Einstein's Theories

Einstein's theories of relativity literally changed physics forever at a time when most people didn't even understand Newton's laws of gravity. Einstein literally blew many peoples' minds, mostly because they had no idea what he was talking about. Space-time can be bent and stretched? Time is not constant? Gravity isn't really a force? What gives?

Einstein created two relativity theories. Special relativity and General relativity. So, what's the difference?

Special relativity deals with the structure of space-time, and it was controversial because it declared that the speed of light is a constant, not time or space like everybody thought. Einstein linked space and time together as if it were a fabric that could be bent, stretched, and compressed. However, Einstein dealt more with this idea in his theory of General relativity.

Special relativity says that the speed of light is the same no matter how fast you, the observer, are traveling or how fast the light source is traveling. Where the relativity comes in is the fact that time is relative to how fast you are going relative to an observer that is not moving. As one goes faster, time slows down, but only relative to the observer that is not moving. In other words, your clock moves slower as you speed up and at the speed of light your clock stops moving. This is the idea of time dilation.

Another important idea of special relativity is that the speed of light can't be exceeded. Thus the speed of light is finite. No physical object can exceed this cosmic speed limit.

Special relativity also introduced the idea that matter and energy are related by the now famous E=mc^2 equation. The reason for its inclusion is the speed-of-light-squared term.

General relativity deals with Einstein's concept of how gravity works and his theory depends on the idea that space-time is relativistic, which means that it can be distorted around anything that has mass. A large mass like the Sun distorts space-time so that other objects are forced to fall into it. The only way to not fall in is to be traveling fast enough or be in orbit around it. So, it means that the Earth is always falling toward the Sun but it's moving fast enough to keep from falling in. The same thing goes for the moon. It's always falling toward the Earth but travels fast enough to remain in a stable orbit.

Einstein's idea that space-time can be curved was very controversial and many physicists refused to believe it until there was observational proof, which was obtained during an eclipse by measuring how the starlight from a star whose light traveled near the edge of the sun was curved by the Sun's mass. The amount of curvature matched Einstein's theory.

Some of the strange consequences of the General relativity are that a rotating mass pulls space-time around as if it were dragging it. The universe is expanding because space-time is being expanded, and the furthest parts of space-time are expanding faster than the speed of light. Orbits precess near large masses like the Sun and as in the case of binary pulsars. This (precessing) is like a spinning top action. Clocks run slower in a deep gravitational well. This is known as gravitational time dilation.
Okay, this describes the basic nature of Einstein's two theories of relativity. In the next post, I will delve into the theories more physically.

Thanks for reading.