3. The Hypothesis of Coordinate Homogeneity
The Lorentz Transformation process is typically treated as a sequence of coordinate substitutions or as a single-step LT matrix multiplication by a 4-vector. While the latter is sufficient for vectors not containing an explicit time variable, the resulting vector has a 'mixed-representation' of coordinates—containing the variable remaining present, where could be reasonably expected—causing significant interpretation problems. To address this issue, we put forward the following hypothesis.
Hypothesis: For an inertial system S' to be functionally equivalent to S, its physical state must be expressed as a homogeneous 4-vector, reflecting the original representation in system S. Furthermore, there is only one, unique mathematically consistent form possible for each vector to maintain this functional equivalence.
Problem: Standard 'raw' result of the LT matrix multiplication yields a mixed-coordinate representation containing the stationary frame variable .
Necessity: Because observers in S' have no direct awareness of time variable the other system, must be eliminated.
Objective: Achieving true covariance requires that all components of the transformed vector are explicit functions of the local time .
The most reliable EOM of light emitted from the origin in S is represented by the following 4-vector:
The transformation of the EOM 4-vector
using the LT matrix yields:
The result does not yet constitute a functional EOM for moving observers. There is no explicit
coordinate and the spatial component
does not immediately imply the invariant speed of light. It is still a representation of the light propagation 4-vector in S'; however, it is not in the covariant form directly comparable to
. The presence of the other system's time variable
, of which S' has no direct awareness, makes it a 'mixed-representation'. Traditionally, it would require some narrative and algebraic manipulation to demonstrate that the speed of light is invariant. To achieve full coordinate homogeneity in S', we must eliminate the stationary parameter
A simple two step conversion makes this straightforward. The equation
validly introduces the
variable and can be solved for
from the first temporal element as follows:
Substituting
using the formula from Equation (6) is the only possible way to make the resulting 4-vector covariant.
Therefore, it is unique as stated in the hypothesis.
The truth of the hypothesis is demonstrated, however; this is only one specific case, and this is not a formal proof, which is physically valid in general case. After substituting
to equation (5) the covariant form of the light vector in S' is:
This confirms the postulates of special relativity. Therefore, when the 4-vector is expressed using explicit time , the presented conversion is a necessary step. Now we can apply the same methodology to events. Since the interpretation of the intermediate form of the EOM in Equation (5) was initially problematic, we can anticipate difficulties in interpretation after transformation of events coordinate
Coordinates of events in the stationary frame S and locations
and
are:
For the event
and
LT matrix transformation yields:
After substituting the time expression from Equation (11), the covariant form of the first event vector in S' is:
For the event
by the same process we get:
While Equation (10) represents the standard coordinate mapping, Equation (14) represents the functionally complete state where relative simultaneity vanishes. Similarly for equations (12) and (15).
Note that the conventional mixed-coordinate subtraction of the raw transformed time components from Equations (10) and (12), immediately yields the familiar non-zero result . However, once each event is expressed in the fully covariant form by solving the temporal component for the time variable and substituting back yielding Equations (14) and (15), both events naturally acquire the same value of . Consequently . This shows that the textbook claim of relative simultaneity arises from the intermediate mixed-coordinate representation, whereas the completed covariant representation enforces coordinate homogeneity naturally. The apparent disappearance of is therefore a direct consequence of demanding that every component of the transformed 4-vector be an explicit function of the local time of the moving frame including relative concurrent motion of light signal as in Equation (7) and that of the system S itself at velocity. The relative simultaneity claim approved by overwhelming consensus does not mean this is an error but rather one aspect of the more nuanced interpretation of conventional simultaneity.
The term ‘conventional` does not carry a negative connotation because it was a deliberate stipulation which Einstein admitted deciding on the definition of simultaneity of his own free will [
9] (p.28). Strohm [
10] (p.109) confirms the convention as the correct classification, because there are other valid alternatives including the Tangherlni transformation (TT) operating in absolute time, also known as the absolute transformations.
The
conclusion appears to be at variance with the standard interpretation of simultaneity first presented by Einstein [
2], (p.42). Our approach may be questioned, because of what seems as a deliberate choice of assigning different events the same value of
. However, assigning
to the first spatial component in the event coordinate 4-vector is not different than having an equation of motion but with zero velocity, which is perceived like any other relative motion in S'. The fact that without the discussed substitution there would be no valid equation of motion, is compelling. We now attempt to falsify the assertion about absolute simultaneity of distant events. It is natural to assume that in system S two concurrent light beams emitted from the origin at a delay
and
can generate events simultaneously expressed as:
The LT applied to those EOMs using the previously described procedure yields:
From the above we see that, for any pair of delays and , the two originally simultaneous events can be re-expressed in S' such that both occur at the same local time . This confirms that the time difference vanishes () once the full covariant representation is enforced. The construction demonstrates that absolute simultaneity can be recovered in the homogeneous 4-vector form while remaining fully consistent with the Lorentz transformation and all its empirical predictions. However, how do we know this solution is physically meaningful? Is Lorentz time absolute?
