Chapter 2
The Ether and the Wave Equation
For the Greeks ether is ‘fine air’. Chemically, ether is a group of especially volatile
substances. Ether as gas has a characteristic smell. In the field of physics, ether has
for a long time produced an anaesthetic effect—similar to the anaesthetic effect of
ether during a medical operation.
Ether concerns itself physically with wave propagation. The first thing we associate with the word wave is probably a wave in water. Mathematically, however,
these waves are not so elementary as it seems, since these waves are related to the
surface of the water. We are, however, interested in the waves that completely exist
inside of a medium (inside of the ‘space for the waves’). Examples of these types of
waves can be found in acoustics in the form of sound waves and in electrodynamics
in the form of radio waves, light waves and X-rays. Even though these waves possess extremely different physical properties, they can be described mathematically
in the same way. Wave propagation in either a medium or in space, the transmission
of waves, their deflection around obstacles and the transmission of signals through
space with the help of waves—the fundamental base for all these phenomena are one
single equation, J. Le R. d’Alembert’s wave equation.
The wave equation is without doubt the common denominator that connects all
wave phenomena, regardless of their acoustic or electromagnetic nature. We get a
completely different picture with regard to its meaning for our physical comprehension of nature, for a modern foundation of electromagnetic theory s. Hehl, F. W. and
Obukhov, Y. N. [41].
Up to the turn of the century, to be more precise until AD 1905, mechanics was
the fundamental base used for the theoretical description of all physical processes.
Mechanical wave phenomena were accepted as fundamental facts. Propagation of
sound through air or any other gas, fluid or solid medium was widely researched
and understood. One was also convinced that electromagnetic processes functioned
in exactly the same way. One was convinced that light waves moved the same way
© The Editor(s) (if applicable) and The Author(s), under exclusive
license to Springer Nature Singapore Pte Ltd. 2020
H. Günther, Elementary Approach to Special Relativity,
https://doi.org/10.1007/978-981-15-3168-2_2
5
The Ether and the Wave Equation
For the Greeks ether is ‘fine air’. Chemically, ether is a group of especially volatile
substances. Ether as gas has a characteristic smell. In the field of physics, ether has
for a long time produced an anaesthetic effect—similar to the anaesthetic effect of
ether during a medical operation.
Ether concerns itself physically with wave propagation. The first thing we associate with the word wave is probably a wave in water. Mathematically, however,
these waves are not so elementary as it seems, since these waves are related to the
surface of the water. We are, however, interested in the waves that completely exist
inside of a medium (inside of the ‘space for the waves’). Examples of these types of
waves can be found in acoustics in the form of sound waves and in electrodynamics
in the form of radio waves, light waves and X-rays. Even though these waves possess extremely different physical properties, they can be described mathematically
in the same way. Wave propagation in either a medium or in space, the transmission
of waves, their deflection around obstacles and the transmission of signals through
space with the help of waves—the fundamental base for all these phenomena are one
single equation, J. Le R. d’Alembert’s wave equation.
The wave equation is without doubt the common denominator that connects all
wave phenomena, regardless of their acoustic or electromagnetic nature. We get a
completely different picture with regard to its meaning for our physical comprehension of nature, for a modern foundation of electromagnetic theory s. Hehl, F. W. and
Obukhov, Y. N. [41].
Up to the turn of the century, to be more precise until AD 1905, mechanics was
the fundamental base used for the theoretical description of all physical processes.
Mechanical wave phenomena were accepted as fundamental facts. Propagation of
sound through air or any other gas, fluid or solid medium was widely researched
and understood. One was also convinced that electromagnetic processes functioned
in exactly the same way. One was convinced that light waves moved the same way
© The Editor(s) (if applicable) and The Author(s), under exclusive
license to Springer Nature Singapore Pte Ltd. 2020
H. Günther, Elementary Approach to Special Relativity,
https://doi.org/10.1007/978-981-15-3168-2_2
5