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I can't wrap my head around time being anything other than the measurement of movement, and until someone can prove otherwise, that's where I'll be.
- I'm going to take your definition just a step further and say it's a measurement of causality specifically.
  
  Isn't literally everything a measurement of causality?
  
  yes, struggler
  
  The slap was worth it.
- A definition I saw recently that I like is that time is the direction of entropy. You follow time one direction and you get the big bang where everything is chaotic and happening, and in the other direction you get the heat death of the universe, where everything has settled into a base state and nothing's happening.
  
  Do you mean, like reverse time? From my understanding of the concept of entropy, it strives to a maximum, meaning maximum disorder, by your definition the big bang.
  Or maybe do you have link where I can look into it? Sounds interesting
  
  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.
  
  entropy
  To me that's more of an emergent property of large numbers of particles moving from higher to lower energy states. Like temperature is just the velocity of an atom when you have lots of atoms moving and interacting.
  
  I'm not sure that's quite right in the sense that entropy is still meaningful on the level of individual particles—phenomena like proton decay, for example. But yeah, fundamentally it's an emergent property from the way energy works, and on a grand scale that tendency is a way to view time.
  
  proton decay
  A proton isn't an individual particle but made up of quarks. If a proton decays (which hasn't been observed) it's still a transition from its component quarks to lower energy particles.
- That is the scientific definition as well is it not? Time didn't exist before movement.
  
  If it did, how could you tell?

145 comments