All the matter that makes up the human race could fit in a sugar cube
Atoms are 99.9999999999999 per cent empty space. As Tom Stoppard put it: "Make
a fist, and if your fist is as big as the nucleus of an atom, then the atom
is as big as St Paul's, and if it happens to be a hydrogen atom, then it has
a single electron flitting about like a moth in an empty cathedral, now by
the dome, now by the altar."
If you forced all the atoms together, removing the space between them,
crushing them down so the all those vast empty cathedrals were compressed
into the first-sized nuclei, a single teaspoon or sugar cube of the
resulting mass would weigh five billion tons; about ten times the weight of
all the humans who are currently alive.
Incidentally, that is exactly what has happened in a neutron star, the
super-dense mass left over after a certain kind of supernova.
