"A structure in the early universe at z~1.3 that exceeds the homogeneity scale of the R-W concordance cosmology"

I think that's quite a mouthful for a title

That is not a catchy title

It isn't really a catchy title, no

Um but, the physics and the astronomy behind it is rather interesting

Give me a better title

Um, "The discovery of an implausibly large structure in the universe"

Wow, that's better! You should have written the title.

There's some big structure out there, a long way away from Earth, and it's- they're saying it's the biggest structure that there is in the universe

So this is basically a collaboration which are looking at quasars in the universe, or these very bright active nuclei in galaxies

Not to study the quasars themselves, but because where there's a quasar there's a galaxy

So they're a good way of figuring out where galaxies are in the universe, where the galaxies themselves are too faint to see

And they're mapping out these quasars in three dimensions to figure out whether they're randomly spread in space

Or whether they're clustered together, and if they are clustered together how they're clustered together

Such a large structure is incompatible with a universe which is homogeneous on very large scales

Homogeneous means you're in no special place

That what we see around us is representative of everywhere else in the universe

And so, um, you don't expect, that the argument goes, I'm not so sure I buy it yet

You don't expect to see such a big structure in a universe that is meant to be, on average, homogeneous

So a quasar is a very, very bright nucleus of a galaxy

It's so bright it actually outshines the whole galaxy around it

The picture we have of these things is, we believe that pretty much every galaxy has one of these massive black holes in the middle

And probably what's happening where you see a quasar, it just means that that black hole is particularly active

Which means stuff is falling into it, which is making it light up

And so when these things were first discovered, they were called quasars

Because they were called "quasi-stellar objects"

Which means they look basically like stars because all you see is this bright nucleus of the galaxy

It's only when you look very carefully you see actually there's a whole galaxy around it

But they're very useful as sort of lighthouses

Because you can see a quasar at enormous distances all the way across the universe

Even if you couldn't see a normal galaxy

What is the scale above which you would say everything looks fairly uniform,

And below which you expect there to be structures?

As you said, you know, we are, you and I are quite different (laughs)

In many ways, and then you can just go up

Planets are different

Stars and then galaxies, they're different from one another

And you keep going to bigger and bigger scales, and you think, "Well, there's nothing homogeneous here"

"When I look around, things are looking quite different"

But the idea is that if you go on to large enough scales

And by "large enough," we're really talking on scales of more than 100 megaparsec

A parsec is about 3 lightyears, so we're talking about 300 million lightyears

You have to go before you begin to sort of suggest that above that scale things should start looking very similar

So what these people have found is that looking at the distribution of quasars in space

They're not randomly distributed. That's not news

But what they've actually found is that they form these incredibly large structures

When you start kind of mapping out the quasars, you find they form these enormous filaments

The latest thing that they've found, which this paper is all about

is a structure where the largest dimension of it is fairly elongated

and the longest dimension of this collection of quasars is about 4 billion lightyears long

And bearing in mind that the entire universe is only about 13 billion lightyears across

So this is almost a third the size of the universe, this structure

So it's a huge collection of these things

That sounds like the ultimate elephant in the room!

That sounds like it's the dominant beast of the universe.

And actually it causes a problem because the picture we have

is that when you go to large scales, the universe is supposed to be homogeneous

There's this thing called the Cosmological Principle, which says that

one bit of the universe is really very much like another bit of the universe

And of course if you've got a structure this big

it really means that one bit of the universe isn't really like another bit of the universe

because one bit's got this massive structure in it, and another bit hasn't got this massive structure in it

The big question is whether that is

A) Is it real? Is it a real feature? I can't really comment on that

I just find it mindblowing that the idea you can have 73 quasars linking across a distance of 4 billion lightyears

It just blows my mind

So how did they determine that they've got this structure? But let's assume it is, let's assume it's a real structure

The next question is: Is it compatible with an idea that the universe, on large scales, is homogeneous?

