The followers of Newton in the 17th century believed that time was absolute, it just went on, irrespective of the position and the frame of the observer. However, the Theory of Relativity proposed by Einstein forced the people to abandon their age-old beliefs and adopt a new approach, that time is just another dimension, just like the three spacial dimensions of length, height and breadth. It is a property of our universe that began when the universe was born and will end when it finishes. Time is relative and not absolute, and depends upon the position and the frame of reference of the observer.

To understand the view that time is just a higher dimension, one has to first understand the concept of higher dimensions. One of the most effective methods for imagining the fourth dimension is the method of analogy. One can assume that a 4-D world means to us, what a 3-D world will mean to a being that lives in just 2 dimensions.

Such ideas first found mention in Edwin A. Abbott's book, Flatland, published in the 1880's. Such 2 dimensional beings mentioned in his book had their names beginning with the letter, A, like A.Square, A.Triangle etc. Let us see how three dimensional objects would appear to these creatures.

Let us assume that A.Square lives in a particular plane, B. If a sphere is now made to pass through this plane, A.Square will describe the event in the following way: "Suddenly, a small dot appeared, and enlarged to become a circe. This circle stopped enlarging after some time, and again contracted to a point which finally disappeared".

Using analogy, we can say, that if a sphere in four dimensions (which is often written as a 'hypersphere'), is made to pass through our world, what we will see is just a little dot, which expands to become a complete sphere, and then contracts to disappear again. Hence, just as a circle is a cross-section of a 3 dimensional sphere, a sphere can be considered as a cross-section of a 4-dimensional hypersphere.

Lets now consider another case. One can easily see that boxes and safes for 2 dimensional beings will be squares or rectagles. The statement that "the box is closed" for A. square will mean that all four sides of the rectangle are joined. However, for a three dimensional being the box is still open, since the rectangle is exposed on both sides of the papar. Similarly, extending this fact, one can assume that a four dimensioal being can remove money from our safe without cracking it, remove the yolk from an egg without breaking it etc.

Another situation that is assumed, and can convince a being of the presence of higher dimensions, is when A.Square is made to rotate about a line that passes through his body in the plane. After A.square is rotated by B radians, A.square is back in its world, but not as the original being. Instead, it is now the cross-section of the original being. Also, as it was being rotated, the only part of its bosy that was present in the original plane was a line, or in other words, its cross-section. Similarly, if a four-dimensional being were to rotate as about a plane, we will be in inverted when we come back into our plane. Also, a cross-section of our body wil be revealed during the process!

The idea of a higher dimension being established, one has to understand why time is one of the higher dimensions. For this, lets assume that A.Square is resting at one position in his plane, when A.Triangle comes to meet him. If we think of time as the next dimension, which in this case, is the third, we get a picture. The plane in which A. Square is resting is assumed to move continously in thi fourth dimension. Hence, these beings are not just two-dimensional people who move from here and there, but can be considered as trails in 3-D spacetime. Similarly, even we can be considered as trails in 4-D space time, of which, at any instant, our space is just a cross-section. Time, hence is not anything different from the other three dimensions. But a question that can be asked here is that if time, is indeed just another dimension, then why can't one move forward and backward in it? Why is there a feeling that time is passing?

Many people have tried to give an explanation to this. Some say that this is because we always think of the future, and always have in mind as to what is to come. Hence we are propelling ourselves forward in time. Another theory says that the human mind is such that, we only have memory about what has passed, and not what is to come. One can perform the same action fifty times, but every time he moves back in time, his mind thinks in the same way as before, and he performs the same action again. Practitioners of yoga claim that by either thinking nothing at all (which is not easy) or focussing one's attention on a repetative thought loop, one can excape the feeling that time is passing. Some scientists believe that there is no law in Physics today that bars us from time-travel. But even then, a time-machine is still considered a science-ficiton.