We should perhaps be looking at mass, not volume, since the amount of matter in a cubic foot of space at the center of Jupiter is much greater than the amount of matter in a cubic foot of Mars' dusty surface. In other words, by looking at volume alone, we're losing information about how much matter exists in these volumes, which was the original question.
Okay, so we want to look at this ratio:
r3 / R3 ,
since the (4/3)pi cancel, where r is the radius of the Sun and R the radius of the Oort Cloud from the Sun out to the Oort Cloud's outer edge.
Now, (r/R)3 = (430000 mi/ 20 x 1012 mi)3
= 9.9 x 10-24.
In other words, matter in the Solar System occupies only ten trillion-trillionths as much volume as empty space. Roughly speaking.
Thank you.
I believe the ratio supports my notion that space is essential empty.