3. Kinematics of Light
The kinematics of light based on the ballistic law arises from a series of articles [
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
13] regarding light emission, propagation, and reflection applied to a few fundamental experiments. The reflection of light as a mechanical phenomenon [
1,
2,
3] was the first step. The experiment regarding the reflection and emission of light, [
13] summarized in
Appendix A, was the turning point in our understanding of the kinematics of light.
We used the expressions “observer in the absolute frame” and “observer in an inertial frame,” meaning that these hypothetical observers observe phenomena as they are in their frames. These expressions may be eliminated to avoid confusion with human observation and to state directly how the phenomena are, as in Newtonian mechanics. The expression “local observer” is particularly essential.
A local observer perceives the phenomena through light coming directly from a source or reflected by objects from the observer’s frame or others, as well as through partially reflected wavefronts of light by some particles of the transparent medium, such as air, through which light travels. Therefore, a local observer perceives a physical phenomenon differently from the reality of Newton's laws. Nevertheless, we may better understand reality by applying Newtonian laws and local observations of light.
Electromagnetic theory gives the universal constant speed of light emitted by a source at rest or in motion in the empty space of the absolute frame. The speed of light behaves similarly to the emitted speed of a ball, as presented in Subsections 2.5 and 2.6.
3.1. Ballistic Law Applied to Light Emitted by a Source in Motion
This study considers light propagation as a continuous phenomenon in which each wave point is a wavefront. The ballistic law of massless balls applies to light: A wavefront emitted at the velocity by a source at the velocity travels in the absolute frame at the propagation velocity , given by the vector sum of the emitted velocity and the source’s velocity , , unless a restriction arises in its propagation direction. Velocity varies in direction and magnitude according to the velocity direction from the velocity direction.
Suppose a light source at rest in the absolute frame emits waves in all directions. The spherical wavefront has its center at the source at all times, waves are uniformly distributed to the source, and waves travel at the emitted speed with wavelength , period , and frequency in any direction. The phenomenon is a sphere with the center at the source at rest, continuously expanding with a radius increasing in time with . At each point of the spherical wavefront, a local observer observes the wave coming from the source with a delay according to the time from its emission, traveling at the speed of , wavelength , period , and frequency .
Figure 8 illustrates the circular wavefront emitted in the paper plane by a light source at the origin of an inertial frame that travels at the velocity
in the absolute frame.
Figure 8 presents the case when
to scale for
m/s,
m/s. At the initial instance, at the point
, the source emits a spherical wavefront. After time
s, the source is at point
.
When the source is at the point , the figure shows the circle of the instantaneous velocities with the center at , which belongs to the inertial and absolute frame and the instantaneous propagation velocities , originated at and ending at the circle with the center at the point , which belongs to the absolute frame. Both circles have a radius of m. Velocities , , and are shown as vectors in thick lines. A specific velocity applies to each wavefront emitted in the absolute frame. The vector sum of velocity of the wavefront emitted at in the direction and the common velocity along gives propagation velocity along the path traveled in one second. With the same reasoning, each velocity can be distinguished from the multiple lines.
At point , after s from the initial instance, the circular wavefront emitted at has a radius of m. The wavefront emitted at in the direction traveled the path at speed in the absolute frame and the path at speed in the inertial frame. The traveling direction of the wavefront does not change along . A local observer at point observes the wavefront coming from , not . The traveling path of each wavefront in the absolute frame is shown in a thin dashed line, and in the inertial frame is shown in a thin continuous line.
Each emitted wavefront inherits the velocity of the source in the absolute frame, such that in the source inertial frame, waves in any direction travel at the emitted speed with wavelength , period , and frequency . The phenomenon in the inertial frame of the source is like that in the absolute frame. In the absolute frame, the phenomenon of the inertial frame travels at the velocity .
3.2. Reflection of Light by a Moving Mirror
illustrates, in the absolute frame, a mirror traveling at velocity and the source of coherent light at rest. Wavefronts, reflected at a point of the mirror, belong to waves originating from the sequential points of the source.
This section employs Eq. (4),
, in which the electromagnetic speed
replaces
and the reflected speed of the wave
in the absolute frame replaces
:
In the inertial frame of the mirror, in the instant of collision, the speed of the mirror in the direction opposite to the incident light is
. In the absolute frame, the speed of the mirror in the direction of the reflected light is
. Another form of Eq. (7) is
where angles
and
are measured counterclockwise from the velocity
.
