Can We Picture an Expanding Universe with No Edge?

Welcome, dear readers of FreeAstroScience. Here’s a question that quietly keeps many people awake at night: If the universe is expanding, what is it expanding into, and where is the center?

Today’s article, written by FreeAstroScience only for you, takes that unsettling feeling and turns it into clarity. We’ll walk through simple analogies, real numbers, gentle equations, and even a small JavaScript applet you can embed on your own page. If you stay with us to the end, you’ll have a much sharper mental image of our expanding universe—and a new respect for how strange reality really is.

Why is a centerless, edgeless universe so hard to picture?

Our brains evolved on a planet with borders and centers.

A room has walls.
A city has limits.
Earth has a center of mass.

So when we hear “the universe is expanding,” we instinctively ask:

Expanding from where?
Expanding into what?
And where is the middle of everything?

Cosmology’s answer is shocking: there is no special center and no outer edge in the usual sense. Every galaxy sees other galaxies receding, and every observer can claim to be “at the center” of their own observable universe, but none of those claims is unique.

The challenge isn’t that the idea is complicated. It’s that our everyday intuition simply wasn’t built for it.

To really feel what cosmologists mean, we need a good analogy.

What does the surface of Earth teach us about “no center”?

The article from Universe Today by cosmologist Paul Sutter uses a clever analogy: not the whole Earth, just its surface.

Imagine only the two-dimensional surface of our planet. Creatures living only in that 2D world can walk north, south, east, and west—but never “up” or “down.” For them:

Latitude and longitude are coordinates drawn by humans.
Zero longitude runs through Greenwich because we decided so.
The “equator” is defined by the Sun’s position, not by a physical groove.

Now, try to answer this: What are the latitude and longitude of “the center of Earth’s surface”?

You quickly notice:

You can pick the North Pole, the South Pole, or (0°, 0°)…
But any point you pick is just a convention.
Every location is equivalent; the surface has no preferred center.

The entire surface is finite (you can measure the total area), yet unbounded (you can travel forever without falling off an edge). There is no border you can walk to and say, “Here, the surface ends.”

Cosmologists suspect the universe might work similarly:

Space itself can be finite or infinite.
But in either case, it can lack both a special center and a physical edge you could ever reach.

What if the surface of Earth started expanding?

Let’s upgrade the analogy.

Picture Earth’s surface again, but now:

Continents stretch.
Cities drift apart.
Oceans widen.

The whole 2D surface is expanding. If you could hover in 3D space and watch, you’d see a growing sphere, like a balloon inflating.

However, our 2D beings living on the surface never leave the surface. They can’t see the sphere from outside. They can only:

Measure distances between cities.
Notice that long journeys take more time.
Detect that light signals from faraway cities are “redshifted” (stretched to longer wavelengths).

From their point of view, the surface gets bigger, but there is:

No center on the surface itself.
No boundary they can reach by traveling.

Every city can claim, “Look, all other cities are moving away from me. I must be at the center!” And every city would be equally correct—and equally wrong.

That’s the key “aha” moment:

Being everywhere at once is very different from being somewhere in particular.

The expanding universe is like that surface, but with one higher dimension: space itself stretches, and every galaxy sees others receding, without any single galaxy sitting at a true central point.

Why can we only see a tiny part of the universe?

Paul Sutter also talks about horizons, and this is where the analogy with Earth becomes even richer.

On Earth’s surface:

You can’t see forever.
The planet curves away.
A ship disappears over the horizon.

That visual limit exists even though the surface continues beyond what your eyes can see.

The universe has a similar concept: a cosmic horizon.

How does the speed of light create a “bubble” around us?

Light has a finite speed, roughly:

( c \approx 299{,}792 ) km/s.

The universe also has a finite age, about:

13.8 billion years.

Even if space were not expanding at all, we could only see light that has had time to reach us since the beginning. That naturally defines a bubble around us:

Inside the bubble: regions whose light has arrived.
Outside the bubble: regions whose light hasn’t had time to reach us (yet or ever).

In a non-expanding universe, the radius of this bubble would just be:

Simple light-travel distance

R = c t

where:

( R ) is the radius of the observable region,
( c ) is the speed of light,
( t ) is the age of the universe.

