The Fourth Dimension and Time
by, November 3rd, 2009 at 08:08 AM (2184 Views)
You've probably heard it said that the fourth dimension is time. This idea is especially popular with SF authors when writing time travel stories. But what does this mean? And what are the implications?
Forgetting about time for a while, in ordinary life we deal with three dimensions: left-right, forward-back and up-down. What this means is that every material object and every location in the universe can be described mathematically using only three numbers. When we measure a material object, its width, length and height are called its dimensions. If we want to describe the location of an airplane, we give its coordinates as latitude, longitude and altitude. Longitude is the distance from an imaginary line cutting through Greenwich England, latitude is the distance from the equator and altitude is its distance above the earth; in other words, the three dimensions of its location. For objects located on the surface of the earth, only two dimensions are required since altitude is not considered because from a human viewpoint, the earth is a relatively flat surface as long as we don't consider such features as mountains and tall buildings.
In mathematics, the number of dimensions is shown by a superscript. For example, a cube exactly 2 inches at each dimension can be said a 23 inch cube (a two cubic inch cube). A two-inch line is a one dimensional object and can be written as 21 inch line. A two-inch square drawn on a sheet of paper would be 22 inch square (two square inch square). This also shows that objects of one, two or three dimensions can be illustrated by simple drawings or models. But, what about an object with four or more dimension? They can be shown mathematically by using superscripts (sometimes called powers) of 4, 5, or any number. But how do you illustrate such an object? For example, in a fourth dimensional object, how do you show a dimension at right angles to the other three?
Before I attempt to give an answer to the questions in the last paragraph, let's consider the attributes of objects in the lower dimensions. Imagine an infinite flat surface. On this surface, there is a line of infinite length. Let's say that there are number of points that live on that line. They can move left or right on that line but have no concept of the other dimensions. A point can never pass another point. Another race living on the surface are the Flatlanders. They can move left-right and forward-back but have no concept of up-down. A Flatlander could take one of the points and move it through the mysterious second dimension and put it on the other side of a fellow point. However, to the Flatlander, the line is an impassable barrier.
Now, as a three dimensional being, I have magical properties to the Flatlander. If I put my five fingers on the sheet of paper, the Flatlander sees me as five small blobs. If I remove a flat object into the third dimension, I can reverse it. The Flatlander first sees the object disappear and then returned reversed, an impossibility from his standpoint. I have other powers that Flatlanders are in awe of. I can appear and disappear within a closed space. I can see inside objects, including the Flatlanders' bodies. I can pick up a Flatlander and carry him across the barrier line. From this you can see that a fourth dimensional being would have similar extraordinary powers in our three dimensional world.
To get back to the question of illustrating a fourth dimensional object, we can show a three-dimensional object in two dimensions by opening it up. For example, a cube has six surfaces. If we unfold these surfaces into the form of a cross, we show the cube in two dimensions. The equivalent fourth dimensional object is called a hypercube and consists of eight cubes connected in four dimensions. If we unfold this into a three dimensional object, we would see eight cubes, four stacked on top of each other and the other four attached to one of the cubes in the stack, one on each side.
Time as the Fourth Dimension
Now it is debatable whether time is actually a fourth dimension. But, for sake of argument, let's assume that is. The implications of this are threefold. One is that all time, past, present, and future exist together in some way and that what we consider time passing is really only our traveling along a fourth dimension from past to present to future. It also seems to imply the possibility of travel in the reverse direction from the present to the past or speeding up our travel forward into the future. Thirdly, from the foregoing you can only come to conclusion that the future is predetermined, since it already exists and cannot be changed.
If you could view the fourth dimension (if it is time), you would see yourself extending to the point where you were born in one direction and up to the point of your death in the future. The same with everything around you. If not too distant in the fourth dimension, you could view any object from the point of its origin to its dissolution and all the changes that occurred to it.
Now a person who could travel into time would have some of the powers of a fourth dimensional being. He could appear in a locked room simply by going back in time when the room was not locked. He could disappear and appear somewhere else. He could predict the future.
In a previous paragraph, I stated that if time is the fourth dimension, our future is predetermined. This would also hold for the past. Thus, a time traveler who went to the past would not have a choice. He would by necessity have to have arrived from the future at the exact time of his arrival. This implies no free will, that even our thoughts are predetermined. To get around this problem and other paradoxes involved with time travel, one must conjecture other dimensions in which one can travel at right angles from not only to the usual three but from the fourth time dimension. This introduces the concept of parallel time.
The concept of parallel time is that starting from the beginning of the universe, each moment introduces infinite possibilities and each possibility exists somewhere (possibly in a fifth or higher dimension). So, if I go back in time and prevent my mother from meeting my father, two universes exist, one where I did not prevent my parents from meeting and one where I did. When I return to what I consider my own present, I actually return to a different universe from the one where I started from, one in which I was never born.
I hope this essay throws a little light on a confusing subject.