Not my theory, but if the universe previously contacted to a mass no bigger than your fist, all the previous skeletons would be gone.
However, the theory that the universe continues to expand and contract may have been around for hundreds of billions of years.
The beings in those previous phases of the universe.
In other words, if God has existed forever, why is our universe only 6 billion years old?
When you exist outside of time, when you are the one that creates time, because matter and time are intertwined, you exist outside of time and are not bound by it. When you have always existed you are by default infinite.
Not 6, but 14.5 billion for this universe, His other ones are gone, as this one will be at some far distant point, perhaps when all this universe finally reaches the Great Attractor toward which everything is moving.
“...if God has existed forever, why is our universe only 6 billion years old?”
THAT, is a very good question.
Because time began with the universe.