# Philosophy Dictionary 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.

Author Item Summary Meta data
I 657
Time Reversal/Movement Reversal/Reversibility/Feynman: E.g. A movie played backwards: here entropy is not as high as you might think, since all elements have exactly the right speed to return to their starting point.

Reversibility/Irreversibility/Physics/Time Inversion/Feynman: E.g. retarded electric field:
t: time, r: distance from the charge: field corresponding to the acceleration at the time t r/c and not t + r/c.
Consequently, it appears that the law of electricity is not reversible.
Vs: but in fact Maxwell's equations are reversible! In addition, we could take the advanced field instead of the retarded field and everything goes the same way. This also means that an oscillating charge in a closed container (black body) will lead to an equilibrium.
I 729
Time Reversal/Time/Backward Movement/Film/Reversibility/Feynman: e.g. movie playing backwards: if we were able to see the individual molecules, we could not see if the machine was moving forward or backward. Nothing contradicts the physical laws.
On the other hand, if we do not see all the details, it will be clearly detectable, e.g. as a forward movement.
For example, if we looked at the individual atoms of an egg, we could not determine whether the egg was bursting or assembling.
At the level of the individual atoms the laws look completely reversible.

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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.
The note [Author1]Vs[Author2] or [Author]Vs[term] is an addition from the Dictionary of Arguments. If a German edition is specified, the page numbers refer to this edition.

Feynman I
Richard Feynman
The Feynman Lectures on Physics. Vol. I, Mainly Mechanics, Radiation, and Heat, California Institute of Technology 1963
German Edition:
Vorlesungen über Physik I München 2001

Feynman II
R. Feynman
The Character of Physical Law, Cambridge, MA/London 1967
German Edition:
Vom Wesen physikalischer Gesetze München 1993

> Counter arguments against Feynman

Ed. Martin Schulz, access date 2020-06-06