Just about anyone who has taken an adult-level course in one of the natural sciences has
encountered something called "scientific method." However, it is common
for people who do not enter the sciences as a profession to
forget this fundamentally important, if less than thrilling,
chapter. Thus, when we encounter evangelists deriding
a scientific idea as "only a theory," or parents demanding
that "alternative theories" be taught in their children's
science classes, the topic of scientific method inevitably comes up—or
should. "Do you
understand the rigorous challenges and demands of scientific
method, which an idea
must withstand in order to qualify as a scientific
theory?" (Those who use the phrase "only a
theory" evidently do not understand the term as it is used
in science.) "Have your alternative theories
satisfied the demanding criteria of scientific method?"
(Unless the alternative theories have survived being
independently scrutinized and
methodically tested by those professionally trained in
natural science, they have not satisfied these criteria,
and thus do not qualify as scientific theory.)
The
Purpose of Scientific Method Science is the methodical investigation of nature, and
scientific method is the accepted process for conducting
that investigation, with the fundamental understanding that
science cannot create or shape reality, but merely attempts
to describe and explain it. Of course, these
descriptions and explanations are sometimes found to be less
than perfectly accurate (and on rare occasions, utterly
false). Since science accepts that it cannot change
reality to conform to its ideas, it must change its ideas to
make them conform to reality, as nearly as current methods
of observation allow. Scientific method is a rigorous and thorough
discipline for systematically determining, by careful
observation and cogent reason, whether or not an idea is in
accord with natural reality. Only after an idea
has satisfied all criteria of the scientific method can it
be classified as a scientific theory. Scientific
method thereby ensures that the term "scientific theory" is
reserved for ideas that have withstood prolonged and intense
scrutiny under the unrelenting light of all available
pertinent evidence. Scientific method thus assures us
that the scientific theories of today are solidly supported
by substantial factual evidence, cogent reason, and
exhaustive testing, and have so far survived all attempts to
discredit them.
The Basic
Work Cycle Scientific method demands
adherence to principles of meticulous observation, careful
reasoning, factual verification of ideas, honest reporting
of findings, and critical peer review. While
application of scientific method is in most
cases very demanding, its process is relatively easy to understand in principle.
In its simplest form, scientific method employs a basic loop
of activity: observation, explanation, prediction,
and back to observation, in a progressive cycle.
-
Observation of a phenomenon gives rise to
speculation about an explanation for it.
-
The tentative explanation is used to formulate
a testable prediction.
-
The prediction is revealed to be correct or
incorrect by subsequent observation.
A correct prediction causes the cycle to be repeated, in
order to explore other aspects and limits of the phenomenon,
refining the explanations and predictions in the process.
However, if a prediction turns out to be incorrect, the
cycle branches.
-
If a discrepancy can be accounted for, the explanation
may be revised and a new prediction tested.
-
If a discrepancy cannot be reconciled, the explanation
may be rejected or replaced.
If a faulty explanation is revised or replaced, the new
version is then run through the cycle in like fashion.
However, if we run out of explanations or predictions, then
we set the matter aside as unresolved, until either
additional evidence comes to light or new ideas emerge.
Important considerations in scientific experimentation
include:
-
Repetition: Does the same phenomenon occur
repeatedly and consistently?
-
Universality: Does the same phenomenon occur
under all conditions?
-
Verification: Do accumulating results support
or contradict the prediction?
-
Exception: In cases where the phenomenon
changes or does not occur at all, can those variations and
exceptions be rationally explained?
The
Overall Process Beyond the basic
observation-explanation-prediction cycle, scientific
method entails a number of interconnected stages: initial
development, independent investigation,
demonstration of value, and
conflict resolution. The overall sequence can be outlined as follows:
At any stage of the process, if significant discrepancies are
discovered and cannot be credibly accounted for, then the
hypothesis is effectively "falsified," and must be either rejected, or else revised and started
through the process once again. In addition,
especially in the case of slow processes or rare events, it
might well take years or decades (indeed, sometimes
centuries or longer) to acquire the necessary data to
confirm a hypothesis, so scientific method can be
frustratingly time-consuming. (That is where accurate
measurement and record-keeping become important. Old
but reliable data, considered in ways not previously
imagined, sometimes lead to significant new perspectives,
insights, and discoveries.)
