In 1929, astronomer Edwin Hubble published a paper demonstrating that the universe is expanding. It gave rise to the Hubble constant, the number that describes how fast the universe is expanding.
But it eventually created a puzzle, called the Hubble tension, because this cosmic expansion differs depending on what cosmic objects are used to measure it. Quantum FFF Theory says however:
NO, not omly merging of small black holes is the origin of expansion, In stead: : the expansion of the universe is mosly based on my new theory about micro travellingTadpole Black Holes propelled by self generated plasma tails around each BH, guided by the variable pressure of the local Axion vacuum away from the strongest gravitating BH and material centers. Below: the growing baby universum by merging black holes. ( artist impression.)
see also: https://rxiv.org/pdf/1306.0065v1.pdf
Below: the 12 fold anti symmetric raspberry shaped multiverse of the Q-FFF Theory.
Below: The cyclic Raspberry Multverse of Q-FFF Theory.The Roger Penrose Trapped Black Hole Horizon as Fermion creator out of the Axion vacuum by head on collision and transformation into charged fermions (equally Positive and Negative charged !!etc. at the Penrose horizon. Negative at the outside of the BH horizon and positive at the inside of the global horizon. ( see cross section)