Even if we cannot easily grasp the real nature of “time,” we can understand its aspect of being a “dimension.” For example, specifying only a place without specifying a “time’’ for an appointment would not be sufficient. Let us presume that we are on board a space vehicle or a helicopter and we are announcing our present location by giving the ground coordinates, that is, the latitude, the longitude and the height. We have to specify our current time, that is, the date and the hour, in order to make such an announcement meaningful and proper. Space–time is thus a four-dimensional measurement system, the dimensions inseparable from each other, like the nail and the quick of a finger.

We certainly fail if we try to consider time as only a matter of determining the hour. It is, in fact, a dimension like depth, height and length. One reason of our difficulty in perceiving time may be caused by the fact that our optical perception is sensitive only to three dimensions, but no others. Many animals cannot comprehend the dimension of depth. Some animals see their environs in two dimensions as in pictures. We have difficulty perceiving other dimensions just as animals which see the world in two colors live without any awareness of other colors.

Humankind, with the most sophisticated aspects, has a very different and privileged position above all creation. In spite of this, we have limited sight, hearing, and other senses. Many a world that is beyond our senses remains imperceptible to us.

Another aspect of time that supports its dimensional feature is that it is in full conformity with and proportional to other dimensions. In terms of its extent, duration of events increases or decreases in parallel with spatial dimensions. Man lives for around sixty to seventy years, while microscopic animals live around one or two days. The life of the sun and the universe which constitute the macrocosmos is expressed in billions of years. On the other hand, the life of subatomic particles is expressed in billionths of a second. Thus, we assume them as being resonances. There is time reduction together with and compatible with space constriction on the sub-atomic scale, and this fact is yet another proof that time is also a dimension.

How shall we understand the other dimensions of space? What does the fourth dimension of space mean? Let alone describing, it is not easy to even imagine this.

If a is the length, a2 is the area and a3 is the volume of a thing, then what is a4? If we see space as a giant plain sheet of paper, that sheet of paper has no depth but only a surface. If we fold crumple it into the shape of a sphere, we obtain “Riemann space.” Just like we perceive the three-dimensional earth as a two-dimensional surface while we are on it, this 3-dimensional sphere made of 2-dimensional paper will be perceived as 2 dimensional by us. We can only talk about the third dimension after we generate a depth, that is, after we step outside the paper and move above and below it.

The fourth co-ordinate of space is a tunnel. Let us suppose that the universe is two-dimensional, that is, it is like a thin sheet of paper, and let us human beings be like pictures with no thickness over its surface just like the pictures on a newspaper. We are free to move in all directions on this sheet of paper. We can sense four directions. But we will never perceive the terms “up” and “down” (or “upper” and “lower”) since we will never leave the surface of this sheet of paper. Such terms will seem unacceptable to us even we are told of them. Accordingly, we will never hear of a third dimension and our vocabularies will never contain such terms as “up” and “down.”

If a three-dimensional object existed above our fictional paper realm and if this object even slit our paper realm and went away, we still would not see it in three dimensions but only the part of it intersecting our paper realm. If such a thing were a sphere, for instance, we would see its projection in a circular form. Its latitudinal sections would gradually expand starting from the poles, reach their largest on the equator line and its ring-like (circular) shape would gradually decrease and finally disappear at the other pole. That is, we would see it only as its cross section or shade. Such a three-dimensional object would seem two-dimensional to us since we would suddenly see its cross section. The sudden appearance, expansion, decrease and final vanishing of that spherical object in our two-dimensional realm would seem quite amazing to us since our shapes are fixed and immovable.

The three-dimensional shade of an extraterrestrial four-dimensional object overshadows our three-dimensional space. We see the linear tunnels in cross-section, not longitudinally, just as we see the sphere as circular. Though the sphere is a simple object, it amazes us.

Let us now imagine a more complex form. Let us, for instance, reflect the shadow of a vase onto a wall and obtain various shades by turning it repeatedly. A fixed and immovable portrait on the wall would regard the shadow and its variations reflected over the same plane with surprise and fear, since that portrait, or that person without depth, sees only what is reflected on the wall, but not us and the vase. The wall is the only realm for him and there is nothing for him beyond and behind the wall even if we say so.

We humans tend to assess events within the narrow limits of space and within certain dimensions, since we are bound within a single space–time cone. The conceptualization of space with its dimensions of height, length and depth is possible for us. However, the fourth dimension, time, is an abstract and metaphysical measure even though it is studied within physics. The tunnel thus seems to us like an incredible dimension.

Our perceptions with the five senses in the visible universe can be considered as the projections of non-physical and multi-dimensional realities (the eighteen thousand realms) to our domain. Clearly, in order to gain a better understanding of those realms, which we do not see but which we feel exist, with the help of the physics, we need to emancipate ourselves from the narrow patterns of time and space in this world of trial. We need to travel toward the horizon of spirit and develop an all-new scientific language which approaches physics and metaphysics together. Finally, we can say, in Bediüzzaman’s words, that the physical and observable universe which is the domain of research for modern physics is an ornamented curtain veiling the world of the unseen.

Osman Cakmak is a professor of chemistry at Gaziosmanpasa University, Tokat, Turkey.