In the absolute frame, the mirror moves in one direction, but the inclination of the mirror reflects light in multiple directions.
A second after the collision at , the wavefront from is at , and the mirror is at . Wavefronts reflected between and travel in the absolute frame in the direction at speed . In the inertial frame of the mirror, wavefronts travel at velocity given by the vector subtraction of the wavefronts’ velocity and the velocity of the source , . A local observer at point perceives the wavefront as coming from , not from the actual location of the mirror at .
The source may not be at rest, therefore, the speed of light propagation is in the absolute frame. In this case, the mirror may also perceive the source’s velocity, not only the emitted velocity. In References 6 and 7, we approached this general consideration.
3.3. Emission, Propagation, and Reflection of Light as Mechanical Phenomena in the Absolute Frame and an Inertial Frame
The study of the emission, propagation, and reflection of light is based on that of massless balls, as described in Subsection 2.6. The mechanical velocity is the same as that for massless balls. The emitted velocity replaces the velocity of the balls.
Figure 10 illustrates an identical light source and reflecting mirror at rest in the absolute and an inertial frame. The source and mirror have the same geometry; each source is at the origin of its frame.
In the absolute frame , the source at the origin emits a wavefront at velocity at an angle from the axis . After time , the wavefront is at point of the mirror . At point , the wavefront is reflected at velocity , then travels the path in time . The velocities and have the magnitude . The light travels paths and in time at speed , wavelength , period , and frequency .
The inertial frame travels at velocity , and the source is at its origin . Points and and origin belong to the inertial frame, and their instances in the absolute frame receive a corresponding index. The source emits a wavefront at the velocity in direction at the angle from axis . The wavefront travels on the propagation path at the propagation velocity , given by the vector sum of the emitted velocity and the source’s velocity . The velocity does not change its direction and magnitude along the path . At point , the wavefront is at ; it has traveled the path at speed in time , and the direction makes angle from axis . Path is path in the inertial frame, which is identical to in the absolute frame. The wave’s wavefronts that are emitted in the direction at point between and are on the path .
At point of the reflection, the mirror perceives only the magnitude and direction of the emitted velocity because the wavefront and mirror have the same velocity . The incident and reflected angles are measured from the normal to the mirror at the collision point to the incident velocity and reflected velocity . After reflection, the velocity keeps the wavefront moving in the same direction with the same magnitude . The wavefront travels on the propagation path at the propagation velocity , given by the vector sum of the reflected velocity in the direction and source velocity . The velocity does not change its direction and magnitude along path . At point , the wavefront emitted from is at , the direction makes angle from axis , and the wavefront has traveled the path at speed in time and the path at speed in time . Path is the path in the inertial frame, which is identical to that in the absolute frame. At point , light has traveled the path and in the time at speed , with wavelength , period , and frequency , as in the absolute frame. A local observer at point observes the light coming from the origin , and another at the point observes the light from point .
The kinematics of light makes the difference between the emission and propagation of light. Maxwell’s equations give the instantaneous velocity of the emitted light, a universal constant, relative to the source in motion in the absolute frame. When the source is at rest in the absolute frame, the waves travel at the emission speed with wavelength , period , and frequency . When the source is in motion, the waves emitted in the absolute frame at the speed inherit the source velocity of mechanical nature, and according to the ballistic law, the propagation of light speed in the absolute frame is given by . In the inertial frame of the source, light travels at the speed with wavelength , period , and frequency as in the absolute frame.
In the inertial frame of a source, a mirror at rest perceives only the emitted directions of the waves, which are then reflected accordingly. The reflected waves inherit the source’s velocity such that in the source's inertial frame, the reflected waves are as in the absolute frame, having the same speed , wavelength , period , and frequency .
The ballistic law, applicable to massless balls and light, is embedded in mechanics because it is derived from mechanics. It works in the absolute frame, which is the background of any source’s inertial frame and acts on each massless ball and light wave emitted by a source in motion, creating in the source’s inertial frame a phenomenon identical to that in the absolute frame. Therefore, the kinematics of light explains and confirms the principle of relativity, according to which no experiment in an inertial frame can prove its motion. It also explains why the laws of physics have the same form in each inertial frame and why the speed of light is a constant in inertial frames when the source and reflected mirror are at rest.
