While this rule in nature is more often associated with the study of chemistry, we mention it here for the sake of completeness. One of the great conclusions rendered by science in the eighteenth century was the notion that in any chemical reaction mass is conserved; that is to say, there exists after a reaction just as much mass before the reaction. This is not immediately obvious to anyone who has hauled into the house several cords of wood and have subsequently carried out a few pails of ashes. The person most responsible for suggesting that matter is neither created nor destroyed in a chemical reaction is the French chemist Antoine Lavoisier.


The nineteenth century ended with many of the fundamental ideas in physics and chemistry in serious peril. J.J.Thomson showed that atoms have constituent parts and were therefore not indivisible. Becquerel, the discoverer of radioactivity, was on his way to showing that some atoms were changeable. Max Planck was suggesting that light, which had been declared a wave phenomenon by Thomas Young in 1801, now had particle properties under the right conditions.

Despite all of this upheaval in physics, it is unlikely that anyone anticipated the spate of change unleashed by Albert Einstein in 1905. In other parts of this web site, the reader will see the consequences of Einstein's work with the photoelectric effect, for which he was awarded the Nobel prize in physics in 1921. Later in this unit we will take a first look at special relativity and the odd effects on space and time that follow when objects travel close to the speed of light.

However, his most famous work in 1905 was the synthesis of that which is lumpy and tangible (mass) together with that which is wavy and intangible (energy). He did this ever so succinctly with the relationship E = mc*2, perhaps the most famous equation for anyone who has not studied physics. The rule suggests that there is but one kind of stuff, mass-energy. Under the proper circumstances, a small amount of mass can be annihilated to produce an enormous quantity of energy. Or a high-energy gamma ray, upon colliding with some target, can be converted into matter. It is this famous equation that stands center-stage in nuclear fission and fusion.


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