I have studied these problems for many years and have come to the conclusion that not only does the Universe oscillate but so do galaxies, and many other ‘fundamental systems’ such as the protons and electrons in atoms. There are two ‘forces’ in nature, one is ‘that which can move’ (fundamental ingredient of mass) and the other is ‘potential for motion’, (potential energy or a force) when one force is at minimum the other is at maximum. Energy is a word describing the ‘act of moving’.
In other words for ‘energy’ to exist there must be ‘something that can move’ and there must be ‘room’ for it to move. In scientific circles, ‘that which can move’ is called ‘mass’ and the ‘room’ where the mass can move is called ‘space’. The fundamental mass can have different densities in space and the motion of the mass can attain different velocities within that space.
‘That which can move’ within a photon (photon is a dipole oscillation and mass is a monopole oscillation) ‘accelerates’ with a force that it obtains from the ‘activity of its creation’ and propagates at a velocity that the surrounding ‘space/mass density’ allows for. If the ‘space/mass density’ (space-time continuum) is greater in density than the area between the planets in our solar system then the ‘light speed’ can be slower and if the ‘space/mass density is lower than that standard then the ‘speed of light can be higher.
I think that the reason why it has been calculated that the universe is speeding up and expanding at the same time, is that the observations that were used to show such effect were taken from positions that had collapsing galaxies. The stars in such galaxies would be speeding up as they travel closer to that ‘local big crunch’ and eventually a new explosion that will create a new galaxy.
That’s my story anyway. So let the force be with you. If you have a simpler explanation let me know.