It is that distances and times change in order to render the speed of light constant in all frames of reference." Renders the speed of light as conditionally hard fixed and universal as strong force rock diamond and, at once, as conditionally soft and universal as gravity force bubble elasticity. The reflection of their affinity?!
I've written many times of the universe traveler in the mind's eye. My version of Einstein's traveler in the mind's eye. The universe traveler travels horizon to horizon, the horizon ahead always opening up toward the oncoming traveler from infinity's / origin's point of horizon (one of an infinity ahead). And always recoiling space for space and time for time, into the closing point of infinity's / origin's horizon behind. From out of merger ahead, receding into merger behind . . . The multi-facet, multi-dimension, 'Multiverse' analogue and physic: The 'white hole' ("Exit Only Door") event horizon 'evolutionary set' ever ahead of the traveler || The 'black hole' ("Entry Only Door") event horizon 'devolutionary set' ever behind the traveler. The traveler, ever dead point between the two. Why the recoil is always observed to be constantly precisely exact regarding the "relative universe," the "observable universe," the constancy of the speed of light.
Now someone might see the horizons to be precisely the same as the horizons of the sphere of Earth, always coming round to the same point. Never happen! The traveler is always at the same dead center point of a constant of change, horizon of change always observed oncoming from ahead (always observed oncoming within an oncoming light) to horizon of change always observed receding behind (always observed receding away within an oncoming light), white hole event horizon to black hole event horizon! Einstein's observer in rest frame witnesses both procession and recession of universe in the same horizon.
The traveler will never come back round to exactly the same space and time universe. Fractal self-similar frontier universes always evolving from out of a "Horn of Plenty" horizon ahead, yes, duplication of the gone (though remaining existing infinities apart), no (exclusionary principles will apply also to space and time).
The traveler will trade observed light time (((-) (+)) > (t = 0)) for observed light time reversal ((t = 0) < ((+) (-))), more or less precisely, but the traveler's local time onboard clock will always advance a reality of change, not only for itself, but as a local (quantumly entangled) reflection of distant destination points ahead (in reality, (m-e point-bubble) universe cell divisions, infinitely plural) and distant departure points behind (in reality, (m-e point-bubble) universe cell divisions, infinitely plural).
Universe (U), the united in merger 'set' (t = '0') / universes (u), the countlessly divided, offset, 'constituency' (t ='1') inside / outside, the 'set' (t = '0'). The Cosmological Constant is Base'2' primal base, '0' and/or '1' (infinity (origin) = '1', constant). The CC base is ["and/or"]. You could say the 'Schrodinger's cat' third dimension of two . . . or the second dimension of one . . . or maybe even the first dimension of zero?!