L} \; \;##,##\frac{dmL_f}{T_0}= dS_2 \; \;##,##\frac{dmL_f}{T_1}= dS_1 ##

In heat engine we define a heat source from where heat is transferred to the system, we say that heat source has a temperature ##T_h## , When we define a Carnot heat engine, the first process we have is an isothermal expansion and we say heat has to come in system through this process and here...

Planck states that all perfect crystalline system have the same entropy in limit T approaches zero,so we can put the entropy equal zero.Can we demonstrate that or is it only a presumption?

What is the relation of the arrow of time and entropy according to thermodynamics?