We can compare “the influence of gravitation on the propagation of light in regions with weaker gravitation” and
“the influence of gravitation on the propagation of light in regions with stronger gravitation”.
The main characteristic of our time-spatial region is that the intensity of the gravitational field is practically the same, although the force of gravitation decreases with increasing altitude.
According to classical electromagnetism:
Propagation: In our reference physical system (as well as in any time-spatial region 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 region “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 region with a uniform intensity of the gravitational field.
Energy: Mechanical waves are oscillations of matter (vibration of material particles) around a stationary point in a medium with elastic characteristics. 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 themselves, are not transported in the medium of propagation. Once a push (of energy) is given to it, each material particle vibrates in relation to a stationary point in relation to the medium of propagation (although the medium can move). That is why, in the case of mechanical waves, the Doppler effect is observed if the source or receiver moves in the medium of propagation.
However, electromagnetic waves are completely different. They are waves, in which no material particles are involved. The energy of electromagnetic radiation is tied up with the electric and magnetic fields, which exist on (and in) the space. When propagating in vacuum in regions with a uniform intensity of the gravitational field, the electromagnetic waves do not change their wavelength (λ) and frequency (ν), which means that the electromagnetic quanta (photons) do not change their energy in regions where the gravitational field intensity is the same (uniform). The energy of the electromagnetic wave is associated with the electrical and magnetic fields. In the case of an electromagnetic field in 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 region “in the vicinity of the Earth’s surface”, where the strength of the gravitational field is the same, uniform. Here you can also see the relationship between the energy per unit volume “u” and the “vacuum density” introduced in the book. In other words, we come to the conclusion that :
The “empty space” is energy, and the electromagnetic waves are energy vibrations of the space itself!
From the point of view of quantum theory:
Propagation: As we have mentioned, the electromagnetic quanta (photons) are emitted at the quantum level. They propagate in the stationary space, and move in the space (as opposed to the mechanical waves where the material particles vibrate around a stationary point in the space). They do not change their energy, do not change their frequency (and wavelength) when they propagate in vacuum in a time-spatial region with a uniform intensity of the gravitational field.
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 vacuum.
Speed: The speed of the electromagnetic quanta (energy packets) in vacuum (regardless of their energy), is a local constant (c = λν) in a time-spatial region with a uniform intensity of the gravitational field. The electromagnetic quanta (photons) are emitted at the quantum level, which means that the speed in vacuum of the emitted quantum does not depend on the speed of the source.
Energy: From the point of view of quantum theory, the particles themselves (quanta, photons) are energy (energy packets). The energy (the non-material particles themselves) is spreading in the space. The electromagnetic energy that is transferred in the space by 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 a region with a uniform intensity of the gravitational field, the number of quanta passed per unit volume decreases, but the quanta themselves (photons) do not change their own energy (the frequency ν), wavelength λ and speed c. In regions 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 by modern physics as the Doppler effect, which does not exist at electromagnetic waves).
We know that an electromagnetic quantum is emitted 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, respective to the gravitational field intensity in the region where the atom is located. 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, respective to the specific transitions between the energy levels of the hydrogen atom (hydrogen spectral series). That is why spectral series are important in astronomical spectroscopy for detecting the presence of hydrogen.
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