**9. Nature of light**

*Progress in Relativity*

**8. Position is relative**

Gravity intensity at a given distance from a mass is spatially irreducible. This is because even a miniscule electron senses its presence at any position at which it is located at a distance **r**. Pluto is a huge 6 billion km from the sun and nevertheless is smoothly turned by gravity at every position in its orbit, not only preventing its escape into space but also causing the tracing of an orbit that follows an elliptic mathematical function. Gravity is not reducible at any spatial position along the orbit. All planets in the solar system fall endlessly in perpetuity along elliptic paths in a dynamic equilibrium that is always striving to increase entropy while minimizing orbital energy [9]. Orbiting bodies around the sun instantly detect changes in gravity from the wobbling travel pattern of the sun even at great distances, which causes the bodies to change speed to travel in a smooth elliptic orbit. Galaxies in the universe may also behave in such a way, where each are gravitationally attracted to maintain order in the universe of matter where rotating galaxies maintain relative positions possibly in a dynamic equilibrium steady state.

The question, where are you?, requires context and relativity to answer. If the position of a person is desired in relation to the longitude and latitude coordinates on earth's surface, or in relation to a street address or city on earth, then an answer can be given because the spatial coordinate is provided in relation to a particular described position. However since the earth and all objects in the solar system are in constant motion, the true spatial coordinate of where one is located is not actually known with respect to a theoretic stationary 3-D (x, y, z) coordinate in space that one might refer to as an origin from which other coordinates may be measured and stated. And even if the entire universe of matter (as a whole unit) were not rotating or undergoing translational motion so that an origin point in space could be defined, the answer would also depend on time. Due to motion of the particular galaxy and solar system on which one might be located, the position one provides is technically only true at the particular time when the answer was given. The spatial coordinate is quickly changing while one provides the answer. Finally, the definition of you is also relative, where the position in space of the head is different than the

feet or the body's center of mass, all at different elevations in 3-D space.

*Photographs of the full moon Feb 23, 2019 traversing behind a pine tree as time proceeds.*

**Figure 5** shows the position of the moon in perigee (at its closest approach to the earth) in relation to a tree on earth as a function of time. The moon shifts toward the tree about 5° of angular rotation in 20 min. This observation cannot distinguish whether the shift is caused by the orbiting motion of the moon (that does not spin), being accelerated while continuously changing its direction, or rather is due to either the spinning or to the orbiting motions of the earth. However, with extra data it is indeed possible to determine the major contributor. The moon orbits the earth and returns to its full moon position again in 28.3 days, at an angular velocity of 9.4 h

**48**

**Figure 5.**

Unlike gravity that contains no energy itself, light is composed of individual photons of electromagnetic energy hf, formed from electrons that drop to lower energy levels in a source such as the sun, or a tungsten filament in a bulb, or a radio antenna. Light consists of orthogonal electric and magnetic field components that self-induce and self-annihilate rhythmically in perpetuity when uninterrupted. Thomas Young (1801) first demonstrated the wave nature of light which thus can undergo diffraction and interference and can be reflected, scattered, refracted, and absorbed by various media. Light in the visible frequency range is actually not visible to the naked eye. For example most light from the sun emanates into outer space and is not seen. Only light that reaches one's eyes is sensed. This means that anything assumed to be seen is actually a sensed image made by light reflected from the object at an earlier time. Since physical objects in the universe and on earth are always in a state of motion, objects are actually in a different spatial position at the time their light image is sensed. For example it takes 7.5 min for sunlight to reach the earth, so sunrise and sunset actually occurred 7.5 min before these events are actually sensed or "seen".

Photographs of light reflected from a candle prove that light emanates in all three dimensional space even though that light cannot be directly seen (**Figure 6**). The mirror reflects light directly toward the camera for detection from any position, reflecting light that was produced by the candle on the right while the light that exists on the left is invisible. The light on the left is made visible upon reflection by the mirror relocated on the left, while the original light that still exists on the right remains invisible.

