A Fourth Spatial Dimension and its Implications on Perception (2024)

Trying to conceive of the geometry of a fourth dimension involves disregarding everything you thought you “knew” about reality, existence, and your ability to perceive the world around you. Typically when one hears about the fourth dimension, the mind goes directly to time, but in reality it doesn’t matter whether you call time the fourth dimension or the fortieth dimension. Each dimension must be perpendicular to all of the other dimensions, and it doesn’t matter what order you examine them in. In terms of this paper, the fourth dimension refers to a fourth spatial dimension. By looking at differences between dimensions, specifically the second and third dimension, it is possible to gain a greater understanding about our own dimension-dependent spatial perception, and to explore what this tells us about the fourth dimension.

Before delving into complex examples of perception differences between different dimensions, it is necessary to develop a foundational understanding of the spatial components of each dimension. Dimensions are built upon one another by moving perpendicularly in space from all points in the lower dimension. Speaking in these terms, the fourth dimension is all of the space that one can get to by traveling in a direction perpendicular to three-dimensional space. To start from the beginning, however, means starting with a single point in space. A point defines the zeroth dimension. Essentially a point has not height, width or length, and is infinitesimally small. 1-D is defined by a single line. 2-D is the x-y plane, defined by two perpendicular lines. It is useful to picture the different structural components of a cube when examining dimensions, and in the case of 2-D, the cube is just a square. Similarly, 3-D is the x-y-z plane, with three lines extending perpendicular to each other in space, creating a cube. The fourth dimension becomes tricky because it is difficult for our 3-D minds to visualize a spatial direction perpendicular to our three existing ones. A four-dimensional cube is known as a tesseract, and it is typically drawn as one cube inside a slightly larger cube with the vertices of both cubes connected. (1) This is, of course, a distorted image of a tesseract because it cannot be drawn in three dimensions, but it is a useful tool in trying to visualize or at least understand the geometry of the fourth dimension.

Another useful method of comprehending the fourth dimension is to note how objects are bounded in each dimension. In 2-D, a square is bounded by one-dimensional objects, lines. In 3-D the cube’s boundaries are composed of six squares. Similarly, in 4-D, a tesseract is surrounded by eight cubes, eight objects with volume. Additionally, looking at the shadows objects of differing dimensions project can be an interesting way to compare dimensions. Think of your own shadow: your 3-D body projects a 2-D image, and likewise, a 4-D object will project a 3-D object. (7)

With a working knowledge of the basic concepts behind the construction of each dimension, and the geometry of each, it’s possible to begin to understand perception differences between the dimensions. Again, it’s useful to begin by examining lower dimensions so that we can readily visualize before moving on to explanations about the fourth dimension. Think of a square drawn on a sheet of paper. You can simultaneously see all of the points of square. If the square has dots drawn in the center of it, you can see these, even though they are on the inside of the square. For a being that can only perceive two dimensions, this would not be possible (more detailed explanations and examples of this below). Likewise, a being that can perceive four dimensions would be able to see all of the points in three-dimensional space “at once.” Our insides would be just as easily exposed as those of the square. Our perception abilities (and limitations) are a result of the arrangement of receptors in our retina: they are organized in a two-dimensional array (the third dimension is perceived through indirect information and visual cues such as shadowing). (7) A theoretical being who could visualize four dimensions would have a three-dimensional array of receptors.

Getting into more specific examples about perception differences between the dimensions and their inhabitants illuminates some fascinating spatial anomalies in our 3-D world that do not seem physically possible based on our understanding of space, but are completely valid within the context of the fourth dimension. First, however, as usual we begin with discussion of 2-D space and perception. A two-dimensional being experiences restrictions on movement and perception compared to beings that can perceive three dimensions. For example, in terms of movement, a 2-D being can only move along two axes in space. Let’s say this is forward and backwards, as well as up and down. This being has no concept of moving left or right. Think of a 2-D drawing on a piece of paper: the figures are “trapped” within the plane of the page. In this same scenario, perception of even a 2-D object, a square, is limited, and depends on its orientation in relation to the 2-D space the being occupies. If the square lies within the 2-D plane outlined, then the 2-D being looking at the square will only see a line, the boundary of the square facing it. This 2-D being can perceive a square by imagining many lines stacked together, similar to how we see in two dimensions but can perceive three. (2) However, if the square is perpendicular to the 2-D plane, then our being will see two dots, the points where the lines of the square intercept the plane. Likewise, a cube can appear as a line (where two sides of the cube meet), a square (one side of the cube), or a single point (one of the vertices of the cube) within 2-D space, depending on its orientation within the 2-D space. Three-dimensional objects can only appear as cross-sections of themselves within two dimensions, and their shape will depend on their orientation in relation to the plane of the two-dimensional space. It is possible to use the 2-D to 3-D transition model as an analogy for what happens when we, as 3-D perceivers, encounter four-dimensional objects. Coming across a tesseract, for example, we would see it simply as a cube. (3)