Mario Bacelar Valente

According to Dennis Dieks, in the theory of relativity, the «flow of time» results from the succession of events along time-like worldlines. We have a flow of time per worldline. This leads to a view of now as local to each worldline. In this approach there is no global temporal order of the now-points of different worldlines. For a consistency reason it is imposed a limitation on the assignment of different now-points. Here it is made the claim that this consistency requirement is inbuilt in the theory, and it is presented a detailed analysis of this approach.

A re-evaluation of the notion of vacuum in quantum electrodynamics is presented, focusing on the vacuum of the quantized electromagnetic field. In contrast to the ‘nothingness’ associated to the idea of classical vacuum, subtle aspects are found in relation to the vacuum of the quantized electromagnetic field both at theoretical and experimental levels. These are not the usually called vacuum effects. The view defended here is that the so-called vacuum effects are not due to the ground state of the quantized electromagnetic field. Nevertheless it is possible to maintain an empirically demonstrable notion of vacuum state that is consistent with the interpretation of the formalism of the theory.