
The Logical Origin of Relativity The theory of relativity is generally taken to be complicated and difficult to comprehend. But this view is based on a misunderstanding of the underlying physics.
In fact, relativity is not complicated. It is only that Einstein managed
to make it complicated. How come? Einstein started his work with a basic misunderstanding in view of the speed of light.
The situation has a certain analogy to the history of astronomy.
Ptolemais followed the apparent view that the earth was the centre of the universe
and the sun and the planets were orbiting the earth. This view caused the necessity
of the complicated epicycle theory to determine the motion of the planets relative
to the earth. When Copernicus corrected this view by putting the sun into
the centre of the planetary system, this caused a dramatic simplification
of the mathematical formalism.
In analogy Einstein followed the apparent result of the Michelson Morley
experiment that the speed of light c is constant relative to any frame.
This assumption caused the necessity of the known fourdimensional spacetime
based on Minkowski metrics and Riemannian geometry. In contrast Lorentz explained
the Michelson Morley result as a measuring phenomenon caused by the relativistic behaviour
of clocks and rulers. The application of this approach facilitates the
mathematical formalism by returning to the traditional application of Euclidean geometry.
"The speed of light is constant with respect to every inertial system." Einstein's position is affected by the following measurement aspects about the speed of light:
When the MichelsonMorley experiment yielded the unexpected null result in the 1880s, several physicists looked for an explanation of it. Some of them (Heaviside, Fitzgerald,Lorentz) explained the null result of the MichelsonMorley experiment in Terms of the contraction of matter in motion. This was  in contrast to Einstein's impression at that time  not an adhoc assumption, but followed from the contraction of field in motion. Einstein on the other hand explained the null result of the experiment by assuming that the speed of light has ontologically the same constant value in any inertial system. This approach by Einstein had considerable consequences. Einstein had to solve the problem of the summation of velocities. In the Galilean transformation, which is based on Euclidean geometry, velocities are transformed by the linear addition of the components. This is, however, incompatible with the assumption that the speed of light is retained in any transformation. Einstein solved this problem in a formal way. He came up with a geometry in which he combined space and time to produce a fourdimensional coordinate system which changes its shape during a transformation. This means that its coordinates vary in size depending on the velocity. Minkowski formalized Einstein's approach as a complex formal 4dimensional spacetime system. The combination of Einstein's idea and the geometry of Minkowski is today known as the "Einsteinian interpretation of relativity". From the present point of view, Minkowski's formalism is on the one hand elegant, but on the other hand it is physically unnecessarily complicated and leads to logical conflicts. And it contradicts the physical imagination. In Lorentz's approach, the relativistic behavior of matter and objects follows from the behavior of fields, in his days electrical fields as described by Maxwell's equations. The temporal behavior follows from a particle model corresponding to the particle approach later presented by Louis de Broglie. About the easiness of relativity: The according particle model is presented here. It is compatible with the actual experimental state of particle physics. (Note: This site is also available as a pdf file.)
The concept is:
If all matter is assumed to be made up of such particles, the wellknown relativistic effects are a necessary consequence; as are a number of observations which are otherwise explained with the help of quantum mechanics. This model explains relativistic dilation and contraction and it explains the inertial mass of elementary particles, as well as the relativistic increase of mass in motion. For details we refer to the following sites: 

4. Bibliographical References [1] Prokhovnik, S. I., The Physical Interpretation of Special Relativity  a Vindication of Hendrik Lorentz. Z. Naturforschung 48a, 925 (1993). [2] F. Selleri et al., Die Einsteinsche und lorentzianische Interpretation der speziellen und allgemeinen Relativitätstheorie. Karlsbad:VRI 1998. [3] Louis de Broglie, RADIATIONS  Ondes et Quanta, Comptes rendus, Vol. 177, 1923, pp. 507510. 

NOTE: This concept of the "basic model" of matter was presented initially at the Spring Conference of the German Physical Society (Deutsche Physikalische Gesellschaft) on 24 March 2000 in Dresden by Albrecht Giese. Comments are welcome. 20210527 