Modern Physics
Probably the most famous equation in all of physics comes, as should be no surprise, from the crazy-hair-covered head of Albert Einstein. He theorized, in 1905, that energy was really just the same thing as mass. In Albert's words, "the mass of a body is a measure of its energy-content."1 You've heard the formula before:
E = mc2
Einstein was saying that the amount of energy in a small amount of mass is massive (pun most definitely intended). The speed of light is 3 × 108 m/s, a huge number—and squaring it means 1 kg of mass has 9 × 1016 J of energy.2
To put this in perspective, on December 26, 2004 there was a gargantuan earthquake in the Indian Ocean, with a magnitude of over 9.0 on the Richter scale. It dropped 1,000 miles of Earth's crust down about 50 feet and caused catastrophic destruction in Indonesia.
The earthquake produced, according to the US Geological Survey, right around 11 × 1016 J of energy, or right around what you'd get from all the energy stored in the mass of a decently sized meatloaf.
Einstein's discovery was a tremendous success for the early pioneers of conservation of energy (like our friend Joule), showing that these conservation laws extend beyond one quantity and could connect multiple aspects of our universe. Physicists are always trying to unite what seem like disparate phenomena in an overarching idea—just ask any particle physicist about the Theory of Everything, the coveted Holy Grail of modern physics. Einstein firmly took science one step in that direction with his paper, titled "Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?'' ("Does the Inertia of a Body Depend Upon Its Energy Content?'' for those of us who aren't Swiss patent clerks).
For better or for worse, one of the major innovations that Einstein's derivation of E = mc2 paved the way for was the atomic bomb. While Einstein had only a very minor role in the Manhattan Project (the US effort to develop the bomb), it was his idea that proved the physics behind the bomb were sound.
Einstein's discovery of mass-energy equivalence led to the law of conservation of mass and energy, a grander version of the law of conservation of energy. It says that, since mass and energy are really two forms of the same quantity, a system really conserves the total amount of mass plus energy. In all the examples we've seen in this chapter, the masses of our objects—blocks, balls, cars, and so on—aren't changing, so we only need apply the law of conservation of energy. But nuclear fission works very differently than blocks and balls.
In a uranium bomb (or a uranium power plant, if that makes you feel better), uranium-235 is bombarded with free neutrons to form uranium-236, which splits into smaller elements, such as barium and krypton. But the mass of these smaller elements is less than the starting mass of 236U—the missing mass is converted into energy via the law of conservation of mass and energy and Einstein's formula, E = mc2. One fission of a 236U atom creates 3.2 × 10-11 J of energy.3
Admittedly, that isn't very much energy. But a bomb with just 1 kg of 236U can create 83 × 1012 J of energy—the energy of almost 20,000 tons of TNT, twenty-five Airbus A330s, or every single explosion ever depicted in a Michael Bay film—excluding Armageddon, which has a nuclear bomb in it (spoiler: it explodes) and so doesn't count.