The main characteristic of our time-spatial area is that the intensity of the gravitational field is practically the same, although the force of gravitation decreases with increasing the altitude.
According to the classical electromagnetism.
Propagation: In our reference physical system (as well as in any time-spatial area with a uniform intensity of the gravitational field), the wavelength (λ) and frequency (ν) of every electromagnetic radiation of the electromagnetic spectrum do not change at their propagation in the vacuum.
Speed: It means that the speed of the electromagnetic radiation in vacuum (c) is also constant (c = λν). What is more, the speed of the electromagnetic radiation in vacuum in the local area “near the Earth’s surface” is a local constant for any frequency of the electromagnetic spectrum. That is why, this local constant is actually a mutual constant correlation (c = λν) – which is the same for every electromagnetic wave in the whole electromagnetic spectrum in any time-spatial area with uniform intensity of the gravitational field.
Energy: The mechanical waves are oscillations of matter (vibration of material particles) in the stationary space. The energy that the mechanical wave transmits is actually the transmission of vibrations of material particles in the stationary space (from particle to particle), but the material particles itself, are not transported in space. Once a push (energy) is given to it, each material particle vibrates in relation to a stationary point in the stationary space. Therefore, in the case of mechanical waves, the Doppler effect is observed if the source or receiver moves in the stationary space.
However, the electromagnetic waves are completely different. They are waves, in which no material particles are involved. The energy of the electromagnetic radiation is tied up with the electric and magnetic fields, which exist on (and in) the space. When propagating in a vacuum in areas where the gravitational field intensity is the same, the electromagnetic waves do not change their wavelength (λ) and frequency (ν), which means that the electromagnetic quantа (photons) do not change their energy in areas where the gravitational field intensity is the same (uniform). The energy of the electromagnetic wave is connected to the electrical and magnetic fields. In the case of an electromagnetic field in a vacuum, the accumulated electromagnetic energy in the unit volume “empty space” (vacuum) “u” (see formula (26)), is determined by the sum of the energy density of the electric field plus the energy density of the magnetic field:
, where μ0 (permeability of free space) and ε0 (permittivity of free space) are constants in the local time-spatial area “in the vicinity of the Earth’s surface”, where the strength of the gravitational field is uniform. Here you can also see the relationship between the energy per unit volume “u” and the “vacuum density” introduced in the book.
From the point of view of the quantum theory:
Propagation: As we have mentioned, in our local domain “in the vicinity of the Earth’s surface”, the electromagnetic quanta (photons) are emitted at the quantum level. Therefore, their speed in vacuum does not depend on the speed of the source. They do not change their energy (do not change their frequency) when they propagate in a vacuum.
Speed: The speed of the electromagnetic quanta (energy packets) in vacuum is constant (regardless of their energy) in a time-spatial area with a uniform intensity of the gravitational field.
Energy: From the point of view of quantum theory, the particles themselves (quanta, photons) are energy (energy packets). The energy non-material particles themselves are spreading in the space. The electromagnetic energy that is transferred into the space by the electromagnetic radiation represents, on the one hand, the number of quanta (the flow of energy packets) passed through a unit of volume at the speed of light in vacuum. On the other hand, the quanta themselves (the energy packets) have different energy (frequency). At the propagation of electromagnetic waves in an area with the uniform intensity of the gravitational field, the number of quanta passed per unit volume decreases, but the quanta themselves (photons) do not change the own energy (the frequency ν), wavelength λ and speed c. In areas with a uniform intensity of the gravitational field, the quanta can change their energy (frequency) only in a case of energy exchange (collision) with a material body (that change is incorrectly considered to be a Doppler effect).
We know that an electromagnetic quantum is emitting at a transition between two hyperfine energy levels of an atom. (The electromagnetic quantum is often called a photon, although the term “photon” has arisen as a designation of the electromagnetic quantum with energy corresponding to the visible part of the electromagnetic spectrum). Actually, at a transition between two specific hyperfine energy levels of a particular atom, the emitted energy (frequency) of the electromagnetic radiation is fixed – which means that the emitted quantum is with fixed energy and frequency. The energy of each emitted or absorbed quantum of energy by a particular atom is given by the Planck relationship. It is equal to the difference of energy between the participating pair of quantum energy states of the atom (Ephoton = E2 – E1 = ħν), where ν is the frequency, ħ is the Plank’s constant and E is the quantum energy. In other words, the “quantum energy states” of an atom are fixed. This determines exactly the permanent constant differences between the pairs of quantum energy states of the atom, which in turn determines exactly the energy of the emitted (or absorbed) photons. This determines the specific atomic spectral lines for a particular atom. For example, the emission spectrum of the atomic hydrogen is divided into several spectral series, corresponding to the specific transitions between the energy levels of the hydrogen atom (hydrogen spectral series). That is why, the spectral series are important in the astronomical spectroscopy for detecting the presence of hydrogen.