My understanding of time, gravity and speed of light:
Earth revolves around the Sun. Sun revolves around Milky Way centre. Milky Way also keeps moving. All these movements are caused by gravity. Thus, all that what is formed by fermions (particles causing mass) has been affected by gravity...
As I understand "Dark Matter" is an _assumption_ of existence of matter in certain space, to explain gravitational effects on the matter around that space. But when it comes to "Dark Energy" it is another assumption to explain why universe is expanding.
But by Einstein's theory, mass and energy...