Albert Einstein developed the theory of relativity. After university, Einstein could not find a teaching job and took a job at the patent office. Einstein became a Swiss citizen in 1901. In 1905 he also earned his doctor's degree from the University of Zurich. Albert Einstein became famous around the world. Einstein won the Nobel Prize in Physics. In the 1920s, Einstein traveled to give lectures in Europe, America and the Far East. In 1933, Einstein left Germany for America. He never returned to Germany. He began work at the Institute for Advanced Study in Princeton, New Jersey. Einstein became a United States citizen in 1940.
In 1913, Einstein urged astronomers to measure the effect of gravity on starlight. He published his general theory of relativity in 1915. In 1919, astronomers photographed stars during a total solar eclipse to test whether the Sun's gravity bends starlight. The 1919 eclipse expeditions went to Principe and Sobral. Sobral gave 20 useful photographic plates and Principe gave two. By the 1920s, special and general relativity were widely accepted by physicists. General relativity gave a more accurate prediction of planetary orbits around the Sun than Newton's theory did. General relativity was the first major theory of gravity since Newton's, more than 250 years before. Gravitational lensing happens when a massive object warps space and time so that light bends, distorts and magnifies as it passes around the object.
Special relativity says the speed of light in a vacuum is the same for any observer. Einstein recognized that if you move away from a clock near the speed of light, the clock you see will be slow. It is impossible for any matter to travel faster than the speed of light. When the GPS satellites were launched, engineers realized they needed to correct for relativity to get accurate time on Earth. For GPS satellites, special relativity says their clocks should fall behind by 7 microseconds per day, while the weaker gravity in orbit speeds them up by 45 microseconds per day. As of November 2026, atomic clocks on GPS satellites run 38 microseconds per day faster than clocks on Earth.
General relativity says that gravity is how mass warps space and time. Einstein's mathematics showed that massive accelerating objects, such as neutron stars or black holes orbiting each other, would send waves of undulating space-time in all directions. Einstein was convinced it would never be possible to measure gravitational waves. In 1974, Hulse and Taylor found the first proof that gravitational waves exist. Gravitational waves were first observed directly on September 14, 2015. The first gravitational waves seen came from two black holes of about 29 and 36 times the mass of the Sun that collided 1.3 billion years ago. Einstein predicted gravitational waves in his general theory of relativity, about a hundred years before they were first observed. His ideas changed how scientists think about time, space and the universe.
