Hey Crazies.
Whenever someone starts talking about an expanding universe
there’s always at least one person asking this:
What is it expanding into?
OK, we can tackle this, but I’m not sure you’re going to like the answer.
Demo time!
Let’s say you have a balloon with some little thingies attached.
These represent galactic super-clusters, which contain 10s of 1000s of galaxies.
Yes, super-clusters.
We don’t see the expansion of the universe on scales any smaller than that
because other forces like gravity are strong enough to hold things together in spite of
the expansion.
Stick it to the man, galaxies!!!
Alright, back to the balloon.
These represent galactic super-clusters, whereas the balloon itself represents space.
If you blow air into the balloon, it expands carrying the superclusters with it.
They got farther apart without having to do any actual moving in space.
Pretty cool, huh?
Well, hold up a sec.
There are a few problems with this demo.
First, we’re representing our 3D space on a 2D balloon surface.
The balloon demo is 1 dimension short.
It really only represents a slice or cross-section of the universe,
but, then again, we drop from 3D to 1D in spacetime diagrams all the time and nobody
questions it.
The second problem is the expanding balloon has curvature, positive curvature.
You can see it’s finite and has no edges.
However!
We said in the last video that all evidence suggests we live in a very flat, zero-curvature
universe and, if it’s simple, an infinite universe.
If that’s the case, this balloon is a terrible model.
On top of that, the fact that it’s only a model can be misleading.
This balloon is in a room full of air and all sorts of other stuff.
There’s a space it expands into.
But none of that applies to the universe.
Remember, the entire universe is everything.
Even if the universe were finite like that balloon… the balloon is all that there is.
There is no room, no air, no person blowing that air, just the balloon.
So if that’s the universe, it’s not expanding into anything.
There is nothing outside it, not empty space, literally nothing.
Nothingness can be hard to imagine for a lot of people,
but your only other option is an infinite universe and that comes with its own problems.
You might wonder how the universe could have gone from microscopic
to an infinite size in a finite amount of time.
Well, it couldn’t have.
If the universe is infinite, then it always was for all measurable time.
What?!?
No, for real!
While it is true that everything we can see was, at one time, the size of microscopic
speck.
“Everything we can see” is just our observable universe, not the entire universe
and, if the universe is infinite, it solves our nothingness issue
because the universe can just expand into itself.
As space stretches, we get more and more space, but, if space is infinite, that’s just more
and more infinity.
When you run the clock in reverse, a similar thing happens.
As space contracts, you just have less and less infinity,
but infinity is infinity, no matter how small.
Infinity is so weird.
There’s also no reason to assume that our observable part is anything special.
No matter where you are in this infinite universe, you’ll see an observable part that’s about
the same size, with you at the center.
Further into the past, that bubble was a lot smaller, denser, and hotter,
but that was true everywhere.
In an infinite universe, there is no edge, there is no center
and the big bang happened everywhere.
Which kinda bothers me a little.
If the universe is infinite and nowhere is special,
does that means there are also an infinity of me out there somewhere beyond the cosmic
horizon?
Am I wasting my time cloning when I should just invent FTL travel?
I didn't realize I was going to get to be on camera.
If there are infinite possibilities, why does it all look the same?
What do you think?
Are there infinite copies of all of us?
Let me know in the comments.
Thanks for liking and sharing this video.
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And until next time, remember, it’s OK to be a little crazy.
Hey, this is normally where I do comment responses, but they were so good this time I turned them
into this entire video.
Don’t worry.
We’ll still answer questions for this video in the next one.
Oh, and Joee Green, I’ll ask whatever science question I dang well please.
Alright crazies, thanks for watching!