The 1905 Theories
The months when the papers were submitted to the journal suggests that most of the work was done in 1904 and early 1905, a conclusion supported by Einstein's letters to friends and peers.
MARCH: Quantum of Light and the Photoelectric Effect
This article about the structure of light was the work that earned Einstein the Nobel Prize. Before 1905, the exact nature of light was an important research topic. The accepted idea, at the time, was that light was a wave. Newton had earlier speculated that light is matter, and other scientists had proposed that light consists of discrete entities. Neither theory could explain certain electrical effects of light, such as fluorescence. In 1900, Max Planck had shown that radiating energy, such as heat, is transferred in discrete packets of energy, which he called quanta of energy. It was in 1905 that Einstein applied this principle to the structure of light. Einstein suggested that light has a dual nature, with properties of both waves and particles. It was a radical idea. Even after experiments proved the equations were correct, many physicists still rejected the concept of light particles (now known as photons).
MAY: Brownian Motion and Atomic Theory
Robert Brown had reported in 1827 random movements of tiny pollen particles in liquids, but no one knew why they moved. At the same time, physicists were debating whether atoms were real, or just a useful idea. Einstein's paper gave reasons for the motion, and evidence, that atoms exist. The paper's statistical approach to atomic behavior even gave experimental scientists a way to count atoms using a standard microscope.
JUNE: The Special Theory of Relativity
The basic idea of relativity was understood long before 1905. Relativity simply means that two physicists conducting identical tests will obtain identical results, if they remain at the same speed relative to each other. In other words, if one stays in the lab while the other is on a ship moving away at a constant speed, their test results will be the same. Unless, according to the dominant theory in 1905, the physicists were measuring the speed of light. But Einstein believed that relativity should apply to light as well. He used fairly basic math, and a fresh view of space and time, to prove it. It is today called the "special" theory to set it apart from his "general" theory of 1916, which factored in gravity and acceleration. (Consider a third physicist in a space shuttle, measuring the speed of light during the shuttle launch.)
SEPTEMBER: Equivalence of Mass and Energy
The equivalence of mass and energy for a moving object was discussed by Newton in 1717. In a logical extension of the Special Theory, Einstein linked energy (E), mass (m) and the speed of light (c), in a way that implied that a little bit of matter could be converted into a large amount of energy when traveling at speeds approaching the speed of light. Later on, Einstein would express this relationship in the terms: E=mc2. His 1905 work with mass and energy was not related to the later physics of nuclear fission. But the 1945 nuclear bombing of Japan was often described as an example of mass being converted into energy. As a result, many people came to believe, incorrectly, that Einstein and his formula were responsible for the Nuclear Age.
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