Similarly, because light from sources such as stars propagates in all dimensional space even though it cannot be seen, distances to stars can be directly and conclusively determined by parallax. A star is at a particular time of night from an earth location positioned among background stars in shifted locations depending on the location of earth in its orbit. At summertime, the earth shown on the right in **Figure 7** detects light emanated from a star, while light from that star of course exists on the left but is invisible, being not reflected to the eye. In the winter when the earth is positioned on the left, the light is detected from the star while light on the right still exists but remains invisible. From the shifted relative position of the star between summer and winter, the distance to that star can be properly computed

#### **Figure 6.**

*Light from a source propagates in all directions in space but is invisible. It is sensed by either directly entering the eye (as seen here directly from the candle) or after reflecting the invisible light from the candle to the eye.*

**Figure 7.** *Earth view of star in relation to distant background stars at summer and winter.*

by triangulation. For example the secant of the elevation angle is **r**/(1 AU) where **r** is the distance from the earth to the star and 1 AU is 93 million miles. The picture is distorted intentionally for clarity, where the nearest star to the sun is the Alpha Centauri group at 4.37 light years away (25.6 trillion miles or 266,000 AUs) so that its elevation angle is actually greater than 89.9°. The farthest stars capable of being triangulated with modern space telescopes have a parallax angle so close to 0° that the distance is over 6000 light years. This means the these stars, where light is now arriving here on earth from them, must be at least as old as 6000 years and are at a distance of about 35 quadrillion miles from earth [(6000 years) (365 days/year) (24 h/day) (3600 s/h) (186,000 miles/s)].

Newton first proved in 1665 at Woolsthorpe Manor in England that light beams are actually composed of individual units he called corpuscles which we now call photons. Light has no mass since each photon must propagate in a given medium at a fixed speed c = E/B determined by properties of that medium. Photons speed up upon entering a more favorable medium and slow and retain that lesser fixed speed c in a less favorable medium. Photons follow one another in succession along a fixed bearing in cases where the light source is either stationary (which does not exist in nature since all galaxies rotate, and perhaps undergo translational motion and may vibrate with respect to each other over time, etc.) or moving in the direction photons propagate. Most light from either natural or artificial sources is actually composed of photons that are traveling in directions determined by the lateral motion of its source. This is because the first photon is emitted when the source is at location (x, y, z) but the next photon is produced when the source is at a slightly shifted location due to star or galactic motion. A laser light beam directed to a target while the source and target are in lateral motion consists of photons that traveled different paths to arrive at the

**51**

**Figure 9.**

*Clarifying Special Relativity*

**Figure 8.**

*(= 0.25 m/500 × 10<sup>−</sup><sup>9</sup>*

*DOI: http://dx.doi.org/10.5772/intechopen.86401*

*A light ray made visible in a steam cloud. Over the distance of 0.25 m there are approximately 500,000 photons* 

*orbiting earth is small compared to light, each photon travels one after another forming a light ray where the paths of each successive photon essentially overlap. If the light source moved at near light speeds, the linear ray would be composed of photons having the same bearing but from shifted locations in space, where the photon arriving at the target on the right traveled the longest distance to arrive there, having left the source when at an earlier position. The photon on the left was produced last from the position where the source is now located. This is essential to understand why lateral moving light clocks do not prove that time dilates, but rather that* 

*Light produced by a lateral moving source actually forms a ray consisting of photons having slightly different travel path histories. Each photon departs from the moving source at different spatial coordinates. The photon shown arriving at the target actually left the source when it was at the leftward position. Photons produced from the source when the original photon arrives at the target are produced from the source in its pictured* 

*location and will arrive at the target when at its future shifted location further rightward.*

*travel distances for light depend on the relative motion of the source and target.*

 *m per wavelength) that illuminate the field in about 0.9 ns. Because the speed of the* 

