Synopsis
All kind ofinformationfrom distant celestialbodies comestous intheform of radiation. Inmost the of electromagnetic cases thisradiation propagation be can as a reasonable in described, terms of This is approximation, rays. truenot inthe but also inthe radio only ofthe electro opticalrange range Forthis the of reason laws areoffundamental magneticspectrum. optics ray for importance and astronomy, astrophysics, cosmology. to According arethe of general relativity, light light likegeodesics a rays Lorentzianmetric whichthe is described. how by spacetimegeometry This, is true as as the under the ever, only long light are rays freelypropagating influence ofthe fieldwhich is coded in the only gravitational spacetime ge If a is in an medium ometry. light ray influenced, addition, by optical (e. g., then it will not follow ofthe by a a plasma), light like geodesic spacetime metric. It is true that for radiation the electromagnetic traveling through universe the influence ofamedium on the ofthe and usually path on ray the is small. there are several cases inwhich this influ frequency However, ence is well in inthe radio For measurable, particular very range. example, the deflection ofradio inthe field oftheSun is consider gravitational rays influenced the Solarcorona. currentand ably by Moreover, planned Doppler with microwaves in the Solar reach in the an experiments system accuracy 5 of 10 15 whichmakes it totakethe influence frequency Awlw necessary ofthe medium into account.
From the Back Cover
This book is about the mathematical theory of light propagation in media on general-relativistic spacetimes. The first part discusses the transition from Maxwell's equations to ray optics. The second part establishes a general mathematical framework for treating ray optics as a theory in its own right, making extensive use of the Hamiltonian formalism. This part also includes a detailed discussion of variational principles (i.e., various versions of Fermat's principle) for light rays in general-relativistic media. Some applications, e.g. to gravitational lensing, are worked out. The reader is assumed to have some basic knowledge of general relativity and some familiarity with differential geometry. Some of the results are published here for the first time, e.g. a general-relativistic version of Fermat's principle for light rays in a medium that has to satisfy some regularity condition only.
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