Is the symmetry-to-reality inference justified? Time-symmetry as a study case

CRISTIAN LÓPEZ

Buenos Aires

Workshop; International Workshop on Foundations of Science; 2018

Sociedad de Análisis Filosófico (SADAF)

It is a widely-held view that the problem of the arrow of time in physics necessarily depends on the notion of time-reversal invariance: if fundamental physical laws fail to be time-reversal invariant, then there are grounds for a fundamental, objective physical arrow of time. Furthermore, there is also a common idea that the overwhelmingly majority of fundamental physical laws are in fact time-reversal invariant, being so blind to any privileged direction of time. These two closely-related claims heavily relies on three assumptions: (a) that the property of being time-reversal invariant is quite relevant to the problem of the arrow of time in physics (being a sufficient and necessary condition for argument against or for an arrow of time); (b) that only fundamental physical laws are relevant for the discussion; (c) and that the very notion of time reversal is an univocal and fully-shared one. In this presentation, I shall argue that these assumptions conflict each other: firstly, though frequently unnoticed, philosophers and physicists disagree upon how time reversal should be formally characterized, leading to quite different conclusions on the direction of time discussion. Secondly, physicists typically take symmetries as principles guiding theory construction, demanding that physical theories must a priori satisfy time-reversal invariance, which would be equivalent to discard any arrow of time from the very outset if (b) is assumed. Finally, such three assumptions might run the risk of circularity and triviality when the problem of the arrow of time is at stake.