The Properties of Space
In the study of communications and broadcast antennas, physical dimensions are all important. This is due to the velocity of electromagnetic radiation (including light) through space. Knowing this velocity and a particular radio frequency, dimensions and spacings of antenna elements can be calculated and performance predicted for a specific antenna design.
The velocity of electromagnetic radiation (EMrad for short) has been accurately measured to be about 299.7 megameters per second in a vacuum (such as outer space). This can be to rounded off to 300 megameters per second for most applications. This value is accepted without question by most and is used frequently by anyone with a serious interest in antenna technology. However, one seldom questions or hears what determines this velocity.
Why Not Some Other Speed?
Why is it this particular velocity? Why is it not faster or slower than 299.7 megameters per second? Does it ever change? Under what conditions would it change? Has it ever changed in value with time during the life of the universe? Does it travel at the same velocity throughout the far reaches of the universe? All space, inner and outer, has two characteristics that determine this velocity, which is so important in electronic communications and life itself.
In his book, “Electromagnetics”, Dr. John D. Kraus, W8JK, describes and defines these characteristics, their values and how they determine the velocity of light (and all EMrad). This book and Dr. Kraus’ book “Antennas” will be the principal references for this article.
Inductance and Capacitance
In the study of electricity and electronics, one learns about inductance, the storage of energy in a magnetic field, and capacitance, the storage of energy in an electric field. In each case, this energy may be concentrated in fields within, near or surrounding electrical conductors or other bodies. However, it is also found in fields which are great distances from any object.
Any electrical conductor of finite dimensions has inductance. However, inductance is a function not of the conductor itself, but of the medium surrounding it. Increasing the length of a wire can increase the value of its inductance, but the inductance itself is a function of the medium near and surrounding the wire. A vacuum (such as outer space) is an energy storage medium and as such has a property called permeability which describes the storage of energy in a magnetic field. The permeability of a vacuum has been determined to be

Within a medium other than a vacuum, the permeability may be from slightly to vastly different depending on the characteristics of the medium. In some cases, there may be no difference at all. As an example, ferrous materials near or surrounding a wire can cause a great increase in its value of inductance. Winding a wire around material of high permeability can multiply this effect even more and is a technique frequently used by the electric power and electronics industries in many applications (examples: transformers, motors, relays, inductors, etc.). Other materials such as water and plastics have relative permeability values near or equal to that of a vacuum so have the same effect as a vacuum on the inductance of a length of wire. Remember that it is the medium surrounding or near to the wire rather the wire itself that determines the inductance.
You may have noticed the term “relative permeability” in the preceding paragraph. The value of permeability for a vacuum is used as the reference, so most materials have been assigned values of permeability that are relative to the permeability of a vacuum which is defined as one (1.0).
Capacitance is also the function of a medium. All space (including that within apparently solid materials) has another property called permittivity which describes its ability to store energy in an electric field. The permittivity of a vacuum has been determined to be:

The now obsolete term for permittivity is dielectric constant (K). This term is still sometimes used in textbooks to describe how permittivity affects capacitors used in electrical and electronic applications. When material of high relative permittivity (dielectric constant) is placed between the plates of a capacitor, the capacitor’s value of capacitance (energy storage capacity) increases greatly from that of air or a vacuum.
As an example of how velocity is affected, the velocity of an EM wave within a coaxial cable is determined by the relative permittivity of the dielectric between the inner and the outer conductors of the cable. Normally, its speed is slowed because of the increased value of permittivity of the dielectric.
As in permeability, the permittivity of a vacuum is used as the reference and is also assigned the value of one (1.0).
Relative Values of Permittivity and Permeability
Since both of these values have been determined or measured for a vacuum, all other materials are valued relative to a vacuum. As an example, some glass has a dielectric constant K of 3.78 which means that its relative permittivity is 3.78 times that of a vacuum. This permittivity has two effects:
1. If a sheet of this glass is placed between the metal plates of a capacitor, the capacitance will be increased, and
2. An electromagnetic wave will propagate through the glass slower than it does through a vacuum. (Bear in mind that there are also frequency effects which will be discussed later).
Likewise, certain materials have greater values of permeability which have two similar effects:
1. If a wire is located near material of high permeability or is wound around material of high permeability, the inductance will be increased, and
2. An electromagnetic wave propagating along such a wire will have a decreased velocity relative to that of a straight wire located within a vacuum. This is a principle by which delay lines are designed and manufactured.
Thus, increased permittivity and permeability do more than just increase capacitance and inductance. They can, separately or together, affect the speed of an electromagnetic wave (including light) that is traveling through a medium depending on the combined effect of their relative values within that medium.
The Effect of Combining These Two Factors on the Velocity of EMrad
The combined effect of these two properties permit the propagation of electromagnetic energy through space and their values also determine its velocity. Recall that both are energy storage properties which complement one another.
Again referring to Dr. Kraus’ book, the values of the permeability and permittivity of a vacuum can be combined into a single equation which determines the velocity of all EMrad including light itself.

