Philosophy Lexicon of Arguments

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Time reversal, reversal invariance: invariance with respect to the time direction (T-symmetry) is a property of physical laws. It states that a natural law is valid even if the algebraic sign for the time component is changed. See also symmetries, laws, laws of nature, systems, invariance.

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Annotation: The above characterizations of concepts are neither definitions nor exhausting presentations of problems related to them. Instead, they are intended to give a short introduction to the contributions below. – Lexicon of Arguments.

 
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II 254
Time reversal symmetric/Genz: For example, "angle of incidence" = "angle of reflection" is time reversal symmetric, i. e. it would not be possible to determine whether a film with billiard balls runs backwards.
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II 255
Reflection/time reversal/Genz: the same applies to all reflection processes, forward as well as backward deterministic n.
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II 256
If there was a law: "angle of reflection = half angle of incidence", we would have no time reversal symmetry and we could see a film running backwards.
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II 256
Time inversion invariant/Genz: e. g. Newton's laws of planetary motion: the directions in which the planets move could be reversed. Therefore, a film running backwards would not be recognizable.
Quantum mechanics/not time inversion invariant/Genz: the laws for elementary particles are excellent in one direction.
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II 259
In the last 200 years, the Earth was 4 hours slow, if one wanted to calculate a solar eclipse. Eventually the moon will stand still for the earth in the sky.
N.B.: in a backward running film, the tides would have the opposite effect that the earth rotates faster instead of slower! Thus the time directions have become distinguishable. By comparing the two processes.
N.B.: but we cannot tell from them which one is the real one and which one is the manipulated one.
Tides: their laws cannot be fundamental like those of the K mesons. They do not include the origin of deformations. They are not time-reversal symmetric.
Time-reversal symmetric: are fundamental laws about the collisions of molecules.
Time reversal symmetry/problem: how can symmetric laws of nature lead to processes that are not symmetric themselves?
Asymmetry/Genz: it is not the laws that are responsible for them, but the initial conditions or circumstances.
Order/Law/Genz: the superordinate law in such cases is that order cannot increase.
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II 258
Asymmetry/time reversal/Genz: is much more pronounced in macroscopic (tides) than in microscopic (K mesons).
Tides: the law that the rotation of the earth slows down is forward deterministic, but not backward! For example, because it is not possible to tell from a standstill how long ago the rotation came to rest. There are many ways in which it has come to a standstill, but only one more to rest. The direction of time cannot be inferred from the observation of the standstill.
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II 260
This does not mean absolute rotation, which is marked by centrifugal forces, but relative to the moon.
Friction/Genz: leads to time reversal asymmetry. (If you brake until standstill). Then we see in the reverse film a course of events prohibited by the laws of nature.
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II 261
Statistical fluctuation/Genz: does not indicate a time direction.


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Explanation of symbols: Roman numerals indicate the source, arabic numerals indicate the page number. The corresponding books are indicated on the right hand side. ((s)…): Comment by the sender of the contribution.

Gz I
H. Genz
Gedankenexperimente Weinheim 1999

Gz II
Henning Genz
Wie die Naturgesetze Wirklichkeit schaffen. Über Physik und Realität München 2002


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Ed. Martin Schulz, access date 2018-05-22