In space-time continuously a process is going on, everywhere and in each direction, of changes in mass, energy, space and time and the ratios between them, causing them to change again etc. Whatever these changes may be and whatever proportions these variables may bear to one another, the result must always be the same, C. This is an inescapable property of the world to which the four variable dimensions are fully subjected. The values of each variable cannot be 0 or infinite, because that is incompatible with C (post 6).
Any event, originating in a particular point at a particular moment, will unfold histories from that point and that moment on into each and every direction. Moreover events will develop faster into directions where the course of time is relative fast and slower into directions where the course of time is relative slow. Therefore histories of events in space-time are predictable to a certain extent (post 3). Furthermore the earlier mentioned four variable dimensions mass, energy, space and time are not independent, because any change of one dimension produces changes in the other dimensions etc., under the constraint of C.
As soon as there is some energy (= mass) anywhere, there is some time and consequently some space. If gravitation increases, time runs slower. If gravitation decreases, time runs faster. So one can say that time varies between zero (very short) and infinite (very long). Not 0 or infinite, because that is incompatible with C. Therefore some energy (= mass) or some fluctuation/information must exist anywhere at all times. This means that gravitation is an inescapable property of the world.
How can we measure and determine the speed of C? In fact we cannot unless there is some time. For instance we can measure the speed of light because it has some energy (= mass) or information and therefore some time (close to zero). By measuring the speed of light we find c for C. In doing that we must take into account that gravitation continuously changes the speed of light (post 12).
The above means that it is impossible to measure time/distance relations with absolute certainty. This intrinsic uncertainty of time is an inescapable property of the world. Both neutrinos and photons are subject to gravitation and cannot therefore escape from its influence. By the same token it is not surprising that the fine structure constant (alpha)does not appear to be constant after all.
Apart from the principle of uncertainty of time, there are many observations which show that all kinds of radiation share the same speed in vacuum under the ceteris paribus proviso.