The potential for a thermodynamic process to be reversed in time. Alternatively, a quantification of how far an irreversible process is from being reversible, which relies on a comparison to a corresponding theoretical reversible process.
Questions tagged [reversibility]
663 questions
33
votes
5 answers
Efficiency of Stirling engine and Carnot's theorem
I want to calculate the efficiency of this Stirling cycle for an ideal gas $pV = nRT$
The mechanical work is
$$
\Delta W_{12} = - \int_{V_1}^{V_2} p(V) \mathrm{d}V = -nRT_2 \ln \frac{V_2}{V_1}\\
\Delta W_{23} = \Delta W_{41} = 0\\
\Delta W_{34} =…
frankundfrei
- 433
29
votes
6 answers
Is there a quasistatic process that is not reversible?
I have seen several questions and good answers on the link between reversible and quasistatic processes, such as here or here. However, these questions only adress one side of the problem : a reversible process is necessarily quasistatic.
I am…
Dimitri
- 2,569
24
votes
7 answers
Quantum and classical physics are reversible, yet quantum gates have to be reversible, whereas classical gates need not. Why?
I've read in many books and articles that because Schrödinger's equation is reversible, quantum gates have to be reversible. OK. But, classical physics is reversible, yet classical gates in classical computers are not all reversible ! So the…
Anarchasis
- 1,397
22
votes
4 answers
How slow is a reversible adiabatic expansion of an ideal gas?
A truly reversible thermodynamic process needs to be infinitesimally displaced from equilibrium at all times and therefore takes infinite time to complete. However, if I execute the process slowly, I should be able to get close to reversibility. …
Mark Eichenlaub
- 53,961
21
votes
2 answers
If entropy is a state function, then why is all the talk about reversible vs. irreversible processes?
So I'm preparing for my Thermodynamics undergrad exam, and I just can't wrap my head around the significance of reversibility vs. irreversibility of a process in relation to entropy. I mean if entropy is a state function, and a system in state A has…
Benjamin Márkus
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21
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Principle of Caratheodory and The Second Law of Thermodynamics
Background
Constantin Carathéodory formulated thermodynamics on a purely mathematical axiomatic foundation. His statement of the second law is known as the Principle of Carathéodory, which may be formulated as follows:
In every neighborhood of any…
noir1993
- 2,226
20
votes
4 answers
Hawking radiation and reversibility
It's often said that, as long as the information that fell into a black hole comes out eventually in the Hawking radiation (by whatever means), pure states remain pure rather than evolving into mixed states, and "the universe is safe for quantum…
Scott Aaronson
- 2,492
19
votes
4 answers
How is entropy a state function?
Is there only one reversible way to move from one state to another?
If we consider two states $A$ and $B$ on an isotherm and we move from $A$ to $B$ by first reversible isochoric process and then reversible isobaric process. Now the path…
oshhh
- 1,017
18
votes
5 answers
Again: why do quantum computations need to be reversible?
In quantum computing, there is famous "law" which is to say that all the computation must be reversible. I understand that, for simplicity, it may be easier to consider reversible operation, and that they are general enough to make us happy to stick…
tobiasBora
- 289
17
votes
3 answers
Reversibility = non-causality. Can this be right?
I read yesterday the Norton Dome's paper, which shows that some Newtonian systems can be non-causal, based on specific solutions of Newton's laws. The author justifies the solutions in very nice, logically consistent ways, that made me unable to…
The Quantum Physicist
- 3,517
16
votes
8 answers
How is this process not quasi-static yet reversible?
Consider a (adiabatic) canister with a piston containing some gas kept in a vacuum. There are two weights on the canister which equalize the pressure of the gas on the piston. Assume the system is at equilibrium.
I remove one weight from the…
Gerard
- 2,838
15
votes
2 answers
Hysteresis and dissipation
Hysteretic phenomena are often linked to dissipation. When there is a hysteresis loop, the dissipated energy can usually be computed as the area of the cycle.
For example, in ferromagnetic materials, the relationship between the magnetization and…
Georg Sievelson
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15
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11 answers
Where does the irreversiblity came from if all the fundamental interaction are reversible?
There isn't too much to explain:
We know that all fundamental forces are reversible then where does the irreversibility come from?
Edit: The following is edit based on comments:
Consider a block of wood and you just make it slide on a desk, it…
Himanshu
- 12,211
15
votes
6 answers
Why is heat transfer reversible when temperature difference is infinitesimal?
I don't understand why heat transfer from hot reservoir to the system is considered reversible in this case:
$$T_\text{reservoir}=T_\text{system}+\mathrm dT$$
but it's considered irreversible in this case:
$$T_\text{reservoir}=T_\text{system}+\Delta…
matori82
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15
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5 answers
Intuitively, why is a reversible process one in which the system is always at equilibrium?
A process is reversible if and only if it's always at equilibrium during the process. Why?
I have heard several specific example of this, such as adding weight gradually to a piston to compress the air inside reversibly, by why should it be true in…
Mark Eichenlaub
- 53,961