Roger Penrose's Arrows Of Time (1)1. Subjective - We can't remember the future2. Radiation - Non converging electromagnetic waves 3. Quantum - Heads and tails don't merge4. Neutral Kaon - Disintegration rate rules out reversed time5. Black Hole - No white holes6. Universe - Collapsing universe would not reverse time7. Entropy - Total entropy does not decrease Other arrows of time1. Biological aging - Stephen J. Gould2. Cause precedes effect (finite transmission time)

Ludwig Boltzmann (1844-1906)But the problem did not become acute until the statistical approach to the thermodynamic laws was begun by Boltzmann, because previously no one was faced with the comparison between the reversible character of the elementary law and the irreversibility which had to be explained on its basis. Boltzmann, of course, actually introduced a new law in order to produce the irreversibility, namely a statistical element governed by a parabolic equation. It is only when the statistical element is combined with the mechanical laws that we get the irreversibilty of the second law. (L. Rosenfeld) (3:189)

Boltzmann believed that the two directions of time are indistinguishable. (2:6) It is quite obvious that the Boltzmann equation, far from being a consequence of the laws of classical mechanics, is inconsistent with them. (Bergmann) (3:191) Albert Einstein (1879-1955)What is new in Einstein's relativity is the complete separation between past and future. ... Einstein assumed time-symmetry in his theories, but this assumption was superimposed and not needed. It simply does not play any role, because of the complete distinction between past and future. (L. Brillouin) (4:108) The Ritz and Einstein Agreement to Disagree (1909)The electromagnetic arrow was the subject of a lively discussion by Einstein and Ritz in 1909. Einstein (1909) argued that the retarded and advanced descriptions of radiation processes occurring in any finite region are equivalent, since the equations of wave propagation are symmetric with regard to time, but that the auxiliary conditions giving the precise circumstances of emission and absorption are very different. In the retarded description it is sufficient if all the macroscopic sources are known whereas in the advanced description all the absorption processes must be known, but unlike the former they must be fully specified in microscopic detail. In practice, we do not have this information concerning the absorption processes and so we are obliged to use the retarded description. On the other hand, Ritz (1909) asserted that only the retarded waves have any physical significance, since advanced waves are not experimentally observed. The initial conditions characterizing the source (or sources) of the radiation are the causes of its transmission and consequently are responsible for the special role played by retarded waves. [According to Brillouin (1964), Ritz was the first to make this point.] (L. Brillouin) (2:339-340)

Lewis (1930) [Winford Lewis (1878-1943)?]Claimed that nearly everywhere in physics and chemistry the ideas of unidirectional time and unidirectional causality have been purged. These ideas have been used to support some false doctrine, for example, that the universe is actually running down. Predecessor of absorber theory.(2:7-8) No satisfactory quantum electrodynamics could be developed until the retarded and advanced potentials were used simultaneously and symmetrically. (2:8-9)

Wheeler & FeynmanJ. A. Wheeler and R.P. Feynman attempted to derive the ordinary irreversibility of radiation from the time-reversibility of Maxwell's equations. They argued that the observed properties of an electric charge, that it radiates energy and suffers damping of its motion can be explained in terms of an "absorber theory of radiation". They used the Schwarzschild- Tetrode-Fokker equation for a flat space and found that they had to postulate both "advanced" (future) and "retarded" (past) fields; the divisions of time seemed to be "inextricably mixed". ...Wheeler and Feynman assumed that (a) time-asymmetry is initially present; and (b) persists on a purely statistical basis. J.E. Hogarth(5) showed that assumption (b) is inconsistent with any realistic absorber theory of radiation.

He and D.W. Sciama argued that the Wheeler-Feynman theory of radiation holds in the Steady-State cosmologies of Hoyle and Narlikar, but not in general, in the Einstein-de Sitter models. (C.T.K. Chari) (4:216)

The depend of the electromagnetic arrow of time on the thermodynamic arrow was a feature of the absorber theory formulated by Wheeler and Feynman (1945).

If the radiation is confined to an opaque enclosure, so that all of it is absorbed, the waves striking the walls will cause the charged particles therein to radiate likewise into both the past and the future. Wheeler and Feynman showed that if the enclosure is fully opaque, the advanced waves emitted by the walls will just cancel those from the source particle and only the retarded waves will be left. ... Moreover, since all attempts to produce a quantum-mechanical version of the absorber theory lead to the same difficulties as previous theories of the interactions of charged particles with the electromagnetic field, there is no strong argument in its favour and in fact its original proponents have abandoned it. (2:341-342)