What is the shape of the universe? It’s kind-of an impossible question to answer. But thanks to studies of the cosmic microwave background radiation, we do have an idea of what spacetime is shaped like. And the answer is… strange.
TRANSCRIPT:
The universe. It’s big. It’s everywhere. It’s all there is. And it follows a strict set of rules… until it doesn’t.
We see stars rotating around galaxies faster than we think they should and blame it on dark matter.
We see galaxies flying apart faster than they should and blame it on dark energy.
What’s dark matter? What’s dark energy? We don’t know! But it keeps messing stuff up.
Some of these inconsistencies might be explained by the shape of the universe itself.
Because we really don’t know the actual shape of the universe.
We usually visualize the universe like this.
Or like this.
But what if it actually looked…
Like this.
I haven’t bought Pringles in a long time.
Kinda forgot how to do it.
Point is, depending on what you’re observing, the universe could be one of three shapes
Flat, like a Triscuit, round like a cheese puff, or saddle-shaped. Like a Pringle.
There’s probably only one of those that makes sense to you intuitively, but I’ll try to make the others make sense while woofing down some processed snacks while I talk about the shape of the universe, today, on Answers With Joe.
What is the shape of the universe? This was a question that was asked in one of my lightning round videos from a few months back and in my lightning round videos, I take questions from Patreon supporters, and I let the audience vote on which topics I should make a full video on.
Well this topic got a lot of votes so today we’re going to talk about it. Because I, Joe Scott, am a man of my word.
Integrity.
The question is challenging because there’s no way to really know the answer. We can’t just take a picture of the universe. I mean JWST is awesome but it’s not THAT awesome.
And the fact of the matter is, we’ll never be able to make a telescope that can see to the end of the universe because the universe is expanding, and it’s expanding everywhere all the time.
Which means the further away something is, the faster it’s traveling away from us, to the point that the furthest galaxies are moving away from us, proportionally, faster than light… meaning its light will never reach us, and we will never know they were there.
To add to the confusion, as we look out to the universe, the light we see from the furthest visible galaxies has been traveling for billions upon billions of years, some of it pretty close to the big bang… when the universe was much smaller. And yet it’s still out in different directions… My head hurts.
The point is, when we talk about the shape of the universe, we’re really talking about the shape of spacetime. Some of this gets a little theoretical, and I’m definitely not the most educated person to talk about this, but I do have something that other creators out there don’t have…
Snacks.
What Does “Shape” Mean?
So imagine that you’re trying to get from one end of an empty room to another. And there are two possible paths. One is straight across, the other one curves around. Which path is the shortest distance from A to B?
It’s the straight line, obviously, which is kind-of a universal fact, the shortest distance between two points is a straight line, you learn that in middle school. But that’s not always the case.
For example, if the room happened to have a mountain in the middle, the distance you’d have to travel in that third dimension might be longer than the curved path. So in this case, looping around would be shorter.
Imagine the room is the universe and I think you’ll see what I’m getting at. In a flat universe, straight lines are the shortest. In a curved universe, things get trickier.
Cosmic Topology
The study of the universe’s overall shape is called cosmic topology. It’s like being a surveyor… for the universe.
Cosmic topologists deal with things like local geometry, relativistic curvature, and just the nature of the universe as a whole.
You know, little stuff like that.
The problem is it’s kinda hard to study the structure of a thing when most of that thing is… invisible.
Density Rules
So you’ve heard all about dark matter and dark energy but did you realize that they make up 93% of the universe?
Yeah, all the matter in the universe, all the stars in the sky, all the galaxies in the deep fields from Hubble and JWST, the countless billions of galaxies that we know about… is only 7% of the universe.
Cool.
Yeah, so it’s estimated that dark matter makes up 25% of the universe and dark energy takes up 68% of the universe.
It takes a lot of dark matter to keep those galaxies together. And it takes a lot of dark energy to yeet all those galaxies away from each other.
So you’ve got these two forces that make up the bulk of the universe, you can think of dark energy as an expansion force and dark matter as a contraction force. And the shape of the universe depends on the balance of those two forces.
The light and the dark side of the force, if you will.
If the contraction force, dark matter, wins out, then you get a closed universe, a spherical universe. A cheese ball universe.
If the expansion force, dark energy, wins out, then you get a saddle-shaped universe. A Pringles-shaped universe. This will make more sense later.
But if the two forces balance themselves out, you get a flat universe. A Triscuit universe
By the way if you’re wondering why I didn’t just pick a random flat, square-shaped cracker like a saltine, it’s because I wanted a Triscuit.
Shut up!
It can help to imagine two perfectly parallel lines traveling perfectly straight beside each other across the vastness of the universe. If the universe was a sphere, those lines would eventually converge. Like they would over the surface of the cheese ball
If the lines curved away from each other, that would mean expansion was winning out, which can be visualized by two lines cruising down the surface of a Pringle.
And if they remain parallel for infinity, then no forces are winning out, and the universe is flat. As flat as a Triscuit.
Spoiler alert… The universe is a Triscuit.
Though there are some interesting implications for what would happen in a cheese ball or Pringle universe.
Sorry.
Pringle Universe
In a Pringle Universe, where straight lines fly away from each other over a long enough distance, navigation would be next to impossible. Again, over a long enough distance.
Astronauts would need to be able to know what direction the straight line they’re in would take, while having to calculate what direction the stars they’re traveling to would actually be traveling. It would be a mess.
