Theories in Physics: Special Relativity

Albert Einstein is considered one of the greatest minds of all time due to his creation of a very large branch in present-day physics called Relativity. Relativity is a theory that consists of two other theories. The first is called Special Relativity, but really what’s so special about it?

Special Relativity was proposed by Albert Einstein in 1905 and essentially connects space and time. It was based on two postulates:
1. The laws of physics are the same in all inertial frames*.
2. The speed of light in a vacuum is the same for all observers. (299,792,458 m/s).

A very famous example of this that many physicists use is imagine that you’re standing at a train station and you’re waiting for a train to arrive that your friend is on, and you are also in a vacuum. The train is moving at half the speed of light, and the train also has a headlight on its front. So how fast would the light from the headlight be approaching you? If you said: the light from the headlight travels at the speed of light and the train itself is traveling at half the speed of light so therefore the light would be approaching you at 1.5 times the speed of light, you would be wrong.

So in this example there are actually two inertial frames, since the speed of the headlight can be calculated from both the train station and the train. It can be calculated from the perspective of your friend on the train and yourself on the train station. From the perspective of your friend he or she is not moving, but simply the train station is moving towards them. Where as from your perspective, you are not moving and it seems that the train is coming towards you. So therefore since you are both in an inertial frame the laws of physics will be the same for both you and your friend, which proves postulate one, and since you are both in a vacuum the speed of light is still the same as well which proves postulate two. Therefore the speed of the light from the headlight is the actual speed of light and not one and a half times it.

So special relativity is pretty special after all; however today we simply understood the basics of it. There are many other properties of special relativity like bending time and changing speed from different points that have been experimented on by scientists throughout the ages. Maybe one day you’ll be diving into the possibilities that the theory os special relativity holds and learning how to bend time all by yourself.

*Inertial frames: the reference points where the light is being observed from.

Two inertial observers move relative to each other

Picture Source: einstein-online.info