78 The Poetry of Physics and The Physics of Poetry
about their respective nuclei, imitating the planets of a miniature solar
system. The force holding the electrons in their orbit is not gravity but
the electric force of attraction between the proton’s positive charge and
the electron’s negative charge. Even the protons and neutrons tightly
bound within the nucleus are moving back and forth with respect to each
other. Nothing is standing still in this "Restless Universe” (the title of an
excellent book on the atom by one of the pioneers of quantum physics,
Max Born).
Not only is our solid page a maze of motion, but also it consists
almost entirely of empty space. The distance between atoms and the
radius of the electron’s orbit about the nucleus are approximately the
same namely 10-8 cm. The radius of the nucleus on the other hand is only
1/100,000 of this distance or 10-13 cm. The radius of the electron is even
smaller. Actually, according to some theories an electron is a geometric
point. Thus like our solar system the atom consists mostly of empty
space and hence so-called solid matter is 99.999 ...% empty space. In fact
if it were possible to compress matter such that all the nuclei were
touching each other so there was no longer any empty space within the
atom, then a library consisting of 10^15 books the size of this one could be
compressed into the space occupied by this book. However, this is pure
fantasy since the force here on Earth, necessary to compress matter to
this extent is impossible to achieve. The existence of such super dense
collections of matter cannot be ruled out, however, as we will discover
later in the book, when we consider cosmological questions and
investigate black holes.
Having briefly sketched the nature of the atomic structure of matter
we will leave the detailed discussion of this topic to the later chapters
when we describe the physics that takes place inside the atom. Instead
we now turn our attention to the implication of the atomic structure of
matter on its macroscopic (large scale) behaviour. The concept of an
atom invisible to the human eye and immutable was first proposed by
Leucippus and Democritus to account for the impermanence of matter.
According to them, although the nature of atoms is unchanging, changes
occur on the macroscopic level of matter as different combinations of
atoms form and then re-form. So for example, as wood burns the atoms
of wood and air form new combinations such that fire, ashes and smoke
result. They believed that the space between atoms was void and that the
properties of matter were determined by the size and shape of the atoms
as well as the nature of their motion in the void between them. Their