A hamster wheel. Yes, you heard me correctly: a hamster wheel.
The engine of the cosmos, perpetually spun by a pair of hamsters, mighty in stride, eternal in endurance. One is the shade of space devoid of stars. The other is the colour of fission, a hot intense white. They run in parallel, matching each other tread for tread. Sometimes one overtakes the other, or the other overtakes the one, but never do they stray far from each other.
Many cultures of humankind have names for them. Of course. Only humans would conjecture something as literal as cosmic hamsters into majestic metaphors: good and evil, yin and yang, dark and light, Law and Chaos, to name a few.
Hmm? What's that? You're asking how the hamsters work? Don't be absurd. It's hamsters all the way down.