It is convenient to compare the physics phenomena from inertial frames with the frame at absolute rest, which is a hypothetical inertial frame at zero speed. The phenomena in each inertial frame are similar to those in the frame at absolute rest. Therefore, each inertial frame can be considered a local frame at absolute rest for phenomena belonging to that inertial frame. The study of a physics system belonging to an inertial frame can be performed in another frame, considered a stationary frame or a local absolute frame, where the inertial frame travels at the relative velocity between the two frames.
3.4. Experiments and Observations that Support the Kinematics of Light as a Mechanical Phenomenon
The kinematics of light explains experiments and local observations that supported special relativity because of an insufficient and incorrect understanding.
3.4.1. Michelson‒Morley Experiment
Light travels through a transparent medium at a specific constant speed independent of the source speed. Michelson and Morley [
14] approached their experiment considering the theory of a fixed ether. Therefore, the speed of light emitted by a source and reflected by a mirror has the same magnitude in the hypothetical ether at rest in the absolute frame, regardless of whether the source and mirror are at rest or in motion. In the ether theory, the speed of light is limited by the ether. The Michelson‒Morley experiment predicted a fringe shift that was not confirmed by the experimental results.
The kinematics of light proves that in an inertial frame where a source of light and a mirror are at rest, the speed of light is constant of electromagnetic nature. Therefore, the kinematics of light predicts a zero fringe shift in the Michelson‒Morley experiment, which agrees with the experimental results.
3.4.2. Experiment Performed at CERN, Geneva
Without rejecting Ritz’s ballistic theory [
15], the emission, propagation, and reflection of light in inertial frames [
4] can explain the experiment performed at CERN, Geneva, in 1964. [
16]
Figure 11 illustrates this phenomenon using a simple approach.
When a boson of mass is accelerated at a mechanical speed near the constant speed of light , it decays into a particle of mass and one massless photon. At speed , particle changes direction, and the photon continues moving freely at the mechanical speed . Bosons are just carriers that give photons their mechanical speed near the constant speed of light . Bosons are not sources of light and cannot give photons the speed of electromagnetic nature. This experimental result confirmed the ballistic law of light.
3.4.3. Observation of a Star in the Universe
a illustrates the observation of a star in the universe according to the kinematics of light. Suppose that a star at a point and the Earth at a point travel at velocity . At the initial instance, the star emits a wavefront of light in the direction at the emitted speed .
After a specific time, the star travels the path and the Earth travels the path , which are of equal length . The ballistic law makes the wavefront emitted in the direction propagate along . At , the local observer perceives the wavefront as coming from . Therefore, the star is observed at its actual location.
Figure 12b illustrates the observation of a star in the universe based on the hypothesis that the speed of light is independent of the source's motion. Suppose a star at a point
and the Earth at the point
travel at velocity
. At the initial instance, the star emits a wavefront of light in the direction
at the emitted speed
.
After a specific time, the star travels the path
and the Earth travels the path
, which are of equal length
. The wavefront, emitted in the direction
, reaches the point
, where a local observer perceives the wavefront as coming from
. Therefore, the star is observed at the initial location and not at its actual location, which means that the hypothesis of the constancy of the speed of light creates irregularities that are unobserved by astronomers. These irregularities differ from those that De Sitter incorrectly predicted. [
17,
18]
3.4.4. Observation of a Star’s Orbit
Light emission as a mechanical phenomenon [
4] has been applied to star orbit observation. [
5]
Figure 13 depicts an actual star’s orbit with the center at the point
of radius
in the plane of the paper and an imaginary circle of radius
with the center at the point
and with its plane parallel to and in front of the paper plane.
The distance is perpendicular to the orbit and the imaginary circle planes. The observer at rest is located at the point . The observed star orbit of radius is centered on . The view is from the back right of the observer, enabling a clear image of the actual and observed orbits.
The distances in each set of ( and (), including all other similar distances corresponding to points , and are equal.
The waves emitted by the star in motion inherit the velocity of the star corresponding to each orbital point and travel through different paths to the local observer . At point , the star emits a wavefront of light at the velocity in the direction , but this wavefront travels along the path at the propagation velocity . The direction and magnitude of the velocity do not change along the path . At point , the observer observes the wavefront originating from point traveling at speed . At point , the star emits a wavefront of light at the velocity in the direction , ; this wavefront travels along the path , , at the same propagation velocity . The direction and magnitude of the velocity do not change along the path . At point , the observer sees the wavefront coming from the point traveling at speed along path . The observer perceives a similar observation for each point in the circular orbit.
