Radioactive tracers and radiation sources have become indispensable to
all phases of agricultural research. They have helped answer questions
that seemed unanswerable. But there will always be more questions to put
to Nature. The physicists-philosophers of 1890 were confident that they
had obtained all significant knowledge of the physical universe.
Discoveries of the next twenty years revealed the immaturity of that
conviction.
The modern poet Archibald MacLeish has dramatized the meagerness of
knowledge:[3]
I will tell you all we have learned ...
the lights in the sky are stars
We think they do not see
we think also
The trees do not know nor the leaves of the grasses hear us....
Perhaps the most characteristic realization of the scientist today is
that the universe is too complex to be fully described, that concepts
must change repeatedly to absorb new findings, and that the recurring
miracle of life is more majestic than any formula, any computer, or any
rocket that man’s brain can devise.