#### **Figure 8.**

*Progress in Relativity*

by triangulation. For example the secant of the elevation angle is **r**/(1 AU) where **r** is the distance from the earth to the star and 1 AU is 93 million miles. The picture is distorted intentionally for clarity, where the nearest star to the sun is the Alpha Centauri group at 4.37 light years away (25.6 trillion miles or 266,000 AUs) so that its elevation angle is actually greater than 89.9°. The farthest stars capable of being triangulated with modern space telescopes have a parallax angle so close to 0° that the distance is over 6000 light years. This means the these stars, where light is now arriving here on earth from them, must be at least as old as 6000 years and are at a distance of about 35 quadrillion miles from earth [(6000 years) (365 days/year)

*Earth view of star in relation to distant background stars at summer and winter.*

Newton first proved in 1665 at Woolsthorpe Manor in England that light beams are actually composed of individual units he called corpuscles which we now call photons. Light has no mass since each photon must propagate in a given medium at a fixed speed c = E/B determined by properties of that medium. Photons speed up upon entering a more favorable medium and slow and retain that lesser fixed speed c in a less favorable medium. Photons follow one another in succession along a fixed bearing in cases where the light source is either stationary (which does not exist in nature since all galaxies rotate, and perhaps undergo translational motion and may vibrate with respect to each other over time, etc.) or moving in the direction photons propagate. Most light from either natural or artificial sources is actually composed of photons that are traveling in directions determined by the lateral motion of its source. This is because the first photon is emitted when the source is at location (x, y, z) but the next photon is produced when the source is at a slightly shifted location due to star or galactic motion. A laser light beam directed to a target while the source and target are in lateral motion consists of photons that traveled different paths to arrive at the

(24 h/day) (3600 s/h) (186,000 miles/s)].

**50**

**Figure 7.**

*A light ray made visible in a steam cloud. Over the distance of 0.25 m there are approximately 500,000 photons (= 0.25 m/500 × 10<sup>−</sup><sup>9</sup> m per wavelength) that illuminate the field in about 0.9 ns. Because the speed of the orbiting earth is small compared to light, each photon travels one after another forming a light ray where the paths of each successive photon essentially overlap. If the light source moved at near light speeds, the linear ray would be composed of photons having the same bearing but from shifted locations in space, where the photon arriving at the target on the right traveled the longest distance to arrive there, having left the source when at an earlier position. The photon on the left was produced last from the position where the source is now located. This is essential to understand why lateral moving light clocks do not prove that time dilates, but rather that travel distances for light depend on the relative motion of the source and target.*

#### **Figure 9.**

*Light produced by a lateral moving source actually forms a ray consisting of photons having slightly different travel path histories. Each photon departs from the moving source at different spatial coordinates. The photon shown arriving at the target actually left the source when it was at the leftward position. Photons produced from the source when the original photon arrives at the target are produced from the source in its pictured location and will arrive at the target when at its future shifted location further rightward.*

shifted target because each photon departs from a different location during the lateral motion of the source [3]. A ray in a steam cloud (**Figure 8**) made continuously visible by reflection to an observer appears to have traveled in a direct, follow-the-leader path by an observer moving along with the source and target. A theoretic observer at some fixed coordinate could notice the actual travel path the photons all followed along linear but shifted diagonals if the source were moving laterally (if light could be made visible). Like an airplane that points at an angle skewed from a runway when a lateral wind is present, light photons would point toward a bearing other than the direction the ray follows. But since earth and planetary speeds are miniscule compared to that for light, this effect would not be observable but could be computed. Although Physics texts commonly claim that the illusion sensed by the moving observer means that time dilates for him, it is simply that a longer time is required for light to reach a shifting target, because the actual path traveled is determined by the photons, not the observer. Here each photon travels slightly further than 0.25 m because each leaves the source at propagation direction speed c from different coordinates, while forming a ray having a component velocity less than c [3]. The fact that photons in a linear ray would have distinct travel path histories if the source were moving laterally at near light speed (which is of course not actually possible for sources with mass) is diagrammed in **Figure 9**.