Points
, and
give the corresponding points
, and
, points which offer in this particular case the observed orbit with the center at
. The local observer sees the star's orbit rotated; this orbit has a larger diameter than the actual orbit, and the observed orbital velocity is greater than that of
. The observed circular orbit increases with increasing distance d. This phenomenon compensates for our vision of seeing objects smaller with increasing distance. The speed of light from any point on the observed orbit to the observer is constant
. Therefore, no time irregularities exist to refute Ritz’s ballistic theory, [
15] as De Sitter explained. [
17,
18] Observing a star’s orbit supports our understanding of the kinematics of light based on the ballistic law.
3.4.5. Miller Experiment
Studying the emission, propagation, and reflection of light in inertial frames [
4] helps us to predict zero fringe shifts for any location and altitude in Earth’s inertial frame. This explains Miller’s experiments [
9,
10] at the Cleveland Laboratory in 1924, [
19] which employed light from local sources, as well as sunlight; the fringe shift with sunlight was of the order of
. The fringe shifts of 0.08 in 1921 and 0.088 in 1925, recorded by Miller using local sources at a high altitude on Mount Wilson, remain unexplained.
3.4.6. Airy Experiment
In addition to the interactions of the emission and reflection of light with matter, there are other examples, such as the velocity of light through a moving medium [
8] and the refraction of light when it travels from one medium to another, both at rest, according to Snell’s law. Airy’s experiment is an example of the dragging of light by a moving medium. Observing the star γ Draconis, Airy [
20] expected to adjust the inclination of the telescope after introducing a tube with water along its axis; however, this was unnecessary. Considering the dragging of light by moving water and the experimental results, we obtained the Fresnel dragging coefficient
from a mechanical perspective, where
is the refractive index of the medium. [
11]
3.4.7. Majorana Experiment
Majorana’s experiment [
21] in Earth’s inertial frame employs a fixed light source. The light travels through three stages, each consisting of one movable and one fixed mirror, and enters a Michelson interferometer with arms of unequal lengths. The movable mirrors are fixed on a rotational disk in both directions. A fringe image is observed when the disk is at rest. When the disk is rotated from maximum speed in one direction to another, a 0.71 fringe shift is observed.
Similar to the Michelson interferometer, Majorana’s experimental device offers an outstanding contribution to the physics of light, despite changes in the interpretation of the experiment over time. Majorana misunderstood the phenomenon within the device and the significance of the fringe shift observed during the experiment, explaining the fringe shift favorably for special relativity. The reflection of light as a mechanical phenomenon [
1,
2,
3,
4] applied to the Majorana experiment [
21] shows that the speed of light changes after each stage, causing a fringe shift in the Michelson interferometer. Reference 12 approximates rotational mirrors as inertial frames and derives a shift of 0.27 fringes. However, the observed fringe shift of 0.71 confirms the kinematics of light, rejecting the constancy of light propagation.
3.5. Galilean Transformation
This section studies the Galilean transformation for light, as it is in mechanics, not observed.
When extended to infinity, all the inertial frames overlap. A phenomenon in an inertial frame is instantly shared with any other inertial frame. The inertial frame that shares a phenomenon is considered at relative rest or a stationary frame.
The Galilean transformation presents how the physics phenomenon of light emission from a stationary frame is instantly shared with an inertial frame.
Figure 14 depicts a stationary frame
in which an inertial frame
travels at velocity
along the
axis, and the planes
and
are common.
The kinematics of light proves that any inertial frame can be considered a local frame at absolute rest, a frame at relative rest, or a stationary frame; we do not assume this fact.
Origins and coincide at the initial instance when the source, belonging to the origin of the stationary frame, emits a spherical wavefront of light formed by each wave’s wavefront.
After a time
s, the spherical wavefront of light has the center at
, and the origin of the inertial frame
is at a distance
from
. Therefore, each path length traveled by a wave’s wavefront represents its velocity vector
and
in the stationary and the inertial frame, respectively. The Galilean transformation provides the coordinates of each point on the spherical wavefront along the
axis in the inertial frame.
