All Questions
Tagged with reversibility time-reversal-symmetry
21 questions
5
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354
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Are Hamilton's equations reversible?
Say I define a time dependent vector field $\Psi(t):\mathbb{R}^d\to \mathbb{R}^d$ as reversible (also here) if, for $f(x,y)=(x,-y)$, we have:
$$ f\circ \Psi \circ f =\Psi(-t)=\Psi^{-1}(t).$$
Just to ...
- 51
5
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1
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Proving that the diffusion equation is not time-reversible
The diffusion equation (in appropriate units) is
$$
\frac{\partial\rho}{\partial t}(\mathbf r,t)=\nabla^2\rho(\mathbf r,t).
$$
By time-reversibility, I mean that there exists a function (bijection?) $...
- 1,999
5
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0
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257
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What does the time reversibility of the laws of physics mean for causality?
Does the fact that the fundamental laws are symmetric with respect to direction of time show that causation does not exist? Since causality always requires the cause to precede the effect, but laws of ...
4
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1
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1k
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Reversibility of Hamiltonian dynamics
I'm trying to understand a very basic property of Hamiltonian dynamics. I don't have a physics background but I do know some mathematics. I want to understand why negating the momentum is equivalent ...
- 153
4
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3
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426
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In a "universe" where time runs backwards, is cause/effect preserved?
Caveat: I'm a layman not a physicist, and this may be more semantics than physics.
In a universe where time runs backwards (think of a movie run backwards, where a vase that is shattered on the floor ...
- 161
3
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1
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447
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Unitary Time Evolution and Reversibility
I have a system as follows:
$$\frac{d\mathbf{x}}{dt} = -iA \mathbf{x},$$
which describes the time evolution of variables $\mathbf{x}$ according to the matrix $A$. Now, $A$ is not Hermitian, but has ...
- 51
2
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2
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451
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Are the thermoelectric effects reversible?
On the one hand, it is commonly said that thermoelectric effects are reversible. For Wikipedia they are thermodynamically reversible because as the factor of merit ZT approaches infinity, the ...
2
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1
answer
48
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Equivalence of various definitions of reversibility in classical mechanics
I was reading Classical Mechanics: The Theoretical Minimum by Leonard Susskind, and the definition of reversibility in that was:
Given a state of a system, then we know exactly what state it came ...
- 430
2
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1
answer
86
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How do we physically reverse a classical wavepacket?
Imagine a classical dispersive Gaussian wavepacket (GW). In a wonderful answer by @Qmechanic, to this question (who seems to do much tagging these days, with an occasional well-aimed-and-hit answer), ...
2
votes
1
answer
185
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Does time symmetry still holds when a particle drops into a black hole?
When a particle drops into Earth, it hits the ground and rebounds, if time reverse, it is equivalent to another particle moves with same speed but opposite direction.
But at the case that a particle ...
- 917
1
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1
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77
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Reversed time in Norton's dome
"Norton's Dome is a thought experiment that exhibits a non-deterministic system within the bounds of Newtonian mechanics. "
A ball rolled to the top can reach it in finite time with zero ...
- 3,001
1
vote
1
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65
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Could our physical universe be time-irreversible?
Suppose that in our universe, there were two initial states which lead to the same outcome state after one time step. How could we possibly remember which of the two steps we came from if the ...
0
votes
1
answer
105
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Is determinism broken in special relativity?
Under classical mechanics, in an isolated system everything is deterministic given some initial conditions. Otherwise, we would have to consider some probabilities of interactions with the outside on ...
- 91
0
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2
answers
50
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When considering the air friction, does the missile trajectory reversable?
When seeing a video of a missile hitting a target, someone would argue that it is fake, since the video is played backwards. I know that Newtonian mechanics is time reversal if we do not considering ...
- 6,187
0
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30
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Asymmetry when $t\rightarrow -t$ [duplicate]
If we consider the equation of critical damping $$x=(a+bt)e^{-ct}$$
then the graph is
However, it is asymmetric for positive and negative time values. I have an intuition that this should be the case ...
0
votes
2
answers
122
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Entropy of a deterministic reversible system
Suppose a deterministic reversible system evolving from state A of gas located in a small bottle in an otherwise empty room, to state B where the gas is dispersed throughout the room.
Why is the ...
- 696
0
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0
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40
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If I add one particle to the system at a time, When does the time reversal symmetry breakdown?
Suppose I have a system in my mind which consists of two elementary particles interacting with each other via fundamental interactions. We know that fundamental interactions have $T$-symmetry and ...
- 12.1k
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1
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123
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Reversibility of Physical Process : QM vs CM
It is often stated that the processes in quantum mechanics are reversible as they follow the Schrodinger's Equation : $$ - \frac{\hbar^2}{2m} \nabla^2 \Psi(x,t) + V(x,t)\ \Psi(x,t) = i \hbar\ \frac{\...
- 698
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42
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Reversibility of equation $F=mv$ [duplicate]
Please read the following text.
This text is part of Leonardo Sauskind's book.
It says that the relation F = m v is reversible. Why?
- 1
0
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0
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27
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Do irreversible processes indicate that time reversible symmetry is a limited phenomenon instead of a universal law? [duplicate]
Physics and chemistry indicate various irreversible processes, while physics also proposes the theory of time reversible symmetry (T-symmetry). I suppose that evidence of irreversible processes ...
- 541
-2
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1
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Is interpreting information conservation as time reversibility non-mainstream physics?
I understand the following as standard results in modern physics.
Black holes evaporate over time via Hawking radiation.
Small black holes evaporate over very short times.
There is an "...
- 931