The Fourth Dimension

The Dimensions

The first dimension is just a line. The second dimension can be drawn on a piece of paper. There's length and width, but no depth. When the third dimension, we add depth: Length, width, and height.

Note: I'm talking about spatial (space) dimensions. Time is not part of space, and therefore cannot be the fourth spatial dimension.

Humans Are Three Dimensional Beings

Humans are three dimensional beings. Because we have two eyes and binocular vision, we see in three dimensions, and understand these three dimensions very well. But it stops there. Humans struggle with the fourth dimension. What is the fourth dimension? The idea sounds crazy to us. But the fourth dimension isn't as crazy or foreign as it sounds.

Don't forget, if you cover one eye and look at an unfamiliar scene, you'll lose your depth perception. If the scene is familiar or you recognize familiar object sizes, your brain will compensate and will trick you into seeing depth, but that's only because you've seen in three dimensions already.

But without your second eye, you'll see only in two dimensions, like one-eyed animals. These one-eyed animals who have never seen the third dimension, likely struggle with the third dimension as much as we struggle with the fourth. But we humans know it exists. We've seen it!

Dimensions on Flat World

Maybe this story will help illustrate. Imagine the people who live on flat world. They are two dimensional creatures living on a flat, two dimensional world. They can see left, right, forward, and backward, but there is no up or down to them.

One day, one person on flat world decides to walk in one direction. He walks and walks and walks, then finds something shocking. He ended up back where he started!

How could this have happened? Even though flat world is two dimensional to its people, it is round like a planet. Without any concept of up or down, the walker managed to walk around the circle and end up where he started.

Naturally, the flat world people are baffled. Even though they can't see it or understand it, they've discovered the third dimension.

The Fourth Dimension