The Fourth Dimension

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

Well we humans live in a similar world, just add one. We see in three dimensions, and can go as far as we want left, right, forward, backward, up, and down. But what happens if we go into space and keep going, going, and going?

It turns out that scientists can determine how big the universe is by analyzing microwaves left by the big bang. The big bang was a huge explosion. The universe expanded faster than its waves, so we are constantly receiving microwaves from the explosion. The key here is that the edge of the universe emits microwaves to us, and we are constantly receiving them.

Believe it or not, these big bang microwaves make up a "sizable amount of the static on your television set." So when you watch TV static, you're actually watching the big bang. (Source: NASA)

Scientists have found something shocking about these microwaves. They are completely equal in every direction. To be fair, this could mean that we are in the exact center of the universe. That would explain the equalness.

But it seems very unlikely that we're in the exact middle of the universe. Why should we be so lucky? But if we're not in the center, then we would receive more or stronger microwaves on the side of us that's closer to the edge of the universe. And we don't. Why is that?

There is really only one other possibility. Every spot in the universe must receive equal amounts of big bang radiation. So the edge of the universe looks the same no matter where you are in the universe. How could this be? There must be a fourth dimension.

Back to the flat world. If person A is in one spot on the planet's surface and person B is somewhere completely different, how far is each from the core? Well they're equally far from the core. The planet is a circle. The concept would seem foreign to them, but we three-dimensional beings know they are equally far from the core.

It's the same with us. This means that if we traveled in any direction of space, we would likely end up back in the same spot. Just like the flat world person who traveled all the way around the apparently two dimensional (but really three dimensional) world, we would travel all the way around the apparently three dimensional (but really four dimensional) world.

Barring other explanations, either the fourth dimension exists or we happen to be lucky enough to be the center of the universe.