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from https://www.space.com/astronomy/is-the-universe-infinite-or-does-it-have-a-limit

Is the universe infinite, or does it have a limit?
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By Paul Sutter published 22 hours ago
If the universe is expanding, then what is it expanding into, and what
is it expanding from?

Comments (42)
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a red field of bright gas on a starry background
Where's the center of the universe, and where is its edge? (Image
credit: Roberto Machado Noa/Getty Images)

After a century of observations spanning the breadth of the cosmos and theoretical insights that push humanity's vision of the universe to its
utmost limits, we can finally, confidently say that the universe is
infinite.

Or not. It's complicated.

Let's start with something we can say for certain: We live in an
expanding universe. But if the universe is expanding, then what is it expanding into? And what is it expanding from? Where's the edge of the universe, and where is its center?

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It's easy to imagine an expanding universe, and there are plenty of
analogies to help guide our thinking. We can imagine drawing little
galaxies on the surface of a balloon and inflating that balloon to see
the galaxies getting farther apart. We can imagine baking a loaf of
bread with raisins in it and seeing how, as the bread rises, the raisins
get farther apart.

But the balloon has both a center and an edge. And the bread has a
center and a crust. So where's the center of the universe, and where is
its edge?

Here's the uncomfortable answer: The Big Bang has no center, and it has
no edge. How can this make any sense?

Let's start with the center. Where did the Big Bang start? Right here.
And right over there. And in the next galaxy over. The Big Bang happened everywhere, all at once. It had to happen everywhere, because everywhere
is, by definition, part of the universe. It was not an explosion that
occurred somewhere in space. It was an explosion of space rCo when the expansion of the universe first got started. It was not a place but a time.

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Now what about the other side of the coin? If the universe is expanding,
what is it expanding into? Where's the crust in our expanding loaf of
bread, and what's the oven we're sitting in?

A blue cylinder with a flared end on a black background

An illustration that shows the timeline of our universe, from the Big
Bang to today. (Image credit: RubinObs/NOIRLab/SLAC/NSF/DOE/AURA)
This is going to get weird. I don't even want to say something like "the universe isn't expanding into anything," because that still conjures up
the wrong mental image. It's too tempting to imagine a wall or boundary,
with galaxies and stuff on one side and nothingness on the other, with
the universe expanding to fill that nothingness.

But that's wrong. Even the vacuum of space is something. There are still points, locations and existence. There's no "outside" of the universe
because "outside" implies existence, even an empty one. But the universe
is, by definition, all there is. There is nothing to physical reality
except the universe. Walls separate one region from another, but the
universe comprises all of the regions simultaneously.

If there were an edge, you could imagine working hard enough to get
outside that edge. But that's not possible. There is no outside; there
is no side. There is just the universe.

Join our Space Forums to keep talking space on the latest missions,
night sky and more! And if you have a news tip, correction or comment,
let us know at: community@space.com.

Paul Sutter
Paul Sutter
Space.com Contributor
Paul M. Sutter is a cosmologist at Johns Hopkins University, host of Ask
a Spaceman, and author of How to Die in Space.
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Comment by christophe_dupin.

john.miles.fimeche
46 min ago
We we accept our universe as all there is, we must also accept the fact
that man has done for thousands of years. Science cannot work with what
it cannot see. Talk is of a balloon or baking bread, not of the big bang
being one of a million such bang happening every second, somewhere.

All we can hope to do, whilst constrained by the limit to the speed of
light, is study what we observe, to interpret where parts of our
universe are being affected by events outside our universe, and where
parts of our universe are being infiltrated by external matter, not of
our Big Bang.

Take the loaf if bread analogy. A ball of dough the size of the solar
system, with a grenade exploding at its centre our Big Bang, still
witnesses expanding raisins. And the expansion will come to a halt. And
the universe will collapse again.

Better still though, imagine a night sky full, horizon to horizon
exploding with massive chrysanthemum fireworks. As they explode, their
matter gravitates into another mass causing another chrysanthemum
explosion, perpetuating across the sky throughout the night.

reply

aarongrayson84
2 hrs ago
Depends on the mind observing it.

sw

shane watt
6 hrs ago
There is no infinity in another dimension.

Gibsense
3 hrs ago
Reply to shane watt - view message
I am not sure what you mean. In flat space (no curvature) a hypothetical
line (dimension) is infinite no matter what label (1,2,3 or4) you
assign. If curved, like the surface of a sphere, then it could be
endless (going around and around) but limited to the sphere. If you wish
put your statement in a context

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