Despite having a day job at the patent office, Einstein spent much of his time developing his own scientific theories. By 1905, he was ready to present his theories to the world. He published four scientific papers that year, each covering a different subject, in a physics journal called the Annalen der Physik. These papers were groundbreaking and set the foundation for modern physics. This burst of scientific discovery is often called the "Miracle Year" by historians.
Photoelectric Effect and Light Quanta
The first paper Einstein published in the Miracle Year was titled "On a Heuristic Viewpoint Concerning the Production and Transformation of Light." This paper introduced the idea that light was not a continuous wave, but was composed of packets that he called quanta. Later, the term "photons" would be used to describe Einstein's small particles of light.
Einstein didn't just pull this idea out of thin air, he deduced the idea from current scientific theories and experiments ran by other physicists. Max Planck's work (Planck's Constant) as well as experimental work on the photoelectric effect performed by Philipp Lenard had a great impact on Einstein's theory.
Photoelectric Effect Source: Wikimedia Commons
This idea that light existed in quanta was initially rejected by the scientific community including most of the great physicists of the day (even Max Planck rejected this hypothesis). It wasn't until many years later, in 1919, when experiments demonstrated the accuracy of Einstein's theory that the theory of photons became more widely accepted. When Einstein was awarded the Nobel Prize in 1921, his work on the photoelectric effect was specifically mentioned. Today, the photon is a fundamental part of modern physics.
Brownian Motion
Einstein's second paper in 1905 was not as groundbreaking as his first, but still proved an important milestone in the history of physics. The paper was titled "On the Motion of Small Particles Suspended in a Stationary Liquid, as Required by the Molecular Kinetic Theory of Heat."
In this paper, Einstein used the random movement of molecules to explain Brownian Motion in liquid. Up until this point, explaining Brownian Motion in liquid had been a stumbling block in the effort to prove the existence of molecules and atoms. By using statistical physics, Einstein was able to explain how the small random effects of millions of tiny molecules could cause the movement of a larger particle (i.e. Brownian Motion). This paper not only proved the existence of molecules and atoms, but also demonstrated the importance of statistical physics in science.
Graph showing the diffusion of Brownian particles Source: Nonequilibrium Statistical Thermodynamics
Special Relativity
Einstein's third paper of 1905 was titled "On the Electrodynamics of Moving Bodies." This paper would later become known as Einstein's Theory of Special Relativity. This paper introduced major changes in the mechanics of physics as the relative velocity between objects approached the speed of light. The results of Einstein's theory introduced several ground breaking concepts including the idea that time, mass, and space are not constant to objects moving at different velocities.
In the paper, Einstein postulated that the speed of light, however, was always constant. It did not change based on the relative velocity of the observer and the light source. He then explored the idea of simultaneous events and concluded that events which appeared simultaneous to one observer may not appear simultaneous to another observer. Unlike many scientific papers, Einstein explained his new theory by describing thought experiments rather than complex mathematics. He used the example of person traveling on a train versus one standing the platform to illustrate how his theory worked.
Einstein also claimed that the mysterious "ether" that scientists had been trying to define for hundreds of years did not exist. This may not sound groundbreaking today, but the concept of the "ether" was an important idea in physics at the time. Dismissing the idea of the "ether" was a daring statement and changed the course of physics.
Einstein drew on the work of Dutch physicist Hendrik Lorentz in defining Special Relativity Source: Royal Library
Mass-Energy Equivalence
The final paper of Einstein's Miracle year was titled "Does the Inertia of a Body Depend Upon Its Energy Content?" This paper introduced one of the most famous scientific equations in history: E=mc2. This paper used some of the concepts Einstein first proposed in his paper on Special Relativity. It demonstrated that the mass of an object is the measure of the object's energy content. Basically, mass and energy were the same thing.
This idea, and Einstein's famous equation, had huge implications. The equation demonstrated that even a small amount of mass contained huge amounts of energy. If you look at Einstein's equation you will see that energy (E) equals the mass (m) times the square of the speed of light (c). The speed of light (c) is a constant and a large number (approximately 300,000 km/sec or 186,000 miles/sec). So, even a small amount of mass multiplied by c2 is going to be a lot of energy. This idea eventually led to the atomic bomb and nuclear energy.
Einstein's famous formula E=mc2 Author: Derek Jensen
Interesting Fact
Einstein also presented his dissertation "A New Determination of Molecular Dimensions" during 1905 earning him a doctorate in physics from the University of Zurich.