Obviously, that’s not really a problem we would need to deal with for thousands of years but still.
The Cheese balls, too!
Cheese Ball Universe
In a closed, cheese ball universe, things get a bit more interesting.
Because if our proverbial astronauts flew straight for far enough, they could end up back where they started.
Astrophysicist and author Jean-Pierre Luminet used a soccer ball to explain how this would work. Which is the same idea s my cheese ball metaphor except a soccer ball is less edible.
Unless you’re my dog
Luminet has also compared the universe to a video game.
You know how when you go past the edge of the map in Pac-Man, you wind up on the other side? According to Luminet, the universe is like that, only in 3D.
There’s no edge in Luminet’s universe, it just loops around, which would create some optical illusions, like the stars that we’re seeing in the sky would actually be behind us.
And because of that looping, the universe would actually be way smaller than it appears. Instead of being 93 billion light years across, it would actually be a little bit smaller than that, something more like… your mom.
So even though the actual physical dimensions of space are finite, because of this looping effect, you could travel in a straight line forever.
And if that hasn’t broken your brain completely, Luminet describes his soccer ball universe as having 12 sides, so it’s technically a Poincaré dodecahedral space.
I’ll stick with cheese ball.
Now there was some evidence found for a closed, soccer-ball universe, it was found in data from NASA’s WMAP satellite. It made some headlines a few years back, but more recent data seems to contradict it. Anyway, but the idea hasn’t been ruled out. But it’s heavily debated.
Triscuit Universe
But really, the vast majority of observations and studies point to the universe being flat.
One way that we know this is through the cosmic microwave background radiation.
So when we’re talking about the parallel lines thing, we’re talking about over unfathomable distances, and no light has traveled further across the universe than the first light from the big bang, which has been stretched over space and time into the microwave spectrum and cooled down to just 2.7 degrees above absolute zero. And it’s everywhere.
And observations from the Planck telescope have studied tiny variations in the temperature of the CMB from various regions and it turns out that those temperature differences coincide with large-scale structures in the universe today.
Areas that were a fraction of a degree warmer at the beginning of the universe produced galaxy clusters. Cooler spots created voids. And we can see all this today.
If the universe was curved in one way or another, we’d see a lot more distortions in these observations, but we don’t. So… flat universe.
As always, we have to add the disclaimer that there is still a tiny degree of uncertainty to our measurements and future instruments might find something different. But for now, we believe the universe is flat.
Enter the Triscuitverse.
The Problem With Flatness
The frustrating thing about it though is that a flat universe doesn’t answer maybe the biggest question of all – how the universe will end.
Because in an expansive Pringles universe, we know that the universe will continue to expand forever, maybe even accelerate to the point that it all tears in half, the Big Rip scenario.
In a closed, cheese ball universe, gravity and dark matter would win out and slow the expansion to a stop and pull everything back together again in a Big Crunch.
But in a flat universe… we’re not entirely sure.
Either of those options might win out if there’s enough of an asymmetry in the forces. And in fact, we still don’t know for sure if there is a limit to the universe or it just keeps going infinitely. Like if we could somehow travel to that cosmic horizon where we can’t see the light from the galaxies anymore… would we just see countless more galaxies?
Triscuits may be delicious, but they create a lot of cosmological headaches.
Also, there’s nothing saying that the topology of the universe couldn’t change. It’s definitely changed before – the universal expansion that we think of as the Big Bang in the early universe is kind-of the perfect example of an expansive Pringles universe. Which eventually settled into a Triscuit universe.
To me, this is just another example of how fine-tuned our universe is.
I’ve talked before about how the universal constants like gravity and the strong and weak nuclear forces, if they were even just a fraction of a percent different, we wouldn’t have the universe we have today. Maybe the dark matter/dark energy ratio could be added to that list.
Which if the universe is all there is, that’s kind-of remarkable that it all worked out like that. But maybe that’s just survivor bias.
We see it this way and saw that it led to us and think that we’re special because of it but in a multiverse scenario, there might be all kinds of universes with different constants that create vastly different scenarios. 99% of which probably blink out of existence immediately after forming.
Who’s to say that there aren’t universes trying to form inside our universe all the time, bubbling up in the quantum foam, but none of them have the right constants so they just evaporate.
A rice cake universe, if you will.
Anyway, long story short, we most likely live in a flat, Triscuit universe. But the Pringle and Cheese ball theories keep popping up.
At this point you might be saying, Joe, aren’t you stepping outside your lane a bit here? To which I would respond…
Ya think?
If you want to take a deeper dive into these topics by people who actually know what they’re talking about I’d recommend Dr. Becky or Fraser Cain, two friends of the channel with much more credibility on this.
The thing is though anytime you talk about the universe and cosmology, you’re just dealing with distances and sizes that are incomprehensible to the jello molds in our heads.
It’s kinda like when we looked into atoms and found this subatomic quantum world where things just don’t work the way they do in our world, there were some new rules we had to discover – maybe there’s an extreme opposite version of that, when we look at things on infinite scales, whole new physics come into play.
That’s just speculation on my part but the concept of infinity is bonkers, you get a whole bunch of paradoxes and nonsensical scenarios, but if you want to try to make sense of infinity, you know I talk about Brilliant a lot on this channel well they have an entire course on infinity over on Brilliant.org
Add comment