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.
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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 ...
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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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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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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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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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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
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Understanding orthochronous, proper and improper Lorentz transformations
The Lorentz group has four connected components that can be characterized as follows:
$\det A = 1$
$\det A = -1$
$A^0_0 = 1$
$A^0_0 = -1$.
I think I understand the third and fourth components well, ...
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Does Einstein's Relativity contradict the Arrow of Time? [closed]
If according to Einstein spacetime is relative & not absolute, and the order of events can change depending on the observer's frame of reference, does this contradict the idea of the Arrow of Time/...
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Why did the Big Bang happen first?
As far as I know, the laws of physics are time-reversal invariant, which means there is no preferred direction of time. The arrow of time emerges with entropy which is a property of macrostates, not ...
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Why thermodynamic arrow of time will not reverse during the big crunch (considering our universe is above the critical mass)?
As the question states, Why thermodynamic arrow of time will not reverse during the big crunch (considering our universe is above the critical mass)?
The doubt arised because I thought the ...
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Causation and radiation
Electromagnetic radiation phenomena exhibit a temporal asymmetry: we observe radiation coherently diverging from a radiating source, such the light emitted by a star, but we do not observe radiation ...
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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 ...
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Making sense of particles going backwards in time [duplicate]
Physicists sometimes talk about particles going backwards in time. Help me make sense of this. I thought things don't "go" in any particular direction in time. They just "are" ...
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Why is any real process which proceeds through non-equilibrium states necessarily irreversible?
As per the title, why is any real process which proceeds through nonequilibrium states necessarily irreversible?
The question came up when reading Callen's definition of "reversible process" ...
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Why is causal order not related to directionality of time?
Hans Reichenbach argues for the causality and causal chain to define a topological coordinative definition of time order. Here is an excerpt from his textbook, The Philosophy of Space and Time, Dover(...
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