The reality of mythology isn't the reality of reality. God is only as real as Ra, Ea, El, Elohim, Allah, Apollo, Arjuna, Jupiter, Brahman, Marduk, Mithra, Theos, Zeus, Zoroaster, or any of a thousand others that superstition invented to explain phenomena for which there was no science. Nor can anything be real which was fabricated from remnants of pre-exisiting myths, as God was. The impossibility of God isn't a matter of physics. It's one of history.