In science, light speed is absolute and not relative; and that represents a serious problem; to this day physicists did not provide any explanation regarding the obvious contradiction that exist between ABSOLUTE speed of light and motion RELATIVITY.
Let's face it, science is shunning light's very MOTION absolute REALITY.
Per definition MOTION is RELATIVE to an observer
Consider the MOTION of a car for instance, RELATIVE to you an observer on Earth; that MOTION is furthermore RELATIVE to Earth's motion on which you are resting; and Earth's motion is relative to the Sun's around which it is revolving; and through our Milky Way galaxy the motion of that car ends up being RELATIVE to the Universe, which in science is expanding.
Even though the theory of RELATIVITY has been proven true over and over, the position of the observer on which the theory is relying is always in motion apparently defeating RELATIVITY's fundamental concept.
Making RELATIVITY fit REALITY
In gravimotion interpretation of Nature, the ultimate reference for motion RELATIVITY is the absolute speed of light (electromagnetic waves), which speed is well defined no matter the LIGHT direction and energy (that is no matter the light frequency or color).
The MOTION of the car that you are observing is, in gravimotion interpretation of Nature, physically RELATIVE to the absolute MOTION of light. With this new definition the RELATIVE motion of matter is limited to the 2 unreachable speeds that are light's MOTION and zero MOTION.
A material body cannot reach light's MOTION because of its physical constitution (as described later), and it cannot reach zero MOTION because in gravimotion interpretation "zero" does not exist.
In this gravimotion interpretation of Nature you and I are living in a dynamic world, in which MOTION RELATIVITY is occurring just as MOTION REALITY is; MOTION RELATIVITY that is the observation of motion is mandating MOTION REALITY.