That's what Einstein's official theory of relativity tells us.
   Special theory of relativity = special relativity = relativistic mechanics - a theory that describes the motion, the laws of mechanics and the space-time relations that determine them, at velocities close to the speed of light. In the framework of the special theory of relativity, Newton's classical mechanics is an approximation of low velocities. The generalization of STR for gravitational fields forms the general theory of relativity - general relativity.
   The deviations in the flow of physical processes, described by the theory of relativity, from the effects predicted by classical mechanics, are called relativistic effects, the rates at which such effects become essential-relativistic velocities.

The postulates of Einstein
   SRT is completely deduced on the physical level of rigor from three postulates (assumptions):
1. The principle of Einstein's relativity is valid - the expansion of Galileo's relativity principle.
   The principle of relativity is a fundamental physical principle, according to which all physical processes in inertial frames of reference flow identically, regardless of whether the system is stationary or it is in a state of uniform and rectilinear motion.
   It follows that all laws of nature are the same in all inertial frames of reference.
   Distinguish between the principle of relativity of Einstein (which is given above) and the principle of relativity of Galileo, which claims the same, but not for all laws of nature, but only for the laws of classical mechanics, implying the applicability of Galileo transformations, leaving open the question of the applicability of the principle of relativity to optics and electrodynamics .
   In modern literature, the principle of relativity in its application to inertial frames of reference (usually in the absence of gravity or neglecting it) usually appears terminologically as Lorentz-covariance (or Lorentz invariance).
2. The speed of light does not depend on the speed of the source in all inertial frames of reference.
3. Space and time are homogeneous, space is isotropic.
   Note. In recent years, great work has been done by astronomers in the study of dark matter. It is established that dark matter is distributed throughout the cosmos. In the global sense, when galaxies move, the trajectories of galaxies do not obey Kepler's laws. This means that Einstein's principle of relativity does not hold. And this, in turn, means that studies of dark matter are not true (and these are studies on very modern equipment and very modern methods). Or Einstein's principle of relativity is not true, and with him the whole theory of relativity (and it was done on very weak equipment and very primitive methods and experiments). In any case, Einstein's dark matter and the theory of relativity mutually exclude each other.
   
Early assumptions of Gukuum theory.
   The hypothesis mentioned by Einstein, and earlier researchers about the jelly-like universe is known. The cosmic vacuum by its properties transmit electromagnetic waves close to the elastic body, to the "elastic jelly". However, Einstein, being in captivity of his own worldview, capturing his senses and the views that existed in his epoch, threw off the hypothesis about the possibility of a jelly-like universe. He considered it impossible that "the planets pass through the air - jelly without encountering resistance" (quote). That is, Einstein could imagine any Vacuum in space, but matter, matter on the atomic level were for him invariably something solid, sharply different from outer space. Empty Cosmos and solid atoms - this is the essence of his Theory of Relativity. This is the essence of all modern physics. We do not suggest anything else to the senses. The theory of Einstein is an extension of our subjective perception of the world around us to the category of Truth. This is as ridiculous as if creatures that perceive the world in black and white would find the world truly black and white. But it's amazing that it's just as ridiculous as if the people perceiving the world were considered colored by color. There is no color, no length, no time in the universe. All this is a comparative means for our perception of reality and tools for orientation in our life, worked out in the process of evolution and in the struggle for existence.
   A lot of modern physicists addressed the model of elastic vacuum. It is enough to include the search engine with the phrase "elastic vacuum". But none of them advanced further than empty exercises with matrices and verbal gymnastics. When the time comes, a survey of these works will certainly be done.
   The universe was arranged quite differently than all the best minds of Mankind had expected until February 2003. And more accurately: one of the hypotheses of the 19th century, which were mentioned at the same time, with all of them rejected and spaded, at first glance hopelessly stupid and ridiculous, was absolutely true. This is a hypothesis, mentioned by Einstein, and even earlier researchers, but immediately rejected by all of them. This is the hypothesis of a jelly-like universe. Einstein, being in captivity of the views existing in his epoch, threw off the hypothesis about the possibility of a jelly-like universe on the move, because it is impossible that "the planets pass through the ether-jelly without encountering resistance." However, now, in the light of new ideas about the possibility of localized stress and strain fields in Guccum, a very plausible hypothesis appears that all the elementary particles that make up "solid bodies" are oscillations of the jelly itself, through which they would have to "wade through". But it will not be difficult for them now. This hypothesis easily describes both elementary particles and ball lightning and a flash zipper. In the same way as electromagnetic waves under the new hypothesis are simply waves of the type of sound in this ether-jelly. If we take into account the gravitational field as a field of elastic stresses in cosmic jelly, then a single, comprehensive theory of all fields and all elementary particles appears. There is no contradiction with the theory of relativity of Einstein here. Because the very notion of a "solid body" is discarded, which lies both in the basis of Einstein's theory, as well as in all the experiments confirming it, and in interpreting the results of these experiments. Because the choice of the coordinate system for description simply changes.

