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Astronomical observations have shown that the expansion of the universe is atpresent accelerating, consistently with a constant negative pressure ortension. This is a major puzzle because we do not understand why this tensionis so small compared to the Planck density; why, being so small, it is notexactly zero; and why it has precisely the required value to make the expansionstart accelerating just at the epoch when we are observing the universe. Therecently proposed conjecture by Afshordi that black holes create agravitational aether owing to quantum gravity effects, which may be identifiedwith this invisible tension, can solve this coincidence problem. The fact thatthe expansion of the universe is starting to accelerate at the epoch when weobserve it is a necessity that is implied by our origin in a planet orbiting astar that formed when the age of the universe was of the same order as thelifetime of the star. This argument is unrelated to any anthropic reasoning.

The Invisible Tension of the Universe from Astrophysical Black Holes: a Solution to the Coincidence Problem of the Accelerated Expansion