Picture several scientists at a New Year’s Eve social gathering. They would provoke amusement among the guests by wishing them "Happy Arrow of Time" instead of the more conventional "Happy New Year." The scientific term arrow of time is an expression describing the relentless forward direction of the flow of time, helping us distinguish the past from the future.
Someone may ask if the forward flow of time and our awareness of the distinctions of past and future are worth contemplating, obvious as they seem. Most evident is our ability to remember the past but not the future. This is called the psychological arrow of time.
Two other arrows are less obvious to the non-scientist, but they describe an overlay of necessary conditions in the universe in which we operate. The two conditions are the thermodynamic arrow of time and the cosmological arrow of time.
The thermodynamic arrow of time is related to the second law of thermodynamics, also called the law of entropy. Briefly, this law describes the natural tendency of our universe to move toward a state of increasing disorder (entropy) in which energy is continually being transformed to a less useful state. The direction of this arrow of time is established by the direction in which disorder increases. Check out one of my previous posts on this topic for examples of increasing entropy:
Related to the thermodynamic arrow is the cosmological arrow of time. As the universe expands, time moves forward. In 1998 scientists were amazed to discover the universe’s rate of expansion was not slowing, as had been thought, but was actually accelerating. Suddenly the speculation that the universe would some day stop expanding and perhaps begin contracting under its own gravity was shown to be impossible. There would be no “Big Crunch” and there would be no reversal of the arrow of time!
Our “gut feeling” that time proceeds in a certain direction is connected, then, to our observation that (a) disorder is increasing, and (b) the expansion of the universe is ongoing. Light conversation at the coffee table and a friendly “Happy New Year” certainly has its place to enhance our social health. But more serious discussions involving the arrow of time may help us understand the kind of universe God designed for man’s benefit. Reversal of either the law of entropy or the expanding universe would preclude life on earth. There is an upside to the law of entropy. The Creator had humanity in mind when He designed this operating system.