Michele's research

The philosophical foundations of spacetime theories


Special-relativistic theories speak the language of uniformly moving (inertial) observers: the Lorentz coordinates have a direct metrical interpretation as the distances and times measured by inertial observers; and the physical quantities of the theories, when expressed as tensors, refer directly to the measurements of the inertial observers.

Nevertheless, there is a special interest in the consideration of accelerated observers, even in a special-relativistic context. First, accelerated frames are historically the germ from which general relativity was born: Einstein came to the principle of equivalence through the investigation of uniformly accelerated frames, and his primary pretense for the general theory was to extend the relativity of physical laws from inertial to generic observers.

Second, there are special topics in relativistic theories (such as the now-famous Unruh effect, or the problem of radiation reaction) where a subjective description (made from the point of view of accelerated observers) is desirable. In collaboration with Prof. Massimo Pauri, I have studied the physics of accelerated observers from several points of view.

Our results

We have identified the origin of the Unruh effect (and of its analog in black-hole spacetimes, the Hawking effect) in the classical principle of perspectival semantics, according to which some familiar notions defined in special-relativistic theories (such as particle and radiation) inevitably lose their coherence when they are transported to accelerated frames or to curved spacetimes.

We have proposed a general scheme to build an accelerated system of coordinates (Maerzke-Wheeler coordinates) adapted to the motion of a generic accelerated observer, and we have suggested two applications for this new system (the first application is related to the special-relativistic paradox of the twins; the second to the generalized Unruh effect).

The definition of coordinate systems (both inertial and accelerated) is intimately tied to the choice of a relation of distant simultaneity between events: we have reviewed the perennial debate (among relativists and philosophers of physics) on the conventionality of simultaneity in special relativity, and we have examined the conventionality of Maerzke-Wheeler simultaneity.

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© M. Vallisneri 2014 — last modified on 2012/10/19