Esfeld, Michael (2005) Popper on irreversibility and the arrow of time. [Preprint]
Popper challenges the mainstream account of irreversibility, which refers to thermodynamics, by putting forward three theses: (1) There are irreversible processes of wave-production. (2) These processes are independent of the irreversible processes described by thermodynamics. (3) The irreversible processes described by thermodynamics do not have a cosmic significance. Hence, Popper traces irreversibility back to radiation instead of increase in entropy. However, I shall argue that Popper’s account runs into the same problem as the mainstream account: Both these accounts presuppose initial conditions of the universe that seem to be at least as improbable as anything that is explained by referring in the last resort to these initial conditions. Thus, neither thermodynamics nor radiation provides for an explanation of irreversibility. The appropriate place to look for such an explanation is cosmology. Popper’s main motivation in favouring radiation over entropy increase as the source of irreversibility is that he regards a statistical theory of the arrow of time as being unacceptable. By the arrow of time, he means the flow of time in the sense of a temporal view of the universe. I shall claim that irreversible processes do not provide an argument for assuming an arrow of time in this sense. A Newtonian world can include an arrow of time without having to contain irreversible processes. Special relativity suggests an atemporal view of the universe, the so-called block universe view. The block universe can include irreversible processes such as the ones of radiation and entropy increase. General relativity does not change that matter. Hence, in order to make a case for a physical basis of the arrow of time in the sense of a temporal view of the universe, other arguments would be needed than Popper’s argument building on irreversible processes.
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