Since, the time of Sir Isaac Newton, the mysterious force of gravity has intrigued many physicists for centuries. 
The classical anecdote of the apple falling on Newton’s head led Newton to propose that some mysterious force must be pulling that apple downwards. While this was a great leap forward in the field of physics, Newton was not able to explain the nature of gravity. The mechanism by which gravity worked was a problem that puzzled physicists for about two hundred years. The man to solve this fundamental problem was Albert Einstein.
Einstein initially began studying the speed of light in different frames of reference with constant speed. He was able to conclude that the speed of light would always be measured at 300 million meters per second no matter the position of the observer. However, Einstein realized this theory was insufficient to explain the real world, which includes acceleration. In order to do this, Einstein needed to create a theory, which incorporated gravity. As I think more about gravity, it’s easy to understand what it is now. However, during Einstein’s time, it was a very difficult problem to solve because it’s not clear where to begin. How can anyone describe the nature of gravity without any real experimentation? Where do you begin? What experiments can be carried out to confirm the nature of gravity?
Einstein was known for his ability to think in pictures. To solve the problem of gravity, Einstein turned to his usual way of solving problems. This was the thought experiment. As Einstein thought about a person going up in an elevator, he imagined what it would be like if somebody cut the cord. It’s amazing how this simple thought experiment could lead to such profound implications for the universe. Einstein concluded that when the elevator cord was cut, the person would feel weightless. The combination of the person free falling and feeling weightless led to the result that the space around an object must be curved. From this, Einstein knew that an object brought into space curves the space around. Space is a malleable fabric that can be distorted when objects of mass are brought into that space. However, for this radical theory to be accepted, there must be scientific proof. To find the proof, Einstein needed to turn to the astronomers.
How can Einstein show that an object distorts the space around it? What in our nearby universe has the greatest mass? The Sun contains the greatest mass in our solar system and is a great place to study Einstein’s 
theory. Einstein proposed that because the Sun is so massive, during a solar eclipse when the stars are clearly visible, the light from the stars should appear to bend due to the Sun’s curvature of space. The experimental results confirmed that the stars did appear to shift slightly from their position as a result of the light bending to the curvature of space due to the Sun’s mass. It took several years to collect this astronomical proof necessary to convince the physics community that Einstein’s theory of general relativity was accurate.
From Einstein’s thought experiments, we now have a much better understanding of what gravity is. Gravity isn’t some mysterious force that pulls us to the Earth’s surface. Rather, gravity is the curvature of space around an object of mass. This curvature of space is responsible for the force of gravitational attraction, represented by: Fg= G x (m1m2/ r^2). An example of general relativity’s implications includes what is now common to us: GPS. Without Einstein’s calculations that correct for gravity, GPS would be extremely inaccurate.
Further ambitions that stem from this theory of general relativity include unifying it with the quantum world today. A new theory has been proposed to explain what Einstein wanted to do, which was to create a theory of everything. String Theory is a modern theory that seeks to unify relativity with the quantum world. However, currently String Theory is not very testable and so it will be a long time before there is experimental evidence to support this theory.
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