When NASA astronaut Scott Kelly completes his yearlong mission on the International Space Station next year, he'll come back just a little bit younger than his twin, Mark, than he was before. This is because time travels more slowly in space, a phenomenon first described by Albert Einstein's 1915 theory of general relativity. This December, universities and academies around the world are celebrating the 100th anniversary of the theory's publication. Even 60 years after his death, Einstein is still the most important scientist of the modern era. Looking back as far as 2,400 years ago, only Newton, Galileo and Aristotle were his equals. Born in the era of horse-drawn carriages, his ideas started a technological revolution that brought about more change in one century than in the 2,000 years before. In 1905, Einstein published four important scientific papers. These completely changed people's ideas about space, time, light and matter. In one of these papers Einstein. introduced his theory of special relativity. Two groundbreaking parts of the theory were about the relationship between mass and energy and the speed of light. Einstein was able to show that mass and energy were connected through the formula E=MC2. The theory also says that no object can travel faster than the speed of light. About 10 years later came his theory of general relativity, the theory that modern physics is really based on. In Einstein's mathematics, space has three dimensions, and the fourth dimension is time. Space and time are part of one continuum, called space-time. The presence of mass changes space-time, which explains where gravity comes from. Computers, satellites, telecommunication, lasers, television and nuclear power, many of the biggest developments in the modern world, can be linked to Einstein's work. "We are a different people than we were a century ago," said astrophysicist Michael Shara of the American Museum of Natural. History, "completely different, because of Einstein." However, there's more to him beyond the image of a science mastermind. Einstein, as a person, has also become a grandfatherly icon in our culture. He liked playing Mozart on his Violin and keeping fit by hiking and walking. Power was not his goal. In 1952, the young nation of Israel asked Einstein to be its president, but he refused. And, yes, he was eccentric. With hair like that, how could he not be? From the article, it can be concluded that  _  .
the theory of general relativity is mainly about space and time the theory of general relativity proves that the speed of light is the fastest of all speeds the theory of general relativity is about math and has nothing to do with physics the most important parts of the theory of special relativity are about space and energy