What is the Fourth Dimension?

While your question may appear simplistic, soliciting simple answers, it is actually quite complex and deserves a proper answer.

It is commonly said in science that we live in a universe of three physical dimensions (vertical motion, horizontal motion, and crosswise motion) which are manifested as space and that time is the fourth dimension. It is with these four coordinates that the location of anything in the universe can be stated.

However, the fourth dimension could be instead yet another direction, one which we do not understand or can not picture easily. The simplest way to explain this strange concept is to consider an imaginary universe that is two-dimensional and to consider the effects that can be produced by having this two-dimensional universe interact with the three-dimensional universe.

It is easily to imagine a two-dimensional universe. An ordinary piece of paper is an excellent example. Draw some figures on it, such as circles. You then imagine these circles as beings that live solely within the piece of paper.

They know two dimensions, crosswise motion and horizontal motion (left/right and forwards/backwards). No other direction is possible to them. And that is all that they know.

Everything is fine and dandy until we curve their universe using the third dimension. Let us say that we make a paper ball, a sphere. The two-dimensional inhabitants still live only in the surface of this new world. They do not see that their universe is curved because light in their universe travels only within that universe, so it curves. Images of far away objects travel relatively unimpeded throughout their two-dimensional universe. They look in a straight line and they can see as far as the eye can see (or resolve).

Everything is wonderful and fine until the day that one of them invents the telescope and looks far away in a straight line; and he sees himself from behind. What is the explanation? Only that his universe is curved positively in a higher dimension; a dimension that is beyond his understanding.

This has not happened to us... yet. It may never happen as it is commonly determined that our universe is flat, that it is not curved in the fourth dimension. It would also be very tricky for us to look so far in a straight line to see ourselves as that which we observe in our telescopes is a record of the past.

In other words, it could be that when we push our telescopes to billions of light-years away, we are looking at ourselves from behind EXCEPT it would be a record of how things were billions of years ago when our sun and Earth were not even formed. It would not look familiar at all.

So there you have it, time can be the fourth dimension as far as a co-ordinate system is concerned. A fourth dimension could also be a physical or spatial dimension beyond our own.

We have not even begun to consider the ramifications of dimensions of space beyond a fourth dimension; even though it is often stated that at the Big Bang there may have easily existed over twenty dimensions.

And so little has been released to the general public what the ramifications of additional dimensions of time would be. Yet more than one dimension of time has been considered mathematically in the field of quantum cosmology.