According to General Relativity, space and time are aspects / dimensions of a unified whole. If the speed at which wave energy travels through spacetime is constant, $c$, then as distance expands, should not time expand by corresponding amount? If so, then would 1 Plank time from Plank Epoch, be something like ~1 picosecond in today's space-time?
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It’s a meaningless question. Intervals of the cosmological time used in the Friedmann metric don’t change, but intervals of conformal time do. You can use any time coordinate you want in cosmology, and can make coordinate time intervals get longer, shorter, or stay the same relative to proper time intervals as the universe evolves.
Precisely because “space and time are aspects/dimensions of a unified whole”, what is happening to individual coordinate differences such as spatial intervals or temporal intervals has no absolute significance. Only what happens to invariant spacetime intervals matters.
By the way, some energy, such as that of light, travels at the speed of light, but other energy, such as the mass and kinetic energy of an electron, does not and can not.
G. Smith
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