atomic collapse

The atoms that make up your body are mostly empty space, so despite there being so many of them, without that space you would compress into a tiny volume. The nucleus that makes up the vast bulk of the matter in an atom is so much smaller than the whole structure that it is comparable to the size of a fly in a cathedral.

If you lost all your empty atomic space, your body would fit into a cube less than 1/500th of a centimetre on each side.

Neutron stars are made up of matter that has undergone exactly this kind of compression. In a single cubic centimetre of neutron star material there are around 100m tons of matter. An entire neutron star, heavier than our sun, occupies a sphere that is roughly the size across of the Isle of Wight.

http://www.guardian.co.uk/science/2013/jan/27/20-human-body-facts-science