I wish I had a link, I think acollierastro talked about it briefly in one of her videos but I think it was a sidebar on something else so I have no idea which one. It was just one of those things where I heard the statement and it clicked on some weird intuitive level.
I probably used “chaotic” inaccurately, but entropy strives towards maximum disorder in that there is energy holding things together and that energy won’t hold forever. The big bang was basically a big explosion where a whole lot of order was imposed on the universe, for example by forming particles, and since then there’s this general trend towards things falling apart. Energy can be used to fuse a particle, but left alone that particle will eventually fall apart, even if it’s not moving. That’s entropy. So time is that quantity where, given enough of it, things fall apart.
Does that make sense? I have no idea if I’m explaining it properly, my physics background is super scattered.
Entropy is a measure of a number of distinct possible configurations that result in an equivalent outcome.
It’s pure statistics. Given time symmetric laws of nature and a state that can be achieved by a relatively small number of configurations, in the absence of potential barriers, the system inevitably approaches a state that’s achievable by a larger number of configurations. Simply because an elementary change is more likely to fall into the latter mode. Thus, arrow of time emerges.
There seems to be a slight misunderstanding here: If you imagine the “moment before” the big bang that is a state where the entire universe is compressed into a singularity, which necessarily has no entropy, because it can only have one state. Once the universe started expanding, you get a whole lot of disorder, because, while you are forming particles (introducing order) those particles are moving away from each other at relativistic speeds. The available volume for the particles (the volume of the universe) increases extremely rapidly, meaning you have more possible microstates than if all particles were compressed into a point.
