Albert Einstein changed Physics forever when he published the theory of special relativity, which showed that mass and energy were interchangeable. This meant that since mass could be converted to energy, the law of conservation of mass was in fact no different from the law of conservation of energy. The equation E=mc2 showed that even a particle at rest has energy, that Einstein named rest energy.
As you already know
E=mc2
You hear the formula all the time but what do the variables mean?
• E = energy (measured in joules, J)
• m = mass (measured in kilograms, kg)
• c = speed of light (measured in meters per second, ms-1)
Note: speed of light has a constant value in a vacuum of 299 792 458 ms-1.
Upon further reflection, the implications of the equation E=mc2 are staggering.
Physicists would conclude that matter is nothing but the condensation of vast amounts of energy, so in other words, if one could somehow unlock all the energy stored in an alkaline AAA battery’s mass that would erupt with force comparable to an atomic bomb.
The most infamous use of this principle was during world war 2 when the worlds first deployed atomic bomb was dropped on Hiroshima, this bomb had the energy of 84TJ.
Now if we were to take a regular alkaline AAA battery of mass 11.5 grams, such a battery would have a rest energy of 1.03 * 1015 joules (Verify with the E=mc2 calculator). Hence if one were able to unlock all the energy in the mass of an alkaline AAA battery (Currently impossible), one would cause destruction equivalent to 12 of the nuclear bombs that were dropped on Hiroshima. Nuclear power plants are a Morden day example of this principle in action.
This helped the scientific community better understand the universe and develop innovations such as the Global Positioning System (GPS). It helped us understand distant phenomena like stars not running out of hydrogen even after billions of years and things close to us like radioactive decay lasting hundreds of years.