Light Speed Invariance is a Remarkable Illusion
Stephan J. G. Gift
Department of Electrical and Computer Engineering
Faculty of Engineering
The University of the West Indies
St. Augustine, Trinidad, West Indies
“Einstein’s special theory of relativity requires that the one-way velocity of
light be a constant. If that turns out not to be so, special relativity falls.”
Paul A. LaViolette, Genesis of the Cosmos, 2004.
“Any clear sign of a variation in c, the speed of light, as the Earth [revolved]
would prove that the aether existed.”
George Smoot, Wrinkles in Time, 1993.
“Those physicists - and they are many - who now regard belief in the
possibility of an ether as a superstition have simply not learnt the lessons of
history, which teach us that discarded ideas have a way of returning to
Herbert Dingle, Science at the Crossroads, 1972.
Abstract. Though many experiments appear to have confirmed the
light speed invariance postulate of special relativity theory, this postulate
is actually unverified. This paper resolves this issue by first showing the
manner in which an illusion of light speed invariance occurs in two-way
light speed measurement in the framework of a semi-classical absolute
space theory. It then demonstrates a measurable variation of the one-way
speed of light, which directly invalidates the invariance postulate and
confirms the existence of the preferred reference frame of the absolute
A fundamental tenet of Einstein’s Special Theory of Relativity is the Light Speed
Invariance Postulate according to which the speed of light is constant in all inertial frames [1-4].
This postulate is used to derive the Lorentz Transformations relating the coordinates in different
inertial frames and these transformations are in turn used to derive the length contraction and
frequency reduction formulae of special relativity.
The light speed invariance postulate has been subjected to numerous tests over the past
century  as a result of which most scientists believe that it has been confirmed. Thus it is often
claimed that the postulate has been verified by the classic experiments of Michelson and Morley
 and Kennedy and Thorndike  and by the many later improved versions of these
experiments such as those by Brillet and Hall  and Hils and Hall . However while the
results of this class of experiments suggest a constant light speed c, they do not directly test one-
way light speed. In experiments that do attempt a one-way light speed test such as those by
Gagnon et.al.  and Krisher et.al. , Zhang  has pointed out that these are not true one-
way tests because of the inability to independently synchronize the clocks involved. Thus 100
years after the introduction of the relativistic paradigm, light speed invariance on which the
paradigm is based remains an open issue, despite the strange declaration by the scientific
community that it is correct by definition! Ives has in fact described it as untenable .
One-way light speed testing is therefore necessary in order to determine the validity of
the light speed invariance postulate. This test can differentiate between Special Relativity
Theory, which involves light speed invariance, and the Maxwell-Lorentz Ether Theory, which
involves light speed variation relative to a moving observer. This latter theory in its modern form
is a semi-classical Absolute Space Theory in which light propagates isotropically at a speed c in
a preferred or absolute reference frame. In such an absolute frame and in keeping with classical
analysis, the one-way speed of light changes according to the observer’s motion relative to the
preferred frame. The theory incorporates the ether-induced Fitzgerald-Larmor-Lorentz (FLL)
contractions experimentally confirmed by Ives  according to which a rod of length lo in a
preferred frame, when moving with speed w relative to that preferred frame, is shortened to a
length l given by
2 / 1
and a system of frequency fo when stationary in the preferred frame, has a reduced frequency f
2 / 1
/ 1 (
This incorporation is achieved by the adjustment of the classical Galilean transformations
Here the zero-subscript coordinates are the coordinates of space and time in the preferred frame,
the unsubscripted coordinates are coordinates in a reference frame moving at speed w relative to
the preferred frame andγ is the FLL contraction factor given by
Many researchers [14-17] have observed that the Absolute Space Theory is in close agreement
with Special Relativity Theory over virtually its full range of predictions.
However the two theories make quite different light speed predictions. In the case of the
Absolute Space Theory, for measurements made by an observer at rest in the preferred frame, the
(real) speed u relative to the moving frame is given by
is the speed relative to the preferred frame. This is the Galilean law of velocity
composition. For measurements made by an observer moving relative to the preferred frame,
Levy [16 p42-43] has shown that because the FLL contractions result in contracted metre sticks
and retarded clocks, the (apparent) speed
a u′ relative to the moving frame is given by
which can be written as
This is the Galilean law of velocity composition when contracted metre sticks and retarded
clocks are used to measure speed relative to the moving frame. From (1.5) and (1.7), the real
speed u and the apparent speed u are related by
The law of velocity composition in Special Relativity Theory corresponding to equation (1.6) of
the Absolute Space Theory is [1-4]
where u is the speed relative to the moving frame. If
cu = in (1.9), then
i.e. the measured speed in Special Relativity Theory is c. This result is independent of the
and consistent with the light speed invariance postulate. If in (1.6) of the
Absolute Space Theory, then
i.e. for sufficiently low relative speed
, the measured speed in Absolute Space Theory is the
and not c. If the direction of is reversed, then (1.11) becomes
Thus for light speed measurements made by an observer in a frame moving at speed
relative to the preferred frame, Special Relativity Theory predicts light speed invariance
while the Absolute Space Theory predicts classical light speed variation c
. In this paper
therefore, we examine the possibility of light speed variation and its measurability in the
framework of the Absolute Space Theory. To this end, we summarise the careful results of Ives
relating to out-and-back optical tests which show how experiments such as the Michelson-
Morley and Kennedy-Thorndike involving light speed variation in a preferred frame yield a
measured constant light speed c. We then show that light speed variation can indeed be detected.
