What makes a theory a scientific theory?
A scientific theory is a deductive statement accepted by a recognized element of the scientific community, and that represents the only possible conclusion of a thorough, rigorous, and disciplined series of scientific testings of successive critically reasoned hypotheses. A scientific theory is often a set of statements that collectively describe how one facet of the universe works. Unlike common theories, scientific theories must be:
- consistent with all existing scientific laws and constants;
- consistent with, and supported by, all reproducible scientific observations and experimental results; and
- self consistent - that is, it does not contradict itself in any way.
#1 is questionable. Darwin's theory of evolution by natural selection directly contradicted and invalidated Lamarck's theory of evolution by the inheritability of acquired traits.
A scientific theory must be:
1. Naturalistic. It cannot invoke the intervention of a deity, or of a "superior" being or beings, or of unknown physical laws not in operation today (a common creationist claim). It also must be supported by observable facts and reproducible experiments. "Cold fusion theory" is naturalistic, as it does not invoke divine or supernatural intervention, but it is not supported by reproducible experiments. It is therefore not scientific.
2. Falsifiable. It must be open to being disproven when a newer theory, accounting better for all the facts, is formulated. To claim that present life-forms were created by an all-powerful, essentially unknowable Divine Creator, is an unfalsifiable claim, and therefore scientifically invalid.
3. Predictive. A scientific theory should be able to predict
what will happen under specific conditions. Because creationism
cannot predict anything (since everything depends on the will of
the Creator), it is not scientific. In the field of evolution,
predictability works this way: given certain environmental
conditions, scientists can predict that the life-forms developing
under those conditions will show adaptations to take the greatest
advantage of such conditions. For example, it can be safely
predicted that, in the Sahara desert, life-forms, whether animal or
plant, will have metabolisms that work to conserve optimally
moisture. Evolution does not specifically predict the development
of camels, or true xerophyte plants, but any animals or plants that
make their permanent home in the Sahara (or other extremely arid
areas) will necessarily show water-conserving metabolisms.
A scientific theory is a hypothesis based on a scientific topic.