Fluctuation theorem

Fluctuation theorem is a rule that helps us understand how things change and how we measure those changes. Imagine you have a toy car that you like to push around on the floor. Sometimes it moves faster, sometimes slower, but on average it moves a certain amount each time you push it.

Fluctuation theorem helps us understand that even though the car doesn't always move the same amount every time, there is an average amount it moves when you push it. This rule applies not just to the toy car, but also to things happening in the world around us, like how heat moves around or how electricity flows through wires.

The rule says that when things change, there is a certain likelihood that they will change in one direction versus the other direction. For example, if you roll a dice many times, it's very likely that you'll get a 3 or a 4 (because there are two ways to get those numbers), but it's less likely you'll get a 1 (since there is only one way to get a 1).

Similarly, when we measure things like temperature or energy in a system, there is a certain likelihood that the system will become hotter or colder, or that energy will be added or removed. Fluctuation theorem helps us predict these changes and understand how likely they are to happen.

So even though things in the world may seem chaotic and unpredictable, fluctuation theorem helps us see patterns in how things change, which can be very useful for understanding how the world works.