oops
My old idea has been..,
As Mass and dark matter keep colliding and collapsing from gravity ultimately into black holes,

Space keeps expanding and accelerating (dark energy) from singularities where time and mass change places with space and time.
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Penrose diagrams show how this can happen. So
as mass makes more black holes, black holes makes more space from those singularities.
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7 billion years ago there were fewer black holes and the expansion of space was much slower. Now there more BH's and faster space creation formation. The young universe looked like a dense sponge or internal bone structure. An old universe will look like osteoporosis.

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How long can this perpetual motion, like a snake eating its tail, continue? Until an entropic state change happens when space stretches no further and mass has collapsed all it can.
A big rip happens ending with a universe with a lower energy state.
So for now galaxies keep merging and space keeps accelerating.


Therefore we are living inside the bones of the cosmic dog.