This post is a continuation of The Origin of Evolution Theory
As strange as it may sound, modern science is not directly concerned with reality, but rather with models of it. Reality is the realm of philosophy. The essence of science is the scientific theory, whose purpose is to provide coherent explanations to observations; an objective aptly summed up by the physics Nobel laureate, Richard Feynman (1918–1988):
No one has ever seen the inside of a brick. Every time you break the brick, you only see the surface. That the brick has an inside is a simple theory which helps us understand things better. The theory of electrons is analogous … The electron is a theory that we use; it is so useful in understanding the way nature works that we can almost call it real.
Although theory is at the heart of science, not every theory is scientific. For a theory to be scientific it must first be internally consistent, that is, it should lead to no logical or mathematical paradoxes. If, for instance, a theory could lead to a conclusion that an object may simultaneously exist in two different places, the theory would not be consistent and cannot be deemed scientific. (This example is a paradox that contradicts the principle of space and time: a physical object exists separately in space and time in such a way that they are localizable and countable.)
Unlike mathematical models – which being the creation of the human mind require internal consistency only – scientific theories based on these models must be testable: that is, it does not matter how elegant or internally consistent a theory may be, if it does not agree with observations external to the theory, it is wrong. This requirement means that a theory can be considered scientific only after test criteria can be defined. That is, every theory is potentially refutable. Contrary to the common belief, turning an idea into a scientific theory does not necessarily improve it or make it more reliable. In many cases, it will lead, inadvertently, to the refutation of the idea.