The scenario you described demonstrates a concept that some things cannot be undone. Now, I could duct-tape the paper together again but the paper would not be in the same condition as it was before it was torn. Another example that demonstrates this concept is an incandescent light bulb. If I turn on the light bulb, the electrical energy going into the light bulb is converted into light energy and heat energy. So what happens to that light and heat energy after I turn off the light bulb? The light and heat energy is like the torn paper. It is no longer in a useful form. The increase in unavailable energy is called entropy. Entropy is the term we use to describe the increase in disorder, randomness, or unavailable heat energy in a system or nature. Entropy is part of a greater topic called thermodynamics. Some of the laws of thermodynamics state that: 1) energy cannot be created or destroyed, only converted between the different forms, 2)the efficiency of energy systems will be less than 100%, 3)and because efficiency is less than 100%, the unavailable energy is increasing or entropy is always increasing.
Now as far as the name for the reverse process, I am not sure if there is a science term for it? Order, or re-order better? Perhaps one of the other tutors here can come up with it? In the meantime for the paper, un-tear? Or if you're a chef, un-cook? Time travel to the past? Ohh, how about un-dead? Best wishes.