It could be that, we know there are fluctuations in a universe that's homogeneous

There has to be because without those fluctuations, we wouldn't form, you wouldn't form structures

So it could be that what we're seeing is just a rather extreme fluctuation, which is perfectly consistent

And in fact there is a slightly smaller structure that was observed a couple of years ago

called the Sloan Great Wall

This was also seen in the Sloan survey

This is a structure of 200-300 megaparsecs, so it's not quite as big as this one

And even then that was pushing the idea of homogeneity

So here's this structure that they've identified

Which, as I say, is about, as I say, from end to end here, is about 4 billion lightyears long

And so they've sort of played this game of join the dots

They've found where all the quasars are and found where all their nearest neighbors are

and used that to kind of span between them to say it looks like there's a structure here

You have to be very careful when you're playing this game because

If you just threw down a bunch of quasars at random, once in a while they'd start forming things that looked like structures

And so the exercise that you have to go through once you've found something that looks like a structure

is to say, "Is this consistent with just part of a random collection of things and I just happen to have seen them arranged in this way?"

And the statistics they've done in this paper show that what they've found

is very unlikely to be just a random distribution of things

It really looks like they've found a real structure in that sense

A collection of these quasars which have formed into this arrangement of quasars

which is not consistent with them just being randomly spattered around the place

The model that we're talking about, just to give this, trying to put some flesh to these bones

is the universe is very smooth on very large scales

so if I think of the matter distribution in the universe, if I think of it as a mill pond

And that matter distribution is perfectly flat, that mill pond is perfectly flat

that's your homogeneous bit

but on top of it there are these little ripples, right?

coming from fish, some of those are fish

And um, so these ripples are there, and those are the small fluctuations

So you've got the background, homogeneous. Everything's smooth.

And then you've got the small fluctuations,

And where you've got slight excess fluctuations, that means the gravitational pull

You've got slightly more matter, so from Newton's law

Where the force of attraction is proportional to the mass, you've got slightly more here, that will cause things to attract to it

And then it will leave regions where it's attracting matter from. They'll be devoid of matter.

They actually will create voids.

The force that we think shapes the large-scale structure of the universe is gravity

It forces things to collapse in certain dimensions

and actually you end up forming these sort of sheets of things and filaments and those kinds of things

which we've seen all the time when we look at galaxies in the nearby universe

We find that they're not randomly spread. There are some places where there are clusters of galaxies

Some places where there are none at all, some places where they form into these sort of sheet-like structures or filament-like structures

So presumably the physics is the same on these scales

When forming these very large structures, this gravity's forcing things to collapse in certain directions

The problem is that that's not what theory predicts, right?

The picture we have of the universe is that gravity shouldn't have formed structures on these kind of scales.

So that's why it's starting to kind of start to challenge our picture of cosmology

is that it seems to be there but we're struggling a bit to come up with an explanation as to how it might have formed

which of course, that's when science starts getting interesting

when you start finding things that you weren't expecting to find.

In that analogy you made with the fish or whatever it was making little ripples on our mill pond

What's the reality? In the real universe, what's causing these fluctuations that allow large structures to form?

Okay, so this is where it gets really fun

Now we're moving back to the very early universe

How early? About 10^-35 seconds into the universe

That's really...Point zero zero zero zero zero zero, 35, 34 zeroes and a one, okay? Seconds into the universe

And this is a period known as, where the universe expanded exponentially quickly

And so the space expanded exponentially rapidly

And in that universe was a thing called a scalar field, a bit like the Higgs field

permeating the whole of the universe, and it fluctuated because of quantum mechanics

just like the Higgs field fluctuates. (Randomly?) Randomly

And those fluctuations, the big difference that goes on here, is that those fluctuations don't just remain small

Because the universe is expanding so rapidly, they quickly get--they--get grabbed hold of

I'm getting too excited and I'm speaking too quick--slow down

They, they (Ed, I will never accuse you of speaking too quickly)

These fluctuations get grabbed hold of by the expansion of the universe, and stretched onto big, big scales

and those are the cosmological scales

and it's there that the initial seeds came from.

So what we're seeing when we look at the large-scale structures in the universe

When we look at the microwave background fluctuations in the W map

and see these hot and cold spots

What you're actually seeing is an imprint of those very early moments,

way before a microsecond, way before a nanosecond into the universe's history

when these fluctuations from the field emerged.

(A big, blown-up projection of just a funny little wobble in a field) Wow