Limitations
Is scientific method perfect? No,
just as our knowledge, senses, and tools of measurement are
not perfect, to say nothing of our often biased interests.
Faulty hypotheses sometimes do become accepted as theory.
However, scientific method is an ongoing process. It
continually reexamines existing theories in light of new
evidence, and odds are overwhelming that any error will come
to light eventually. The rigorous process ensures that
surviving scientific theories are very durable.
If a theory is shown to be flawed, it is often the case that
it need not be discarded, but only qualified or modified to
bring it back into compliance with advancing knowledge.
A case in point is Newton's theory of gravitation, whose
calculations were regarded as "natural law" for three centuries,
until superseded by
those of Einstein, which better explain the workings of
gravity and predict its behavior under extraordinary conditions,
as confirmed by actual observation. Notwithstanding,
Newton's simpler calculations continue to provide adequate
accuracy for most practical purposes, even to calculating
multi-year, multi-billion-kilometer space vehicle
trajectories.
Assembling
the Puzzle Occasionally there arises a theory that ties several
other theories together, bringing a grand order and cohesion to what
previously seemed disconnected bits and pieces. In the
17th century, Isaac
Newton's laws of motion constituted the first such
unifying advance for modern physics. In the 19th
century, Charles Darwin's
theory of biological evolution did much the same for
biology, making sense of the underlying connectedness and
relationships among a bewildering diversity of species, as
well as enhancing understanding of genetics, geology, and
paleontology.
In the 20th century, Alfred Wegener's theory of plate tectonics performed the
same service for geology, at once explaining a variety of
phenomena, from the complementary coastlines of Africa and
South America to mirror-image magnetic patterns on opposite
sides of seafloor trenches, from earthquake fault lines to
chains of volcanoes, and even the fossil record of
identical biological species on long-separated landmasses.
When such a theory reveals the previously hidden
relationships among centuries of diverse disciplines and
locks them into place, there can be little doubt that the
theory is thereby confirmed in its essentials, even if some
of its details have yet to be ironed out.
Misperceptions
A common myth (a remnant of smug overconfidence
of the 19th century, that science had essentially answered
all questions worth asking) is that science is supposed to
prove
ideas true or false. This is not the case.
Science deals in probabilities, not certainties (though some
probabilities approach certainty closely enough that the
minuscule margin of doubt can be disregarded for practical
purposes). Science draws conclusions only on the basis of currently
available evidence within the current constraints of
observation and measurement, with the full understanding that any
conclusion might subsequently be invalidated by evidence yet to be
discovered. So the most science can say about a theory
is that all evidence discovered so far supports it, and none
contradicts it. Confirmation of a single wrong prediction or
contradictory fact can cause even the most widely accepted
theory to be challenged and rejected. Thus the
existence of an extensive body of coherent theory that has
withstood decades or even centuries of intense scrutiny
attests to the rareness with which such rejection occurs,
and to the effectiveness of scientific method in weeding
out ideas that are not in accord with the reality of nature.
Perspective
In dealing with nature, there is always a risk
of error or misinterpretation; where humans are involved, it
simply cannot be avoided. Indeed, in science a margin
of error is always expected and is routinely taken into
account, and the whole point of scientific method is to
identify and reject the inevitable
misinterpretations. But no human process is perfect,
so science makes no claim
that its findings are absolutely certain.. On the
other hand, science is one discipline that tends to be
self-correcting, through continual reexamination and
retesting of existing theories in light of new evidence. Consequently, despite its
shortcomings, scientific method has demonstrated itself the
most reliable and verifiable way yet to learn about nature
with a high degree of confidence, even if we must accept
that reliability, verifiability, and confidence do not
equate to certainty.
Thus, if someone claims to know that an idea is "an
absolutely scientifically proven fact," we can be sure only
that he or she knows nothing of the sort, and understands
little if anything about science itself. On the other
hand, if we know that an idea is a
scientific theory, we can be confident that, though the idea
is not absolutely certain, it is better supported by
abundant evidence and cogent reason than are most ideas in
human experience—a far cry from the mere speculation that
typically passes for "theory" in non-scientific pursuits.
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