Early life and education
Albert Einstein was born on March 14, 1879, in Ulm, in what was then the German Empire. His family soon moved to Munich, where his father and uncle ran an electrical business. As a boy he was curious about mathematics and science, and he read widely on his own. The common story that he failed math at school is a myth; he was strong in math and physics, though he disliked rigid, memorization-heavy teaching.
In his teens he moved to Switzerland and later studied physics and mathematics at the Polytechnic in Zurich, graduating in 1900. He did not immediately get an academic job. In 1902 he began work as an examiner at the patent office in Bern, a post he held for several years while continuing his research in his spare time.
The 1905 papers
In 1905, while still working at the patent office, Einstein published several papers that are now seen as landmarks. The year is often called his “miracle year.” Four of the papers are most often cited:
- a paper on the photoelectric effect, suggesting that light can behave as discrete packets of energy
- a paper explaining Brownian motion, the jittery movement of tiny particles in a fluid, in a way that supported the reality of atoms and molecules
- the special theory of relativity
- a short follow-up paper on the relationship between mass and energy
He also completed his doctoral degree at the University of Zurich that year.
Special relativity
Special relativity starts from two principles: the laws of physics are the same for observers moving at constant speed relative to one another, and the speed of light in empty space is the same for all such observers. From these, Einstein showed that time and space measurements depend on the observer’s motion. Moving clocks tick more slowly as seen by a stationary observer, and lengths along the direction of motion shrink. These effects are tiny at everyday speeds, but they are measured routinely in particle accelerators and must be accounted for in satellite systems such as GPS navigation. The deeper reason is tied to why the speed of light is a universal limit.
The mass-energy relationship, written E = mc², says that a body’s energy content is linked to its mass. It does not mean that ordinary objects can be easily turned into energy, but it helps explain how nuclear fission releases energy, since a small amount of mass is converted in the process.
The photoelectric effect
When light shines on certain metals, electrons can be knocked out. Experiments showed that the effect depends on the color (frequency) of the light and not simply its brightness, which was hard to explain if light were only a smooth wave. Einstein proposed that light energy comes in small packets, later called photons, each carrying energy proportional to its frequency. This explained the observations and became an important building block of quantum physics. It was this work, not relativity, that was cited when he received the Nobel Prize in Physics, awarded for 1921.
General relativity
Special relativity did not include gravity. Over about a decade, Einstein worked toward a broader theory, and he presented the general theory of relativity in late 1915. In it, gravity is not a force pulling through space but a result of mass and energy curving space and time, with objects following the straightest possible paths through that curved geometry. It was a major step beyond Newton’s description, and it is the center of the story of the theory of gravity.
The theory made testable predictions. One was that starlight passing near the Sun would be deflected. Measurements made during the solar eclipse of 1919 by teams led by British astronomers were reported as supporting the prediction, and the result made Einstein internationally famous. Later tests have been far more precise. General relativity also underlies modern ideas about black holes and the expansion of the universe, and the 2015 detection of gravitational waves matched its predictions.
Later life
Einstein held university positions in Zurich, Prague and Berlin and became director of a physics institute in Berlin. After the Nazis came to power in 1933, he, who was Jewish, did not return to Germany from a trip abroad. He settled in the United States and joined the Institute for Advanced Study in Princeton, New Jersey, where he worked until his death on April 18, 1955.
In 1939 he signed a letter to President Franklin Roosevelt, largely drafted by the physicist Leo Szilard, warning that nuclear weapons might be possible. Einstein did not work on the Manhattan Project. Afterward he spoke publicly in favor of arms control and civil rights.
Einstein also had a long, uneasy relationship with quantum theory. He contributed to its beginnings but doubted that it was a complete description of nature. His later decades were spent searching for a unified theory, which he did not find. Physicists still look for a way to combine gravity and quantum physics.
Legacy
Einstein’s name became shorthand for genius, which can obscure the fact that his ideas were developed with help from contemporaries such as Max Planck, Hendrik Lorentz, Henri Poincaré and Marcel Grossmann, who assisted him with the mathematics of general relativity. His work changed how scientists think about time, space, light and gravity, and many technologies rely on the physics that grew from it.