Technical point on the use of the term "theory".
In casual conversation, a theory is a nice idea that may or may not be wrong, we don't really know.
In science, however:
A
hypothesis an idea that might work, but lacks convincing evidence. For instance, the concept of parallel universes is a hypothesis. There are hints in the equations that they could exist, but no evidence to back it up.
A
theory is worlds away from a hypothesis. It is an idea that has been tested to destruction, and survived. It is the best possible way of describing or explaining a concept or phenomenon with the available evidence.
This is not a secret definition. Anybody that has passed high-school science should know the difference between the two uses of the word theory, but it is a common, but ultimately dishonest tactic of the Creationist movement to deliberately misuse the word.
They refer to evolution as
"just a theory", as if it were a nice idea that doesn't really hold up to examination.
In fact, evolution is a theory in the same way that electricity is just a theory (yet the lights still come on), gravity is just a theory (yet we remain firmly on the ground and planets never stray from their orbits), quantum mechanics is just a theory (yet the chips in your computers work), fusion is just a theory (yet the Sun still shines).
Evolution happens. We can observe it on a daily basis, even without the fossil record.
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In my experience (and I have been having this argument for many years), the real reason creationists are desperate to dismiss evolution, unexamined, as "just a theory", is because the facts of evolution show that any religion with a creator god is worshipping a fraud:
1. If evolution is true, then the god is a con man, claiming to have created from scratch a universe that already existed. The theological equivalent of selling the Eiffel Tower to a passing tourist.
2. If evolution is not true, then the god is a deliberate deceiver, creating a universe with all the signs of great age already intrinsic in its structure. That's the theological equivalent of faking an antique.
Worse, in option 2, if the residents of the created world take that world at its face value, they find themselves condemned to eternal punishment
purely for believing what their god presented to them.