This well-known image inspires awe and curiosity. Can it really be that our chaotic universe looks like this at large? So structured, it's almost elegant. In order to understand figure why our universe looks the way it does today, we need to turn back time to see how it all started...

Turning Back Time

While the big bang itself still dwells in mystery, we can tell with certainty that our universe is experiencing expansion at ever increasing speeds. Therefore, should we dare wind back the cosmological clock, our universe would shrink.

And as we do, the universe’s expanse starts diminishing, becoming smaller and smaller… and just how small? Well, no one knows for sure. For it is a common misconception, that many who claim to know fail to specify that their results only apply for the observable universe. The part from which light can still reach us. Anything beyond is causally disconnected from us. Any message we’d send would be in vain, as the universe's expansion stretches space further so that it may never go past that we call the observable universe.

Cosmic Microwave Background

When we extrapolate backwards, we can only do that for the observable universe because we do not know how far it stretches past that. Regardless, we know that it was many orders of magnitude smaller than it is now. And what happens when you take something and you make it really really small? Just like the forces of gravity pressing together the atoms inside of a star generate heat that lights up the night sky, so does the universe get hotter as we turn back time.

And what happens when you take something and you make it really really small? Just like the forces of gravity pressing together the atoms inside of a star generate heat that lights up the night sky, so does the universe get hotter as we turn back time.

So then, the early universe was a boiling pot filled with vacuum fluctuations, self-creating and annihilating matter and antimatter particles, releasing photons in all directions. Until space-time started expanding rapidly. This expansion caused the wavelengths of the photons to stretch. This effect, very similar to the Doppler effect, is called redshift. This stretching meant that the wavelengths of these primordial photons now fall into the microwave spectrum. The so-called cosmic microwave background emits electromagnetic waves similar to your WiFi router or cell phone.

Once could call it, an afterglow, an echo of the Big Bang itself. It whispers to us secrets of the early universe permeating the entire cosmos. As such scientists of course studied the CMB, its patterns and fluctuations trying to unravel the secrets of the ever-present ripples almost like cosmic fingerprints imprinted onto space-time. What has been uncovered?

Primordial Whispers

No doubt, many insights have been gained. In particular, one theory arose that proposes that these beautiful web patterns are remnants of primordial gravitational waves. Remember, the CBM is caused by the boiling pot of matter-antimatter pairs that are constantly releasing energy. This energy then counteracts the gravity of these particles that presses them together. Amidst this tug-of-war, ripples were created by the pressure. We call them baryon acoustic oscillations.

What happened next, is that as our universe expanded and the energy density lowered, its temperature dropped as well. Amidst this cooling-off process, the pressure pushing outwards was released due to photon decoupling and some matter was pulled back into the center of the ripple by the dark matter. The remaining matter stayed in these rings. Now then, it is time to put the puzzle pieces together…

Baryon acoustic oscillations

Decrypting the Image

Art in Astronomy usually requires some degree of interpretation as scientists often map invisible wavelengths and other features into color so that they become more easily perceptible for us humans. In this case, my research has come to the conclusion that indeed something similar has happened here. In the construction of this image the redshift data of distant galaxies was used to interpolate the relative distance between them. The resulting structure consists of galaxy clusters, branches of galaxies stretching out, so-called filaments and voids. Voids that as we discover are a result of the CMB.

The absence of gravity around the void bubbles and the influence of dark energy, which serves as a model for our universe's expansion, make it easier for space to expand. This expansion causes the voids to grow, while the gravitational pull of galaxies leads to their clustering. These factors likely played a fundamental role in shaping our universe on this astronomical scale. Here you can see Nasa's visualization of the great cosmic web and develop a better understanding of the structure in 3 dimensions.

One mystery may be solved, however, the never-ending vastness of space carries many more secrets waiting to be explored.