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Lemaitre's theory was known as the "primeval atom," but it is more commonly known today as the big-bang theory.
"He understood that looking backward in time, the universe should have been originally in a state of high energy density, compressed to a point like an original atom from which everything started," according to a press release from the Observatory.
The head of the Vatican Observatory, Jesuit Brother Guy Consolmagno, says Lemaitre's research proves that you can believe in God and the big-bang theory.
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"Lemaitre himself was very careful to remind people — including Pope Pius XII — that the creative act of God is not something that happened 13.8 billion years ago. It's something that happens continually," Consolmagno said Monday.
Believing merely that God created the big bang means "you've reduced God to a nature god, like Jupiter throwing lightning bolts. That's not the God that we as Christians believe in," he said.
Christians, he said, believe in a supernatural God who is responsible for the existence of the universe, while "our science tells us how he did it."