Questions tagged [time-reversal-symmetry]
The theoretical symmetry of physical laws under the transformation of time reversal, that is t ↦ −t.
491 questions
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Irreversibility of wave function collapse
The equations of classical physics are time reversible -- unchanged when t is replaced by -t. The Schrodinger equation in quantum mechanics is time reversible -- unchanged when t is replaced by -t ...
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2 votes
1 answer
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Is Big Crunch time reversed Big Bang - before it there would be formed black or white holes?
Big Crunch is often presented as time reversed Big Bang, e.g. https://www.sciencealert.com/physicists-predict-when-the-universe-will-end-in-a-reverse-big-bang I wanted to ask how true is it especially ...
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Breaking of time reversal symmetry (TRS) and emergent magnetic field
Let us start with the Heisenberg Hamiltonian with nearest neighbour interactions, $$H = \sum_{<ij>}S_i \cdot S_j$$ which perseveres time reversal symmetry. In the presence of an external ...
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1 vote
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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 ...
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Regarding time reversiblity argument in classical nucleation theory (CNT) to calculate trasient/lag time
I am reading the paper of Feder et. al (Advan. Phys.,15(1966),111) on Classical Nucleation Theory (CNT). It is a classic paper on CNT where they try to build up the Nucleation theory (NT) using Fokker–...
1 vote
1 answer
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Can time reversal symmetry be realized as a coordinate transformation $t'=-t$ in classical EM?
My hunch is that it can't. Physically, electric charge $j^0=\rho$ should be unchanged while $j^\mu$ should. But if I apply the Jacobian diag(-1,1,1,1) to transform the current 4 vector, it's the ...
0 votes
1 answer
166 views
Uncoupled representation of the time reversal operator
Simple question, but upon reading Sakurai's modern qm book, he writes $ \Theta \propto \exp(-i \pi J_y /\hbar ) K$ in chapter 4. The use of $ J_y $ is a little questionable to me as I'm guessing most ...
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1 vote
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Time evolution of time reversed wave function
If $\psi_r(t)$ be the time reversed counterpart of $\psi(t)$, and we have the evolution of $\psi(t)$ from time $0$ to $t$, what is the direction of time evolution for $\psi_r(t)$? Is it from $0$ to $-...
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2 votes
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Projective unitary representations of the full (disconnected) Poincare group
For the identity component of the Poincare group $ISO^+(1,3) \cong SO^+(1,3) \ltimes R^4$, all projective unitary representations can be lifted to unitary representations of the universal cover $ISpin^...
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2 votes
2 answers
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Action of time-reversal on Dirac bilinears
I am sorry if this may sound like a duplicate but I couldn't find any satisfying answers anywhere online or on the forum. In Peskin and Schroeder, it is said that $$T\bar\psi \gamma^\mu \psi T^{-1} = \...
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11 votes
2 answers
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Why is time reversal not a natural part of the Galilean group?
Let me begin by explaining what I mean by "natural". Consider the Poincare group in $4$ spacetime dimensions, $$\mathbb{R}^{3, 1} \rtimes O (3, 1).$$ The Lorentz group $O (3, 1)$ within it ...
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5 votes
1 answer
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Why are the Dirac points in graphene gapless?
Like the question, we all know there is $C_{2z} \mathcal{T}$ for the Dirac points (valley) in graphene. So how does this symmetry connect with the gapless property and why doesn't the particle-hole ...
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1 vote
2 answers
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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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6 votes
2 answers
291 views
The effect of time-reversal on worldlines and $n$-point functions
I am interested in the effects of the discrete symmetry operation that reverses the time-orientation of a manifold, i.e., flipping past by future. To give some context, I'm thinking about classical ...
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2 votes
1 answer
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$T$-symmetry on force
Wikipedia on $T$-symmetry states, Classical variables that do not change upon time reversal include: [...] $\vec F,$ force on the particle. Is this true, because linear momentum changes sign upon ...
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