Numerically, ( c \times t ) is roughly 13.8 billion light-years in that simplified picture.

Cosmologists call a closely related scale the Hubble radius (or Hubble distance) and denote it by:

Hubble radius (approximate)

R_{H} = \frac{c}{H_{0}}

Here ( H_0 ) is the current Hubble constant, a measure of how quickly the universe expands today.

Because the real universe does expand, the true radius of the observable universe is larger, about 46 billion light-years. Light has been traveling a long time while space has been stretching underneath it.

So even though the light took 13.8 billion years to reach us, the present-day distance to those regions is much bigger.

Why do we see the past when we look far away?

Light doesn’t teleport. It travels.

So every time you look at something far away, you’re seeing how it looked in the past:

The Sun, 8 minutes ago.
The Andromeda galaxy, about 2.5 million years ago.
Very distant galaxies, billions of years ago.

That means the observable universe is not only a sphere in space around us. It is also a time machine. The further out you look, the earlier the cosmic epoch you’re seeing.

At the very edge of what we can detect, we see the cosmic microwave background (CMB):

Light released when the universe was ~380,000 years old.
Today, that light shows up as a faint microwave glow in every direction.

So the boundary of our observable bubble is both:

The farthest places we can see, and
The earliest time we can peer back to.

To make this more concrete, here’s a small table.

Object / Region	Approx. Distance (today)	Light Travel Time	“Age” of Universe Then
The Sun	1 AU (~150 million km)	~8 minutes	Almost 13.8 billion years
Andromeda galaxy	~2.5 million light-years	2.5 million years	13.8 billion years minus 2.5 million
Typical distant galaxy	~10 billion light-years	~10 billion years	~3.8 billion years after the Big Bang
Cosmic microwave background	~46 billion light-years (comoving)	~13.8 billion years	~380,000 years after the Big Bang

Reading this table, you can literally see the universe ageing as you move inward from the CMB to local space.

Is there any “edge” we could reach if we traveled long enough?

Short answer: not in the way you might imagine.

There are a few ideas people mix up:

Edge of what we can see (the observable universe)
- That’s the horizon defined by the speed of light and cosmic history.
- As time passes, we can in principle see more.
Edge of space itself
- In most standard cosmological models, space has no sharp boundary.
- It may be infinite, or it may loop back on itself like a higher-dimensional surface.
Edge where matter stops existing
- As far as we know, matter distribution becomes smoother on large scales.
- There’s no observed hard cutoff beyond which nothing exists.

If the universe is infinite, there simply isn’t an outer border. If it’s finite but unbounded (like Earth’s surface), you could travel in one direction forever and never “fall off.”

The universe’s expansion doesn’t create a new wall. It just increases the distance between far-flung regions of space.

What does the Hubble law actually say about expansion?

To make expansion a bit more mathematical, cosmologists use the Hubble–Lemaître law. It relates:

The recession velocity of a galaxy, ( v )
Its proper distance from us, ( d )
The current Hubble constant, ( H_0 )

Hubble–Lemaître law

v = H_{0} d

Roughly speaking:

( H_0 \approx 70 ) km/s/Mpc (megaparsec).

That means:

Each megaparsec (~3.26 million light-years) of distance adds ~70 km/s of recession speed.

For example:

A galaxy ~100 Mpc away will typically recede at roughly ( v \approx 70 \times 100 = 7{,}000 ) km/s.

Importantly, this recession isn’t motion through space like a rocket. It’s motion with space as it stretches. The rubber sheet carrying the coins, not the coins sliding across it.

Can galaxies recede faster than light without breaking physics?

They can—and they do.

This sounds illegal because special relativity tells us nothing can move faster than light. But that rule applies to objects moving through space, not to the expansion of space itself.

Two distant galaxies can have a recession speed ( v > c ) because:

The metric that defines distances between them is changing.
No signal leaves one and arrives at the other faster than light.
Locally, in any small region, physics still obeys relativity.

Think of two ants on opposite sides of a rapidly inflating balloon. The surface itself can grow so quickly that the distance between them increases faster than any ant could run, even if each ant always respects its own “speed limit.”

So, yes, parts of the universe drift away from us at effective speeds greater than ( c ), and that’s entirely allowed within general relativity.

How does the picture on page 1 relate to spacetime curvature?

