Pop Quiz - Does a photon have mass?
More like: Does mass bother to involve itself with photons?
Think of mass as an aftereffect of the frame of reference......
Same for gravity. And time.
Ergo the speed of light is finite, and as a wall (constant).... but only in the frame of reference.
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Put the whole question and answer set on backward, and see where the train of thought takes you....
There is research that finds the speed of light to not be constant or as a limit. We have it as a stable data point, yes. (lots of experiments in this area)
And we have dimensional models, where the constants are not the fundamentals that they are ’here’ (so to speak).
And we have the violations, happening all over the place, bits of oddities, here and there...throughout pretty well all branches of science, these anomalies exist. As well as existing in places science is uncomfortable with. Millions of examples. (Reality is not limited by objective models. But science is)
Ie ’dark matter’ may not be anything but a dimensional placeholder, a spacer where the translation into Einsteinian reality is bridged, across a dimensional fulcrum. As dark matter is not following the rules and it’s protrusion or act of being is also causing problems in the current standard model itself.
If one starts going down that road of trying to figure this out, then they might find themselves arriving at Musk’s conclusion of this not being a fundamental reality, that the odds of this place ’we all understand as being reality’ being the ultimate original frame of reference.. the odds of that..are so close to zero that it is not worth bothering with the idea. (billions to one, is the deal. This is what the meta-studies of the 'compleat' extant/emergent science says. Ie, not where we've been, but where we're going, intellectually and in observation of our space)
History, ie, the past, and unidirectional time, and an unknown future...this violates energy conservation laws as an idea and observation, alone. If the universe is symmetrical, energy wise, thermodynamics, and so on, then unidirectional time cannot exist, as unidirectional time inherently indicates an asymmetrical frame. To paraphrase Dire straits, "Two theories say they are Jesus, one of them must be wrong..."
Then it really gets strange, as this above....is the simple stuff. The cheap seats.