Universe Today
This is Part 1 of a series on topological defects.
Every time you flip a light switch, or check the time, or feel the sodium ions wiggling in your brain — don’t think about that one too much—you’re assuming something fundamental. You’re assuming the universe is a finished product. A completed work. You think the Big Bang happened, the forces of nature settled into their seats, and we’ve been cruising on a smooth, predictable ride ever since.
It's just…done.
No, the universe isn’t perfect. In fact, its total lack of perfection is exactly why we’re here. Long ago, like in the earliest moments of the big bang, things were a lot more even, uniform, and just kind of ok. Then flaws appeared, and those flaws grew to become stars and galaxies, you and me – all the good stuff that makes this universe such a fun place to be.
We have a beautiful mathematical model for how that process unfolded. Tiny, random ripples in the quantum fields that soak all of space time grew up during inflation to become not so tiny random ripples in the quantum fields that soak all of spacetime.
It’s an elegant theory. It works. It matches observations. It’s the "standard" story. But I’m not interested in the standard story today. I’m interested in where the standard story breaks down.
The thing, that process of giving flaws to the universe didn’t stop with just that. The universe wasn’t content with JUST making a few galaxies and being done with it.
Think about a lake freezing over in the dead of winter. If the water freezes perfectly and all at once, you get a sheet of clear, black ice. But that never happens. Instead, you get cracks. You get white lines where the crystals didn't quite line up. You get defects. The phase transitions of the early universe – the same ones that laid down the conditions for the cosmos to be not-quite-so-perfect – were FULL of defects. We’re talking a residue of creation, scars in the fabric of space-time itself. We’ve talked about the big ones before: cosmic strings, magnetic monopoles, domain walls. The usual suspects. But where are they? If these defects are real, they should be everywhere. Yet, we look at the sky and it seems… empty. Maybe those defects aren’t gone. Maybe they’ve just evolved into something far more exotic. Something so strange we wouldn’t even recognize it, even if it was right in front of our noses the whole time. Maybe the defects of the early universe are here in the room with us right now. Let’s go back in time a bit when things were simpler. Easier. More orderly. There was just…the universe. A hot but mostly bland soup of who knows was, some sort of perfect symmetry of all the forces of nature into one unified whole – one big happy physics family. There was no distinct gravity or light. We don’t know exactly how to describe this era, so we’re just going to skip on past that for today.
What comes next is what we care about. And what comes next is perhaps the single most consequential event in the entire history of the universe. This was inflation, which is exactly what is described on the label: a period where the universe underwent radical, huge, massive expansion in less time than it took to say this sentence out loud…several billion times over. Inflation was powered/triggered/driven/encouraged by the splitting of the forces. No, we don’t understand inflation either so we’re ALSO going to skip that for today, but we by and large suspect that something LIKE inflation happened based on a lot of circumstantial evidence, so we’re going to go with that and move on.
Now, the splitting of the forces is when the universe…made a choice. When the universe was perfect and whole and unified, there was only one way for it to be perfect and whole and unified. But when the forces split apart, they had a million different ways that they COULD have split apart. We live in one particular choice, with one particular arrangement of physics and forces and fields and constants and so on.
Like, when a pencil is balanced on its tip, there’s only one way for it to be balanced on its tip. You walk in a circle around it and – yup, it looks the same. Tip down, eraser up, balanced. But when the pencil tips over, it has a choice (no, it’s not an actual choice, it’s just random, but you get the idea) it points in one particular direction on the table. You walk around in a circle, and it looks different from different perspectives.
We live in one particular direction of the tipped pencil. What’s really changing here is various quantum field properties existing in a hyperdimensional phase space…that’s all wonderful math that I am NOT going to get into here, because the point is that depending on which way the quantum winds blow, you can potentially get completely different rules of physics.
And there’s no reason at all that that process had to be perfect.
Just like a pond freezing over, it doesn’t freeze over in the exact same way all across the pond. Some ice crystals choose one direction, other crystals choose other directions. If I had a table with a thousand pencils balance don their tips, and I shook the table…I mean, sure, some would fall in the same direction if one pencil dominoes into another…but in general it would be chaos.
And this is where the universe gets its defects.
If the universe transitions in different ways across its volume (which at this stage is less than the size of a basketball), then eventually there will be places that get caught between two regions. It’s like if a pencils on one part of the table are falling in one direction, and pencils in another part are falling in a different direction, and then those two places meet…and the pencils just get stuck on each other.
The defects are places where the universe gets stuck on itself.
And what happens in those places where the universe gets stuck on itself? The best way I can describe is that they retain a memory of the before-times. All around the defects, the universe reaches its new expression of reality: the forces, particles, fields, and all the other goodies that we’re familiar with.
But NOT in the defects. They’re stuck. They didn’t ever get the chance to settle down and pick a direction. So they become these tiny little hot pockets of the extremely early, unified universe. While the rest of the cosmos broke, they stayed pure.
There are three kinds of standard defects: one dimensional, two dimensional, and three dimensional. The one dimensional ones are the points, the monopoles, tiny little pinpricks in space. The two dimensional ones are the cosmic strings (which are NOT the superstrings of string theory, sorry, lots of string based action going on here in theoretical physics). Same deal: surrounding a string you have normal as-you-have-it universe. Within the string you have a relic of the earliest moments of the universe.
And then you have the two-dimensional ones. The domain walls. These are the universe-killers. With monopoles and cosmic strings, yeah, they’re weird nasty defects that the universe can’t get rid of, like that one annoying friend that ALWAYS shows up to every group event. But AROUND them the universe eventually smooths itself out and agrees on the same vacuum. Imagine just one of our pencils getting stuck (that’s a monopole) – all the other pencils shift around it to agree on a common direction, with just that one pencil remembering what it was like to live a balanced life.
But the domain walls? Oof, they cut the universe in half! There’s no way around a wall that stretches across the entire breadth of the universe. There’s no way for the pencils – our quantum fields in this gloriously tortured analogy – to work themselves out and at least settle down. The cosmos would simply exist in a permanent state of division, with one kind of physics on one side and another kind of physics on the other.
AS you can imagine, that would be…bad. Really bad. A house divided against itself cannot stand, and all that jazz. The immense gravitational pressures and energies contained within that kind of defect would kind of sort of rip apart the vacuum of spacetime. We would also kind of have noticed it by now, because it would stretch across the entire horizon and there would be a clear and obvious region where the stars and galaxies just…stop.
But there ain’t none of that, which is a relief.
To be continued...
