What is matter? Matter is the stuff from which we and all the things in the world are made. Everything around us -- from desks, to books, to our own bodies -- are made of atoms, which are small enough that a million of them can fit across the breadth of a human hair. Inside every atom is a tiny nucleus and orbiting the nucleus is a cloud of electrons. The nucleus is made out of protons and neutrons, and by zooming in further, you would find that inside...