E = mc²
E = mc² is the most famous equation in the world. Albert Einstein set it up and used it to describe the equivalence of mass and energy. Einstein actually set them up to describe radiation that leaves a body. He said that when radiation leaves an object, it always loses mass. Because of the equivalence of space and time, the equation can be given more abstract meaning.
E = mc² from the perspective of absolute theory
According to the absolute theory, E = mc² always applies, because the absolute energy content of a body is always the mass multiplied by the speed of light squared. Albert Einstein also attached greater importance to the formula, as he based his theory of relativity on space-time with c as velocity. However, one must recognize that E = mc² is an absolute equation, not a relative one. When I read a book about Albert Einstein for the first time at the age of 11 and came into contact with E = mc² for the first time, I was already in doubt whether this equation was even true. Because energy is still a term made up of mass and speed. If E = mc² also applies to me, then I would have to move at the speed of light, which I couldn't imagine at the time.
The solution to this question is the absolute theory that we are moving at speed of light relative to the origin that was created during the Big Bang. In the end, however, movement does not only consist of locomotion, as can also be read under Equivalence of space and time. Ultimately, I can't say exactly what speed consists of, but at least it is about locomotion, rotation and pulsation.
It is clear to me today that of course the table that stands in front of me only has an absolute energy of E = mc², and that this energy does not affect me relatively. Accordingly, E = mc² only makes sense in the absolute context. Of course, matter ultimately consists of particles that move with speed of light, but E = mc² applies and must apply not only to these small particles, but also to me and every other object in this universe.
Nuclear bomb and E = mc²
The atomic bomb was quickly constructed from the equation E = mc². So the physicists quickly realized how much energy there is in the mass. One now and then wrongly assumes the conversion of mass into energy. In the atomic bomb, uranium or plutonium is split into two smaller elements. These two smaller elements have less binding energy overall, so this binding energy is converted into the bomb's destructive energy and power. In the case of radioactive materials, this process simply begins when the critical mass is reached. If you collect so much uranium or plutonium in one place, the chain reaction starts automatically and splits all the starting material. It is also believed that mass is lost in this process, but the photons that cause the destruction and explosion also have mass. You can read more under mass and momentum of a photon. Ultimately, this also results from E = mc², because photons definitely have an energy other than zero.