While we know for sure that quarks and electrons are smaller
than 10 to the power of (-18) meters (one billionth of a billionth
of a meter), it is possible that they have no size at all. It
is also possible that quarks and electrons are not fundamental
but are composites of more fundamental particles or are one-dimensional
strings. (Yikes! Will it never end?)
In summary, we know that atoms are made of protons, neutrons,
and electrons. Protons and neutrons are made of quarks, which
are possibly made of more fundamental objects.
