# Does the Fourth Dimension of Time Exist? What You Need to Know

Time is the fourth dimension, other than the three dimensions of space. Time makes change possible or else we would be living in a static universe.

Omkar Phatak

Last Updated: Feb 20, 2018

Now imagine a flying ant like 'atom ant', it can move straight ahead or back, sideways, as well as up and down. Its degree of freedom is three, so it's moving as we all do in three space dimensions because the degrees of freedom are three.

Einstein and the Unification of Space Time

This forced the world to abandon the concept of separate ideas of space and time and a single unified concept of spacetime came into existence. Some found it in Einstein's name itself. 'Ein' means 'one' in German. Split up his name as ' EIN+ST+EIN', ST meaning space time. If you see, it literally means 'one space time'; just a lucky coincidence one would say! Time was realized as the 4th dimension.

Let us try to understand what time dilation is. We are all continuously moving not just in three dimensional space but in four dimensional spacetime. Consider a racing car moving on an absolutely straight race track at a constant velocity. It is moving in one dimension and takes some time to reach the finish line. Now consider that it's trying to reach the finish line, but on an oblique path. Its velocity is now distributed over two dimensions and therefore it's taking longer for the car to cover the same distance. Its velocity in the original one dimension has reduced.

In a similar way, all objects in the real world are moving in a four dimensional spacetime, at a constant velocity as that of light. Sounds astounding but it's true. Only the velocity is distributed over dimensions and most of it is in the time dimension.

When the objects are at rest, they are moving only in the time dimension. Now when they start moving, their velocity increases in the three space dimensions, and therefore it slows down in the time dimension. Therefore, the faster you move in the three space dimensions, the slower you go in the time dimension. This causes time dilation. This is a bit difficult to understand, but if you give it adequate time to sink in, it's simple.

The Arrow of Time

The uniqueness of time dimension is that you can travel only forward in it, not backward. This fact has profound implications. It protects causality, that is the law of cause and effect. That is, cause should precede effect and it should not be the other way round. This irreversibility of time is inbuilt through the concept of entropy.

Creatures living in a two dimensional flat world will find it difficult to imagine what a three dimensional world would look like. Similarly, we, living in a world of three space dimensions find it impossible to imagine four dimensional spacetime! Still, through many indirect experimental tests the idea of four dimensional space time has been tested beyond doubt.