As an example of an area with stronger gravitation – this is the time-spatial area “near the surface of Jupiter”, where the force of gravitation is about 318 times stronger than that in the area “near the surface of the Earth”.
In different areas of the Universe, the level of contraction/expansion of the space-time is different, depending on the strength of the gravitational field. As already mentioned, the electromagnetic field and the gravitational field exist on the distorted by the matter space in the Universe. Therefore, it is logical that in the warped space by the strong gravitational field (high “space density”) – electromagnetic waves will propagate more difficult. It means that in a stronger gravitational field, the electromagnetic waves will vibrate more difficult (the frequency ν of their oscillations will decrease), and that the wavelength of the electromagnetic radiation λ will also decrease ‒ will be smaller compared in the areas with weaker gravity. This logical conclusion coincides with the idea of the general theory of relativity (as well as with the following three consequences):
The first consequence is that in areas with a strong gravitational field, the time there goes/ passes slower (which coincides with the idea of the general theory of relativity). Indeed, the so defined “second” (the base unit of time in the International System of Units), will be longer, because the duration of exactly the same number of “time periods” Ns_s of the same standard electromagnetic radiation, we have chosen, will be longer because its frequency v will be lower.
If the reader logically analyses this case, they will see that the lower frequency can be detected only, if the used unit of time was defined in another area with different (weaker) gravitation. Otherwise, if we use the unit of time, defined in the same area, there is no way to obtain other numerical value as a result of measurement of the frequency. This is because of the so-called “circular reference”: In the case, if we use the new changed unit of time (defined as a duration of the same number of oscillations Ns_s of the decreased “standard” frequency), then the result obtained from the measurement of the frequency of the same electromagnetic radiation will have the same numerical value. Moreover, this is true for any frequency of the whole electromagnetic spectrum! The awareness that we cannot detect the change, using the changing unit of measure (in synchrony), is an important part of understanding the uncertainty in the macro-world.
The second consequence is that in areas with a strong gravitational field, the defined in the same way base unit of length “meter” (according to the way it is defined in the International system of units), will become shorter (as a sum of the lengths of exactly the same number Nm_s) of actually decreased wavelength λ (suppressed by the gravitation) of the same “standard electromagnetic radiation” we have chosen. Again, it should be noted that the reduction of the wavelength of any electromagnetic radiation from the whole electromagnetic spectrum, could be detected only if we use the base unit of length defined in an area, where the gravitation is different (weaker).
The third consequence is more than obvious. It is that in areas with a strong gravitational field, the actual speed of electromagnetic radiation in vacuum will be lower because ν and λ of any electromagnetic radiation are lower (c=λν). It turns out that the lower speed of light in areas with stronger gravity is a consequence of general relativity, i.e. that the speed of light is not a fundamental constant for the whole Universe! The new lower speed of the electromagnetic radiation in vacuum will be valid again for the whole electromagnetic spectrum – it will be again a local physical constant in this time-spatial area with the same, but stronger gravitation. Moreover, we have to emphasize again that:
If we measure the speed of light in vacuum by means of the base units of time and length, which are defined in the same area and in the same way, (for example, by fixing the same numbers Ns_s and Nm_s) – we will obtain again exactly the same numerical value for the speed of light! This is because we have used the changed units of measurement in this area with stronger gravitation – (the longer “second” and the shorter “meter”) … what is an example of a “circular reference”!
The experimental evidence:
The fact that the speed of light in vacuum decreases when photons pass through areas with a strong gravitational field is not only a logical result – it was also proven experimentally. American astrophysicist Irwin I. Shapiro proposed an experiment and performed it in 1964. Gravitational time delay effect was detected when measuring the round-trip travel time of the bounced radar beams off the surface of Venus when Venus is on the opposite side of the Sun while the Earth orbits around it (when the Earth, Sun, and Venus are most favorably aligned). In this way, the radar signals pass through the strong gravitational field (in close proximity to the Sun). Of course, it can be assumed that the radar signals have traveled on a longer trajectory, bypassing the Sun in the distorted space. However, the space near the Sun is suppressed (contracted) by the strong gravitation. It means that if we use the longer unit of length “meter” defined on the Earth’s surface – the resulting number as a result of the measurement of the path length of the radar signal will be less. In this way, however, we can go to uncertainty… The real fact is actually, that the time, but not the path had been measured in the experiment! Thus, lower speed of radar signals was fixed, when they pass through an area with a strong gravitational field. Dr. Irwin I. Shapiro (Massachusetts Institute of Technology, Lincoln Laboratory), reported in 1964 in the Journal of Astrophysics:
“…according to the general theory, the speed of a light wave depends on the strength of the gravitational potential along its path.” (Shapiro, 1964).
Perhaps, Dr. Shapiro had in mind the change of the speed of light, in particular, the idea that Einstein discussed in his article from 1911, “On the Influence of Gravitation on the Propagation of Light”. In this article, Einstein asserts:
“If we call the speed of light at the origin of co-ordinates c0, then the speed of light c at a place with the gravitation potential Ф will be given by the relation:
The principle of the constancy of the speed of light holds good according to this theory in a different form from the one that usually underlies the ordinary theory of relativity.” (Einstein, 1911).
First, Einstein did not mention anything in this article about the used measurement units. Obviously, in all equations of his theories, he uses the measurement units defined on the Earth’s surface, as though if they are the same and valid for the whole Universe (… and he himself comes to the conclusion that they are not the same). In the article Einstein points out that the frequencies (and the frequency defining the base unit of time “second”), change depending on the gravitational potential:
Therefore, the base unit of time “second” also changes in places with different gravitation potential (with different intensity of the gravitational field), because the duration of the same number 9,192,631,770 time-periods will change (see the definition of the “second” in SI).
Second, we know that the gravitational potential in a given location (in relation to a body with a mass M) is equal to the work (energy transferred) per unit mass that would be done by the force of gravitation, if the unit mass was moved from this location in space to the “zero” reference location. (The “zero” reference location is infinitely far away from the mass – where the gravitational potential is equal to zero). Thus, the gravitational potential Φ is always negative at any finite distance from M and is minimum (maximum negative) on the surface of the body (for example on the surface of the Sun). Therefore, according to the given by Einstein formula (27), if the speed of light in vacuum infinitely far away from the mass M is c0, then, the speed of light in vacuum on the surface of the celestial body will be minimal, because the gravitational potential Φ is minimum (maximum negative). Therefore, the speed of light in vacuum (27) and the frequency of any electromagnetic radiation (28) are lowest on the surface of the celestial body, where the gravitational potential is minimal and the gravitation is the strongest. However, incomprehensible why, this is inconsistent (in contradiction) with the interpretation of the “gravitational redshift” according to the contemporary physics of nowadays (see more details in subsection 19.4 of the book).