In a strict mathematical sense, a four-dimensional object cannot exist with only one spatial dimension (a line) because a four-dimensional object, by definition, requires four independent spatial dimensions. However, we can discuss a concept known as a "projection" that allows us to visualize certain aspects of higher-dimensional objects in lower-dimensional spaces.
Consider a three-dimensional object, such as a cube, which has three spatial dimensions (length, width, and height). When we project this cube onto a two-dimensional surface (like a sheet of paper), we can represent it as a two-dimensional shape, namely a square. The square is a representation or projection of the three-dimensional cube onto a lower-dimensional space.
Similarly, we can think about projecting a four-dimensional object onto a three-dimensional space. However, visualizing this projection can be challenging because our perception is inherently limited to three dimensions. We can only imagine or represent projections of higher-dimensional objects in lower-dimensional spaces.
For example, a projection of a four-dimensional object onto three dimensions might involve changing properties of the object as it passes through our three-dimensional space. Imagine a four-dimensional object passing through a three-dimensional space over time, similar to how a three-dimensional object (like a sphere) passing through a two-dimensional space can be seen as a growing and shrinking circle.
In essence, we can't directly visualize or experience a four-dimensional object with our three-dimensional perception, but we can use mathematical and conceptual tools to understand and represent certain aspects of higher-dimensional objects in lower-dimensional spaces. These projections and mathematical descriptions help physicists and mathematicians work with higher-dimensional theories, such as string theory or other multidimensional frameworks.