This talk is going to introduce you to Albert Einstein’s special theory of relativity, a quite difficult concept to grasp but it is very interesting. The theory explains why time slows down at very high velocities and why different observers have different opinions about time.

****Albert Einstein is someone all of you have heard of, one way or another. He was born in Germany in 1879 and is perceived the founding father of modern physics. He started working on the special theory of relativity while working at a patent office and he published his theory in 1905. Like many revolutionizing theories Einstein’s was rejected by some at first, but by our time it is accepted as a cornerstone of modern physics.

****This whole theory revolves around one constant, the constant c. C is the speed of light in vacuum and is exactly, as you can see, 299,792,458 meters per second. Einstein meant that no matter, energy or information can travel faster than light. He also conveyed that the speed of light is the same for all observers.

****The first person to believe that light was of a finite speed was Galileo Galilei and he tried to decide the speed by having two assistants stand on opposite hills with flashing lights and measure the time it takes for the light to reach the other hill. Since the speed of light is so incomprehensibly fast the measurements didn’t even come close to the actual value of c.

****As I mentioned earlier, the speed of light is supposedly the same for all observers. If a person is sitting in the passenger seat of a car moving at 50 km/h, brings out his pistol and shoots a bullet forward and that bullet has a speed of 300 km/h compared to the car an outside observer will perceive the bullet as if it has a velocity of 350 km/h compared to the ground. This is something most people take for granted because it's something we can see and understand but if the speed of light is constant for all observers then time and space has to change in order for the equations to be equal.

****Say we now have two space ships capable of traveling close to the speed of light. The top ship shoots a beam of light that reflects on a mirror  on the second ship. According to the captain of one of the ships the time it takes for the beam of light to travel is the distance between the two ships divided by the speed of light.

****But say we now talk to an observer on a nearby asteroid watching the two ships fly by. According to that person, the time it takes for the light to travel is  longer than what the captain thinks and as you can see on the picture the length between A and B is shorter than between B and C. They're both right because time is relative. So if the same action takes different amounts of time to different people that must mean that time is flowing more slowly for one of them. This effect, where the appreciation of time changes between different observers is called time dilation.

****This little clip will show to you how it actually works. It is the same examples as I explained to you, to the left is the man on the asteroid's perspective and to the right is the captain's.