Principle of Universality and Invariance of time:

Time relative to speed

1.- Universal movement (with its extension and measurement parameter, time) is a physical element that manifests itself in each and every one of the places in space:
Nothing is completely stopped, everything moves.
Therefore, there is no universal frame of reference that can serve as an ideal frame of reference for others:
"All the elements or frames of reference move between them, and only their relative movement and relative speed between them is applicable, appreciable and measurable"

2.- Therefore, if two elements, objects or frames of reference move between them, the relative speed of one with the other will be the same: The relative speed of A with respect to B, is equal to the relative speed of B with respect to A.

3.- As the relative speed between two reference frames that move (closer or further away) from each other is equal (the same), so will the increases in this relative speed. iA = iB.

4.- Which shows us that the time and its increments is always the same, and does not vary with speed.
** Therefore, all the observations that are made and produce a different result will be a distortion of the observation (eg due to the speed of the information received) and not a change in the value of time.

Next, we are going to reference a test, which we can put into practice, to measure the speed of light, as well as the distance between the earth and the moon at any time, and at the same time that it helps us to understand and measure the invariance of time in the different frames of reference of the Cosmos.
For this, it is proposed to carry and establish a fixed mirror on the moon with which we can make measurements by sending and returning light sources, laser beams, etc.
On earth we can mount a good light or laser focus, with a detector that captures the photons that are returned to us by the lunar mirror.
* In order to theorize a bit with relativity, we are going to assume that one or all of the photons we emit are "very intelligent" and know how to measure and realize the space they travel, and can even see when they return, the clock inserted in the device emission laser. (as if the photons were astronauts of a rocket that comes and goes)

1.-

The first thing we consider is that with our emission and return devices, we can measure exactly the volicity of the light, which is supposed to be C.
We can also measure the round trip time which is 2.6 seconds.

2 .-

3.-

In relation to the "intelligent photon": This will have checked and seen its journey from the earth to the moon and back.
He has also been able to verify in the terrestrial clock of the device, that the time has been 2.6 s.

4.-

Sure, a relativist could pull a rabbit out of his hat and say that: "No, the intelligent photon has a hidden miniature clock that tells the passed time is 0."
But it cannot be, since if he has a hidden clock that reads 0 time, then for him the speed at which he has been circulating is infinite: earth-moon distance / 0 = infinity.
And of course, that is not possible because Relativity itself says that the speed of light is a constant for every frame of reference, including for the "intelligent photon".
Therefore, and with this test, which can be practical if we build the requested devices, the principle of invariance of time is established and postulated, as well as the following Principle of Equivalence between the constant speed of light C, and the invariant cosmic time T :
"If we establish that the speed of light C is constant and invariant for any reference frame and place in the cosmos, with this we will also have established that the time T is also constant and invariant for all those reference frames, since said time T is the one who measures and determines C."

Times relative to gravity

As we have said, time precedes and promotes gravity and not the other way around.
It is true that all clocks (some more and others less) can be affected by physical variables, such as gravity, temperature, acceleration, atmospheric pressure, etc., but it is not the time that is affected or changes, but rather the clock mechanism. Watch is the one that is affected and changes.