Hawking (1988: 145-6, 147-8):
The second law of thermodynamics results from the fact that there are always many more disordered states than there are ordered ones. … Suppose a system starts out in one of the small number of ordered states. As time goes by, the system will evolve according to the laws of science and its state will change. At a later time, it is more probable that the system will be in a disordered state than in an ordered one because there are more disordered states. Thus disorder will tend to increase with time if the system obeys an initial condition of high order. …
But why should the thermodynamic arrow of time exist at all? Or, in other words, why should the universe be in a state of high order at one end of time, the end that we call the past?
From the perspective of Systemic Functional Linguistic Theory, the change from a ordered state to a disordered state unfolds as a material process, whereas time is the dimension along which the process unfolds. On this view, physicists routinely confuse the process (e.g. the ticking of a clock) with the temporal dimension (e.g. the interval between each tick, the duration of the ticking, etc.).