Where does used energy go? If it doesn't go anywhere, and still exists after being used, shouldn't infinite energy exist?
well you see, Billy, the there is a very important distinction between usable work and heat. The laws of thermodynamics dictate that the latter will comprise more and more of the energy in the universe until no usable energy is left, and no work can ever be done. This is called the heat death of the universe.
When youre farting youre releasing energy and eventually, in 1000million years, the fart molecules find themself again on another planet, forming a corn of sand on a beatiful beach. Then the planet explodes and your fart becomes energy again, the fart may exist infinitly often but its always the same bunch of energy.
Energy turns into heat which eventually cools, killing us all