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S. Antoci

Publications and source records attributed to S. Antoci.

24 records · Page 2Linked to original sources
arXiv1999

A four-dimensional Hooke's law can encompass linear elasticity and inertia

The question is examined, whether the formally straightforward extension of Hooke's time-honoured stress-strain relation to the four dimensions of special and of general relativity can make physical sense. The four-dimensional Hooke's law is found able to account for the inertia of matter; in the flat space, slow motion approximation the field equations for the ``displacement'' four-vector field can encompass both linear elasticity and inertia. In this limit one just recovers the equations of motion of the classical theory of elasticity.

gr-qc↗
arXiv1998

Does light exert Abraham's force in a transparent medium?

Abraham's force seems to have been observed in very low frequency experiments, but the existence of an Abraham's force exerted by light is still to be proved. Twenty years ago Brevik proposed an experiment for checking what forces light exert in the interior of a transparent medium. It is argued that his proposal is feasible today with a detection method now at hand, thanks to the great improvements achieved in manufacturing optical fibres with the required physical properties.

physics.class-ph↗
arXiv1998

Microscopic Fields and Macroscopic Averages in Einstein's Unified Field Theory

The relation between microscopic and macroscopic entities in the generally covariant theories is considered, and it is argued that a sensible definition of the macroscopic averages requires a restriction of the allowed transformations of coordinates. Spacetime averages of the geometric objects of Einstein's unified field theory are then defined, and the reconstruction of some features of macroscopic reality from hypothetic microscopic structures is attempted. It is shown how a fluctuating microscopic behaviour of the metric field can rule the constitutive relation for electromagnetism both in vacuo and in nondispersive material media. Moreover, if both the metric and the skew tensor density that represents the electric displacement and the magnetic field are assumed to possess a wavy microscopic structure, nonvanishing generalized force densities can appear in the continuum. They originate from a resonance process, in which at least three waves need to be involved. This process only occurs if the wavevectors fulfil the three-wave resonance condition, so ubiquitous in quantum physics. The wavy behaviour of the metric is essential for the occurrence of this resonance phenomenon.

gr-qc↗
arXiv1997

The third way to quantum mechanics is the forgotten first

Quantum mechanics can be formulated in three ways, as Heisenberg, Schrödinger and Feynman did respectively. For the last way, an unknown (i.e. forgotten) forerunner exists, that we have found in a paper by Gregor Wentzel, published before the famous works by Heisenberg and Schrödinger, and contemporary with the fundamental works of L. de Broglie. In that paper, one can find the basic formulae and their interpretation as they were adopted by Feynman twenty years later. We believe that Wentzel's work was forgotten for several reasons: (I) Schrödinger's equation was much simpler to deal with (Wentzel himself contributed to its development in the same way as L.Brillouin and H.Kramers did). (II) The first application was rejected by Heisenberg and Kramers. (III) The approximation used by Wentzel was too na\"ıve and failed. Nevertheless, the foundation laid by Wentzel was sound, as it has been shown by Feynman's work. Therefore, Wentzel has to be considered as one of the founders of quantum mechanics.

physics.hist-ph↗
arXiv1997

A forgotten argument by Gordon uniquely selects Abraham's tensor as the energy-momentum tensor for the electromagnetic field in homogeneous, isotropic matter

Given the present status of the problem of the electromagnetic energy tensor in matter, there is perhaps use in recalling a forgotten argument given in 1923 by W. Gordon. Let us consider a material medium which is homogeneous and isotropic when viewed in its rest frame. For such a medium, Gordon's argument allows to reduce the above mentioned problem to an analogous one, defined in a general relativistic vacuum, in presence of a suitably determined effective metric. For the latter problem the form of the Lagrangian is known already, hence the determination of the energy tensor is a straightforward matter. One just performs the Hamiltonian derivative of the Lagrangian chosen in this way with respect to the true metric. Abraham's tensor is thus selected as the electromagnetic energy tensor for a medium which is homogeneous and isotropic in its rest frame.

gr-qc↗