Our suggestions for the experiment.
© Experiment. Project.
    Definition of the Absolute Countdown System.
    Essence of the experiment. In the city of St. Petersburg there is the Isakievsky Cathedral, in which Foucault's pendulum is hanging and without any benefit. (Alas ... This pendulum is now dismantled, but it can be temporarily restored, and there are other pendulums in other cities, and can be hung in any high room). Therefore, it is only necessary to come to S.Peterburg and agree with his leadership on the need for some scientific measurements and lightly fence the place so that the public does not interfere. Or, you can find a deep well or a high flight of stairs and hang the pendulum there. For example, in the stairwell of the Lenin Library in Moscow.
     It is necessary to calculate how many oscillations, roughly, the pendulum (an integer) does in 12 hours. This is purely a preparatory action. Let this amount equal N. Then measure with high accuracy the time during which the Foucault pendulum makes N oscillations at that time of the day when the motion vector of the cathedral (due to the rotation of the Earth around the axis) in space coincides with the motion of the Earth in space. Roughly speaking, this is from 6.00 to 6.00 in the morning. To fix very precisely this time, to hundredths (yes even to millionth) fractions of a second. Then measure the time of making the same number of fluctuations N in the daytime, from 6.00 am to 6.00 pm. And compare these times. I do not want to immediately guess what will be more, and what is less, but the difference should be! And to "align" the experiment, you can make a measurement from 00.00 nights to 12.00 a day and from 12.00 to 24.00 at night. Each time, the same number of oscillations N is measured, approximately given by the average for this period of 12 hours.
   Variant: to measure the number of oscillations not in 12 hours, but in one hour, when the linear velocity of the Earth's surface in this place is closest to the linear velocity of the center of the Earth when it rotates in orbit. Various variations of the Foucault pendulum experiment are possible.
   The difference should be and this again (after A.Dovzhenko's experiment) will experimentally disprove the main postulate of the EO of Einstein. We live in an era of spurt of technology and a spurt of reason towards the Truth, towards the true picture of the World. And this picture is expected to be very unconventional and mysterious.

Conclusions.
In principle, replacing the Theory of Relativity with the Theory of the Absolute changes little. All the square roots in the formulas will remain, but they will acquire a different meaning and will appear in a different context. The system of calculating the theory of relativity simply changes, as we have always mentioned. However, you will have to change many texts in textbooks, and this is not cheap. However, the renaming of streets is also not cheap. The truth is important and it is she, the truth, which should form the basis of future physics.
In this case, you must be extremely cautious and again and again to check and double-check, seven times to measure before cutting off the theory of Einstein's Relativity. It is the basis of a huge physics building, here the fates of millions of people in the whole world are intertwined. And it will be necessary to replace this foundation very carefully so as not to destroy the whole building.
Yes, here is another author who offers his method of determining the speed of the solar system. About this here: http://ntpo.com/physics/studies/51.shtml.
And one more sentence of the experiment on testing the theory of relativity: http://www.sciteclibrary.ru/rus/catalog/pages/8703.html.