A cubit has a two dimensional hilbert space, which is a lot easier to deal with. The problem with them is that they don't connect with anything you've heard of in classical mechanics. There's no equation of motion for a cubit classically. So i think you can do both. Just do both. I would like to do both. Anonymous says the collection of homeostatic chemical processes we call life self propagate in the direction of the arrow of time. But there exist regions where entropy decreases. In these regions, life in the reverse direction. This mayt very well be something where i just don't understand it well enough to give you the simplest answer here.