No one knows that.. we only know that it is expanding first motivated from Hubble's observations, this led Einstein to throw away his cosmological constant that made the universe static. thus general relativity also wanted an expanding universe. but then came inflation, which needed more density...
well i don't understand onething that is what exactly do you mean by scaling? take a look at this http://arxiv.org/abs/0904.0877 although other things are fine.. but the last two critical points one of them is termed as scaler-fluid scaling solution. what exactly do you mean by scaling?