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S
cience is an ongoing search
for truth—a perpetual
struggle to discover how the
universe works that goes back to
the earliest civilizations. Driven
by human curiosity, it has relied
on reasoning, observation, and
experiment. The best known of
the ancient Greek philosophers,
Aristotle, wrote widely on scientific
subjects and laid foundations for
much of the work that has followed.
He was a good observer of nature,
but he relied entirely on thought and
argument, and did no experiments.
As a result, he got a number of
things wrong. He asserted that big
objects fall faster than little ones, for
example, and that if one object had
twice the weight of another, it
would fall twice as fast. Although
this is mistaken, no one doubted it
until the Italian astronomer Galileo
Galilei disproved the idea in 1590.
While it may seem obvious today
that a good scientist must rely on
empirical evidence, this was not
always apparent.
The scientific method
A logical system for the scientific
process was first put forward by the
English philosopher Francis Bacon
in the early 17th century. Building
on the work of the Arab scientist
Alhazen 600 years earlier, and soon
to be reinforced by the French
philosopher René Descartes,
Bacon’s scientific method requires
scientists to make observations,
form a theory to explain what is
going on, and then conduct an
experiment to see whether the
theory works. If it seems to be true,
then the results may be sent out
for peer review, in which people
working in the same or a similar
field are invited to pick holes in the
argument, and so falsify the theory,
or to repeat the experiment to make
sure that the results are correct.
Making a testable hypothesis
or a prediction is always useful.
English astronomer Edmond Halley,
observing the comet of 1682,
realized that it was similar tocomets reported in 1531 and 1607,
and suggested that all three were
the same object, in orbit around the
Sun. He predicted that it would
return in 1758, and he was right,
though only just—it was spotted on
December 25. Today, the comet is
known as Halley’s Comet. Since
astronomers are rarely able to
perform experiments, evidence
can come only from observation.
Experiments may test a theory,
or be purely speculative. When the
New Zealand-born physicist Ernest
Rutherford watched his students
fire alpha particles at gold leaf in
a search for small deflections, he
suggested putting the detector
beside the source, and to their
astonishment some of the alpha
particles bounced back off the
paper-thin foil. Rutherford said it
was as though an artillery shell had
bounced back off tissue paper—
and this led him to a new idea
about the structure of the atom.
An experiment is all the more
compelling if the scientist, while
proposing a new mechanism or
theory, can make a prediction about
the outcome. If the experiment
produces the predicted result, the
scientist then has supporting
evidence for the theory. Even
so, science can never prove
that a theory is correct; as theINTRODUCTION
All truths are easy to
understand once they are
discovered; the point is to
discover them.
Galileo Galilei