I don't suppose anything, the strongest evidence so far is what led to the theory, supposing anything without evidence is faith. "The beginning" is just a place holder for the period everything seems to have originated, I'm not saying anything or nothing existed before this point. I can't explain how something comes from nothing.What beginning...there was no beginning ...you just suppose there was.. If you have proof there was a beginning, please explain how all that exists come from nothing....
If you want to argue semantics and definitions then I shall quote to you from Britannica:Argue with the editors of WordWeb...that is straight from the dictionary...
"scientific theory, systematic ideational structure of broad scope, conceived by the human imagination, that encompasses a family of empirical (experiential) laws regarding regularities existing in objects and events, both observed and posited. A scientific theory is a structure suggested by these laws and is devised to explain them in a scientifically rational manner."
The National Academy of Sciences:
Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.