Minkowski defined a spacetime interval thus:
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Which explicitly references a proportion for the temporal or tensor component:
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And implicit in the idea for inclusion of this time component of Minkowski's spacetime interval is this:
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You will notice that delta t appearing inthe denominator of this last expression for the TEMPORAL nature of speed of light may be made as small as you like; vanishingly small, in fact. And when you have done this, you have divided by zero. And what you have also done when that happens is to trash the component of this expression which is responsible for holding the most important principle of physics; the conservation of energy.
The conservation of energy normally would simply fall out of the ideas that:
the bound energy that is a particle or collection of subatomic parts of matter or antimatter persists in TIME, from INSTANT to INSTANT, because or something faster than light propagates, i.e. entanglement, and
the unbound energy that is an ENTANGLED photon propagating in free space at c persists in TIME, from INSTANT to INSTANT because it was produced by means of accelerating particles possessing both electric charge and ENTANGLEMENT.
Persistence in time for energy IS the conservation of energy, and we have demonstrated an aspect of this that lies outside of the framework provided by Special Relativity. Entanglement is FTL, and is responsible for the conservation of both forms of energy commemorated in Einstein's most famous relation, E=mc^2. It is not possible for it to exist within the framework of the invariant speed of light, NOR ANY VELOCITY, invariant or otherwise, set to be proportional to time itself, or an instant of time.
Entanglement does not trash conservation of energy even though it is instantaneous, because no net bulk bound or unbound energy is actually transferred by means of an entanglement spin flip.