What Is The Universe Expanding Into?

I get this question... a lot.

"Since astronomers know that the Universe is expanding, what's it expanding into? What's outside of the Universe?"

The short answer is that this is a nonsense question, the Universe isn't expanding into anything, it's just expanding.

The definition of the Universe is that it contains everything.

If something was outside the Universe, it would also be part of the Universe too.

Outside of that? Still Universe. Out side of THAT? Also more Universe. It's Universe all the way down.

But I know you're going to find that answer unsatisfying, so now I'm going to break your brain.

Either the Universe is infinite, going on forever, or its finite, with a limited volume.

In either case, the Universe has no edge.

When we imagine the Universe expanding after the Big Bang, we imagine an explosion, with a spray of matter coming from a single point. But this analogy isn't accurate.

A better analogy is the surface of an expanding balloon. Not the 3 dimensional balloon, just its 2 dimensional surface.

If you were an ant crawling around the surface of a huge balloon, and the balloon was your whole universe, you would see the balloon as essentially flat under your feet.

Imagine the balloon is inflating. In every direction you look, other ants are moving away from you. The further they are, the faster away they're moving.

Even though it feels like a flat surface, walk in any direction long enough and you'd return to your starting point.

You might imagine a growing circle and wonder what it's expanding into. But that's a nonsense question. There's no direction you could crawl that would get you outside the surface. Your 2-dimensional ant brain can't comprehend an expanding 3-dimensional object.

There may be a centre to the balloon, but there's no center to the surface. Just a shape that extends in all directions and wraps in upon itself.

And yet, your journey to make one lap around the balloon takes longer and longer as the balloon gets more inflated.

To better understand how this relates to our Universe, we need to scale things up by one dimension, from a 2-d surface embedded in a 3-d world, to a 3-d volume embedded within a 4-d universe.

Astronomers think that if you travel in any direction far enough, you'll return to your starting position. If you could stare far enough into space, you would be looking at the back of your own head.

And so, as the Universe expands, it would take you longer and longer to lap the Universe and return to your starting position.

But there's no direction you could travel in that would take you outside or "off" of the Universe.

Even if you could move faster than the speed of light, you'd just return to your starting position more quickly.

We see other galaxies moving away from us in all directions just as our ant would see other ants moving away on the surface of the balloon.

A great analogy comes from my Astronomy Cast co-host, Dr. Pamela Gay.

Instead of an explosion, imagine the expanding Universe is like a loaf of raisin bread rising in the oven.

From the perspective of any raisin, all the other raisins are moving away in all directions.

But unlike a loaf of raisin bread, you could travel in any one direction within the bread and eventually return to your starting raisin.

Remember that our entire comprehension is based on 3-dimensions. If we were 4-dimensional creatures, this would make much more sense.

For a much deeper explanation, I highly recommend you watch my good friend, Zogg the Alien explain how the Universe has no edge.

After watching his videos, you should totally understand the possible topologies of our Universe.

I hope this helps you understand why there's no answer to "what is the Universe expanding into?"

With no edge, it's not expanding into anything, it's just expanding.

[calwere]

When scientists try to explain this question it always seems like the best answer would be “we don’t know.”

[antoniodeaguiar]

Your explanation/story/speculation still remains unsatisfactory.

[amojynca]

I dont get the balloon analogy, the balloon has 'space' to move into as it expands so if there is any movement at all wouldn't there be a need for 'space' ?

[OldBadBoy]

No need to "break my brain"... That's already happened. lol

[NOLAMarathon]

To get out of the universe, I've always taken the second door on the left.  How others get there, I don't know.  Regardless, it's wacky out there.  More importantly, there's no McDonalds out there, no cell phone service, and no ATM machines.  I never spend more than a couple hours at a time out there.  

[davidgiardina]

You just blew my mind. My whole out look on physics and the universe is just shattered and i've spent the past like 5 hours studying the string theory and supergravity and all of this stuff together and you shattered it and im so confused and amazed and happy and sad at the same

[kookiespace]

You didn't break my brain but holy bread, that loaf analogy is SO GOOD! :O
Thanks for this great episode ^_^

[EdGloss]

This type of stuff is so incredibly amazing, not just because it's happening but because elements evolved into stars, then galaxies and planets and on at least one of those planets, chemicals changed into living organisms that evolved over billions of years into organisms that are able to learn that this all happened. I find that to be the single most incredible thing. It's mind blowing.

[AntiMessiah]

I like your videos but this one was below par. You should just have said we don't know.

