system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do equations explain the universe around us?
gpt
Long story short; we have equations for describing the universe because we can measure so many aspects of the universe.  

Imagine you're going to the shop to get a pie or something.  The shop is about one kilometer away (and you know that because someone measured it and put it on a map) and it takes you ten minutes to get there (and you know that because you checked your watch).  That means it took you 600 seconds to travel 1000 meters.  Work the math through and you get 10 meters every 6 seconds, 5 meters every 3 seconds or five thirds of a meter every second.  

Hopefully that all makes intuitive sense.  If you look back through that paragraph you'll see we took a measure of distance and divided it by a measure of time to get a measure of speed.  In physics we measure speed in straight lines and call it velocity.  We can describe the relationship like this: **velocity = distance / time** or **v = d / t**

By taking careful measurements of other observable things we can discover all kinds of similar equations that seem to be pretty accurate descriptions of how things actually happen.  We can push weights around to discover the relationship between force, mass and acceleration.  We can play with electricity until we discover the relationship between current, voltage and resistance.  

The cool thing about these equations is not just that they help us understand relationships between things but we can use them to make predictions about what's going to happen in future.  Understanding electricity allows us to plan computers.  Understanding projectiles allows us to bomb the enemy.  Understanding gravity allows us to plan trips to other planets.  

So it's not that equations explain the universe so much as equations are an expression of our understanding of the universe that we've gleaned through careful observation and experiment.