# How Humans Perceive things with Relativity

## 1. The Object Thrown from Train

A boy traveling inside a train passing through a level crossing throws a bag full of finished biscuit packets and sees that the bag fell vertically straight on the ground. A man waiting across the level crossing for the train to pass sees that the bag fell parabolically on the ground from where the boy has thrown it. So, what is it that has made the difference between both observers?

### Relative difference of two Observers

The boy observes the ball to fall vertically straight as both the boy and the train are moving horizontally in uniform motion. But the man outside the train would see it falling parabolically as the ball has a constant horizontal velocity which is the same as that of the train but it has a varying vertical velocity.

## 2. The object in Moving Frame

When we are inside a moving object that is moving with uniform velocity, we feel like we are at rest. But suddenly the brakes are applied and we suddenly get a jerk moving from our places. We are at rest w.r.t the frame of reference of the bus, but for a man outside the bus on the other side of the road, it appears as if we’re also moving. For him, the people inside the bus are moving with the velocity of the bus. The frame of the man standing on the street is the road.

Now consider a girl travelling on another bus in the same direction as yours. What that girl sees in your bus totally depends on the relative speed between the two buses. If both of your buses are moving at the same speed, it will appear to both of you as you’re at rest, or else both of you are in relative motion.

So, now we can see how the frame of reference plays such a massive role in the observation and theory of relativity.

### Is there any absolute Frame

These examples show us that there’s no absolute frame of reference; that nobody is at absolute rest or in absolute motion. Motion is always relative. We can also say that it depends upon the perspective of the observer as to how he or she sees things and from where or which frame of reference.

## 3. Relative Simultaneity:

Simultaneity is based on the concept that whether two spatially different events take place simultaneously depends upon the observer’s frame of reference. For instance, two lightning occurs in the night. A passenger inside a train sees the lightning A first and the lightning B just a moment later. It appeared as if they occurred at different points of time. But to a man stranded on the railway platform, it appeared as a simultaneous event, i.e., both the flashes of lightning took place at the same time.

## Relative Observation of Lightning by two Observers

The lightning A appeared to have occurred first to the passenger on the train as the train was moving towards it. So the light reached the passenger’s eyes earlier than lightning B which occurred behind the train, or we can say the train was receding from lightning B and approaching lightning A.

This is called the Relativity of Simultaneity. This concept is another example of Einstein’s brilliant imagination.

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Author: Som Abhisek.