Specifically we demonstrate that the variation in the period of Jupiter’s satellite Io observed from
Earth as it orbits the Sun (“Roemer Effect”) is a direct manifestation of changes in the speed of
light relative to a moving observer.
2. Light Speed Measurement on a Moving Platform
Consider the Maxwell-Lorentz semi-classical Absolute Space Theory in which light
propagates isotropically at a speed c in a preferred frame. In such an absolute frame, the one-way
speed of light relative to an observer changes according to the observer’s motion relative to the
preferred frame. In addition, FLL contractions (1.1) and (1.2) occur as a result of movement
relative to the preferred frame. These contractions alter the normal Galilean transformations that
relate the coordinates of the preferred frame to coordinates in any other inertial frame, which
now become (1.3).
2.1 Two-way Light Speed Test 
Since one-way light speed methods have failed because of clock synchronization
problems , we here focus on two-way light speed testing which appears to confirm light speed
c. We consider light speed measurement on a platform moving at a speed w relative to the
postulated preferred reference frame and examine the possibility of detecting and measuring the
of similarly directed light relative to the platform . In Figure 1, let ab be the
moving platform on which measurements are to be made with a clock at a and a mirror at b. Let
the speed of the platform relative to the preferred reference frame be w and let
Dbe the distance
from a to b as measured on the platform.
Figure 1. Platform moving at speed w relative to the preferred reference frame
Because of the FLL contractions that arise as a result of movement with respect to the
preferred frame, the true length D is less than the measured length and is given by
/ 1 (
Let the time of transit of a light signal travelling from a to b and back to a as measured by the
clock at a be t. Because of the FLL contractions, the true time of transit t (measured by a clock
stationary in the preferred frame) from a to b and back is greater than tand given by
/ 1 (
Now the true time of transit of a light signal from a to b is
and the true time of transit
from b to a is. Therefore ) /(wcD
Substituting from (2.1) and from (2.2) in (2.3) yields tD
/ 1 (
/ 1 (
It follows from (2.4) that the speed of light cas measured on the moving platform is given by
Therefore even though the speed of light relative to the platform is
out and back, the
light speed measured on the platform is c.
To appreciate the full significance of this remarkable result, it should be noted that the
true average out and back speed
is, using (2.3), calculated to be
)/ 1 ()(
The result in (2.6) indicates that with no FLL contractions, the average two-way light speed
varies with w to second order and is not equal to c: The FLL contractions compensate for the
in (2.6) such that the measured average two-way speed
c is c as given
in (2.5). This result has been generalized for any direction of light travel by Levy  and
validates the standard out-and-back method of determining light speed c relative to the preferred
frame from a moving platform. It means however that this method gives c relative to the
preferred frame but does not yield the one-way light speed wc±
relative to the moving platform.
Light Speed Measurement Using a One-way Signal Pulse Train
Neither one-way two-clock light speed experiments nor two-way one-clock light speed
experiments give the one-way light speed relative to the moving platform. We now describe a
one-way one-clock experiment that does. It is based on the following principle: Instead of timing
a one-way light signal pulse over a known distance using two clocks, we time successive pulses
of a one-way signal train using one clock. It is somewhat similar to timing a passenger train with
one clock by starting the clock as the front of the train passes and stopping the clock as the rear
of the train passes. If the length
of the train is known, then with the time
T T measured by the
single clock, the train speed
T S can be found from
The Roemer Experiment
Consider the Earth-Sun-Jupiter planetary system. As the Earth revolves around the Sun at
speed w, the innermost satellite of Jupiter, Io, is observed to undergo regular variations in its
period To . Because Io, as observed from Earth, is periodically eclipsed by Jupiter, this
occulting source emits what may be described as “pulses of darkness” travelling at speed c to
Earth as Io revolves around Jupiter. This is shown in figure 2. The distance between successive
pulses is fixed at λo given by
Pulses of Darkness
Figure 2. Pulses of Darkness from Earth-Sun-Jupiter Planetary System
As the Earth moves away from Jupiter, the period
of Io, which is the time between successive
pulses, is observed on Earth and found to be greater than To. The light speed relative to the
receding Earth can now be determined using λ and
T in the fundamental speed-determining
equation “speed equals distance over time” which for this system is
Of course, as in the case of the train, in order to determine the actual speed, the distance λo must
be known. This is easily obtained by measuring
corresponding to (by for
example employing a space probe), measuring c using the independent out-and-back method,
and using these values in (3.2) to determine λ
o. Establishing the value of λo using ) 0
an independently determined c may be viewed as calibration of the measurement apparatus; once
this is done, all light speed variations relative to the receding Earth can then be directly
determined by measuring
T and using (3.3).
