The short story "How it Happened" by Asimov explains how the real explanation had to be simplified
My brother began to dictate in his best oratorical style, the one which has the tribes hanging on his words.
"In the beginning," he said, "exactly fifteen point two billion years ago, there was a big bang and the Universe--"
But I had stopped writing. "Fifteen billion years ago?" I said incredulously.
"Absolutely," he said. "I'm inspired."
"I don't question your inspiration," I said. (I had better not. He's three years younger than I am, but I don't try questioning his inspiration. Neither does anyone else or there's hell to pay.) "But are you going to tell the story of the Creation over a period of fifteen billion years?"
"I have to," said my brother. "That's how long it took. I have it all in here," he tapped his forehead, "and it's on the very highest authority."
By now I had put down my stylus. "Do you know the price of papyrus?" I said.
My brother thought awhile. He said, "You think I ought to cut it down?"
"Way down," I said, "if you expect to reach the public."
"How about a hundred years?" he said.
"How about six days?" I said.
He said horrified, "You can't squeeze Creation into six days."
I said, "This is all the papyrus I have. What do you think?"
"Oh, well," he said, and began to dictate again, "In the beginning-- Does it have to be six days, Aaron?"
I said, firmly, "Six days, Moses."
First published in 1979 in Asimov's SF Adventure Magazine