UYal's blog

subtitle : A Question Beyond the 3rd Dimension – Why Did the Universe Need Time?

Listen closely.
The smallest unit is a dot.
Dots connected make a line.
Lines connected form a plane.
And when planes stack up, we get a solid, a 3D object.

So far, nothing new.
We’ve accepted this naturally—through school, books, or just life.

But suddenly, a question came to me:
“What comes next?”

Dot (0D) → Line (1D) → Plane (2D) → Solid (3D)… then what?

Just as a creature living in a 2D world can’t imagine a 3D one,
perhaps we, bound by our 3D senses, can’t grasp the 4th dimension.

Still, I was curious.
So I asked GPT:

“What is the element of the 4th dimension?”

The answer surprised me:

“Time.”

The change of a shape, the transformation of existence, the flow of events—
if there’s a single axis that runs through them all,
it’s time.

At first, I laughed.
Time? Isn’t that just something that passes by?
Why would time be considered a dimension?

But the more I thought about it, the stranger it became.
For a 3D object to change,
there has to be a coordinate system that can capture that change.

Take a simple example:
If a cup moves, tilts, and breaks,
you need to say “when” it happened.

Without time,
there is no movement, no transformation, no causality.

That’s when it hit me.
Time is the dimension that allows space to function.
Our 3D world only becomes a living universe when it has a 4th axis: time.
A flower blooming and withering — it’s the time element that makes it real.

And time always flows in one direction.
We remember the past and anticipate the future,
but we exist only in the now.

This one-way nature of time is even backed by physics —
specifically, the Second Law of Thermodynamics: entropy.

The universe is moving toward increasing disorder.
And that one-way street of rising entropy?
That’s the arrow of time.

So, time being a directional axis
isn’t just a poetic idea —
it’s the structure of the universe itself.

(I’ll revisit and write more about entropy later.)

3D is space.
4D is the framework that allows that space to flow.

So in the end,
my question “What is the 4th dimension?”
led me to the answer:

“For the universe to function, it needs not only space, but time.”

And time doesn’t just exist as a variable —
it exists as a dimension.

That’s how I came to accept the name of the 4th dimension:
Time.

Even when we start exploring the 5th dimension in the next post,
time remains the essential axis that makes space meaningful.

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🇰🇷 Cultural note:

In Korea, calling someone “4D” or “4-dimensional” usually doesn’t mean they’re from the future — it’s a humorous way of saying someone is a bit quirky, unpredictable, or thinks outside the box. So yes, if someone says you’re “4D,” they might just mean you’re… delightfully weird.

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