Albert Einstein was a baller. I think that is safe to say. Without him, our understanding of the cosmos could be severely more limited than it is today. He was ahead of his time in every sense of the phrase. Let's have a look at his two most famous contributions.

Special Relativity:

Einstein liked to do what he called, "thought experiments". One day, when he was young, he tried to imagine himself flying next to a beam of light in outer space. He couldn't conceive how the wave-front of the light would look like if it had no relative motion to the observer. So he decided, like a boss, that light always keeps a constant speed relative to the observer. This speed is about 186,000 miles per second. Holy shite muslim that is fast! Ok, cool. So what? Why does that matter?

Well, if light is going to be so stubborn about its speed, regardless of how fast you are moving, some pretty trippy things happen to time and space when the observer approaches the speed of light. This is how he presented Special Relativity in 1905. At the time, he could only work out the details for observers moving at a constant velocity. This is why it is called "special" relativity, as in it only applies to special circumstances.

So what happens to time and space? The faster the observer is moving, the slower time passes for him. This is called time dilation. The token example is called the twin paradox. If two twins were born on Earth, and one of them is sent on a round trip on a spaceship traveling near the speed of light taking 20 Earth years, when the space twin returns he will be less than 20 years old. He may have only experienced 15 years. This actually isn't a great example because it is not accurate, the spaceship would have to undergo acceleration to make a round trip, and that is not a constant speed situation. It is always taught though, and it gets the point across.

The other effect is called length contraction. When an observer approaches light speed space begins to contract around them. The token example of this is a flying wooden beam that is too long to fit in a barn. How fast would the beam have to be moving to fit inside the smaller barn? You can probably see the point of the exercise.

The final effect is related to simultaneous events. The famous train example has a stationary observer watching a train go by, and a man in the riding in the middle of the train. Two lights go off at opposite ends of the train. In one frame of reference, they are simultaneous. In the other, they are not.

Alright, those are the basics of special relativity. Let me catch my breath...

Ok, General relativity was an extension of special relativity. It includes accelerating reference frames as well as constant velocity reference frames. It is INCREDIBLY complicated, the most difficult mathematics I have ever been forced to do. Every variable in the main equation is a 12x12 tensor i.e. 144 numbers. It is mostly done by computers nowadays, but as a grunt undergraduate, I had to first learn how to do it by hand. Einstein found that being in an accelerated reference frame is no different from being in a gravitational field. The presence of matter or energy will bend the fabric of space and time, and other material objects will follow this curved space. Hence, the Earth's motion around the Sun.

That's it. I hope you enjoyed.