We began this set of activities with the observation of the light
emitted by atoms. By trying to understand light we have learned
about the wave nature of matter and the probabilistic nature of
knowledge. Along the way we have seen that small objects can
sometimes be where they would not be allowed by only energy considerations,
that electrons can be used to see very small objects and that
the spectra of elements is explained by this wave nature.
The theory that incorporates the wave nature of matter is now
called quantum mechanics. The explanation of spectra was an early
triumph for quantum mechanics. However, the story does not end
there. The way atoms join to form molecules and the organization
of the periodic table also need quantum mechanics for an explanation.
All types of small solid devices, such as computer processors
and memories can be built only because the designers understood
quantum mechanics. Thus, a large fraction of our daily lives
are in some way dependent on someone using quantum mechanics to
understand very small objects. The concepts that you learned
here are likely to increase in importance during the 21st Century.