You're (probably) watching this video somewhere on Earth.
A planet going around the sun, a star spinning around the center of the Milky Way, a galaxy
in a swarm with 50 others, all dancing with a hundred other galaxy-groups in our supercluster…
and well… that's as big as it gets.
If we keep zooming out, superclusters don't form super-duper-clusters.
They're connected by thin filaments, making tangled web out of these biggest structures
in the universe.
Threads of superclusters, separated by millions of light years worth of nothing.
But why?
Why not some other structure, like one giant mega-galaxy, sprinkled with stars?
In fact, why does the universe have any structure at all?
[OPEN]
Imagine a different universe from our own, where all the matter is spread out, perfectly
smooth and uniform.
Just like our universe, every piece of matter is attracted to every other piece of matter,
thanks to gravity.
If that universe is finite, if it has an edge where matter ends, then everything would be
pulled to the center and would end up clumped in one place.
Lucky for us this isn't the universe we live in.
But what if this smooth and uniform universe had no edge, spreading out forever?
A particle inside this infinite cloud would feel nothing!
Or rather, it'd feel gravity equally in all directions.
The whole universe would be frozen in place.
But our universe isn't evenly spread out, and it isn't clumped in one place.
It's full of structures at massively different scales.
To find out how our universe ended up this way, let's run the clock backwards.
When scientists simulate the evolving universe, they find that in order to make one that looks
like ours, there needs to be some tiny lumps in the very, very beginning, in order to seed
the structures we see today.
What makes these early microscopic lumps?
They're super tiny random fluctuations due to the quantum nature of particles.
Oddly enough, the biggest things in our universe form thanks to the smallest.
Because the universe is expanding today, we know it was denser in the past.
Go back in time far enough, and it was filled with a super thick plasma, similar to the
inside of a star.
But at the smallest scales, the uncertainty of quantum mechanics sprinkled some randomness
among those particles, forming tiny quantum lumps instead of a smooth matter batter.
Then… the universe expanded so fast that lumps the size of just a few atoms would have
been stretched out over a lightyear in a fraction of a fraction of a second, locking these tiny
quantum fluctuations into place all over the universe.
This is called inflation.
How do we know what happened in those billionths of a second following the big bang?
It turns out we have a baby picture.
The cosmic microwave background, some of the oldest light in the universe, shows these
early fluctuations as they looked a brief 400,000 years later.
Some spots are slightly warmer, and some slightly colder - the size and magnitude of these lumps
exactly match what cosmic inflation predicts!
With some help from the dark matter around it, those stretched out lumps of stuff coalesced,
forming planets, stars, and galaxies, but after inflation, thanks to dark energy, the
universe kept expanding.
On one side, dark energy's pulling everything apart, while on the other, gravity's scrambling
to pull things together.
But gravity can only pull so much.
At the largest scales, dark energy wins, and things get separated.
If the universe had more dark energy, things would be more spread out, with smaller filaments,
and in a universe with less dark energy, our cosmic web would be woven tighter.
Depending on the unknown future of dark energy, in a few billion years gravity might have
formed super-duper clusters, or dark energy might have ripped everything apart.
We live in a universe shaped by the tug of war between gravity and expansion.
The unfathomable hugeness of galaxies and clusters and filaments were set on course
by the tiniest subatomic flickers.
We may not have super-duper-clusters, but this story's still super-duper on its own.
Stay curious.
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