Alex McColgan

That fourth direction, or dimension, is time.

Einstein predicted this connection when he linked space and time into one unified space-time in his theories of relativity.

According to him, time and space are two parts of the same thing.

To me, this connects with 4D space very nicely.

Just as there is no real difference between the z and the x or y directions,

So too would there not be any difference between time and space if time is just another direction, albeit one that we can't see.

And time is important.

Without time, our 3D space wouldn't move.

It would perpetually be in one state, because it's time that allows us to move about in it.

But why can't we see it?

Why can't we look in the direction of time?

To explain this, let's look at the difference between the different dimensional spaces.

We best notice this when we consider what 2D objects might look like if they were to move around in 3D space.

This is where we start to delve into the model.

Let's begin by visualising a standard 3D space, but because we want to eventually see all of space and time in one model, let's cheat a little.

Let's compress all of 3D reality as we know it into a flat, two-dimensional place.

In this plane, let's make that our XY plane, which we will label space, which frees up the Z dimension for time.

In this model, all 3D people are now just 2D.

A 2D person could exist and live their lives in the place marked space at the bottom of our chart.

However, by moving them up on the chart at a constant rate, they are also moving through time.