How would you know that time travels in forward direction? That each passing instant is not going in the backward direction. What is direction, by the way, when we are talking about time. With only time in picture it does not convey any meaning. For example imagine a universe devoid of matter, and having only time. How would time pass in such a place. Time is highly dependent on events. Something must happen after or before something else for time to pass, or at least for us to interpret passage of time. Time therefore needs space for its existence. And not just space but a changing space. Static space is just as timeless as no space at all. Now suppose, there is space and there is change also. But the changes are very closely packed, happen very quickly and in opposite directions, so that they nullify each other, time would not like that too. Meaning thereby there should be a predominant direction of change for time to exist. After a number of events there must be a net non zero resultant change and that should be consistent in its direction. Now what could be the directions of change. Towards order or disorder. Our universe I guess chose the latter. A drop of water falls on the ground and spreads, as soon as you switch on a bulb, light comes out and disperses. Relationships weaken and later get broken, a child lives in home, a man in loneliness. Galaxies tear apart, so do our lives. It might seem like a long shot, but it is this entropy and its ever increasing magnitude that defines time and sets its direction for eternity.