Poincare' invariance for continuous-time histories

We show that the relativistic analogue of the two types of time translation in a non-relativistic history theory is the existence of two distinct Poincar\'{e} groups. The `internal' Poincar\'{e} group is analogous to the one that arises in the standard canonical quantisation scheme; the `external' Poincar\'{e} group is similar to the group that arises in a Lagrangian description of the standard theory. In particular, it performs explicit changes of the spacetime foliation that is implicitly assumed in standard canonical field theory.Comment: 32 pages, Latex. In a non-relativistic history theory there exist two distinct Poincare' groups. The `internal' Poincare' group is analogous to the one that arises in standard canonical quantisation scheme; the `external' Poincare' group performs explicit changes of the spacetime foliation that is implicitly assumed in standard canonical field theor

General relativity histories theory II: Invariance groups

We show in detail how the histories description of general relativity carries representations of both the spacetime diffeomorphisms group and the Dirac algebra of constraints. We show that the introduction of metric-dependent equivariant foliations leads to the crucial result that the canonical constraints are invariant under the action of spacetime diffeomorphisms. Furthermore, there exists a representation of the group of generalised spacetime mappings that are functionals of the four-metric: this is a spacetime analogue of the group originally defined by Bergmann and Komar in the context of the canonical formulation of general relativity. Finally, we discuss the possible directions for the quantization of gravity in histories theory.Comment: 24 pages, submitted to Class. Quant. Gra

The Relationship Between Skilled Labor and Technical Change

This study investigates whether capital-skill complementarity is the explanation for skill-biased technical change. For this to be the case, capital-skill complementarity must exist in the first place and, secondly, all technical change must be embodied in nature, i.e. embedded in new capital equipment. To test if these conditions are satisfied, a capital-age adjusted translog production function incorporating both embodied and disembodied technical change is implemented on a 14-industry panel for Swedish manufacturing 1985-95. The findings cast doubt on the claim that capital-skill complementarity can explain skill-biased technical change. In several industries, the capital-skill complementarity hypothesis is not supported. Moreover, it is found that the demand for skilled labor is affected by both disembodied and embodied technical change. An additional important result is that there is a negative skill-bias associated with embodied technical change.Capital-skill complementarity; skill-biased technical change