In order to verify this method of determining variable light speed, we determine light
speed relative to the receding Earth by the direct substitution of measured values for
in the equation (3.3) for light speed. Thus using (3.2) in (3.3) yields
Substituting in (3.4) the measured values Ts
2 .959, 152
T corresponding to
the increased period of Io  along with the independently determined
gives the relative light speed value
458, 792, 299
667, 762, 299
2 . 959, 152
944, 152458, 792, 299
Note that since
, second-order FLL contraction effects associated with the measurement of
T are small and therefore do not significantly affect this result. We observe that the
experimentally determined light speed value in (3.5) is not c as the light speed invariance
postulate demands. The light speed in (3.5) is almost exactly equal to the classical value of
relative light speed value c
for the receding Earth, which usingfor the Earth
668, 762, 299) 790, 29458, 792,299(
Therefore for movement of the Earth directly away from Jupiter, the relative light speed
R c is
For movement of the Earth directly towards Jupiter, the period
T of Io (which again is
the time between successive pulses) is observed on Earth and found to be less than To. The light
speed relative to the advancing Earth can be determined using
o λ and
T in the fundamental
speed equation for this system which is
Substituting in (3.8) the measured values Ts
T corresponding to
the shortened period of Io  along with c gives the relative light speed
We again observe that the experimentally determined light speed value in (3.9) is not c as the
light speed invariance postulate requires. The light speed in (3.9) is almost exactly equal to the
classical value of relative light speed cw
for the advancing Earth, which
usingw for the Earth is
+ wc (3.10)
248, 822,299) 790,29 458, 792, 299(
Therefore for movement of the Earth directly towards Jupiter, the relative light speed
R c is given
On the basis of the experimentally demonstrated classical light speed variations in (3.7)
and (3.11) relative to the moving Earth, we conclude that the change in the period of the
planetary satellite Io measured by an observer on the Earth, is a direct indication of a change in
light speed relative to that moving observer. The results (3.7) and (3.11) directly confirm the
light speed predictions (1.11) and (1.12) of the Absolute Space Theory and falsify the light speed
invariance postulate of Special Relativity Theory. Additionally, these light speed variations
represent detection of movement of the Earth relative to the ether in the Earth’s approximately
uniform motion around the Sun, exactly the motion that Michelson and Morley failed to detect
also using light speed variation in their unsuccessful second-order experiment of 1887 .
The light speed invariance postulate that underpins Special Relativity Theory has not
been directly confirmed for one-way light transmission. For two-way light travel, the one-clock
out-and-back measurement of light speed on a moving platform always yields the value c and
this appears to confirm the postulate. This is reinforced by the failure to detect light speed
anisotropy in several one-way two-clock tests [10, 11]. However, these one-way two-clock tests
yielding c are flawed because of clock synchronization problems [5, 16]. Further, as shown in
this paper, the light speed invariance observed in the two-way one-clock measurement is an
illusion created by the compensating effect of the FLL contractions and consequent elimination
of platform speed
from the measured speed. By using a one-way one-clock measurement
procedure, we escaped the compensating effect of the FLL contractions as well as the clock
synchronization problems and thereby succeeded in revealing variable light speed c relative
to a moving frame.
We demonstrated that in the Roemer experiment involving the moving Earth and an
occulting light source Io, changes in the speed of light relative to the moving Earth w
occur and are measurable and result in observable variations in the period of Io as seen on Earth.
The light speed variation established in the Roemer experiment directly contradicts Einstein’s
Light Speed Invariance Postulate. Therefore this postulate, which results from what Will
(,p247) referred to as “Einstein’s revolutionary insight” and which Kaku (,p82)
described as “one of the greatest achievements of the human spirit”, is wrong. As a result Special
Relativity Theory, which is based on this postulate and which also predicts it, collapses !
In addition to the falsification of the light speed invariance postulate, the measured light
speed anisotropy in the Roemer experiment represents detection of ether drift and confirms the
existence of the preferred frame of the Absolute Space Theory [16, 17] in which light propagates
at speed c. This detection of the movement of the Earth relative to this preferred frame or ether in
the Earth’s approximately uniform motion around the Sun was recently reported by Gift 
based on light speed variation in the Roemer and Doppler experiments. The existence of this
preferred frame is consistent with the absolute speed measurement of the Earth arising from
anisotropic measurement of the cosmic microwave background radiation  and the apparent
determination of absolute motion in experiments by Marinov  and Silvertooth .
In light of the incontrovertible revelation in this paper of light speed anisotropy occurring
in the physical world and the consequent invalidation of Special Relativity Theory, we urge the
scientific community to reject the century-old relativistic doctrine of Albert Einstein with its
many paradoxes and contradictions and return to the absolute frame of the causal ether embodied
in the space-time framework of the modern Maxwell-Lorentz Absolute Space Theory [16, 17].
The luminiferous ether, whose existence was accepted by all scientists up to the end of the 19th
century but later abandoned because of the failure of the 1887 experiment to detect it, is real and
should now be the focus of exhaustive scientific investigation.
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