MOTION MOUNTAIN

210 5 electromagnetic effects
Ref. 168
Ref. 33
ocean
crust
mantle
liquid core
solid core
F I G U R E 156 The structure of our planet (© MPI-Chemie, Mainz/GEO).
not necessarily do so as well. The exact way a radiation field changes from one observer
to the other depends on the type of relative motion and on the field itself.
A detailed exploration of the problem shows that for a uniformly accelerated charge,
an observer undergoing the same acceleration only detects an electrostatic field. In contrast,
an inertial observer detects a radiation field. Since gravity is (to a high precision)
equivalent to uniform acceleration, we get a simple result: gravity does not make electrical
charges radiate for an observer at rest with respect to the charge – as is indeed
observed.The results holds true also in the quantum theoretical description.
Planetary magnetic fields
The classical description of electrodynamics is consistent and complete; nevertheless
there are still many subjects of research. We explore a few of them.
The origin of the magnetic field of the Earth, the other planets, the Sun and even of
the galaxy is a fascinating topic.The way that the convection of fluids inside the planets
generates magnetic fields, an intrinsically three-dimensional problem, the influence of
turbulence,ofnon-linearitiesandofchaosmakesitasurprisinglycomplexquestion.
The details of the generation of the magnetic field of the Earth, usually called the
geodynamo, began to appear only in the secondhalf of thetwentieth century, whenthe
knowledge of the Earth’s interior reached a sufficient level. The Earth’s interior starts
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net