Almost all celestial objects are rotating in some way about their axes. Why is this and should we expect the rotation to slow as the universe ages?
It comes from angular momentum. Angular momentum is a conserved quantity of physics. That means that the sum of angular momentum of the universe is constant, even though some parts of the universe may transfer angular momentum to other parts.
We do not know the total amount of angular momentum of the universe, but from observations we know that it is not uniformly distributed. This explains why celestial objects rotate.
If the total amount of angular momentum of the universe would be zero it would be theoretically possible that rotation could cease in the future. However, nobody knows the ultimate fate of the universe, so this is purely speculative.
The MinutePhysics channel on YouTube made a wonderful short animation that answers your very question. It explains how a cloud of gas and dust with zero net angular momentum collapses down to form a flat spinning object such as a galaxy or our Solar System.
The answer involves a few things:
- The universe conserves angular momentum in every interaction between physical objects.
- Mathematics says a big cloud of gas and dust must have exactly one plane in which the overall angular momentum is zero.
- When particles of gas and dust collide, any angular momentum they have outside that plane is cancelled, so over millions of years and (countless numbers of collisions) the cloud ends up flattening.
- But as they collide, their angular momenta within that one plane are conserved, so the flattened system ends up spinning.