Josh Arnold, Williamsville East High School
Confucius once famously said “Time flows away like the water in the river” so it seems fitting to start out with an analogy to water. Picture a glass of water sitting on the top of a hill. When we spill that glass, the water inside will rush down the hill and eventually pool at the bottom. Now if we can think of this interaction in terms of energy levels at the top of the hill the water in the glass has a relatively high amount of potential energy. When the glass is tipped over, the water will run down the hill and tries to move it to its ground state, where it has less potential energy. If we look at it from a thermodynamics perspective, we can see that at the top of the hill the water has relatively low entropy, but as it flows down the hill it spreads out and pushes bits grass and dirt out of position, which increases the entropy level of the system. When that water makes it to the bottom of the hill it is not only at its ground state but also in a state where entropy has increased, but the amount of useful work that can be done by the system has decreased.
If we scale up our model by replacing the cup of water with, all of the matter and energy in the universe. If we could go back to the big bang we would observe a singularity consisting of all known matter. If we look at this as a system it would have remarkably low entropy. All mass in existence rigidly packed into a point infinitely smaller than even a human hair. This could be analogous to the cup of water at the top of our hill. When we spill our cup or trigger the big bang, all of that energy will be put into motion, increasing the entropy of the system. If we fast forward googol years, ten to the hundredth power, we reach the universe in a state of heat death. At this point, the universe has reached its maximum possible entropy. This rather dystopian future is similar to our pool of water at the bottom of the hill. This tendency towards entropy is why we feel the flow of time, time can only flow in one direction because our universe can only move towards greater entropy. We are currently experiencing time flowing down that hill, constantly moving towards a more entropic state.