## **10. Intrinsic and relative velocity**

From the photographs of the moon it is clear that the earth rotates on its axis 10° every 20 min. Since the earth latitude radius is 6372 km (3960 mi) in Southern California, then the tangential velocity of the observer due to earth rotation is **v** = **r**ω = 1036 mi/h. However the relative motion between the moon and earth do not detect the additional velocity of the earth and moon system that co-orbits with the sun around their common barycenter near the edge of the sun, at 30 km/s. Further, the rotation of the Milky Way galaxy must add to the total velocity of the observer, and it is very possible that the entire universe of matter exhibits a translational velocity while drifting through space although this is not known for certain. Therefore the actual velocity of the observer with respect to some stationary point from which it travels is far different than the particular velocity due to earth's rotation alone. In most cases the total velocity of objects with mass are not actually known with certainty. However, as is evident from the above discussion, for light which has an intrinsic speed in its propagation direction of constant c in a given medium, since physical motions of its source cannot alter light speed c, this means that light velocity with respect to its spatial point of origin is fixed and known. This is the intrinsic speed of light c. The intrinsic velocity of light however is relative to the direction in which it is desired to be used, where component intrinsic velocities of light have magnitudes that are less than c.

Moreover, relative speed and velocity are different from c for light when detectors (not sources) move toward or away from the light front. Otis first reported that detectors moving toward light in its propagation direction detect a higher frequency of light, while the source does not change the wavelength of the light produced and the intrinsic speed of light remains c [6]. Thus from velocity (in the propagation direction) c' = fλ, a higher (or lower) frequency causes a higher (c' = c + **v**) (or lower, c' = c − **v**) relative velocity c' between the detector and light front due to the velocity **v** of the source. The simplistic notion that light speed cannot be exceeded also needs to be clarified. Two light beams traveling in opposite directions illuminate space at speed 2c, while each beam propagates at fried intrinsic speed c,

**53**

*Clarifying Special Relativity*

greater than c [7, 9].

**Figure 10.**

**11. Conclusion**

and for light that allows us to see.

**Acknowledgements**

*DOI: http://dx.doi.org/10.5772/intechopen.86401*

as shown by experiment earlier [2]. Further, evidence has been presented that changing gravity magnitude may be sensed between two distant masses at a speed

*Palomar Community College Library Learning Resource Center, San Marcos, CA.*

The new Palomar Community College library pictured in **Figure 10** is about 300 feet long situated East–West. The time required for light to travel from one end to the other if the earth were stationary would be about 0.3 ms. Since the earth travels this Eastward direction at 65,000 miles/h at midnight, the time required to reach the other end is longer by 0.03 ns because the library retreats from the light 9.2 mm Eastward while light traverses the building. Because the earth also rotates on its own axis, the time required would be 0.03 ns less at noon when the earth orbits Westward, like a twirling figure skater who also orbits a rink. Moreover, rotation of the galaxy plus any translational motion of the universe of matter would also alter the actual time. These effects seem small but nevertheless emphasize that all matter in the universe is in constant motion with variable velocity components, while massless light is fixed at propagation speed c from a stationary coordinate from which it departs. A ray travels speed c across the library but has a vertical component of velocity **vy** = 0. A ray shined upward would travel up at speed c with a horizontal component of velocity **vx** = 0, where light velocity, but not speed in its travel direction, varies from −c to 0 to

To avoid misunderstanding or false conclusions, relativity must be considered for most questions asked in Physics. Christians are to be grateful for Creation, and gratitude is expressed here for gravity which keeps us from drifting into deep space,

The author thanks the students at Palomar for discussions and all scientists who have done so much work in aiding our understanding of the physical world. The

+c depending on the direction of interest used in a problem.

