We should remember that in every scenario where a substance or object succumbs to stress in a way that changes its nature (as discussed in the previous post), the principles of mass/energy equivalence remain in play, as do those of mass/energy conservation. For instance, the sun’s nuclear furnace works by compressing hydrogen atoms into helium (although, not quite so directly), resulting in a loss of mass in the form of energy. But, using the handy equation, E = mc 2 , we can account for the mass of the original hydrogen atoms even after this fusion takes place. It is important to understand something else about mass/energy equivalence too, which is that it does not imply that mass and energy can be converted between states in some trivial way; it says that the mass of a body is a measure of its energy content . One way of thinking about this is to consider unit of measure conversions: one gallon of liquid is equal to 3.785 liters. Although this analogy is far from perfect (it does