You are holding a document written in the language of light. That faint chemical smell, the way the printing already looks a little tired: the paper has no ink at all. It is coated with a colorless dye and a mild acid locked apart from each other, and inside the register a thin strip of thermal print head heats to roughly 300 degrees Celsius in pinpoint bursts, melting the two together so they react and blacken exactly where a letter should be.
Your total was branded onto the page by a controlled, microscopic burn.
Which is why it fades. Those dark characters are not stable; they are a chemical reaction sitting in a slightly higher energy state, and molecules do not like sitting anywhere higher than they must. Leave the receipt in a hot car, or in a wallet warmed all day against your body, and you are gently feeding energy back into the very bonds you paid to create.
The word MILK, the price, the little barcode, all of it slowly relaxes back toward beige. Entropy always collects its bill.
So this crumpled slip is a tiny thermodynamic hourglass. It records a moment, the 4:52 PM you bought bananas, by holding a pattern that the universe is actively working to erase, and will erase, without malice, purely because smooth uniform disorder is overwhelmingly more probable than crisp black letters.
Keep it in a drawer and check in a decade. The numbers will be ghosts. You will have watched, in the palm of your hand, the same arrow of time that will one day cool every star: order paid for, order dissolving, a receipt for the receipt.