There’s a mystery as to why the Universe’s expansion is accelerating.

As per all our educated guesswork, the first 9 billion years found the Universe in a decelerating mode. The last 5 billion years, has shown an acceleration.

The acceleration is based on galaxies being pulled further apart from each other.

This pulling apart can be caused by Dark Energy (the opposite of regular energy).

However, it can also be caused by something else pulling on the galaxies. That something else can be OTHER UNIVERSES (multiverses).