Alex McColgan

This is clearer if we add a second 2D person.

Initially, both of our individuals do not move in space.

All of their vector is pointing in the direction of time.

Nothing that strange seems to happen so far.

However, if our stick man on the right turns and vectors at near the speed of light for a bit, then reorients himself, while the second 2D man on the left just stays where he is, it becomes clear that our 2D men have not moved at the same rate through time.

Assuming that our two stick men can somehow still see each other, let's imagine that they somehow project an image of themselves onto the other person's space plane, they immediately notice that there is a difference in age.

one who travelled at the speed of light did not advance so quickly through time as the other, who remained stationary and so is younger.

But why do we find this model so compelling?

Well, it is because of what those projections would look like during changes in direction.

From the point of view of the first stickman, initially the projection of their friend seems fairly normal,

However, as they start travelling very quickly in space, and their vector oriented in a direction away from time, a 2D shape reveals its inherent flatness.

And from a face-on perspective, it goes from this to this.

The speedily travelling stickman appears to flatten, with an effect that's more pronounced the faster they go, and the flattening takes place in the direction of their travel.

The stickman who remains stationary might wonder at the strange change that is occurring to their friend, never comprehending that it represents a reorientation of a 2D figure in 3D space.

Now what captures my imagination about this is that this same thing happens in real life.

According to Einstein's theories of relativity, objects travelling at great speeds in 3D space would appear from an external observer to flatten in the direction of their travel.

This squishing effect happens exactly in line with this model and is to do with time dilation.

However, from the person who's travelling's perspective, they do not flatten, but it is the rest of the universe that warps.

I talk about this in greater depth in another video of mine, where we can see the effects of spatial warping in a computer model.

From their perspective, everything would stretch at the edges of their vision, while their destination would seem further away, which is again what this model would predict.