Question

Whose inventions and theories transformed many concept related to space

Answer 1

Einstein's career was peripatetic. He earned his doctorate in 1905, and subsequently took on professor positions in Zurich (1909), Prague (1911) and Zurich (1912). Next, he moved to Berlin to become director of the Kaiser Wilhelm Physical Institute and a professor at the University of Berlin (1914). He became a German citizen. 

A major validation of Einstein's work came in 1919, when Sir Arthur Eddington, secretary of the Royal Astronomical Society, led an expedition to Africa that measured the position of stars during a total solar eclipse. The group found that the position of stars was shifted due to the bending of light around the sun. Eddington's results rocked the foundations of science, according to Rowan Hooper, a film critic for New Scientist. Set against the backdrop of World War I, the British Eddington's acceptance of the German Einstein's theory meant that the ordered universe of Isaac Newton, also British, was replaced with an entirely new philosophy. (In 2008, a BBC/HBO production dramatized the story in "Einstein and Eddington.") 

"When that was published in the press, Einstein became this global celebrity," Cliff told Space.com. "Even today there aren't many scientists who are household names, like Stephen Hawking. Einstein was the first of those [modern] celebrities."

Einstein remained in Germany until 1933, when dictator Adolf Hitler rose to power. Einstein then renounced his German citizenship and moved to the United States to become a professor of theoretical physics at Princeton. He became a U.S. citizen in 1940 and retired in 1945.

Einstein remained active in the physics community through his later years. In 1939, he famously penned a letter to President Franklin D. Roosevelt warning that uranium could be used for an atomic bomb. 

"It was one of the key triggers behind the Manhattan Project," Cliff said, referring to the successful effort the United States initiated to build nuclear weapons during WWII. "That letter persuaded the government to take it seriously. His voice was heard at the top of government."

Late in Einstein's life, he engaged in a series of private debates with physicist Niels Bohrabout the validity of quantum theory. Bohr's theories held the day, and Einstein later incorporated quantum theory in his own calculations. 
Scientific work
Einstein's legacy in physics is significant. Here are some of his key scientific principles that he pioneered:

Theory of special relativity: Einstein showed that physical laws are identical for all observers, as long as they are not under acceleration. However, the speed of light in a vacuum is always the same, no matter at what speed the observer is travelling. This work led to his realization that space and time are linked into what we now call space-time. So, an event seen by one observer may be seen at a different time by another observer. 

Theory of general relativity: This was a reformulation of the law of gravity. In the 1600s, Newton formulated three laws of motion, among them outlining how gravity works between two bodies. The force between them depends on how massive each object is, and how far apart the objects are. Einstein determined that when thinking about space-time, a massive object is a distortion in space-time (like putting a heavy ball on a trampoline.) Gravity is exerted when other objects fall into the "well" created by the distortion in space-time, like a marble rolling towards the large ball.

Photoelectric effect: Einstein's work in 1905 proposed that light should be thought of as a stream of particles (photons) instead of just a single wave, as was commonly thought by the time. His work helped explain some curious results scientists saw at the time. The photoelectric effect refers to how electrons are ejected from the surface of a metal due to incident light. The "wave" theory of light suggests that the electrons should be ejected with more energy when the incident light is increased, but experiments showed that the energies are actually independent of the radiation intensity. "It was a difficult idea to accept at the time," Cliff said. "It contradicted the 19th-century wave picture of light."

Unified field theory: Einstein spent much of his later years trying to merge the fields of electromagnetism and gravity. He was unsuccessful, but Encyclopedia Britannica suggests that Einstein was ahead of his time because, for example, the strong force in quantum mechanics was better understood in the 1970s and 1980s. Other physicists are still working on this problem.