General Relativity

You’ve no doubt heard of Albert Einstein before. His name and likeness have become synonymous with “genius.” The story, as it is often told, is that Einstein was an uncommon prodigy who didn’t take school seriously. His success in physics came early and was somewhat miraculous. In 1905, at the age of 26, Einstein had his “Annus Mirabilis” (miracle year) in which he published multiple original scientific papers - any one of which was significant enough to have earned him the Nobel Prize.
Historians have discovered, though, that Einstein’s story is a little more complicated (and a lot more interesting) than what we’ve been told in the past. They say, “Behind every great man is a great woman,” and this seems to have been especially true of Einstein. Read the article, The Forgotten Life of Einstein’s First Wife from Scientific American.
While many important discoveries are attributed to Einstein, none have revolutionized our fundamental understanding of the universe more than Special and General Relativity. Before we can understand “Special Relativity,” we first need to consider plain old “relativity” (sometimes called “Newtonian Relativity”.) The core idea is that the laws of physics are the same for all “inertial reference frames.” Watch the video Frames of Reference for an introduction to what that means.
Einstein’s great innovation was to consider what happens when the proverbial train speeds WAY up. As you will discover, it leads to some truly mind-bending conclusions. Watch this excellent introduction to Special Relativity from Crash Course.
It is important to remember that all of Einstein’s discoveries were built on the prior work of others. For example, the second postulate of Special Relativity (that the speed of light in a vacuum is the same for all observers) was not just a hypothetical assertion, it was based on observations made of starlight back in the 1880s. (If you’re interested in learning more about this famous experiment, you can watch the video, The Greatest Failed Experiment Ever, which is optional.)
Special Relativity only describes objects and reference frames moving at a constant speed. To make his theory more general, Einstein had to extend the mathematics to describe the motion of an object under the influence of an outside force (causing it to speed up or slow down). It took Einstein a full ten years, but when he published his new work, the results were once again astounding. Read 24.1 Introducing General Relativity to understand Einstein’s equivalence principle and its implications for the theory of general relativity.
To see one of the coolest applications of the equivalence principle, check out this brief video about the Star Tours ride at Disney World.