Space

A hunk of iron bigger than Mt. Everest compacted almost instantly to the size of a grain of sand.  That's how a recent article in National Geographic Magazine described the collapse of the core of a giant star on the way to becoming a black hole.

Iron seems pretty solid, but if gravity can pull a mountain sized chunk of it into the size of a sand grain, then the mountain of iron is almost entirely space.  Space that is occupied by a tiny amount of matter in a particular energy form called iron.  Of course, when compressed to the size of a grain of sound, which comes also with a temperature of about 100 billion degrees, it isn't iron anymore. It seems, in a simplistic way, that matter expands into space-occupying forms as it cools.

What is space?  Is it a substrate - a medium - or is it just emptiness between things?  I need to do some more reading - I haven't kept up well with physics since I was interested in it as a kid.  One thing that does seem clear is that there is a lot of it.  And, that I am mostly space - compressible, under the right conditions, to something much tinier than a sand grain.  Of course, it wouldn't be me anymore - just some extremely hot and compressed matter.  I'm one of those cool space-occupying forms.