"A theory is scientific if it has the property where a person can articulate an instance in which it would be wrong, in which it can be falsified.
If I tell you 'if the light is blue, x is true, and if the light is red, x is true,' that's not a scientific statement because there's no way that it will not be true at the end. I have to be able to propose an instance in which you might prove me wrong.
This is a very appealing idea, it has a bravado and a wagering quality to it, that a scientist must risk being wrong in order to be a scientist.
In 1919, eclipse expedition which confirmed Albert Einstein's theory of general relativity, and what most impressed him about it wasn't the ambition of the theory or the fact that it was confirmed. What he liked about it was Einstein said, 'if starlight isn't measured to bend around the sun during this eclipse then my theory is incorrect.'
He liked the wagering on being wrong. And he thinks that's the basic status of what a scientific theory is."
This is why religious ideas not just aren't scientific, but cannot be scientific. "Faith" insulates people from figuring out they're wrong.
Source: twitter.com