The big bang theory is a very good theory but we are NOT 100% sure that is a fact. As you mentioned in one of your earlier videos, the light we receive from stars was emitted lightyears ago and those stars may not even exist anymore.

Similarly, who knows what regions of the far distanced universe whose light only now has reached us exists or not.

Call me crazy but we should not accept things just because the world is comfortable with it.

Nonethless, thank you for your videos. I appreciate the knowledge you share.

[Chawitsch]

Damn you Fraser and Jason! I was eating while watching this episode and I laughed so hard when "bananas" popped up near the end that I almost spat food on my monitor. I learned my lesson.

[nicholaspavanel]

"So now, I'm gonna break your brain."*Straight face killa*

[randy]

None of us are truly capable to comprehend that our ever expanding Universe has NO Edge.  You can travel in any direction for eternity and not come to a particular Star that is going into a "void" where there are no Stars.  NO EDGE, yet it IS expanding??  That should blow your mind...

[EdalBrock]

0:39 I'm telling my mom on you!!! :)

[Mlogan]

If the universe is curved with a straight movement eventually returning to it's origin point. Then instead of the scenario that all galaxies will be lost form sight over time, we should expect everything to eventually be heading back toward each other.

[indigovisualsfilms]

Whenever this question is asked, people come up with answers through examples that quite frankly cannot be applied in this case to expand it such as an infinite line, balloon or bread. None of these answers or examples ever answer the question. So let me back up and clarify the question and the reasoning behind it.

The Universe supposedly came into existence out of the singularity. Singularity is infinitely small, hot and dense. However, even singularity has to exist within something. If you say that there was nothing because Universe is all there is and the singularity cannot be measured then how do we even know it existed if there was nothing. Since nothing is another form of something, there was no space, no energy, no size or direction, i.e. no singularity.

Secondly, let’s assume singularity can indeed be measured and therefore it is NOT nothing, it is just, for all intents and purposes infinite, at least to us and our comprehension of singularities. And let’s assume there was nothing outside of the singularity. Then we have a massive problem the moment we state that the Big Bang happened as well as expansion and inflation. What did it expand into, if there was nothing outside of the singularity? If you say that it expanded into itself, I say okay. Let’s assume that but then that would mean the entire Universe is still confined within that singularity and since we know of other singularities in this Universe the initial singularity was obviously not infinitely small otherwise it would not be able to contain expansion, the cooling of the Universe, entropy as well as billions and billions of other singularities in the hearts of black holes.

In my mind, the only way anything like that could have happened was that inflation happened but only to the intrinsic space within which Universe as a whole is contained. That space must have always been here but it was empty and inner and BB was essentially the birth of matter, physics, time etc…

That being said not have a problem that there is seemingly no centre of the “Universe”, no obvious point from which such expansions, BB, would have happened.

This kinda brings me the whole circle to the only obvious answer. The universe is not infinite, expansion has not happened, we don’t exist inside of a singularity and honestly, the simulation makes the only sense meaning that everything beyond outreach is just a never-ending procedural generation of space created depending on how far we look…

[uytuyt]

I finally, after all these decades, understand everything!!!

[sandybhan]

There is a space outside universe and space inside universe, Universe is expanding into external space, Universe is Finite But Space is Infinite. If you consider everything (all galaxies, stars,space everything) as Universe then Universe as Infinite, Now even if Universe is everything and is Infinite then it cannot expand because it already infinite and so is already present everywhere, that means for universe there is no extra space after infinite to expand, as it's infinite i.e endless. So the term Universe is expanding is then wrong But if you consider all matter, celestial object, stars,galaxies as Universe and understand that Universe is created in space and is expanding in space then you can understand that Universe is Finite and is expanding into Infinite Space.

[nexus]

You have drawn a very nice analogy to explain the real fact ... Lots of kudos buddy

[SCwarms]

Hey Fraser, love your videos. I have a question:) : You say we can see ourselves if we look out into space far enough, considering the universe is expanding faster than light can travel, and when we look far away we are also looking back in time, is it not practically impossible to actually see into the back of our heads? or is that only because we are limited by only looking at light sources and thus limited by the speed of light to see anything?     

[ThomasKop]

The analogy DOESN'T make up. A piece of bread is SEPARATE and PRESENT inside whatever it's in. Same goes for a hot air balloon. You cannot give 3D examples because then you contradict yourself: A hot air balloon too needs to exist in a different space.

For something to expand, to get bigger, further away from you, it still needs to expand into a space, so we're back at starting point, isn't this basic laws?