Relativity is a term used to describe the theories of Albert Einstein that fundamentally changed our understanding of space, time, and gravity. There are two main branches of relativity: special relativity and general relativity.

Special relativity, published by Einstein in 1905, is based on two postulates. The first postulate is that the laws of physics are the same for all observers moving at constant velocity relative to one another. The second postulate is that the speed of light in a vacuum is always the same, regardless of the motion of the observer or the source of the light.

From these postulates, special relativity derives some unusual and surprising consequences. For example, it predicts that time and space are not absolute, but instead are relative to the observer's motion. Specifically, an observer moving at high speed relative to another observer will measure time and distance differently. For example, time will appear to be slowed down and distances will appear to be contracted in the direction of motion.

General relativity, published by Einstein in 1915, is a theory of gravity that builds on the insights of special relativity. It proposes that gravity is not a force between objects, as described by Newton's theory of gravity, but is instead a result of the curvature of space and time caused by the presence of matter and energy. General relativity makes many successful predictions, such as the bending of starlight by massive objects and the existence of black holes.

Overall, relativity has revolutionized our understanding of the universe and has been confirmed by numerous experiments and observations.

Albert Einstein was born on March 14, 1879, in Ulm, a small town in southern Germany. His father, Hermann Einstein, was a salesman and engineer, and his mother, Pauline Koch, was a homemaker. Einstein had a younger sister, Maja, who was born two years after him.

When Einstein was six years old, the family moved to Munich, where he started his schooling at a Catholic elementary school. However, he did not enjoy the strict and regimented environment of the school, and his teachers thought he was lazy and unteachable. In 1889, when Einstein was ten years old, the family moved again, this time to Italy. There, Einstein was enrolled in a Swiss school in Aarau, where he excelled in math and science.

In 1896, at the age of 17, Einstein applied to the Swiss Federal Institute of Technology in Zurich (ETH Zurich), but he failed the entrance exam. He spent a year studying at a Swiss school to improve his math and science skills and was eventually admitted to ETH Zurich in 1896. Einstein graduated from ETH Zurich in 1900 with a degree in physics.

Throughout his childhood, Einstein was interested in science and mathematics, and he enjoyed reading books on science and philosophy. He also played the violin and continued to play throughout his life. Einstein's childhood experiences and interests played an important role in shaping his later scientific work and his views on the nature of the universe.