Lorentz called the combination _t′_ of (_t_ and _x_) as the _local time_
(_Ortszeit_) of the uniformly moving electron, and used a physical
construction of this idea for a better comprehension of the
contraction-hypothesis. But to perceive clearly that the time of an
electron is as good as the time of any other electron, _i.e._ _t_, _t′_
are to be regarded as equivalent, has been the service of A. Einstein
[Ann. d. Phys. 891, p. 1905, Jahrb. d. Radis. ... 4-4-11-1907.] There
the concept of time was shown to be completely and unambiguously
established by natural phenomena. But the concept of space was not
arrived at, either by Einstein or Lorentz, probably because in the case
of the above-mentioned spatial transformations, where the (_x′_, _t′_)
plane coincides with the _x_-_t_ plane, the significance is possible
that the _x_-axis of space some-how remains conserved in its position.
We can approach the idea of space in a corresponding manner, though some
may regard the attempt as rather fantastical.
According to these ideas, the word “Relativity-Postulate” which has been
coined for the demands of invariance in the group G, seems to be rather
inexpressive for a true understanding of the group G_{_c_}, and for
further progress. Because the sense of the postulate is that the
four-dimensional world is given in space and time by phenomena only, but
the projection in time and space can be handled with a certain freedom,
and therefore I would rather like to give to this assertion the name
“_The Postulate of the Absolute world_” [World-Postulate].