Figure 14 shows the wavefronts at points
,
,
,
,
, and
on the circular wavefront in the plane
and their coordinates
along the axis
of the inertial frame
.
The Galilean transformation applies to the inertial frame and consists of a set of four equations applicable to each point of the spherical wavefront that can be written as follows:
Equation applies for any direction of any point on the spherical wavefront, not only for one direction of the common axes and . Indeed, in the stationary frame, for angle , is positive, which gives , and for the angle , is negative, which yields . The path has the same direction at all times. We study light propagation, as it is, in any direction of the inertial frame, not just in one direction.
The wavefront, emitted at the initial instance from towards , travels the path at speed . It is on this circular wavefront, which enlarges continuously. In the inertial frame, this wavefront travels the path at propagation speed given by the vector subtraction of velocity along and along . Angle and speed vary according to the angle . For m/s and m/s, the speed of wavefronts varies from m/s for along , to m/s along for , to m/s along for , and to m/s along for .
In
Figure 14, the circular wavefront and vectors shown in a thick line are related to the Galilean transformation; those in the thin line are associated with the ballistic law.
The physics phenomenon consists of the source, the circular wavefront, and light waves like those along , , , , , and ; all belonging to the stationary frame and none to the inertial frame. A phenomenon in an inertial frame is unique in the universe; it is independent of any other inertial frame, even if it is instantly shared in each of them through coordinates. There is no transformation of a phenomenon that undergoes changes from an inertial frame considered a stationary frame to another inertial frame that may or may not affect the laws of physics; thus, the phenomenon is not duplicated. The word "transformation" may be inappropriate; a better wording may be "Galilean coordinates.”
Figure 14 and the Galilean transformation (9) apply to balls when the source emits a circular ball front, with the balls’ speed
.
In the Galilean coordinates shown in
Figure 14, the phenomenon, which includes the light source, the circular wavefront, and the light waves along
,
,
,
,
, and
, belongs to the stationary frame. The circular wavefront has its center at the source located at the origin of the stationary frame. Each point of the circular wavefront has coordinates related to the origin of the inertial frame, given by Equation 9.
The ballistic law was known in Einstein’s time but unaccepted because of an incomplete understanding of its applicability to light; therefore, Einstein had to work with the above case and the following one: In
Figure 14, if the source belongs to the origin of the inertial frame
and the ballistic law is ignored, the phenomenon that includes the light source, the circular wavefront, and the light waves as
,
,
,
,
, and
belongs to the inertial frame. The circular wavefront has its center at the origin of the stationary frame,
, not at the source. Thus, the circular wavefront is common if the source belongs to either of the two origins. The Galilean transformation only gives coordinates of each point of the circular wavefront in the inertial frame.
Einstein considers that, if the source belongs to the origin or , the speed of light in the inertial frame is a constant , and the common circular wavefront is observed as a circular wavefront centered at the origin , such that the phenomenon is similar to that in the stationary frame. To fulfill his hypothesis, Einstein applies a mathematical transformation identical to Lorentz’s.
If the source at the origin of the inertial frame continuously emits light waves, not just a spherical wavefront, the propagation of the waves undergoes corresponding wavelength contractions or dilations of wavelength and variable velocities to maintain time constancy for each wave direction. The phenomenon is not as in the stationary frame; even if we try a mathematical transformation to make each wave travel at the speed , length , and wavelength , because , and the waves in the inertial frame are not uniformly distributed relative to the origin .
When the source belongs to the origin
, the phenomenon in the inertial frame, based on observations and experiments, and what Lorentz and Einstein tried to do through a mathematical transformation, is shown in a thin line that includes waves along
,
,
,
, and
. At points
and
,
is the propagation speed of the wavefronts in the stationary frame.
Figure 14 shows that the phenomenon in the inertial frame is identical to that in the stationary frame if each wave inherits the velocity of its source, which is what the ballistic law does. In the stationary frame, the spherical wavefront, centered at all times at the origin
of the inertial frame, travels at the velocity
and continuously expands its radius with
. This simple understanding leads to the ballistic law.
Understanding Einstein's approach to the two cases above and the ballistic law, we can conclude that the mathematical transformation proposed by Lorentz and employed by Einstein cannot describe the physical phenomenon in the inertial frame and is sufficient to reject special relativity.