Why does entropy invariably increase?

It's simple really. The Universe runs on BigNum rational arithmetic. As small perturbations are accumulated, ever larger rationals are required to represent state without destroying information or losing accuracy.

>>3
That explains what entropy is and states the observed laws of entropy, but doesn't explain fundamentaly where it comes from. It's also using very outdated models of the Universe.

Try something more modern like: http://en.wikipedia.org/wiki/Holographic_principle

From a computational Universe standpoint, BigNum rational arithmetic makes a lot of sense.