There seems to be no doubt that the systems S and S' are properly configured covariant systems. In this representation the temporal component is always or , where and represent the local master origin clock proper time initially projected to all clocks, which remain synchronised in the idealised scenario. Even in conventional synchronisation every clock state is the same as the master clock. All with an implicit assumption, that both local system clocks ensembles along the axes are synchronised by light signals enforcing Einstein's synchronisation. Only then, does the application of the LT matrix yield a physically valid transformed event. The idealised master clocks in uniform motion instantaneously synchronised to 0 when coinciding, subsequently carry their own proper time evolving from the synchronised value onwards, together with their later synchronised local clock ensembles. The clocks on and x' axes can be synchronised at the speed of light immediately after , well before an experiment is conducted. Although in relative motion and different rates, they remain in continuous temporal relation predictable by the theory of relativity. For any location there can always be two independent clocks running at different rates in the respective systems. Any event can be simultaneously recorded by them, providing a lasting record of what and when it happened, in which system.
The apparent absence of relative simultaneity requires further discussions to gain a wider consensus or falsification. We can use traditional LT equations allowing more than one choice. For relative simultaneity, one of the most common methods in literature [
4], (p.51), [
5], (p.15-13), [
6], (p.73), lecture notes
1 ,(page.2) and [
7], (p.93), use the original Einstein's DLT formulation, in other cases by substituting explicit variable
with the equivalent expression from the ILT as in Equation (3), most common in the position 4-vector conversions for example by French ], (p.81).
To convert the 4-vector's component manually, we need to equate the this component content () to the variable: = , then using the ILT from Equation (3) results in =. Solving this for , the final outcome becomes .
This is exactly what happened after the second transformation step: in Equation (15). Using the manual method, if there is any time variable left in spatial components, we need to substitute with the first ILT equation content, thus introducing in the middle of the transformed equation. Then it must be solved for again. The operation equivalent to the second step transformation after the LT matrix multiplication is 'automatically' completed. Now, in the temporal component we can substitute the formula for from the Equation (3). However, it becomes a 'mixed representation' and it is not possible to represent the 4-vector in the covariant form. Therefore, the only choice is to put where it belongs, thus securing a covariant representation. We have just demonstrated that the second step concludes the covariant Lorentz transformation equivalent to using Equation (3) in the manual mode.
The disappearance of relative simultaneity is the result of demanding covariant representations in the equivalent systems, and the 'mixed-representation' contains all necessary information to accomplish this process. So, the moving observer's time found its way out of the shell of synchronisation convention. We can see it as an emergence of the 'absolute-like' time came naturally. The nature of this time is yet to be revealed. Absolute time is not fiction. It is explicit in independently developed Tangherlini's theory [
11] from Einstein's field equations of General Relativity (GR) which preserves all relativistic effects as Einstein's theory. Both theories are equivalent by the virtue of GR coordinate independent formulation; it is not then a surprise that 'absolute-like' time had to emerge somewhere in special relativity as demonstrated.
For more than one hundred years physicists derive correct relativistic equations of motion this way or another, not being aware of what kind of time they are dealing with. It is also not surprising that relative simultaneity has no physical effect because in Tangherlini's theory it is inherently absent. Until this moment it was unthinkable these two theories could ever agree on relative simultaneity, but they did eventually. Furthermore, the TT (or absolute transformation) can be derived using Reichenbach synchronisation approach as demonstrated by Strohm [
10] which is the second non-arbitrary alternative.
The absolute appearance of Lorentz time which we named 'absolute-like' requires more decisive determination. The only way to approach the problem is to compare it with Tangherlini time directly. Tangherlini framework requires one special absolute rest frame (ARF) where one-way velocity of light isotropy holds. For all other inertial frames only the empirically valid, round trip average speed of light is enforced, unlike in the special theory of relativity (STR) which postulated equivalence of all inertial frames.
It is noteworthy that the absolute-like time emerging from the two-step procedure yields physical predictions identical to those obtained in Tangherlini’s absolute-time formulation, which is known to reproduce all observable relativistic effects. A detailed mathematical comparison is left for future work.