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 = mc2, 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 doesn’t entirely hold up since mass and energy are not the same things), it does provide a decent insight into what mass/energy equivalence communicates. In a sense, they are two measures of the same quantity. Furthermore, within a closed system, mass and energy cannot be created or destroyed, only transformed.
Oddly, the principles of conservation of mass and energy are part of the supporting evidence for a Big Bang – they imply that everything that is now, must have always existed. The only thing we can assume then, is that all matter in the Universe must have existed within the singularity that preceded the Big Bang. Part of my intent here, of course, is to show that this is probably not true (and, given the current subject, I must point out that my use of the word probably is non-scientific).
So, where does this leave us? Throughout the many posts of this series on Dark Matter, we’ve talked about Gravity Wells, Gravity Bowls, the expanding Universe (Dark Energy), the rigidity of spacetime, E = mc2, and now, stresses and the conservation of mass/energy. What does it all add up to? To find out, we must add a final piece to the puzzle.