In the beginning, there was something. Probably. We can’t look back all the way to the beginning. So I’ll just say, moments after the beginning, there was something: a hot soup of matter and energy. It has light matter and dark matter, and that matter is either “hot” (fast) or “cold” (slow). The fast and slow matter interacts on a quantum level, causing tiny fluctuations in the nascent universe.
Suddenly, everything expands. This period is called “inflation.” It’s what most people think of when we talk about the Big Bang. Those tiny fluctuations propagate outward, causing huge ripples – it’s almost a Butterfly Effect. Those tiny fluctuations that became huge ripples then start to condense together – the matter forms stars, the stars form galaxies, the galaxies form clusters, and the clusters form superclusters, the largest structures in the universe.
When we look out into the universe now, with all of our sophisticated equipment, we do not see a simple, continuous distribution of objects throughout the night sky. Instead, we see huge sweeping filaments of superclusters, like veins on the universe. These filaments are interspersed between voids, areas millions of light-years across which are nearly entirely empty of galaxies.
Imagine a pile of soap bubbles. Look through it. You don’t actually see the bubbles, do you? Just the spots where the bubbles intersect, where you can see the soap building up. The structure of the superclusters and voids that make up our universe looks strikingly like that pile of soap bubbles: the superclusters are the intersections of bubbles, and the voids are the empty spots in the middles. This is why we talk about the “quantum foam”: not because it’s actually foam, but simply because it looks and acts a bit like bubbles.
Here’s a picture of what it looks like in 3D:
And in case it’s a little hard to see the soap-bubble resemblance, here’s the structure of all the matter in the universe in 2D:
We’ve been able to detect this large-scale structure of the universe for decades, but we’re only recently beginning to understand them. Originally, scientists thought that maybe this large-scale universal structure occurred for the same reasons as, say, planets: galaxies slowly clump together due to gravity, leaving large regions nearly empty, with other, smaller regions full of clusters of galaxies. However, further study shows that it would take far longer than the age of our universe for superclusters to evolve in that way. So, filaments of galaxies must in some way come from earlier, more fundamental properties of the universe and its evolution, from the moments before the Big Bang.
Because of that, studying superclusters gives us a lens through which to look at the early universe and the Big Bang and test theories of inflation (how the universe expanded from a tiny area of hot energy and matter to what we know it to be today), which is not yet completely understood. Also, superclusters give us the largest (and so most effective) scale on which we can look for extra gravity from dark matter. These superclusters of galaxies may well be the largest structures in our universe, and understanding them is crucial to gaining a more complete understanding of how our universe was born and how it works on a larger scale.
In the beginning, there was a hot soup of energy and matter, unstructured and chaotic. Now, there’s a whole universe, with superclusters and clusters and galaxies and stars and planets and us. And studying every rung of that ladder is the only way to work toward understanding how we got here and the nature of our universe.