Re: "the speed of light could have been faster during the early universe"
a community of people who are very capable of putting said theory to the test and either thoroughly trashing it or conclusively proving it, or somewhere in the middle where proof is not definite but could be possible if some more intelligent people could be found to find out.
Scientific theories cannot be proven; they can be corroborated, but that's not proof. Proof is only available in the domains of mathematics and logic.
What Is This Thing Called Science?