Where: C=the velocity of EMrad (light) in a vacuum mu (m) = permeability of the medium epsilon (å) = permittivity of the medium
Plugging the two values of permittivity and permeability for a vacuum (above) into this equation will yield the velocity of EMrad (including light) in meters per second through a vacuum (space). The subscript o indicates the velocity within a vacuum. For any medium other than a vacuum, the subscript r is used which means the relative value (relative to the value for a vacuum).
As an example, water has a relative permittivity of about 81 and a relative permeability of about 1. If you plug these values into equation 1 and solve, you will see that EMrad propagates through water at a much decreased velocity, only about one-ninth the velocity of light in space. If water were absolutely pure with no electrolytes in it, a radio wave could travel through it at this diminished speed indefinitely and antennas submersed in it could be reduced in size by a factor of nine! Bear in mind that this is for radio frequencies. At the frequencies of visible light, the permittivity of water is much less causing the velocity to be greater than radio frequencies, but still less than that within a vacuum.
The Impedance of Space
Again referring to “Antennas” by Dr. Kraus in the chapter titled, “The Electric Dipole and Thin Linear Antennas” the intrinsic impedance of free space may be mathematically derived. Its value is approximately 377 ohms and is described as a pure resistance. Several pages of heavy math beyond the scope of this article lead to this value, but in the end the equation is very simple:

Where:

Note that the determinants for the impedance of space are our old friends the permittivity and the permeability of space. Note also that if either of their values change, the impedance of space is changed, also. Extending this to materials which have values other than that of space, their intrinsic impedances can also be calculated if their relative values of permittivity and permeability are known. It must be remembered that materials are mostly space, the atomic particles occupying but a tiny fraction of their volume. Their values of permittivity and permeability are those of the interparticle space, modified by the structure of the material and its particles.
What is the significance of the impedance of space or materials which contain space? Would an antenna designed to have this value as its input impedance perform differently from any other antenna? What could we learn if we should calculate the impedance of common materials such as glass, water and other materials?
The Sacred Cow
For decades, the one factor or measuring stick that scientists have come to cling to is the velocity of light in free space. Often, it is the single constant to which everything else is referred. However, as you can see from the above discussion, it is not cast in stone, but is affected by many factors and materials in various ways. It must be viewed as a variable. Because the universe is mostly empty space (vacuum), most EMrad travels at the seemingly sacred “velocity of light”. This value is included in the most famous equation of all, Einstein’s famous

