Time Reversal Breaking in Classical Systems

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Discussion Overview

The discussion centers on identifying classical systems that lack time reversal symmetry. Participants explore various examples and concepts related to this topic, including chaotic systems, frictional forces, and external influences like magnetic fields.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks examples of classical systems without time reversal symmetry.
  • Another participant asserts that classical physics is generally symmetric under time reversal, noting entropy as a classical arrow of time.
  • A participant suggests chaotic systems as examples of classical behavior that may not be symmetric regarding time reversal.
  • Another example provided is a pendulum with friction, which is described by the equation $$\ddot x+x=-\dot x$$ and is not invariant under time reversal.
  • Non-reciprocal optics and electromagnetic nonreciprocity are mentioned as systems that exhibit time-reversal asymmetry.
  • A participant notes that any system with loss is also time-reversal asymmetric.
  • A later reply questions whether time reversal affects an external magnetic field in a closed system.

Areas of Agreement / Disagreement

Participants express differing views on the existence and nature of classical systems without time reversal symmetry, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Some claims depend on specific definitions of time reversal symmetry and may involve assumptions about system conditions, such as the presence of external fields or losses.

hokhani
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TL;DR
Classical systems without time reversal
I am looking for an example of a classical system without time reversal symmetry. I would appreciate any help.
 
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hokhani said:
Summary:: Classical systems without time reversal

I am looking for an example of a classical system without time reversal symmetry. I would appreciate any help.
Classical physics is symmetric under time reversal. Entropy is the only arrow that I know of classically.
 
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As example of classical systems that exhibit behavior that (in some practical sense at least) is not quite symmetric regarding time reversal I guess you could look at chaotic systems.
 
the banal pendulum with friction
$$\ddot x+x=-\dot x$$
is not invariant under the change ##t\mapsto -t##
 
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hokhani said:
Summary:: Classical systems without time reversal

I am looking for an example of a classical system without time reversal symmetry. I would appreciate any help.
Check out "non-reciprocal optics" or " electromagnetic nonreciprocity".

Any system with loss is also time-reversal asymmetric.
 
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Thank you all for the responses. How about a closed system which is under an external magnetic field? Does time reversal change also the external magnetic field or it only reverses the time in the closed system?
 

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