The laws of physics are invariant under a change in linear velocity. If you take everything in the Universe and add a constant to its velocity, and then if you

The laws of physics are invariant under a change in linear velocity. If you take everything in the Universe and add a constant to its velocity, and then if you yourself add that amount to your own velocity, then everything will appear exactly the same. The laws of physics are not invariant under rotation. If you take everything in the Universe and give it a nudge so that it's spinning around a particular axis, things will change. For starters, everything will fly apart, unless you also create a force field that pulls everything towards the axis of rotation (with the force increasing linearly with distance from the axis of rotation). A technical way to describe this is to say that the laws of physics have Poincaré invariance (or more properly, just Special Relativity has this invariance).[1] That's why linear momentum is viewed as a trivial property of a black hole, but angular momentum is not. 1. https://en.wikipedia.org/wiki/Poincar%C3%A9_group https://en.wikipedia.org/wiki/Poincar%C3%A9_group