Complex sentence: The universe is expanding at an accelerated rate, but was originally thought to be slowing down, furthermore the rate at which this is changing gives the overall mass density of the universe which is denoted by the Greek letter omega.
Split into simpler sentences: The universe is expanding at an accelerated rate, but was originally thought to be slowing down. Furthermore, the rate at which this is changing gives the overall mass density of the universe which is denoted by the Greek letter omega.