Transcript: Suppose you have a small particle or a grain of sand and a fine knife and you divide the grain of sand in half, and then in half again, and then in half again.  Is there an end to this process, or must you reach a limit, an indivisible particle?  Democritus, the fifth century BC Greek philosopher, imagined that it was illogical that this process of subdivision of matter could continue without end, and so he proposed that all matter was made of atoms, indivisible, microscopic units of matter comprising all the things we know in the natural world.  This was a very advanced idea because Democritus had no way of isolating or seeing individual atoms. But the idea was very modern because it is the basis of modern science, that the properties of matter such as color, taste, odor, are secondary properties, and the fundamental properties apply to atoms themselves.  Democritus also speculated that the fundamental particles of matter, atoms, were in constant motion, something we also know to be true today.  And so Democritus, 2000 years before atoms were actually seen, hypothesized the microscopic nature of the natural world.