In relativity, gravity is negative energy, and matter and photons are positive energy. Because negative and positive energy seem to be equal in absolute total value, our observable universe appears balanced to the sum of zero. Our universe could thus have come into existence without violating conservation of mass and energy — with the matter of the universe condensing out of the positive energy as the universe cooled, and gravity created from the negative energy. When energy condenses into matter, equal parts of matter and antimatter are created — which annihilate each other to form energy. However there is a slight imbalance to the process, which results in matter dominating over antimatter.
I know that this doesn't make sense in our Newtonian experience, but it does in the realm of quantum mechanics and relativity. As Nobel laureate physicist Richard Feynman wrote, "The theory of quantum electrodynamics describes nature as absurd from the point of view of common sense. And it agrees fully with experiment. So I hope you can accept nature as she is — absurd."
"To surrender to ignorance and call it God has always been premature, and it remains premature today."
— Isaac Asimov
"As far as I can see, such a theory [of the primeval atom] remains entirely outside any metaphysical or religious question. It leaves the materialist free to deny any transcendental Being… For the believer, it removes any attempt at familiarity with God."
— Georges Lemaître, Catholic priest who first proposed what became the Big Bang Theory
For more, watch the video at the 1st link - "A Universe From Nothing" by Lawrence Krauss.
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