Why does time flow forward?
As a watch enthusiast and a person who is deeply fascinated by science, I felt like this could be a good idea for a post (keep in mind that I am not an expert in any of the things I'm talking about). One of the reasons why I love watchmaking is the fact that I find the concept of time extremely interesting. I'm here to talk about an english astronomer and physicist by the name of Sir Arthur Eddington, who came up with a theory about why time moves forward.
First of all it's important to have a base understanding of what Thermodynamics is: Thermodynamics is the field of Physics that studies energy and its conversion from one form to another. The second law of Thermodynamics is what we're concerned about: it states that the entropy of an isolated system is always increasing.
What is entropy and why does it always increase? Entropy is the physical quantity that expresses the disorder of a system: the higher it is, the higher the disorder. For a chemical reaction to happen spontaneously, entropy needs to increase. Increasing entropy could mean the molecules of a gas being spaced out over a bigger volume, or a higher temperature that results in those molecules moving faster. Overall, the higher the entropy, the higher the amount of information needed to describe the system will be. Describing the "placement" of gas molecules in a cubic centimetre of space is easier than describing the possible arrangement of those same molecules in a space of one cubic metre, as it requires less information.
At the big bang (not the Unico kind
), all matter was condensed into a really tight space, which means that entropy was the lowest it has ever been. As time moved forward, entropy kept on increasing, resulting in the expansion of the universe and every single process taking place inside of it. This is why we can't travel back in time: the overall entropy of the universe would have to decrease, and that is impossible.
As the universe moves forward and reaches a state of thermal equilibrium, time could stop, as entropy is at its maximum. This could mean that time isn't as eternal as we may have thought when we were the lower entropy version of ourselves.