Albert Einstein was born on March 14, 1879 in Ulm, Germany. As Albert grew up he loved taking lessons on the piano and the violin. Then when he was about ten or eleven he grew the curiosity about mysteries of science. As he grew up into an adult he worked as a patent clerk in Bern, Switzerland. This is when Mr. Einstein published four of his research papers, one of them being the Special Theory of Relativity or as most people know it as E=MC².
By 1915, Albert Einstein finished the General Theory of Relativity. Then in 1921 he was rewarded the Nobel Prize in Physics. This is when his name became popular in all households and was found with all the rest of the stars. Today over half of your devices you use at home has something to do with Albert Einstein. Such as the television, remote control, automatic door openers, lasers, and DVD players. Einstein later passed away on April 18, 1955.
So we begin with the first relativity being the Special Theory of Relativity. Special Theory of Relativity means a physical theory of relativity based on the assumption that the speed of light in a vacuum is a constant and the assumption that the laws of physics are invariant in all inertial systems. Albert Einstein created many different experiments one being where Mrs. Einstein is standing in a field and Mr. Einstein is standing on a railroad car that is moving with velocity while Mrs. Einstein shines a light in the direction Mr. Einstein is traveling. So you wonder what happens. Well because of the principle of the constancy of the velocity of light, each observer will measure the light beam from the flashlight as traveling at the same speed. This may be contrary to what you expected as you might have thought that the observer in the field would have seen the beam moving at (the speed of light) + (the speed of the train). Nevertheless, this is not what is observed in practice. What is actually occurs in the real world is that no one ever measures