The image on page 1 of the source PDF shows a spiral galaxy embedded in a warped, funnel-like grid. That grid represents curved spacetime—a visual metaphor used in general relativity.

What it’s trying to express is:

Mass and energy tell spacetime how to curve.
Curved spacetime tells matter and light how to move.

In expanding cosmology, we often imagine space as a flexible sheet that can stretch, curve, and ripple. The galaxy sitting in a warped grid is a reminder that:

Expansion is not objects flying outward into emptiness.
Expansion is the geometry of the universe itself changing with time.

Want a hands-on feel? Try this simple JavaScript “expanding universe” applet

To really lock in the concept, here’s a small educational applet you can embed in a webpage or blog. It’s deliberately simple and self-contained.

What does the applet do?

Draws a bunch of “galaxies” as dots on a canvas.
Lets you change the scale factor ( a(t) ) with a slider.
As you increase the scale factor, distances between galaxies grow.
You can click any galaxy and declare, “I’m here.”
- The app re-centers the view so that galaxy looks stationary.
- All other galaxies move away from you, mimicking a universe with no unique center.

It also uses a toy Hubble law to estimate recession speeds.

HTML + CSS + JavaScript code

Interactive toy model of an expanding universe

Drag the slider to change the scale factor a(t). Click any galaxy to declare “I’m here”. Notice how the expansion looks the same from every galaxy.

Scale factor a(t): 1.0

Animate expansion

Tip: Click a dot to choose your “home galaxy”. It will be drawn as a ring. The readout below shows approximate distances and recession speeds according to a simple Hubble law.

NUM_GALAXIES to show more or fewer dots.
HUBBLE_KM_S_PER_MPC to explore different expansion rates.
Styles to match your site’s design.

The important conceptual lesson is this:

No matter which dot you click, the others move away from it when the scale factor grows.

That’s exactly the “no unique center” idea we’ve been talking about.

So where was the Big Bang?

This is the classic follow-up question.

If the universe has no center, where did the Big Bang happen?

Cosmology’s answer is subtle but beautiful:

The Big Bang didn’t explode from a point into pre-existing empty space.
Instead, the Big Bang was an event that happened everywhere at once in the early universe.

Every region of space:

Was once squeezed into an unimaginably hot, dense state.
Has been expanding and cooling ever since.

From our point of view:

When we look far away, we see earlier and earlier stages of that process.
At the limit, the CMB shows us a snapshot of the entire universe when it was a glowing plasma.

So the right question isn’t “Where did it happen?” It’s “What did the universe look like at earlier and earlier times?”

And that’s exactly what astronomers keep trying to answer with better telescopes and more precise measurements.

What should we take away from all this?

Let’s gather the main ideas:

The universe can expand without a center and without an edge, much like the surface of a sphere.
Our observable universe is a finite bubble set by the speed of light and the age of the cosmos.
Looking far away means looking back in time. The outer shells of our observable bubble show the younger universe.
The Hubble–Lemaître law, ( v = H_0 d ), links distance and recession speed but describes the stretching of space—not galaxies blasting through a pre-existing void.
Even super-fast recession speeds don’t break relativity because they come from changing geometry, not faster-than-light travel.
Any galaxy can feel like the “center,” yet none truly is. Center is a matter of perspective, not privileged location.

When we accept that our intuition is limited, something interesting happens. Confusing ideas start to feel less threatening and more like invitations to think differently. That shift—from fear of the unknown to curiosity about it—is exactly what good science is about.

At FreeAstroScience, we keep coming back to the old warning: the sleep of reason breeds monsters. When we stop asking questions, myths, conspiracies, and easy fake answers rush into the gaps. By carefully unpacking concepts like the expanding universe, we push back against those monsters and make room for wonder instead.

Final thoughts

So, next time you hear “the universe is expanding,” picture:

A centerless surface with every point as valid as any other.
A glowing bubble of visibility defined by the finite speed of light.
Galaxies riding the stretching fabric of spacetime, not racing through pre-made emptiness.

If this article nudged your intuition even a little closer to that picture, then we’ve done our job together.

This post was written for you by FreeAstroScience.com, which specializes in explaining complex science simply. Stay curious, keep reason awake, and come back soon—we’ve barely scratched the cosmic surface.