The reason is that whenever you convert part of a walnut or any other piece of matter to pure energy, the resulting energy is by definition moving at the speed of light.
Why, then, do you have to square the speed of light? It has to do with the nature of energy. When something is moving four times as fast as something else, it doesn't have four times the energy but rather 16 times the energy—in other words, that figure is squared. If we think of c , the speed of light, as one light year per year, the conversion factor c2 equals 1. Energy and mass are the same. According to scientific folklore, Albert Einstein formulated this equation in and, in a single blow, explained how energy can be released in stars and nuclear explosions.
This is a vast oversimplification. Einstein was neither the first person to consider the equivalence of mass and energy, nor did he actually prove it. Anyone who sits through a freshman electricity and magnetism course learns that charged objects carry electric fields, and that moving charges also create magnetic fields.
Hence, moving charged particles carry electromagnetic fields. In J. Thomson , later a discoverer of the electron, made the first attempt to demonstrate how this might come about by explicitly calculating the magnetic field generated by a moving charged sphere and showing that the field in turn induced a mass into the sphere itself.
The effect is entirely analogous to what happens when you drop a beach ball to the ground. But this is not the whole story. Drag or no drag, in order to fall the ball must push the air ahead of it out of the way and this air has mass. Thomson understood that the field of the sphere should act like the air before the beach ball; in his case the effective mass of the sphere was the entire mass induced by the magnetic field.
These claims have spawned headlines accusing Einstein of plagiarism, but many are spurious or barely supported. Where did he get it from, and why is the constant of proportionality wrong?
He might have achieved much more if he had not been killed in the First World War. All this was based on classical electrodynamics, assuming an ether theory. The greatest hindrance is that they are written from an obsolete world view, which can only confuse the reader steeped in relativistic physics. If he had merely said that E is proportional to m , history would probably have been kinder to him. You can get the right answer with classical physics, says Rothman, all in an ether theory without c being either constant or the limiting speed.
However, the controversies that have been previously aroused over the issue of priority perhaps account for some of the reluctance of historians of physics to comment when contacted by physicsworld.
More practically, it is the amount of energy that would come out of a 1 gigawatt power plant, big enough to run 10 million homes for at least three years.
A kg person, therefore, has enough energy locked up inside them to run that many homes for years. Unlocking that energy is no easy task, however. Nuclear fission is one of several ways to release a tiny bit of an atom's mass, but most of the stuff remains in the form of familiar protons, neutrons and electrons.
One way to turn an entire block of material into pure energy would be to bring it together with antimatter. Particles of matter and antimatter are the same, except for an opposite electrical charge. Bring them together, though, and they will annihilate each other into pure energy.
Unfortunately, given that we don't know any natural sources of antimatter, the only way to produce it is in particle accelerators and it would take 10 million years to produce a kilogram of it. Particle accelerators studying fundamental physics are another place where Einstein's equation becomes useful. Special relativity says that the faster something moves, the more massive it becomes.
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