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E=mc2
Dr Duncan L Copp
August 2005
E=mc2, the world's most famous equation, was formulated by Albert Einstein 100 years ago this year. The equation has totally revolutionised our understanding of the world around us; its implications rippling out to the furthest reaches of the Universe. Through this equation, Einstein was able to describe the incredible and profound connection between energy, matter and light. Yet, as with so many scientists, Einstein came to his conclusion only by 'standing on the shoulders of giants'. The understanding of each letter of this beautifully simple equation came from a long history of blood, sweat and toil.
E is for energy
How would you describe energy? Heat from a coal fire? A bolt of lightning? Sunlight? In fact, all of these are the expression of energy. But remarkably, less than 200 years ago, scientists considered these phenomena as very separate and totally unrelated – no notion of an overarching theory of energy existed.
Michael Faraday changed this perception in the early 1800s. Although he had scant training, Faraday, born in Surrey, had a passion for science. In particular, he was gripped by a newly discovered observation associated with electricity: the mysterious way a compass needle was deflected when placed close to a wire through which an electric current flowed.
Faraday mused on this observation. He noticed that the position of the needle changed with the position of the compass relative to the wire. He concluded that an invisible force was acting on the needle; a force that rotated around the wire. He discovered that when an electric current flows through a wire, a magnetic field is formed at right angles to the direction of flow. But Faraday went a step further.
Next, he turned the experiment on its head. If an electric current in a wire could generate a magnetic force that moved a compass needle, could a magnet deflect a wire with a current flowing through it? Faraday imagined that a magnet also had an invisible force flowing around it. He was right.
Faraday's observations led to the monumental discovery that electricity and magnetism are one and the same thing; they are two expressions of the same energy. He called it 'electromagnetism'.
The discovery of electromagnetism began a revolution in the concept of energy. It was now understood that one form of energy could be transformed into another form of energy; energy was in fact 'conserved'. Energy, not a series of discrete forces, was actually the same force manifested in different ways.
Einstein knew this had big implications for his great equation, since he delved into the nature of energy that is contained deep within the heart of matter.
m is for mass
Understanding matter or mass would fall to a Frenchman Antoine-Laurent Lavoisier, a meticulous taxman and astute scientist. During the last decades of the 1700s, when Lavoisier lived in Paris, the science community thought that as substances reacted, eg when wood burned or metal rusted, the mass of these objects was simply lost.
That loss of matter, it was thought, came from the release of a substance called phlogiston. For example, wood, which contained a certain amount of phlogiston, when burnt, was reduced to ashes weighing less than the original wood. It was thought that during burning the wood lost its phlogiston, which simply vanished into thin air.
Lavoisier changed chemistry from a qualitative to a quantitative science. He didn't believe that an unknown amount of a mystery substance was lost in a chemical transformation like the burning of wood or rusting of metal. He was convinced that if he could trap and weigh the substances given off during a reaction, and weigh the remaining substance after the reaction, the two added together would equal the weight of the original material. In other words, Lavoisier thought that in any transformation of matter, no mass was lost or gained.
After years of experiments, in which he chopped, melted, burned and boiled every conceivable substance, he demonstrated his belief. Metal may rust and wood burn, but the tiny atoms that make up these substances are never lost. Matter is conserved, in much the same way energy is conserved.
Lavoisier's astonishing insight into matter is crucial in E=mc2, since it shows that matter can be broken apart and recombined, but never lost – with 'm', nothing disappears.
Next: Part 2 >>
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