Red, theory; black, fact.
The arrow of time is thought to be thermodynamic in origin, namely the direction in which entropy (disorder of an isolated system) increases. Entropy is one of the two main extensive variables of thermodynamics, the other being volume. I would like to propose that since we live in an expanding universe, the direction of cosmological volume increase makes sense as a second arrow of time; it's just not our arrow of time.
One of the outstanding problems of cosmology is the nature of dark energy, thought to be responsible for the recently discovered acceleration of the Hubble expansion. Another problem is the nature of the inflationary era that occurred just after the Big Bang (BB), introduced to explain why the distribution of matter in the universe is smoother than predicted by the original version of the BB.
Suppose that the entropy of the universe slowly oscillates between a maximal value and a minimal value, like a mass oscillating up and down on the end of a spring, whereas the volume of the universe always smoothly increases. Thus, entropy would trace out a sinusoidal wave when plotted against volume.
If the speed of light is only constant against the entropic clock, then the cosmological acceleration is explainable as an illusion due to the slowing of the entropic increase that occurs when nearing the top of the entropy oscillation, just before it reverses and starts down again. The cosmological volume increase will look faster when measured by a slower clock.
The immensely rapid cosmological expansion imputed to the inflationary era would originate analogously, as an illusion caused by the slowness of the entropy oscillation when it is near the bottom of its cycle, just after having started upward again.
These ideas imply that entropy at the cosmological scale has properties analogous to those of a mass-and-spring system, namely inertia (ability to store energy in movement) and stiffness (ability to store energy in fields). The only place it could get these properties appears to be from the subatomic particles of the universe and their fields. Thus, there has to be a hidden network of relationships among all the particles in the universe to create and maintain this correspondence. Is this the meaning of quantum-mechanical entanglement and quantum-mechanical conservation of information? However, if the universe is closed, properties of the whole universe, such as a long circumnavigation time at the speed of light, could produce the bounce.
These ideas also imply the apocalyptic conclusion that all structures in the present universe will be disassembled in the next half-period of the entropy oscillation. The detailed mechanism of this may be an endothermic, resonant absorption of infrared and microwave photons that have circumnavigated a closed universe and returned to their starting point. Enormous amounts of phase information would have to be preserved in intergalactic space for billions of years to make this happen, and here is where I depend heavily on quantum mechanical results. I have not figured out how to factor in the redshift due to volume expansion.&&