[He-sem] 5th Dennis Sciama Memorial Lecture

[rosanna]

The 5th Dennis Sciama Memorial Lecture will be given by Julian Barbour on
Thursday 12 November starting at 5:30pm. He will be speaking about Mach's
Principle which was the topic of Dennis's own PhD thesis and which has new
connotations now. Here are the details below - all welcome!

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                    Thursday, November 12, 2009
                     17:30, SISSA - Aula Magna

                 5th Dennis Sciama Memorial Lecture

                           Julian Barbour
                      University of Oxford, UK

                                Title

          Mach's Principle as the Universal Basis of Dynamics


Abstract: Mach's principle, the suggestion that inertial motion arises
from some physical effect of the masses of the universe, was the main
stimulus to the creation of the general theory of relativity. However,
Einstein attempted to implement Mach's proposal indirectly, not through an
explicitly relational theory of time and motion. This has led to
much confusion about the status and even definition of Mach's principle.
The key to clarification of this confusion is the realization that Newton
introduced his notions of absolute space and time in order to define
velocity as the necessary first step in the creation of dynamics. The
implementation of Mach's principle therefore requires a relational
definition of velocity, which necessarily requires consideration of all
the dynamical degrees of freedom in the universe. I shall show that there
is a uniquely appropriate manner in which this can be done. It is closely
related to gauge theory and leads to a direct relational derivation of
general relativity, the universal light cone, and gauge theory. Mach's
principle therefore provides the basis of all known fundamental dynamical
theories. This insight has considerable historical and philosophical
interest in connection with the debate about the absolute or relative
status of motion. It is also likely to have significance for the creation
of quantum gravity, the putative quantum theory of the universe.

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