Is matter mostly substance or space?
(Lansing State Journal, May 18, 1994)

All matter is made up of very tiny units called atoms.  How small are atoms?  They are much too small to be seen, even with a microscope.  Generally speaking, atoms have a radius on the order of 1/10^10 meters.  That means that there are many more atoms in your little finger than there are people on the entire planet.

It was once thought that atoms were solid bits of matter.  But, in 1910, Sir Rutherford and two of his students, Mardsen and Geiger, discovered that most of the matter in an atom is condensed at its center, in the nucleus.  In fact, more than 99.9 percent of all matter is packed into the nucleus.  Nuclei are composed of subatomic particles called protons and neutrons.  Measurements done with particle accelerators have shown that the radius of nuclei is about 1/10^15 meters.

The other well known subatomic particles, the electrons, swarm around the nuclei at relatively great distances.  It is the swarming action of electrons, and the associated electromagnetic forces, that determines how closely atoms can be packed.  Between the electrons and the nucleus there is mostly empty space.

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