*Progress in Relativity*

shifted target because each photon departs from a different location during the lateral motion of the source [3]. A ray in a steam cloud (**Figure 8**) made continuously visible by reflection to an observer appears to have traveled in a direct, follow-the-leader path by an observer moving along with the source and target. A theoretic observer at some fixed coordinate could notice the actual travel path the photons all followed along linear but shifted diagonals if the source were moving laterally (if light could be made visible). Like an airplane that points at an angle skewed from a runway when a lateral wind is present, light photons would point toward a bearing other than the direction the ray follows. But since earth and planetary speeds are miniscule compared to that for light, this effect would not be observable but could be computed. Although Physics texts commonly claim that the illusion sensed by the moving observer means that time dilates for him, it is simply that a longer time is required for light to reach a shifting target, because the actual path traveled is determined by the photons, not the observer. Here each photon travels slightly further than 0.25 m because each leaves the source at propagation direction speed c from different coordinates, while forming a ray having a component velocity less than c [3]. The fact that photons in a linear ray would have distinct travel path histories if the source were moving laterally at near light speed (which is of course not actually possible for

From the photographs of the moon it is clear that the earth rotates on its axis 10° every 20 min. Since the earth latitude radius is 6372 km (3960 mi) in Southern California, then the tangential velocity of the observer due to earth rotation is **v** = **r**ω = 1036 mi/h. However the relative motion between the moon and earth do not detect the additional velocity of the earth and moon system that co-orbits with the sun around their common barycenter near the edge of the sun, at 30 km/s. Further, the rotation of the Milky Way galaxy must add to the total velocity of the observer, and it is very possible that the entire universe of matter exhibits a translational velocity while drifting through space although this is not known for certain. Therefore the actual velocity of the observer with respect to some stationary point from which it travels is far different than the particular velocity due to earth's rotation alone. In most cases the total velocity of objects with mass are not actually known with certainty. However, as is evident from the above discussion, for light which has an intrinsic speed in its propagation direction of constant c in a given medium, since physical motions of its source cannot alter light speed c, this means that light velocity with respect to its spatial point of origin is fixed and known. This is the intrinsic speed of light c. The intrinsic velocity of light however is relative to the direction in which it is desired to be used, where component intrinsic velocities

Moreover, relative speed and velocity are different from c for light when detectors (not sources) move toward or away from the light front. Otis first reported that detectors moving toward light in its propagation direction detect a higher frequency of light, while the source does not change the wavelength of the light produced and the intrinsic speed of light remains c [6]. Thus from velocity (in the propagation direction) c' = fλ, a higher (or lower) frequency causes a higher (c' = c + **v**) (or lower, c' = c − **v**) relative velocity c' between the detector and light front due to the velocity **v** of the source. The simplistic notion that light speed cannot be exceeded also needs to be clarified. Two light beams traveling in opposite directions illuminate space at speed 2c, while each beam propagates at fried intrinsic speed c,

sources with mass) is diagrammed in **Figure 9**.

**10. Intrinsic and relative velocity**

of light have magnitudes that are less than c.

**52**

**Figure 10.** *Palomar Community College Library Learning Resource Center, San Marcos, CA.*

as shown by experiment earlier [2]. Further, evidence has been presented that changing gravity magnitude may be sensed between two distant masses at a speed greater than c [7, 9].

The new Palomar Community College library pictured in **Figure 10** is about 300 feet long situated East–West. The time required for light to travel from one end to the other if the earth were stationary would be about 0.3 ms. Since the earth travels this Eastward direction at 65,000 miles/h at midnight, the time required to reach the other end is longer by 0.03 ns because the library retreats from the light 9.2 mm Eastward while light traverses the building. Because the earth also rotates on its own axis, the time required would be 0.03 ns less at noon when the earth orbits Westward, like a twirling figure skater who also orbits a rink. Moreover, rotation of the galaxy plus any translational motion of the universe of matter would also alter the actual time. These effects seem small but nevertheless emphasize that all matter in the universe is in constant motion with variable velocity components, while massless light is fixed at propagation speed c from a stationary coordinate from which it departs. A ray travels speed c across the library but has a vertical component of velocity **vy** = 0. A ray shined upward would travel up at speed c with a horizontal component of velocity **vx** = 0, where light velocity, but not speed in its travel direction, varies from −c to 0 to +c depending on the direction of interest used in a problem.