Where:
E = energy
M – mass
C = the velocity of EMrad (light)
Note that if this velocity (C) changes (due to variations in the permittivity and/or the permeability) everything else (energy and mass) is also affected.
The great pains that have been taken to measure and precisely determine the velocity of light in a vacuum have been done in order to measure a variable rather than an absolute value. It is extremely important to note that this velocity is an absolute value only within the timeframe and spaceframe of the space and time in which we now reside. At a different point in time or within a different frame of space, the values of permeability and permittivity may be different and, if so, will alter the velocity of light and perhaps time itself. Our sacred yardstick now seems to be made of rubber.
The Photon
What is a photon? A dictionary definition states, “A quantum of radiant energy moving with the velocity of light and an energy proportional to its frequency.” In his book, “Antennas”, Dr. Kraus makes several statements about photons:
1. “An antenna interfaces between electrons on conductors and photons in space.”
2. “The antenna, like the eye, is a transformation device converting electromagnetic photons into circuit currents; but, unlike the eye, the antenna can convert energy from a circuit into photons radiated into space. In simplest terms an antenna converts photons to currents or vice versa.”
3. “A photon is the quantum unit of electromagnetic energy equal to hf, where h = Planck’s constant and f = frequency.”
You may be aware that photons have to do with visible light and electrons hopping from one orbit level to another within an atom, but did you realize that each time you transmit or receive a radio signal you are sending or receiving billions of photons by way of your antenna? While we usually think in terms of waves when doing this, the waves themselves are made up of massive numbers of photons.
Each photon is a tiny quantity of electromagnetic energy whose velocity through space is determined by our two factors, permittivity and permeability. If the value of either of these factors changes, then the velocity of the photon also changes.
A New Concept
Theory: Since almost everything within the realm of physics has been quantized, what about the factors permittivity and permeability? Suppose each is composed of tiny individual capacitors and inductors in space having specific values, each capable of storing just one photon, or perhaps a multiple number of photons. As an electromagnetic wave is launched, each photon may be momentarily stored in either a quantum capacitor or a quantum inductor and then passed on to the opposite entity, alternating back and forth between inductor and capacitor.
Each transfer may require a specific quantum of time based on the values of permittivity and permeability of the medium through which it is propagating. Perhaps the values of the individual quantum capacitors and inductors change based on the values of permittivity and permeability within a specific medium. I’ll leave it to someone else to calculate the values of capacitance and inductance needed to store a single photon and their variations with changes in space characteristics.
If the above is correct, then it may lead to some kind of a universal time constant. Analyzing the movement of a single photon, it might travel through space in bucket brigade fashion. First energizing a quantum inductor, then transferring the energy into a quantum capacitor and so on, each transfer of energy requiring a specific amount of time based on the values of the inductors and capacitors within the medium. Don’t forget that these values may vary widely depending on the characteristics of the medium. The path of the photon may not be linear, but may zigzag or oscillate in some other fashion through the maze of the reactive values (or impedance) of the space within which it is travelling.
What values of permittivity and permeability would be necessary to allow a photon to travel in a perfectly straight line? If these values were both zero, then perhaps the photon could travel at infinite velocity and perhaps straight line travel would be realized.
It may be that the photons themselves are not polarized, but the EM waves which are composed of photons may be polarized. A simple analogy is that of ripples in the sand on a beach. While the ripples have distinct shapes and patterns, the grains of sand (photons) are the unpolarized building blocks from which the ripples (polarized waves) are composed. Sunlight is nonpolarized while light that has been reflected from the surface of the moon is. Shadows of polarized light are much sharper while non-polarized light provides diffused shadows due to scattering of the unpolarized photon energy.
Deep Space, Black Holes, etc.
Again, scientists have measured the velocity of light and found its determinants within the environment of our time and space. However, as yet we do not know what determines the values of the permittivity and the permeability of free space. Why does light travel at a velocity of 299.7 megameters per second? It is due to the values of our two properties.
But what determines their values? We don’t really know. It may be related to the density and structure of the mass of the universe. As the universe expands, do the values change? What about some 10 billion light years from here? Dr. Kraus once told me that we assume that the velocity of light across the vast distance is the same, but is this truly the case?
As the light (photons) that we see from a distant star was launched, what was its velocity in the beginning compared to now? Time itself may be affected which would make this determination difficult. However, the important question is: What were the values of our two properties way back then? Were they greater or smaller than they are now and were they in the same ratio to each other as they are now? Is this ratio important? It varies greatly within common materials here on earth.
In a black hole, the material is extremely dense. We learn that if mass or radiation (including light) enters the event horizon of the hole, it accelerates to superluminal velocity and is never seen again. However, what are the values of our two properties within the black hole? Since they are greatly modified in almost all materials here on earth, would they not change by massively greater amounts within the super density of a black hole? It is likely that all or most radiation would be converted into heat energy upon entering the hole, but if this were not the case, wouldn’t the velocity of light be slowed to a crawl relative to that of free space? If the permittivity and permeability greatly increase in value, the velocity of light may decrease greatly as well.
A Challenge
How can we determine the permittivity and the permeability of space and all materials? These two properties carry all light, radio signals and EMrad apparently in a kind of bucket brigade manner and determine their velocities as well. If density determines (or is a factor in determining) the values of our two properties, then as the universe expands, their values may change.
Scientists have measured the temperature of space and concluded that it is still cooling from the big bang. This temperature is now down to less than 3 Kelvins, but the heat energy, being in the form of EMrad, is propagated through space based on the values of the permittivity and the permeability. Since these values change with frequency, the structure of matter (atomic and molecular) may also have effects. Remember that things that we think are solid are still mostly empty space. The fields generated by the tiny particles whizzing around inside materials may very likely affect our two properties.
For all the knowledge that has been accumulated by mankind, we still apparently don’t know what causes the variations in the materials that we use daily. Scientists have measured the values of permittivity and permeability in many materials. In most cases, they have greater values than does a vacuum but we don’t know why.
All electromagnetic waves including radio, X-rays and light itself depend on these properties for their propagation. It might help if we had a better understanding of them and their causes.
Originally posted on the AntennaX Online Magazine by Ron Nott, K5YNR
Last Updated : 16th May 2024