It has been theorized that even empty space contains something, mainly virtual particle pairs. From this stems black hole evaporation, zero-point energy, and a host of other theorized events.
Time dilation and relativity stem from the paradox the speed of light is both a maximum and fixed constant, independent of your frame of reference.
This paradox can be illustrated with a simple clock.
Let’s say we have a clock consisting of 3 pieces, two perfect mirrors and a beam of light. It's set up so that the beam of light bounces back and forth between the two mirrors. Thru the wonders of ascii art, the setup would look something like this:
---Mirror---
^
|
|
---Mirror---
Now your job is to measure how fast the light is traveling between the two mirrors and the amount of time it takes the light beam to bounce between the two mirrors.
Case 1: The apparatus is sitting at rest in front of you.
You measure the distance between the two mirrors and the amount of time it takes the beam of light to bounce from one to the next. You come up with the figure of 2.998 *10^8 meters a second, just as you expected.
Case 2: The apparatus whooshes by you.
To you, the observer, the beam of light no long takes a straight path from one mirror to the next, instead it travels at an diagonal as it bounces between the mirrors like so:
---Mirror---
^
/
/
---Mirror---
You recalculate the distance between the mirrors accounting for the new path the light is traveling and recalculate the speed. To your surprise, light is still traveling a 2.998*10^8 meters a second, but the kicker here is that the amount of time it takes for the beam of light to travel between the two mirrors is longer than in the first case. This is due to this longer path.
The observer just experienced time dilation! To him, the time required for the beam of light to bounce lengthened even though we did nothing more than change his reference point.