Spatial Directions, Anisotropy and Special Relativity

The concept of an objective spatial direction in special relativity is investigated and theories assuming light-speed isotropy while accepting the existence of a privileged spatial direction are classified. A natural generalization of the proper time principle is introduced which makes it possible to devise experimental tests of spatial isotropy. Several common misunderstandings in the relativistic literature concerning the role of spatial isotropy are clarified.Comment: 24 pages, 2 figures. Final enlarged and slightly corrected version. Keywords: relativity, very special relativity, spatial isotropy, reciprocity, differential aging; Foundations of Physics, 201

Simultaneity as an Invariant Equivalence Relation

This paper deals with the concept of simultaneity in classical and relativistic physics as construed in terms of group-invariant equivalence relations. A full examination of Newton, Galilei and Poincar\'e invariant equivalence relations in $\R^4$ is presented, which provides alternative proofs, additions and occasionally corrections of results in the literature, including Malament's theorem and some of its variants. It is argued that the interpretation of simultaneity as an invariant equivalence relation, although interesting for its own sake, does not cut in the debate concerning the conventionality of simultaneity in special relativity.Comment: Some corrections, mostly of misprints. Keywords: special relativity, simultaneity, invariant equivalence relations, Malament's theore

On Selleri's "Weak Relativity''

F. Selleri's main arguments for the restoration of absolute simultaneity in physics are analysed and shown to be faulty. In particular both the classical Sagnac effect and the recent so-called linear Sagnac effect can be dealt with within special relativity in a natural way. The appeal to the conventionality of simultaneity thesis is also shown to be ineffectual. Other arguments, such as the two spaceships' argument and the block universe argument are briefly examined. Notwithstanding a negative overall assessment, the importance of keeping alive the research on the foundations of relativity is emphasized and Selleri's role in this undertaking appreciated.Comment: 27 pages, 8 figure

On the Incompatibility of Special Relativity and Quantum Mechanics

Some of the strategies which have been put forward in order to deal with the inconsistency between quantum mechanics and special relativity are examined. The EPR correlations are discussed as a simple example of quantum mechanical macroscopic effects with spacelike separation from their causes. It is shown that they can be used to convey information, whose reliability can be estimated by means of Bayes\u27 theorem. Some of the current reasons advanced to deny that quantum mechanics contradicts special relativity are refuted, and an historical perspective is provided on the issue

O senso comum, a história e a Teoria da Relatividade

É discutida a relação entre a física moderna e o senso comum investigando se há qualquer papel significativo deixado posteriormente na atividade científica. É mostrada que a opinião comum é necessária em algumas das decisões mais cruciais que um investigador tem que fazer em seu trabalho. A história de uma teoria física notoriamente contra-intuitiva (i. e. relatividade) é citada para fornecer exemplos em defesa desta reivindicação, e são discutidos alguns aspectos pouco conhecidos da recepção desta teoria pela comunidade científica. É descrito brevemente um modelo simples de comportamento coletivo que conduz a formação de um consenso, como exemplo de um argumento não técnico que é, no entanto, útil, dando sentido à atividade científica. São esboçadas, na seção final, algumas indicações para o ensino de ciência que surge desta investigação