A "theory", in the scientific community, means something that has been proven and is accepted as being true.
"Oh, it's just a theory"
This is the typical reaction by those who do not know how the scientific community defines the word "theory".
In laymans terms, if something is said to be just a theory, it usually means that it is a mere guess, or is unproved. It lacks credibility.
In science, a theory implies that something has been proven and is accepted as being true.
Theory A theory is an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers. One scientist cannot create a theory; he can only create a hypothesis.
A theory is developed only through the scientific method, meaning it is the final result of a series of rigorous processes.
All scientific theories are well documented and proved beyond reasonable doubt
Real scientific theories must be falsifiable. That is, there must be something that if found, discovered, invented, etc., would show that tthe theory is invalid; i.e. falsified. For example, the development of genetics as a new field of study in 1950, had the potential to show that evolution was false by showing that genetics did not support the idea that we genetically evolved. Instead, all of molecular biology confirms what evolution had predicted.
Theory VS Fact
A theory is MUCH more powerful than a fact. The biggest difference between a fact and a theory is that a theory is much more complex and dynamic. A fact governs a single action, whereas a theory <b>explains</b> an entire group of related phenomena using relevant facts.
Evolution is an elegant theory that explains the history of life through geologic time; the diversity of living organisms, including their genetic, molecular, and physical similarities and differences; and the geographic distribution of organisms.
"In the century and a half since Darwin, scientists have uncovered exquisite details about many of the mechanisms that underlie biological variation, inheritance, and natural selection, and they have shown how these mechanisms lead to biological change over time.
Because of this immense body of evidence, scientists treat the occurrence of evolution as one of the most securely established of scientific facts.
Biologists also are confident in their understanding of how evolution occurs."
"Nothing in Biology Makes Sense Except in the Light of Evolution," the pioneering geneticist Theodosius Dobzhansky titled a famous essay in 1973.