# Time Dilation and Relativity

Of all that we have known in physics, the Galilean laws, the Newtonian laws, the discovery of the speed of light along with many others govern the mind. In the eyes of Physics, in the 20th century physics the very concept of Relativity was a Renaissance.

Relativity can be said to be  the single most influential physical theory till the 21st  century for the way it has changed our view of the universe. Not that other discoveries in physics were less significant, but few of them have been so well received by the general public. Relativity has grabbed people’s imagination and sparked discussions in philosophy and religion which last until the present day. Quantum physics, although perhaps more pertinent to daily life, is a close second.

The notion of relativity is not as revolutionary as many believe. In fact, spatial relativity is part of our everyday experience. Spatial relativity is also called Galilean relativity in honour of Galileo who first formulated the concept of relative motion.

The pioneer of the special and general theory of relativity, Albert Einstein, opined that  “Relativity teaches us the connection between the different descriptions of one and the same reality.” His Special Relativity is based only on two simple postulates:

1. The  laws of physics are the same in all inertial (non-accelerating) reference frames, and

2. The speed of light in free space is constant.

A preeminent feature of General Relativity is its view of gravitation.

The notion of relativity is not as revolutionary as many believe. Infact, spatial relativity is part of our everyday experience. Spatial relativity is also called Galilean relativity in honour of Galileo who first formulated the concept of relative motion.

One of the most enthralling aspects of Relativity is its new understanding of time. If the speed of light is constant, time cannot be constant. Infact, it doesn’t make sense to speak of time as being constant or absolute, when we think of it as one dimension of spacetime. Special Relativity states that time is measured according to the relative velocity of the reference frame it is measured in. Despite of the simplicity of this statement, the relativistic connection between time and space are hard to imagine.

There are numerous ways to illustrate this:

The four dimensions of spacetime.

In Relativity the world has four dimensions: three space dimensions and one dimension that is not exactly time but related to time. In fact, it is time multiplied by the square root of -1. Say, you move through one space dimension from point A to point B. When you move to another space coordinate, you automatically cause your position on the time coordinate to change, even if you don’t notice. This causes time to elapse. Of course, you are always travelling through time, but when you travel through space you travel through time by less than you expect. We can consider the following example: