Questions tagged [arrow-of-time]
A concept related to the asymmetry of time, usually related to the second law of thermodynamics, which says that entropy always either increases or stays the same.
222 questions
-3 votes
2 answers
100 views
Is A/C (Air Conditioner ) consider as reverse entropy? [closed]
Can we consider the air condition as reversing entropy? what are the other process like that?
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1 vote
0 answers
57 views
How to reconcile the reversible nature of microscopic physics with the irreversible nature of macroscopic reality? [duplicate]
This might be a conceptual question more than a technical one, however it would be very useful to see different conceptual approaches to address this problem physically/mathematically. The question ...
2 votes
0 answers
147 views
Why can you not reverse the direction of the line integral?
I am trying to prove $(1)$ below for irreversible processes, but I have a significant doubt. I will first lay out my attempt, and then explain my issue. Let $\mathcal{Z}$ be any irreversible process ...
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0 votes
2 answers
138 views
Can we reverse entropy system [closed]
Do you think "time has direction and we are experiencing time in forward direction" If the Entropy is reversed then the time will also be reversed means then we experience time in backward ...
2 votes
1 answer
584 views
Negative energy in special relativity
I am currently studying Quarks and Leptons by Halzen&Martin, and I have come across the typical presentation of the negative energy problem in QFT, introducing the free particle field in the Klein-...
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3 votes
3 answers
445 views
Why is information lost over time in real physics, but not in a simulated "integer-only" physics?
In statistical mechanics, entropy tends to increase over time, which is often interpreted as a loss of information about the initial state of a system. Imagine I create an artificial physics ...
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2 votes
2 answers
201 views
Introducing time asymmetry in the Boltzmann equation
The Boltzmann equation: $${\displaystyle {\frac {\partial f}{\partial t}}+\{f,H\}=\left({\frac {\partial f}{\partial t}}\right)_{\mathrm {coll} }}$$ is the first equation that, when we truncate the ...
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1 vote
2 answers
362 views
What Lindbladian-like equation should we use to evolve quantum system toward $-t$?
While unitary evolution is trivial to apply time symmetry, generally Lindbladian is used to evolve quantum systems (hiding unknowns like thermodynamics), and it is no longer time symmetric, leads to ...
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0 votes
0 answers
103 views
Entropy and local flow of time
I have little training in physics or mathematics beyond HS and early undergrad long ago so apologies for any fundamental misconceptions and/or sloppy use of terms. As I understand, the flow of time ...
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2 votes
0 answers
89 views
On time arrow and coordinate change in General relativity
This may be a silly question but I would like to have things cleared up once and for all in my head. I will take the example of a Schwarzschild black hole as a solution to vacuum Einstein Field ...
- 3,066
0 votes
2 answers
142 views
Unidirectionality of Time in Spacetime
I have a question regarding the dimension of time. We all know that an event in spacetime is defined by a point $$ {x}^{u} = (ct, x, y, z) .$$ The only component that breaks the symmetry is $ct$, ...
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8 votes
1 answer
495 views
Does it follow from Least Action Principle that particles do not go back in time, or do we stipulate this?
Consider the action integral, $S[\gamma] := \int L(\gamma(t),\dot{\gamma}(t),t)dt$. We can always re-write it in terms of an arbitrary curve parameter $\tau$ which need not coincide with time $t$: $$S[...
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0 votes
1 answer
101 views
Energy Conservation in Pair Annihilation and Feynman-Stuckelberg Interpretation
The textbook "Modern Particle Physics" by Mark Thomson on p. (98) reads: In the left plot, an electron of energy $E$ emit a photon with energy $2E$ and, to conserve energy, produces an ...
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1 vote
1 answer
159 views
Mathematics behind the thermodynamic arrow of time
Since the thermodynamic arrow of time is related to the second law of thermodynamics, how can I (mathematically) describe the operation of the operator $\hat{T}:t \mapsto -t$ on said law ? In other ...
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0 votes
2 answers
176 views
Can one derive the second law of thermodynamics from von Neumann's equation?
My idea is that from the von Neumann equation i$\hbar\dot{\rho}(t) = [H,\rho (t)]$ one can derive that $\dot{\sigma}(t)\geq 0$, where $\sigma(t):= -$tr $ \rho(t) $ log $\rho(t)$. However, I end up at ...
