We have two scientific theories... The Law of the Conservation of Energy, which states that the amount of net energy in a closed system remains constant (nothing spontaneously creates or disappears) and the Law of the Conservation of Mass, which states the same but for mass. Essentially, both state that in a closed system, things do not appear or disappear. The amount of mass and energy in the universe is the same as it was at the dawn of man and will be the same at its demise, granted that energy and mass will take on different forms, but the quantity of energy and mass remain constant. I would add that mass can become energy (such as gasoline combustion) and energy can become mass (such as weather). They are interchangeable if the correct conditions are present--in the case of weather that condition would be sunlight; in the case of gasoline combustion that would be fuel, oxygen, and ignition. When you die your body decomposes and the electrical impulses...